WO2007031820A2

WO2007031820A2 - Anode assembly for a direct liquid fuel cell

Info

Publication number: WO2007031820A2
Application number: PCT/IB2006/001964
Authority: WO
Inventors: Gennadi Finkelshtain; Yuri Katsman; Ilan Sadon; Mark Estrin; Alexander Litvinov; Boris Ilyushin; Alexander Chinak; Alexander Bluvstein; Michael Lerner
Original assignee: More Energy Ltd.
Priority date: 2005-09-15
Filing date: 2006-03-03
Publication date: 2007-03-22
Also published as: WO2007031820A3

Abstract

An anode assembly for a liquid fuel cell, wherein the assembly comprises at least two of (a) an anode (3) with a hydrophilized side which contacts the fuel, (b) a gas-blocking polymeric material (20) on the side of the anode which contacts the electrolyte, and (c) a membrane (8) on the fuel side of the anode (3) which substantially prevents liquid fuel to contact the anode (3) when the fuel cell is in an open circuit or stand-by regime and hydrogen gas evolves at the anode.

Description

ANODE ASSEMBLY FOR A DIRECT LIQUID FUEL CELL

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present application is a continuation-in-part of U.S. application No. 11/226,222, filed September 15, 2005, which is a continuation-iπ-part of U.S. application No. 10/941,020, filed September 15, 2004, and is a continuation-in-part of U.S. application No. 11/325,466, filed January 5, 2006, and is a continuation-in-part of U.S. application No. 11/325,326, filed January 5, 2006, which is a continuation-in-part of U.S. application No. 10/959,763, filed October 7, 2004, and is a continuation-in-part of International application No. PCT/IB2005/004070, filed October 5, 2005, which is a continuation of U.S. application No. 10/959,763, filed October 7, 2004. The entire disclosures of the above-mentioned applications are expressly incorporated by reference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

[0002] The present invention relates to an anode assembly for a liquid fuel cell and in particular, a Direct Liquid Fuel Cell (DLFC) which uses a (boro)hydride fuel. More specifically, the present invention relates to an anode assembly which helps to prevent or at least substantially reduce problems which are frequently encountered with such fuel cells.

2. Discussion of Background Information

[0003] Direct liquid fuel cells are of considerable importance in the field of new energy conversion technologies. In the literature, the most frequently discussed liquid fuel for a DLFC appears to be methanol. The main disadvantages of Direct Methanol Fuel Cells (DMFCs) include the toxicity of methanol, the very poor discharge characteristics at room temperature and the complexity and cost due to high catalyst loading and poor performance.

[0004] Fuels based on (metal) hydride and borohydride compounds such as, e.g., sodium borohydride (e.g., in alkaline aqueous solution) have a very high chemical and electrochemical activity. Consequently, DLFCs which use such fuels have extremely high discharge characteristics (current density, specific energy, etc.) even at room temperature. fOOOB] Efficient operation of a DLFC which uses a (boro)hydπde fuel requires continuous delivery of the (boro)hydride to the catalyst particles of the anode. For example, borohydride is electrochemically oxidized at the anode by direct reaction with formation of BO₂ ^" and water in accordance with the following equation:

BH₄ ^" + 8OW = BO₂ ^" + 6H₂O + 8e^' (1 )

[0006] Side reactions include the electrochemical oxidation of the borohydride to H₂ and the non-electrochemical decomposition of the borohydride (self-discharge). The decomposition of a borohydride compound occurs in accordance with the following equation:

BH₄ ^" + 2H₂O → BO₂- + 4H₂T (2)

[0007] The formation of hydrogen gas as a result of the above side reactions which are particularly significant in an open circuit regime and in a stand-by (low current) regime causes several problems. One of these problems includes the passage of hydrogen gas through the anode into the electrolyte chamber, leading to the formation of hydrogen bubbles in the electrolyte and, in turn, to an increase of the electric (ionic) resistivity of the electrolyte. Another problem is the parasitic loss of hydrogen gas (which is a fuel for the fuel cell as well) into the electrolyte. Further, hydride and borohydride decomposition at the anode of a fuel cell may result in energy loss, destruction of the anode active layer, and decreasing safety characteristics. As a result, there is a need to develop ways to substantially prevent the fuel from decomposing, especially while the fuel cell is in an open circuit regime or a stand-by regime, and to substantially prevent hydrogen gas to pass through the anode into the electrolyte.

[0008] Further, since most hydride fuels comprise water and inorganic compounds such as, e.g., metal hydrides and/or borohydrides, it is desirable that an anode for a fuel cell which uses hydride fuels is as hydrophilic as possible to ensure an effective operation of the fuel cell. Also, rapid activation of a liquid fuel cell depends on the wetting rate of the anode, which increases with the hydrophilicity of the anode, at least as long as the fuel is hydrophilic.

[0009] The catalytically active layer of an anode for a liquid fuel cell usually comprises a catalyst on a particulate support (e.g., a catalytically active material dispersed in a porous particulate support such as, e.g., a porous carbon support) and a binder (usually a polymeric material such as, e.g., polytetrafluoroethylene (PTFE)). These materials may have different ratios of hydrophilic/hydrophobic properties; in general, they are more hydrophobic than hydrophilic. Activated carbons are usually more hydrophilic than carbon black and graphite. The catalytically active material dispersed in the support usually is hydrophilic. If a conventional binder such as, e.g., PTFE, is used, the binder is a hydrophobic material as well, which adds to the hydrophobic properties of the anode. [0010] In view of the foregoing, it would be advantageous to be able to render the anode of a liquid fuel cell for use with a hydride fuel (i.e., a hydrophilic fuel) as hydrophilic as possible without, however, adversely affecting to any substantial extent desired anode properties such as electrocatalytic activity, mechanical integrity and electric conductivity of the active layer. This would be even more desirable with fuels which comprise alkaline substances such as, e.g., alkali metal hydroxides which tend to increase the surface tension of an (aqueous) fuel and thereby make it even more difficult to wet an anode which comprises hydrophobic materials.

SUMMARY OF THE INVENTION

[0011] The present invention provides an anode assembly for a liquid fuel cell. The assembly comprises at least one, and preferably at least two features (a), (b) and (c):

(a) an anode wherein at least a part of the side of the anode which is intended to contact the liquid fuel has been subjected to a hydrophilization treatment;

(b) a polymeric material which substantially completely covers the surface of the anode which is intended to contact the electrolyte, which polymeric material prevents at least about 80 % of hydrogen gas that is generated at the anode to pass through the anode into the electrolyte;

(c) at least one membrane arranged on the side of the anode which is intended to contact the liquid fuel, the membrane being structured and arranged to allow gas which is formed on or in the vicinity of the side of the anode which is intended to contact the liquid fuel to accumulate adjacent the anode at least to a point where the accumulated gas substantially prevents the liquid fuel from contacting the anode.

[0012] In one aspect, the anode assembly of the present invention may comprise feature (a) and feature (b), or it may comprise feature (a) and feature (c), or it may comprise feature (b) and feature (c), or it may comprise features (a), (b) and (c). [0013] In another aspect of the anode assembly, the anode may comprise a catalytically active metal on a support. By way of non-limiting example, the catalytically active metal may comprise one or more of Pt, Pd, Rh, Ru, Ir, Au and Re and/or the support may comprise one or more of activated carbon, carbon black, graphite and carbon rtanotubes. In yet another aspect, the anode may further comprise a binder, hor example, the binder may comprise polytetrafluoroethylene.

[0014] In a still further aspect of the anode assembly of the present invention, in the case of feature (a) at least the side of the finished anode which is intended to contact the liquid fuel may have been subjected to a hydrophilization treatment. In another aspect, at least the support for carrying the catalytically active metal may have been subjected to a hydrophilization treatment.

[0015] In yet another aspect, in the case of feature (a) the hydrophilization treatment may comprise a treatment with a hydrophilizing agent. By way of non-limiting example, the hydrophilizing agent may comprise at least one substance selected from anionic surfactants, cationic surfactants, non-ionic surfactants, polycarboxylic acids and salts thereof, oxy-acids and salts thereof, sugars, sugar alcohols, sugar derivatives and cellulose derivatives. For example, the hydrophilizing agent may comprise at least one substance selected from alkyl sulfates and alkyl sulfonates and/or at least one substance selected from polyalkylene glycols and ethers thereof. The weight average molecular weight of the polyalkylene glycols and ethers thereof may be not higher than about 1,000. Alternatively or cumulatively, the hydrophilizing agent may comprise at least one substance selected from homopolymers and copolymers of acrylic acid, monomeric polycarboxylic acids and salts thereof and/or at least one substance selected from glucose, fructose, xylose, sorbose, sucrose, maltose, lactose, galactose, sorbitol, xylitol, mannitol, maltitol, lactitol, galactitol, erythritol and gluconic acid and/or at least one substance selected from carboxymethyl cellulose and salts thereof. [0016] In another aspect, the anode may comprise from about 0.001 to about 5 mg/cm² of hydrophilizing agent, e.g., from about 0.05 to about 0.5 mg/cm² of hydrophilizing agent.

[0017] In yet another aspect of the anode assembly of the present invention, in the case of feature (a) the hydrophilization treatment may comprise cold plasma etching of at least the side of the finished anode which is intended to contact the liquid fuel. [0018] In a still further aspect of the anode assembly, in the case of feature (a) the real component of the impedance after 10 minutes of immersion of the anode in 6.6 M aqueous KOH may be not larger than about 50 % of the real component of the impedance of the same anode that has not been subjected to the hydrophilization treatment and/or the real component of the impedance after 20 minutes of immersion of the anode in 6.6 M aqueous KOH may be not larger than about 75 % of the real component of the impedance of the same anode that has not been subjected to the hydrophfetfion treatment and/or the real component of the impedance oτ me anoαe after 10 minutes of immersion in 6.6 M KOH may be not larger than about 3 Ohm-cm², e.g., not larger than about 2 Ohm-cm².

[0019] In another aspect of the anode assembly, in the case of feature (a) the anode may be substantially completely wetted by 6.6 M KOH of 25⁰C within not more than about 60 minutes, e.g., within not more than about 45 minutes. [0020] In yet another aspect of the anode assembly, in the case of feature (b) at least about 90 % of the hydrogen gas may be prevented from entering the electrolyte. [0021] In a still further aspect of the anode assembly, in the case of feature (b) the resistivity of a combination of the anode with the polymeric material thereon may be not not larger than about 1 Ohm-cm².

[0022] In another aspect, in the case of feature (b) the polymeric material may comprise one or more layers of polymeric material having a total thickness of from about 25 μm to about 200 μm.

[0023] In yet another aspect, in the case of feature (b) the polymeric material may comprise at least one polymer with a hydrophilic group. The hydrophilic group may, for example, be selected from OH, COOH and SO3H groups. For example, the at least one polymer with a hydrophilic group may comprise a homopolymer and/or a copolymer of vinyl alcohol such as, e.g., a vinyl alcohol/alkene copolymer. In another aspect, the at least one polymer with a hydrophilic group may be crosslinked at least partially with a crosslinking agent which comprises a polymer that has at least one functional group which is capable of reacting with a functional group of the hydrophilic polymer. By way of non-limiting example, the at least one polymer with a hydrophilic group comprises a polymer having OH groups and the ne crosslinking agent may comprise a polymer selected from polyethylene glycol, polyethylene oxide, a homo- or copolymer of acrylic acid and combinations of two or more thereof. For example, the crosslinking agent may comprise a polyethylene glycol with a number average molecular weight of from about 300 to about 10,000 and/or a polyethylene oxide with a number average molecular weight of from about 35,000 to about 200,000.

[0024] In yet another aspect, the at least one polymer with a hydrophilic group may comprise a polymer having OH groups and the at least one crosslinking agent may comprise a polymer comprising a monomeric unit having a carboxylic acid and/or a sulfonic acid group. For example, the monomeric unit may comprise an ethylenically unsaturated carboxylic acid such as, e.g., acrylic acid, methacrylic acid, maleic acid and any combinations thereof. For example, the crosslinking agent may comprise a homo- or copolymer of acryfϊc acid. The crosslinking agent may, for example, comprise polyacrylic acid, in particular, polyacrylic acid having a weight average molecular weight of from about 2,000 to about 250,000 and/or the crosslinking agent may comprise a copolymer of acrylic acid and maleic acid, in particular, a copolymer having a weight average molecular weight of from about 2,000 to about 5,000.

[0025] In a still further aspect, the at least one polymer with a hydrophilic group may be crosslinked at least partially with at least one crosslinking agent selected from a silicate, a pyrophosphate, a sugar alcohol, a polycarboxylic acid and an aldehyde. For example, the weight ratio of the at least one polymer with a hydrophilic group and the crosslinking agent may be from about 2:1 to about 1:2. By way of non-limiting example, the crosslinking agent may comprise sulfosuccinic acid.

[0026] In another aspect, in the case of feature (b) the side of the anode that is covered with the polymeric material may have been subjected to a surface treatment prior to being covered with the polymeric material. By way of non-limiting example, the surface treatment may comprise a hydrophilization treatment, such as e.g., a treatment with a hydrophilizing agent. The hydrophilizing agent may, for example, the same as that used in the case of feature (a) and may, in particular, comprise at least one substance selected from anionic surfactants, cationic surfactants, non-ionic surfactants, polycarboxylic acids and salts thereof, oxy-acids and salts thereof, sugars, sugar alcohols, sugar derivatives and cellulose derivatives.

[0027] In another aspect of the anode assembly of the present invention, in the case of feature (c) the at least one membrane may comprise a single layer of material and/or it may comprise a hydrophilic material such as, e.g., a metal and/or a metal alloy (for example, stainless steel).

[0028] In yet another aspect, in the case of feature (c) the at least one membrane may comprise a hydrophobic material. By way of non-limiting example, the hydrophobic material may comprise an organic polymer, for example a polyolefin, a polyamide and/or polyacrylonitrile

[0029] In a still further aspect, in the case of feature (c) the at least one membrane may comprise one or more of a non-woven material, a composite material, a laminate material, a composite/laminate material, a foam material, a porous paper material, a cloth material, a carbon/graphite material, a sintered metal material, a ceramic material, and a polymer material.

[0030] In another aspect of the anode assembly, in the case of feature (c) the at least one membrane may comprise a mesh and/or a foam, for example, a stainless steel micrcmesh. By way of non-limiting example, the micromesh may comprise cells having a size of up to about 0.5 mm, e.g., from about 0.06 μm to about 0.05 mm. Also by way of non-limiting example, the mesh may have a thickness of from about 0.01 mm to about 5 mm.

[0031] In yet another aspect of the anode assembly, in the case of feature (c) the at least one membrane may comprise a polymer mesh and/or a porous polymer layer. By way of non-limiting example, the polymer mesh or porous polymer layer may have a thickness of from about 0.02 mm to about 2 mm. Also by way of non-limiting example, the polymer mesh may have a cell size of from about 0.01 mm to about 0.1 mm and the porous polymer layer may have a pore size of from about 0.01 μm to about 0.1 mm. [0032] In a still further aspect of the anode assembly of the present invention, in the case of feature (c) the at least one membrane may be in contact with a surface of the anode which is intended to contact the liquid fuel. For example, it may be attached and/or bonded to the surface of the anode.

[0033] In another aspect, in the case of feature (c) the fuel cell may further comprise a free space and/or a spacer structure arranged between the at least one membrane and the anode. The spacer structure may be comprised of a spacer material having a free space therein and/or the spacer structure may comprise a layer of spacer material having a thickness of up to about 3 mm and at least least 0.1 mm. For example, the layer of spacer material may have a thickness of from about 0.5 mm to about 1.5 mm. Also, the spacer material may comprise a hydrophobic material (and the at least one membrane may comprise a hydrophilic material). The hydrophobic material may, for example, comprise a polymeric material such as, e.g., one or more of an olefin homopolymer, an olefin copolymer, ABS, polymethylmethacrylate, polyvinyl chloride, and polysulfone, in particular, one or more of polyethylene, polypropylene, polytetrafluoroethylene, and ABS. In another aspect, the spacer structure may comprise a net such as, e.g., a wattled net. For example, the net may comprise openings of from about 1 mm to about 50 mm.

[0034] In yet another aspect, the fuel cell may comprise a spacer structure which is comprised of a frame seal that is arranged on the surface of the anode which is intended to contact the liquid fuel. For example, the frame seal may comprise a hydrophobic material such as, e.g., an (organic) polymer, in particular, a fluorinated polymer. Also, the frame seal may have a thickness of up to about 0.1 mm, e.g., from about 0.02 mm to about 0.05 mm. In a still further aspect, the spacer structure may comprise both a spacer material having a free space therein and a frame seai wnicn is arranged on the surface of the anode which is intended to contact the liquid fuel. [0035] In another aspect of the anode assembly of the present invention, in the case of feature (c) the anode assembly may comprise at least a first membrane adjacent to the anode and a second membrane on the side of the first membrane which is intended to contact the liquid fuel, and the at least the first membrane may be structured and arranged to allow gas which is formed on or in the vicinity of the surface of the anode which comes into contact with the liquid fuel to accumulate adjacent to the anode at least to a point where the accumulated gas substantially prevents the liquid fuel from contacting the anode. The second membrane may be structured and arranged to filter solids from the liquid fuel, protect the first membrane, or both. Also, the first membrane and the second membrane may form an integral structure. Still further, the second membrane may comprise a material that is different from that of the first membrane and/or a thickness that is different from that of the first membrane and/or a pore size or cell size that is different from that of the first membrane. Further, the second membrane may comprise a material that is substantially the same as that of the first membrane and/or a thickness that is substantially the same as that of the first membrane and/or a pore size or cell size that is substantially the same as that of the first membrane. By way of non-limiting example, at least the first membrane may comprise a polymer mesh or porous polymer layer having a thickness of between about 0.02 mm and 2 mm and a cell size of from about 0.01 mm to about 0.1 mm or a pore size of from about 0.01 μm to about 0.1 mm. For example, at least the first membrane may comprise a stainless steel mesh having a thickness of from about 0.01 mm to about 5 mm. Also, the first membrane may be bonded to and/or in contact with the surface of the anode that is intended to contact the liquid fuel. In a still further aspect, the anode assembly may further comprise a free space and/or a spacer structure arranged between the first membrane and the anode.

[0036] In yet another aspect of the anode assembly of the present invention, the anode may be fixed within the fuel cell case and/or in sealing engagement with the fuel cell case.

[0037] The present invention also provides a liquid fuel cell which comprises the anode assembly of the present invention as set forth above, including the various aspects thereof. [0038] In one aspect, the fuel cell may comprise a metal hydride and/or a metal borohydride compound in the fuel chamber thereof and/or an electrolyte chamber thereof may eαrøiprisfe a liquid electrolyte such as, e.g., an aqueous solution oτ one or more metal hydroxides.

[0039] The present invention also provides an anode assembly for a liquid fuel cell, which assembly comprises:

(a) an anode wherein at least a part of the side of the anode which is intended to contact the liquid fuel has been subjected to a hydrophilization treatment with a hydrophilizing agent;

(b) a polymeric material which substantially completely covers the surface of the anode which is intended to contact the electrolyte, which polymeric material prevents at least about 90 % of hydrogen gas that is generated at the anode to pass through the anode into the electrolyte, the polymeric material comprising least one polymer having a hydrophilic group selected from OH, COOH and SO₃H groups and being at least partially crosslinked with at least one crosslinking agent which comprises a polymer that has at least one functional group that is capable of reacting with a functional group of the hydrophilic polymer;

(c) at least one membrane arranged on the side of the anode which is intended to contact the liquid fuel, the at least one membrane being structured and arranged to allow gas which is formed on or in the vicinity of the side of the anode which is intended to contact the liquid fuel to accumulate adjacent to the anode at least to a point where the accumulated gas substantially prevents the liquid fuel from contacting the anode. [0040] The present invention also provides a liquid fuel cell for use with a liquid fuel that is prone to undergo decomposition with generation of hydrogen gas. The fuel cell comprises a cathode, an anode, an electrolyte chamber arranged between the cathode and the anode, a fuel chamber arranged on the side of the anode which is opposite to the side which faces the electrolyte chamber, one or more layers of polymeric material arranged on a surface of the anode which faces the fuel chamber, and at least one membrane arranged on the side of the anode which faces the fuel chamber. The one or more layers of polymeric material prevent an at least substantial portion of the hydrogen gas that is present in the fuel chamber when liquid fuel is present in the fuel chamber from passing through the anode into the electrolyte chamber. Also, the at least one membrane is structured and arranged to allow gas which is formed on or in the vicinity of the surface of the anode which faces the fuel chamber to accumulate adjacent to the anode at least to a point where the accumulated gas substantially prevents the liquid fuel in the fuel chamber from contacting the anode [0041 J The present invention also provides a liquid fuel cell for use witn a nquiα τueι that is prone to undergo decomposition with generation of hydrogen gas, which fuel cell comprises a cathode, an anode, an electrolyte chamber arranged between the cathode and the anode, a fuel chamber arranged on the side of the anode which is opposite to the side which faces the electrolyte chamber, and one or more layers of polymeric material arranged on the side of the anode which faces the fuel chamber. The one or more layers of polymeric material prevent an at least substantial portion of the hydrogen gas that is present in the fuel chamber when liquid fuel is present in the fuel chamber from passing through the anode into the electrolyte chamber, and at least a part of the side of the anode which is intended to contact the liquid fuel has been subjected to a hydrophilization treatment.

[0042] The present invention also provides a liquid fuel cell for use with a liquid fuel that is prone to undergo decomposition with generation of hydrogen gas, which fuel cell comprises a cathode, an anode, an electrolyte chamber arranged between the cathode and the anode, a fuel chamber arranged on the side of the anode which is opposite to the side which faces the electrolyte chamber, and at least one membrane arranged on the side of the anode which faces the fuel chamber. The at least one membrane is structured and arranged to allow gas which is formed on or in the vicinity of the side of the anode which faces the fuel chamber to accumulate adjacent to the anode at least to a point where the accumulated gas substantially prevents the liquid fuel in the fuel chamber from contacting the anode, and at least a part of the side of the anode which is intended to contact the liquid fuel has been subjected to a hydrophilization treatment. [0043] The present invention also provides a liquid fuel cell for use with a liquid fuel that is prone to undergo decomposition with generation of hydrogen gas, which fuel cell comprises a cathode, an anode, an electrolyte chamber arranged between the cathode and the anode, a fuel chamber arranged on the side of the anode which is opposite to the side which faces the electrolyte chamber, one or more layers of polymeric material arranged on the side of the anode which faces the fuel chamber, and at least one membrane arranged on the side of the anode which faces the fuel chamber. The one or more layers of polymeric material prevent an at least substantial portion of the hydrogen gas that is present in the fuel chamber when liquid fuel is present in the fuel chamber from passing through the anode into the electrolyte chamber. Further, the at least one membrane is structured and arranged to allow gas which is formed on or in the vicinity of the side of the anode which faces the fuel chamber to accumulate adjacent to the anode at least to a point where the accumulated gas substantially prevents the liquid fuel in the fuel chamber from contacting the anode, and at least a part of the siαe or tne anode which is intended to contact the liquid fuel has been subjected to a hydrophilization treatment.

[0044] In one aspect of the fuel cells set forth above, the fuel cells may be direct liquid fuel cells and/or they may be portable fuel cells.

[0045] In another aspect, the fuel cells may comprise a metal hydride and/or a metal borohydride compound in the fuel chamber.

[0046] In yet another aspect of the above fuel cells, the fuel chamber may be arranged in a cartridge that is connected to the housing of the fuel cell and/or removably mounted thereto. In another aspect, the fuel cells may further comprise at least one member that allows liquid fuel to pass from the fuel chamber of the cartridge to an area adjacent the anode.

[0047] In a still further aspect of the fuel cells set forth above, the fuel cells may comprise a case which accommodates at least the anode, and at least one part of the fuel chamber may be arranged outside the case, and the case may be connected to the at least one part of the fuel chamber that is arranged outside the case through one or more liquid passageways. For example, the at least one part of the fuel chamber that is arranged outside the case may comprise a cartridge and/or the at least one membrane may be arranged (a) at or in the vicinity of one or more locations of the case where liquid fuel from the at least one part of the fuel chamber that is arranged outside the case can enter the case and/or (b) at or in the vicinity of one or more locations of the at least one part of the fuel chamber that is arranged outside the case where liquid fuel can leave the at least one part of the fuel chamber that is arranged outside the case and/or (c) at one or more locations inside the one or more liquid passageways.

[0048] Other exemplary embodiments and advantages of the present invention may be ascertained by reviewing the present disclosure and the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWINGS

[0049] The present invention is further described in the detailed description which follows, in reference to the noted plurality of drawings by way of non-limiting examples of exemplary embodiments of the present invention, in which like reference numerals represent similar parts throughout the several views of the drawings, and wherein:

Fig. 1 shows a schematic cross section view of a prior art fuel cell;

Fig. 2 shows a cross section of a fuel cell which illustrates feature (c) of the anode assembly of the present invention; FIg. 3 shows an enlarged portion of Fig. 2;

Fig. 4 presents a chart illustrating hydrogen productivity in a fuel cell of the type shown in Fig. 1;

Fig. 5 presents a chart illustrating hydrogen productivity in a fuel cell of the type shown in Fig. 2;

Fig. 6 shows a partial view of one non-limiting weave pattern for the wattled spacer material;

Fig. 7 shows a partial view of another non-limiting weave pattern for the wattled spacer material;

Fig. 8 shows a cross section of another fuel cell which illustrates feature (c) of the anode assembly of the present invention;

Fig. 9 shows a cross section of still another fuel cell which illustrates feature (c) of the anode assembly of the present invention;

Fig. 10 shows a cross section of yet another fuel cell which illustrates feature (c) of the anode assembly of the present invention;

Fig. 11 shows a cross section of yet another fuel cell which illustrates feature (c) of the anode assembly of the present invention. This embodiment uses a cartridge containing the fuel chamber (or at least a part thereof) which can be connected and/or removably mounted to the housing of the fuel cell;

Fig. 12 shows an enlarged view of the fuel cell shown in Fig. 11 and illustrates how the membrane and/or spacer material can have the form of small screen filter member. This figure also illustrates how the tubes of the cartridge are sealed relative to openings in the wall of the housing via o-rings; and

Fig. 13 shows a cross section of a fuel cell according to Fig. 11 with the cartridge separated and/or unconnected with the housing of the fuel cell.

Fig. 14 shows a schematic cross section view of a fuel cell which illustrates feature (b) of the anode assembly of the present invention;

Fig. 15 shows a schematic cross section view of a cell for measuring the resistivity of an anode according to feature (b) of the anode assembly of the present invention;

Fig. 16 shows a schematic drawing of a test assembly which is used for determining the gas blocking efficiency of the polymeric material of the anode of the present invention;

Fig. 17 shows a schematic cross section view of an apparatus used in the test assembly shown in Fig. 16; Fi&. 18 shows an exemplary diagram which is used for determining tne gas blocking efficiency from data obtained with the test assembly of Fig. 16.

Fig. 19 shows a schematic cross section view of a fuel cell which illustrates feature (a) of the anode assembly of the present invention;

Fig. 20 shows a schematic cross section view of the fuel cell of Fig. 19 which additionally includes feature (b) of the anode assembly of the present invention;

Fig. 21 shows a plot of the real component of the impedance Z' vs time for an anode of the anode assembly according to the present invention and a comparative anode.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

[0050] The particulars shown herein are by way of example and for purposes of illustrative discussion of the embodiments of the present invention only and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the present invention. In this regard, no attempt is made to show structural details of the present invention in more detail than is necessary for the fundamental understanding of the present invention, the description taken with the drawings making apparent to those skilled in the art how the several forms of the present invention may be embodied in practice.

[0051] In the following features (a) to (c) of the anode assembly according to the present invention will be discussed individually, starting with feature (c). [0052] As illustrated in Fig. 1, a conventional DLFC utilizes a case or container body 1 which contains therein a fuel chamber 2 and an electrolyte chamber 5. Case 1 is typically formed of, e.g., a plastic material. Fuel chamber 2 contains liquid fuel in the form of, e.g., a hydride or borohydride fuel. Electrolyte chamber 5 contains liquid electrolyte in the form of, e.g., an aqueous alkali metal hydroxide. An anode 3 is arranged within case 1 and separates the two chambers 2 and 5. Anode 3 will usually comprise a porous material that is pervious to gaseous and liquid substances. A cathode 4 is also arranged in case 1 and, together with anode 3, defines the electrolyte chamber 5. At anode 3 an oxidation of the liquid fuel takes place. At cathode 4 a substance, typically oxygen in the ambient air, is reduced. [0053] As illustrated fn Fig. 2, the DLFC having an anode assembly wnicn comprises feature (c) of the present invention differs from the fuel cell illustrated in Fig. 1 at least in that it additionally comprises, arranged inside case 1, a frame seal 6, a special membrane 8, a spacer material 9, and an optional pressure bleeding device having the form of, e.g., a capillary needle 7.

[0054] In the DLFC having an anode assembly comprising feature (c) of the present invention, the generated gas, usually hydrogen and usually in the form of micro-bubbles of a size of from about 0.01 to about 2 mm, accumulates into a space between a surface of anode 3 and special membrane 8. The bubbles will usually coalesce and/or unite to form a layer of gas which fills essentially all of the volume between anode 3 and special membrane 8. This, in turn, causes the liquid fuel to be separated from anode 3. The special membrane 8 substantially prevents any further contact between the liquid fuel and anode 3. The space between anode 3 and membrane 8 will usually be from about 0.1 mm to about 3.0 mm thick, and preferably has a thickness of from about 0.5 mm to about 1.5 mm, and most preferably about 0.5 mm.

[0055] Any extra gas which exceeds the volume of the space between anode 3 and special membrane 8 vents or bleeds out and into fuel chamber 2 through the optional capillary needle 7. This bleeding process stops essentially automatically when the pressure in the volume between anode 3 and special membrane 8 equals the pressure in fuel chamber 2.

[0056] Frame seal 6 extends around the perimeter of anode 3 and is arranged between anode 3 and special membrane 8. Frame seal 6 preferably has the form of a thin (non-porous) film and is utilized to prevent fuel from escaping in the area of the borders or outer edges of the anode perimeter. The material of frame seal 6 will usually be hydrophobic (at least on the surface thereof which faces the fuel chamber) and can be formed from a material such as, e.g., polytetrafluoroethylene, although other hydrophobic materials such as, e.g., olefin polymers like polyethylene and polypropylene may also be used for this purpose. In general, frame seal 6 will be made of, or at least include, a fluorinated polymer such as, e.g., a fluorinated or perfluorinated polyolefin. It is to be noted that frame seal 6 may also be made of a material that is not hydrophobic as such but has been rendered hydrophobic on the surface thereof by, e.g., coating with a hydrophobic material, or any other procedure which affords hydrophobicity. Preferably, frame seal 6 has a thickness of not more than about 0.1 mm. It will usually have a thickness of at least about 0.02 mm. A thickness of about 0.05 mm is particularly preferred for frame seal 6 for use in the present invention. Frame seal 6 may be mounted on anode 3 in many ways, e.g., with application of pressure anα/or by using an adhesive. A preferred way of mounting frame seal 6 comprises insert molding. Frame seal 6 can also be replaced by fixing and/or sealingly attaching a perimeter frame of anode 3 to anode 3 by, e.g., friction welding. [0057] Spacer material 9 is arranged between anode 3 and special membrane 8. Spacer material 9 also extends to the inside perimeter of case 1 and, in the perimeter area, is also arranged between frame seal 6 and special membrane 8. The purpose of spacer material 9 is to create a separation distance between special membrane 8 and the surface of anode 3. This separation distance forms space or volume for the gas layer. As the gas is generated, it accumulates within and fills this space. Spacer material 9 will permit the essentially free flow of gas across the surface of anode 3, and may be in the form of a net such as, e.g., a wattled net material. Spacer material 9 must be able to withstand the chemical attack by the components of the liquid fuel and will usually be hydrophobic, at least on the outer surfaces thereof. In other words, spacer material 9 may also be a hydrophilic material which has been made hydrophobic on the other surfaces thereof by any process suitable for this purpose such as e.g., coating with a hydrophobic material. Preferred spacer materials for use in the present invention include organic polymers such as, e.g., olefin homopolymers and olefin copolymers. Specific examples thereof include materials which may also be used for frame seal 6 such as, e.g., homo- and copolymers of ethylene and propylene, polytetrafluoroethylene, and the like. Spacer material 9 can also be made of other materials such as, e.g., ABS, polymethylmethacrylate, polyvinyl chloride, polysulfone and other organic polymers. Spacer material 9 will usually have a thickness of not more than about 5 mm, preferably not more than about 3 mm, more commonly a thickness of not more than about 1.5 mm. Spacer material 9 will usually have a thickness of at least about 0.1 mm, preferably at least about 0.5 mm. In a preferred embodiment of the present invention, spacer material 9 has a thickness of about 0.5 mm. Of course, spacer material 9 can also be dispensed with (its function being performed by another structure and/or the special membrane 8 itself) as is the case with other embodiments that will be described below. As set forth above, the same applies to the frame seal 6. [0058] As explained above, special membrane 8 separates the gas layer which has formed at the anode surface from liquid fuel in fuel chamber 2. Special membrane 8 is made of a material which can withstand the chemical attack by the components of the liquid fuel and will not catalyze a decomposition of the fuel or a component thereof to any appreciable extent. This material may be hydrophilic or hydrophobic. The hydrophϊlϊe material can also be a hydrophobic material which has been renαereα hydrophilic on the outer surface thereof by any suitable process, such as coating, surface treatment (e.g., oxidation) and the like. Preferred non-limiting examples of suitable hydrophilic materials for special membrane 8 include metals, as such or in the form of alloys. Particularly preferred materials include corrosion-resistant metals (e.g., nickel) and corrosion-resistant alloys such as steel, in particular, stainless steel, etc. [0059] Preferred non-limiting examples of suitable hydrophobic materials for special membrane 8 include organic polymers such as, e.g., polyolefins (for example, homo- and copolymers of, e.g., ethylene or propylene), polyamides and polyacrylonitrile. The hydrophilic or hydrophobic material will preferably be present in the form of a foam, a mesh and the like.

[0060] By way of non-limiting example, special membrane 8 may be or at least include a metal mesh such as, e.g., a stainless steel micromesh. The cells of the mesh may, for example, have a size of up to about 0.5 mm, e.g., up to about 0.1 mm, or up to about 0.06 mm. A preferred mesh cell size is from about 0.05 μm to about 0.06 mm, a size of about 0.05 mm being particularly preferred. The metal mesh preferably has a thickness of from about 0.01 mm to about 5 mm, e.g., from about 0.03 mm to about 3 mm.

[0061] Other non-limiting examples of special membrane 8 include a polymer mesh or a porous polymer layer. Preferably, the polymer mesh or porous polymer layer will have a thickness of from about 0.02 mm to about 2 mm. The cell size or pore size thereof will preferably be from about 0.01 mm to about 0.1 mm and from about 0.01 μm to about 0.1 mm, respectively.

[0062] Membrane 8 may also comprise other hydrophilic and/or hydrophobic materials, e.g., composites and/or laminates of hydrophilic materials, hydrophobic materials and combinations of hydrophilic and hydrophobic materials. Membrane 8 may also comprise, e.g., a non-woven material, foam materials (polymeric or metallic) and other porous materials such as porous papers, cloths and carbon (e.g., in the form of graphite), sintered metals, and ceramic materials.

[0063] Capillary needle 7 is secured to special membrane 8 and can be arranged at a convenient position thereon such as, e.g., centrally located (and, preferably, substantially perpendicular to membrane 8). As explained above, the purpose of needle 7 is to balance the pressure between the gas layer and the liquid fuel in the fuel chamber 2. The balance pressure range will usually be from about 1 atm to about 1.5 atm (absolute). Needle 7 is made of a material which can withstand the chemical attack by the components of the liquid fuel and does not catalyze a decomposition thereof to any appreciable extent. This material will usually be selected from the materials which are suitable for making the special membrane 8, but may also be made of other materials, e.g., polymeric materials. Non-limiting examples of polymeric materials include polyolefins such as polytetrafluoroethylene and polypropylene. Preferably, needle 7 is a stainless steel needle. While a suitable length of needle 7 may vary over a wide range (depending, in part on the dimensions of spacer 9, membrane 8, etc.) needle 7 will often have a length of up to about 2 cm, or even longer. The inner diameter of needle 7 will usually not exceed about 2 mm, preferably not exceed about 1 mm, or not exceed about 0.5 mm. Needle 7 may be attached to membrane 8 by any suitable method, e.g., by using a thermoadhesive, welding and mechanical attachment (the latter being a preferred method). Of course, needle 7 is not essential for the operation of the fuel cell of the present invention and can also be dispensed with, as in the case of the other embodiments that will be described below. [0064] Fig. 8 shows another non-limiting embodiment of the fuel cell of the present invention that differs from the fuel cell illustrated in Fig. 1 at least in that it additionally comprises, arranged inside case 1, an anode 3 having a frame, a special membrane 8a, an optional second membrane 8b, and an optional spacer material 9. This embodiment eliminates the need for the frame seal 6 and also does not comprise the capillary needle 7. The perimeter frame of anode 3 can be fixed to anode 3 by, e.g., friction welding. The materials and thicknesses of the devices 3, 4, 9, 8a and 8b can be the same as the corresponding devices described above with regard to the embodiment shown in Fig. 2. The membranes 8a and 8b may be of the same material, types and/or thicknesses as described above or may be different in anyone or more of these respects. [0065] Fig. 9 shows another non-limiting embodiment of the fuel cell of the present invention that differs from the fuel cell illustrated in Fig. 1 at least in that it additionally comprises, arranged inside case 1, an anode 3, a special membrane 8a, an optional second membrane 8b, an optional spacer material 9, and an optional frame seal 6. This embodiment also does not comprise capillary needle 7. The materials and thicknesses of the devices 3, 4, 6, 9, 8a and 8b can be the same as the corresponding devices described above with regard to the embodiment shown in Fig. 2. The membranes 8a and 8b may be of the same material, types and/or thicknesses as described above or may be different in anyone or more of these respects. [0066] Fig. 10 shows another non-limiting embodiment of the fuel cell of the present invention that differs from the fuel cell illustrated in Fig. 1 at least in that it additionally comprises) arranged fnsflde case 1, an anode 3, and a special membrane aa, ana an optional second membrane 8b. This embodiment eliminates the need for the spacer material 9 and the frame seal 6, and also does not comprise capillary needle 7. The materials and thicknesses of the devices 3, 4, 8a and 8b can be the same as the corresponding devices described above with regard to the embodiment shown in Fig. 2. The membranes 8a and 8b may be of the same material, types and/or thicknesses as described above or may be different in anyone or more of these respects. In this embodiment, the membrane 8a is preferably in contact with the anode 3. By way of non-limiting example, the membrane 8a can be rolled or otherwise attached or bound to the surface of the anode 3. In this case, the voids and/or free space in the membrane 8a provide the empty space that can be occupied by the generated gas to thereby form a barrier that substantially prevents the fuel from contacting the anode. [0067] Particularly in embodiments which utilize more than one special membrane 8a, e.g., two membranes 8a and 8b, the first membrane 8a can function in the manner described above with regard to the space and/or spacer material whereas the second membrane 8b can serve a different function such as, e.g., filter solids and the like from the fuel in fuel chamber 2 in order to protect the first membrane 8a and/or substantially prevent a clogging thereof.

[0068] Those of skill in the art will appreciate that not each of the various components of the fuel cell of the present invention has to be present as a single component and also does not have to be arranged completely inside a single case. By way of non- limiting example, fuel chamber 2 may comprise one part that is adjacent to the at least one membrane 8 (e.g., adjacent to membrane 8b) and one or more other parts (e.g., one or more cartridges) that are arranged outside the housing or case of the fuel cell and are connected to the case through one or more liquid passageways. The volume of the part of the fuel chamber that is arranged within the case, if any, may be small compared to the volume of the one or more parts that are arranged outside the case (e.g., not more than about 20 %, e.g., not more than about 10 %, not more than about 5 %, or not more than about 2 % of the latter volume). Further, fuel chamber 2 may be arranged substantially completely outside the case, and may be connected to the case by one or more liquid passageways (e.g., in the form of small diameter tubes and the like). By way of non-limiting example, the fuel chamber may be in the form of an (optionally disposable) cartridge that is connected to the case. Exemplary ways of connecting a cartridge to a case are disclosed, e.g., in co-pending U.S. application Nos. 10/824,443 and 10/849,503, the entire disclosures whereof are expressly incorporated by reference herein.

[0069] In this case, the at least one membrane 8 may be comprised by the case (e.g., at or in the vicinity of one or more points where liquid fuel can enter the case) and/or may be comprised by the fuel chamber 2 (e.g., the cartridge) (e.g., at or in the vicinity of one or more points where liquid fuel can leave the fuel chamber 2) and/or may be arranged somewhere in between the case and the fuel chamber 2 (e.g., within the one or more liquid passageways that connect the fuel chamber 2 and the case). Of course, in this case the details regarding the various components of the fuel chamber may be the same as those set forth above. For example, the at least one membrane 8 may comprise at least a first membrane 8a and a second membrane 8b. [0070] Figs. 11-13 show one non-limiting embodiment of a fuel cell 1 having a cathode 4, an anode 3, an electrolyte chamber 5 which is arranged between cathode 4 and anode 3. A cartridge CA having a fuel chamber 2 is connected and/or removably connected to the fuel cell housing having the cathode 4, anode 3 and electrolyte chamber 5. When the cartridge CA is connected to the housing (Fig. 11), fuel chamber 2 is arranged on that side of anode 3 which is opposite to the side which faces electrolyte chamber 5. At least one membrane 8 is arranged between the gas accumulation space adjacent anode 3 and fuel chamber 2. By way of non-limiting example, the width of this space can be approximately 1 mm, but may be considerably larger or smaller. The at least one membrane 8 is structured and arranged to allow gas which is formed, as a result of the fuel decomposition, on or in the vicinity of the side of the anode 3 that faces the fuel chamber 2 to accumulate adjacent to anode 3 at least to a point where the gas substantially prevents a direct contact between anode 3 and the liquid fuel in fuel chamber 2. As can be seen in Fig. 12, membrane 8 (which can also include an additional layer of spacer material 9) can have the form of a small screen filter member that is fixed to the inner surface of a wall of the housing. Of course, the filter element can also be arranged on the opposite end of the tubes so as to be arranged in the cartridge CA without leaving the scope of the invention. Further, a filter element can be arranged on both sides of the tubes. Still further, the inside of the tubes can include the membrane/spacer material, which can have the form of a cigarette filter of sufficient length. As can be seen in Fig. 13, the tubes (the numbers and sizes of which can vary as desired and can be similar to that described with regard to tube 7) of the cartridge CA are sealed relative to openings in the wall of the housing via one or more o-rings. Of course, any number of sealing techniques or methods may also be employed in providing sealing between the tubes and the openings on tne wan or me housing. Still further, it is contemplated that the tubes can instead be coupled to the fuel cell housing while openings are arranged in the wall of cartridge CA. Fig. 13 shows the cartridge CA being separated and/or unconnected from housing 1 of the fuel cell. Although not shown, valves can be utilized to stop and/or regulate flow from and to the cartridge CA and the housing of the fuel cell 1.

[0071] By way of non-limiting explanation, when the fuel cell is or is placed under no or substantially no load, liquid fuel will initially decompose and generate gas (e.g., hydrogen) in the vicinity of anode 3, thereby pushing the liquid fuel away from anode 3 and preventing further fuel from contacting anode 3, which in turn terminates the generation of gas. When the fuel cell is thereafter placed under load (closed electrical circuit), the gas will be consumed by oxidation on the surface of the anode, thereby creating a vacuum which sucks liquid fuel back and into direct contact with the surface of anode 3, where it will be oxidized to generate electrical energy. When the circuit is opened again (no load), gas will initially be generated through decomposition of the liquid fuel, and the above-described process will start from the beginning. [0072] Regarding feature (b) of the anode assembly of the present invention and as illustrated in Fig. 14, a DLFC comprising an anode assembly according to the present invention comprises a case or container body 1 which comprises therein a fuel chamber 2 and an electrolyte chamber 5. Fuel chamber 2 contains fuel in the form of, e.g., a hydride or borohydride fuel. Electrolyte chamber 5 contains electrolyte in the form of, e.g., an aqueous alkali metal hydroxide solution (it is noted, however, that the electrolyte may also be a solid or semisolid (e.g., gel) material). An anode 3 is arranged within case 1 and separates the two chambers 2 and 5. A cathode 4 is also arranged in the case 1 and, together with anode 3, defines electrolyte chamber 5. The fuel cell comprising an anode assembly according to aspect (b) of the present invention additionally comprises at least one layer 20 of a polymeric material on that surface of anode 3 which faces electrolyte chamber 5.

[0073] In a conventional DLFC without the anode assembly of the present invention which comprises feature (b), all or at least a substantial portion of the hydrogen gas formed at anode 3 and/or in the body of fuel chamber 2 will gradually pass through the (porous) anode and into electrolyte chamber 5 where the hydrogen forms bubbles (usually, micro-bubbles) in the electrolyte. This, in turn, results in an increase of the ionic resistance of the electrolyte. The anode assembly of the present invention which according to feature (b) is provided with the at least one layer 20 of polymeric material on the side of anode 3 which faces electrolyte chamber 5 prevents all or at least a substantial portion (typically at least about 80 %, preferably at least about 90 %, and up to about 98 or close to about 100 %, hereafter sometimes referred to as "gas-blocking efficiency") of the hydrogen gas from reaching electrolyte chamber 5, whereby an increase in the ionic resistance of the electrolyte can be avoided to an at least substantial extent. The percentage of hydrogen gas which is prevented from reaching the electrolyte chamber may be determined according to the method which is described in the Examples below.

[0074] As set forth above, according to feature (b) of the anode assembly of the present invention, one side (major surface) of anode 3 is substantially completely (and preferably completely) covered with at least one layer 20 of polymeric material. Covering anode 3 with polymeric material can be accomplished in various ways. For example, one or more films of polymeric material can be attached to the surface of the anode under pressure and/or by means of a suitable adhesive (applied, e.g. at the edges of the anode). Preferably, the one or more layers 20 of polymeric material are (successively) applied by a coating operation. For example, one or more solutions and/or suspensions of the desired polymeric material(s) may be applied onto the surface of the anode, and after the or each coating operation the solvent(s) may be at least partially removed, e.g., by allowing the solvents to evaporate under ambient conditions, by heating and/or by applying a vacuum. A non-limiting example of a typical coating process is described in the Examples below. The polymeric material does not necessarily have to be in direct contact with the anode surface (although direct contact is preferred), as long as the polymeric material is capable of preventing a substantial portion of the hydrogen gas from entering the electrolyte chamber, and as long as the conductivity of the combination of anode and polymeric layer is not significantly adversely affected by the lack of direct contact.

[0075] Where two or more layers of polymeric material (e.g., two, three or four layers of polymeric material) are applied, the layers may comprise the same or different polymer(s). Layers of the same polymer(s) may be of advantage, for example, if a single coating operation does not afford the desired thickness (and/or mechanical strength) of the polymeric material layer and/or if it is difficult to achieve a continuous coating film (substantially without any holes) with a single coating operation. [0076] Two or more layers which comprise different polymers in at least two of the layers may be expedient for, e.g., imparting a combination of desired characteristics to the polymeric material. For example, a first layer of polymeric material which is in direct Contact wftlπ the anode may comprise one or more polymers which provide a good adhesion to the anode surface, whereas a layer which comprises one or more polymers which is (are) different from the polymer(s) in the first layer and which layer is arranged on the first layer may provide other desired characteristics, for example, a high conductivity. In this regard, it is preferred for the combination of anode and polymeric material to have a resistivity of not substantially higher than about 1 Ohm-cm², even more preferred of not higher than about 0.95 Ohπvcm², particularly not higher than about 0.9 Ohm-cm², not higher than about 0.85 Ohm-cm², or not higher than about 0.8 Ohm-cm². The conductivity (resistivity) may be measured according to the method described in the Examples below.

[0077] Irrespective of whether one or two (or more) layers of polymeric material are provided on the anode surface, each of these layers may independently comprise a single polymer or a mixture of two or more polymers. Of course, if two or more layers are provided, these layers may have the same or a different thickness. [0078] The one or more layers of polymeric material arranged on the anode will usually have a combined thickness of not more than about 0.2 mm, e.g., not more than about 0.15 mm. On the other hand, the combined thickness will preferably be not lower than about 0.025 mm, e.g., not lower than about 0.03 mm.

[0079] Suitable polymers for use in the one or more layers of polymeric material 6 include those which provide, alone or in combination, both a satisfactory conductivity and a high gas-blocking efficiency (a low permeability for hydrogen gas), particularly in the conventional operating temperature range of a DLFC, i.e., from room temperature to about 6O⁰C. Also, the one or more polymers should provide sufficient mechanical strength and maintain mechanical integrity to a sufficient extent even when exposed to an alkaline solution (in particular, an aqueous electrolyte) at a temperature of up to about 6O⁰C for extended periods of time. In this regard, an example of an aqueous electrolyte of the type conventionally used in a DLFC is aqueous potassium hydroxide solution (e.g., about 6M to about 7M KOH). Sufficient adhesion to the anode surface is also a desired characteristic. As mentioned above, it is not necessary for a single polymer to exhibit all of these desirable properties in order to be suitable for use in the present invention. A combination of two or more polymers which together provide these properties is equally suitable.

[0080] Regarding adhesion of the polymers to the anode surface, it may be advantageous in certain cases to subject the surface of the anode that is to carry the gas blocking layer to a surface treatment in order to improve adhesion. Suitable surface treatments are readily apparent to those of skill in the art. A preferred surface treatment comprises a hydrophilization treatment, for example, a hydrophilization treatment as it is disclosed herein with respect to aspect (a) of the anode assembly of the present invention.

[0081] Examples of polymers which provide a satisfactory conductivity include those which are able to dissolve or swell in aqueous solutions. A high gas-blocking efficiency may be achieved, for example, by crosslinking suitable polymer chains, which at the same time will increase the mechanical strength of the polymer layer. [0082] Preferred polymers for use in the present invention include those which comprise one or more types of hydrophilic groups such as, e.g., OH, COOH and/or SO₃H groups. Non-limiting examples of such polymers are homo- and copolymers which comprise units of vinyl alcohol, acrylic acid, methacrylic acid, and the like. Of course, polymers with different hydrophilic groups may also be useful. The term "hydrophilic groups" as used herein and in the appended claims is meant to encompass groups which have affinity for and/or are capable of interacting with, water molecules, e.g., by forming hydrogen bonds, ionic interactions, and the like. Preferred examples of polymers with hydrophilic groups for use in the present invention are polymers which comprise at least OH groups, in particular, the homo- and copolymers of vinyl alcohol. [0083] Non-limiting examples of copolymers of vinyl alcohol comprise units of vinyl alcohol and units of one or more (e.g., one or two) ethylenically unsaturated comonomers. Preferred comonomers include C₂-C8 alkenes such as, e.g., ethylene, propylene, butene-1, hexene-1, and octene-1. Of course, other comonomers may be used as well such as, e.g., vinylpyrrolidone, vinyl chloride and methyl methacrylate. A particularly preferred comonomer is ethylene. Non-limiting specific examples of suitable copolymers include the Mowiol®, Exceval® and Moviflex® vinyl alcohol/ethylene copolymers which are commercially available from Kuraray Specialities Europe (Frankfurt, Germany), in particular, those with a relatively low ethylene content and/or a degree of hydrolysis of from about 97 % to about 99 % and/or a degree of polymerization of from about 1,000 to about 2,000 such as, e.g., Exceval® grades RS 1113 and RS 1117.

[0084] In the copolymers of vinyl alcohol (or any other monomer which comprises hydrophilic groups) and comonomers without hydrophilic groups (e.g., alkenes and the like), the vinyl alcohol units will usually provide the desired conductivity, and the comonomer(s) will preferably promote the adhesion of the polymer to the substrate (the anode surface). [0085] in the Copolymers of vinyl alcohol, the units of vinyl alcohol are preτeraoιy present in an amount of at least about 50 mol-%, particularly in copolymers where the comonomer(s) do not comprise any hydrophilic groups.

[0086] The average molecular weight of the homo- and copolymers of vinyl alcohol (or any other polymers) for use in the present invention is not particularly critical, but will usually be in the conventional range for this type of polymers, i.e., not significantly higher than about 100,000 and not significantly lower than about 10,000, e.g., not significantly lower than about 30,000 (expressed as weight average molecular weight). [0087] In order to increase the mechanical strength and the gas-blocking efficiency of a polymer with hydrophilic groups for use in the present invention, for example the homo- and copolymers of vinyl alcohol set forth above, it will usually be of advantage to crosslink the polymer chains. Suitable sites for crosslinking include the hydrophilic groups of the polymer molecules and/or any other functionalities (including ethylenically unsaturated bonds) that may be present in the polymer molecules. Suitable crosslinking agents include those which comprise in their molecule at least two (e.g., two, three, four of five) functional groups which are capable of reacting (or at least strongly interacting) with one or more types of functional groups present in the polymer molecule. The reaction between the functional groups preferably comprises a polycondensation (including a polyaddition), an ionic or free radical polymerization, or any other type of reaction which results in the formation of (preferably covalent) bonds between the reactants. The crosslinking agent may be of organic or inorganic nature, monomeric or polymeric, and two or more crosslinking agents may be employed, if desired. [0088] Non-limiting and preferred examples of crosslinking agents for the crosslinking of homo- and copolymers of vinyl alcohol as well as other types of polymers include polymeric crosslinking agents such as, e.g., polyalkylene glycols (e.g., those comprising one or more Ci_-6 alkylene glycols such as, e.g., ethylene glycol, propylene glycol, butylene glycol and hexylene glycol), preferably polyethylene glycol, polyalkylene oxides, in particular, polyethylene oxide in its broadest sense (including, e.g., diol-, triol- and tetrol-initiated polyethylene oxides and ethylene oxide/propylene oxide copolymers), homo- and copolymers of ethylenically unsaturated acids such as, e.g., acrylic acid, methacrylic acid and maleic acid, and monomeric species such as, e.g., alkali metal silicates and pyrophosphates (e.g., sodium or potassium silicate and sodium or potassium pyrophosphate), sugar alcohols (e.g., xylitol, sorbitol, etc.), saturated and unsaturated mono- and polycarboxylic acids which may optionally comprise additional functional groups (e.g., oxalic acid, succinic acid, glutaric acid, aefipic acid, maleic acid, fumaric acid, sulfosuccinic acid, malic acid, tartaric aciα, citric acid, etc.) and carbonyl compounds, in particular, aldehydes (e.g., formaldehyde). Of course, these compounds may optionally be employed as precursors and/or derivatives thereof. For example, polycarboxylic acids may be employed as, e.g., anhydrides or esters and in partially or completely neutralized form. These crosslinking agents will usually be employed in the form of a solution. For example, in the case of sulfosuccinic acid, a preferred concentration range is from about 0.1 % to about 2 % by weight, e.g., from about 0.2 % to about 1 % by weight.

[0089] In the case of polymeric crosslinking agents, the average molecular weight thereof is not particularly critical and commercially available materials may be employed. For example, the number average molecular weight of commercially available polyethylene glycols is typically in the range of from about 300 to about 10,000, whereas for commercially available polyethylene oxide the number average molecular weight is typically in the range of from about 35,000 to about 200,000. In the case of polyacrylic acid, the weight average molecular weight usually ranges from about 2,000 to about 250,000 (they will usually be employed in the form of a solution at a preferred concentration of from about 0.1 % to about 3 % by weight, e.g., from about 0.5 % to about 2 % by weight), and in the case of copolymers of acrylic acid and maleic acid, the weight average molecular weight usually ranges from about 2,000 to about 5,000, e.g., around 3,000 (they will usually be employed in the form of a solution at a preferred concentration of from about 0.1 % to about 3 % by weight, e.g., from about 0.5 % to about 2 % by weight).

[0090] When homo- and/or copolymers of vinyl alcohol are to be crosslinked for the purposes of the present invention, the weight ratio of these polymers and the crosslinking agent(s), e.g., the crosslinking agents set forth above, preferably ranges from about 2:1 to about 1:2. Of course, ratios outside this range may be used as well and, depending on the specific components employed, may even afford more desirable results. One of ordinary skill in the art will be aware of or be able to readily ascertain suitable weight ratios for other polymers and/or other crosslinking agents. [0091] The anode of the anode assembly of the present invention may be any anode which is suitable for the present type of fuel and fuel cell. The anode will usually comprise a porous material that is pervious to gaseous and liquid substances, and may have been produced by wet or dry technologies. Of course, the materials thereof should be chemically stable and should be chemically benign with respect to the fuel. A non- limiting example of an anode for use in the present invention comprises a metal mesh current dθϊlefetόfi <β.^r'g., a nϊøkel or stainless steel mesh, which has attached to it a porous active layer. This active layer may comprise, by way of non-limiting example, activated carbon carrying a catalytically active material (such as a metal, for example Pt, Pd, Ru, Rh, to name just a few), and a binder, typically a polymeric material such as polytetrafluoroethylene, and the like. Of course, other materials for making the anode of the present invention may be used as well. For example, instead of the metal mesh, a metal foam, or hydrophilic carbon paper may be used.

[0092] With respect to feature (a) of the anode assembly of the present invention and as illustrated in Fig. 19, a liquid fuel cell which comprises the anode assembly according to the present invention comprising aspect (a) comprises a casing or container body 1 which comprises a fuel chamber 2 and an electrolyte chamber 5. Fuel chamber 2 contains liquid fuel in the form of, e.g., an alkaline aqueous solution of a hydride or borohydride compound such as sodium borohydride. Non-limiting examples of corresponding liquid fuels are described in, e.g., US 20010045364 A1 , US 20030207160 A1, US 20030207157 A1, US 20030099876 A1 , and U.S. Patent Nos. 6,554,877 B2 and 6,562,497 B2, the entire disclosures whereof are expressly incorporated by reference herein.

[0093] Electrolyte chamber 5 contains electrolyte in the form of, e.g., an aqueous alkali metal hydroxide (e.g., NaOH and/or KOH). An anode 3 is arranged within casing 1 and separates the two chambers 2 and 5. A cathode 4 (e.g., an air-breathing cathode) is also arranged in casing 1 and, together with anode 3, defines electrolyte chamber 5. At least a part of anode 3 which faces fuel chamber 2 has been subjected to a hydrophilization treatment. For example, at least a part of side a in Fig. 19 (preferably, substantially the entire side a) of anode 3 may have been subjected to a hydrophilization treatment. The opposite side of anode 3 (side b in Fig. 19) may also have been subjected to a hydrophilization treatment.

[0094] In a conventional liquid fuel cell without the anode assembly according to feature (a) of the present invention, it will usually take a considerable period of time (often in excess of one hour) for the (hydrophilic) fuel to wet the anode substantially completely (this period is referred to herein as the "induction period"). Accordingly, the power output and the efficiency of the fuel cell will reach their maximum level only after a considerable induction period. In the anode assembly according to the present invention that exhibits aspect (a) (at least) a part of the anode that is intended to contact the liquid fuel has been subjected to a hydrophilization treatment, which increases the fuel wetting rate of the anode surface by a hydrophilic liquid fuel and thereby decreases the induction period (often- to less than about 60 minutes, e.g., less tnan aoout 4u minutes, or even less than about 30 minutes). It often shortens the induction period by at least about 50 %, e.g., at least about 70 %.

[0095] As set forth above, according to the present invention, feature (a), at least a part of the side of the anode, e.g., at least a part of one side (major surface) thereof, is subjected to a hydrophilization treatment. The hydrophilization treatment may comprise any treatment which renders the anode hydrophilic or more hydrophilic without adversely affecting, to any significant extent, desirable properties of the anode such as, e.g., electrocatalytic activity, mechanical integrity and electric conductivity of the active layer.

[0096] In this regard, it is to be appreciated that according to the present invention it is not necessary (although preferred) to subject substantially the entire side of a finished anode that is intended to contact the liquid fuel to a hydrophilization treatment. Hydrophilizing only a part of the side that is intended to contact the liquid fuel is sufficient as long as this affords an anode with substantially improved characteristics such as, e.g., substantially reduced induction period and/or substantially improved power output during the initial period of contact between anode and liquid fuel, etc., in comparison to the same anode that has not been subjected to any hydrophilization treatment at all.

[0097] By the same token, according to the present invention it is not necessary to hydrophilize the finished (ready-to-use) anode (or a part or side thereof, respectively). Rather, it may be sufficient to hydrophilize merely one or more components that are to be used for manufacturing the anode. By way of non-limiting example, all or at least a part of the support for carrying the catalytically active species (e.g., a catalytically active metal) may be subjected to a hydrophilization treatment (before or after loading it with the catalytically active species), whereafter it may be combined with the other material(s) used for making the anode (e.g., a binder).

[0098] Of course, according to the present invention it is also possible to combine different hydrophilization methods. For example, the support may first be hydrophilized, an anode may be manufactured by using the hydrophilized support with the catalytically active species thereon, and thereafter the finished anode (or at least a part of the side thereof that is intended to contact the liquid fuel) may be subjected to a (further) hydrophilization treatment. By way of further example, the anode or a part thereof may first be subjected to a treatment with one or more hydrophilizing agents, followed by cold plasma etching. Also, a treatment of the anode with a first hydrophilizing agent may be followed by a treatment Df the anode with a second hydrophilizing agent, or two or more hydrophilizing agents can be used at the same time. In other words, any method and combination of methods that renders (at least) a part of the side of the anode that is intended to come into contact with liquid fuel hydrophilic or more hydrophilic, respectively, can be used for the purposes of the present invention. [0099] Non-limiting examples of hydrophilization treatments which are suitable for the purposes of the present invention include a treatment with one or more hydrophilizing agents, (cold) plasma etching, heating in an oxidative atmosphere, etching in oxidant solutions, strong chemisorption, etc. As pointed out above, any combinations of suitable hydrophilization treatments may be employed as well. According to the present invention, "soft" hydrophilization treatments such as, e.g., treatment with one or more hydrophilizing agents and cold plasma etching are preferred. Preferred is an impregnation of the anode with a (preferably aqueous) solution of one or more hydrophilizing agents which preferably results in a weak adsorption thereof on the catalyst particles.

[0100] In the case of hydrophilizing the finished anode or a part thereof with hydrophilizing agents, since the active layer of the anode usually comprises a porous structure including micro-, meso- and macro-pores, the molecules of the hydrophilizing agent(s) should not be too large to enable them to diffuse into the macro- and meso- pores within a relatively short period of time. On other hand, in order to not get trapped in the pores of the active layer, these molecules should not be too volatile and/or too small.

[0101] The method by which the anode or any part or component thereof is treated (impregnated) is not particularly limited as long as it affords the desired result. For example, a solution (e.g., an aqueous solution or an aqueous organic solution) of the hydrophilizing agent(s) may be applied to at least that side of the anode (or at least a part thereof, respectively) which is to be contacted with the liquid fuel (i.e., side a in Fig. 1) by spraying, brushing, dipping etc., followed by holding the anode in contact with the solution (preferably at elevated temperature) to enable the hydrophilizing agent(s) to diffuse into the pores of the active layer. In a preferred method, the anode is immersed into a (preferably heated) solution of the hydrophilizing agent(ε) and kept therein for a sufficient period of time to allow diffusion of the hydrophilizing agent(s) into the active layer. Thereafter the anode is removed from the solution and dried. This immersion method will afford an anode wherein both major surfaces thereof (i.e., sides a and b in

Fig. 19) have been subjected to a hydrophilization treatment.

example, the (preferably aqueous) solution may nave a concentration of hydrophilizing agent(s) of from about 0.001 % to about 5 % by weight, e.g., from about 0.01 % to about 1 % by weight, and the solution may have a temperature of from about 4O⁰C to about 9O⁰C, with a residence time of the anode in the solution of from about 5 minutes to about 2 hours. Drying conditions may, for example, include drying in air at a temperature of from about 7O⁰C to about 100⁰C for about 10 minutes to about 2 hours. Of course, these conditions are given merely for illustrative purposes and considerably different times, temperatures and concentrations than those indicated herein may afford even more desirable results under certain circumstances. [0103] The amount of hydrophilizing agent(s) that is left on and inside the anode (or one or more components thereof) is not particularly limited as long as this amount affords the desired result, i.e., rendering the anode (or the part thereof, respectively, that will contact the liquid fuel) hydrophilic or more hydrophilic, respectively without significantly impairing other desirable properties of the anode. For example, the amount will often be not less than about 0.001 mg/cm², e.g., not less than about 0.01 mg/cm² _, not less than about 0.05 mg/cm², or not less than about 0.1 mg/cm² of hydrophilized surface area. On the other hand, the amount will often be not higher than about 5 mg/cm², e.g., not higher than about 1 mg/cm², or not higher than about 0.5 mg/cm². [0104] Examples of hydrophilizing agents which are suitable for the purposes of the present invention include substances which provide the anode with hydrophilic groups such as, e.g., OH, COOH, SO3H and amino groups. Often, these substances will exhibit a substantial solubility in water, although this is not a prerequisite. Further, they should be able to withstand a drying operation at elevated temperatures (for example, they should have a sufficiently low vapor pressure at elevated temperatures so as to not readily evaporate upon drying the anode or a component thereof). Non-limiting examples of such substances include non-ionic, cationic, anionic and amphoteric surfactants, mono- and polycarboxylic acids and salts thereof, oxy-acids and salts thereof, sulfonic acids and salts thereof, polyols, hydroxyacids and salts thereof, amines and salts thereof, aminoalcohols, aminoacids, sugars, sugar alcohols, sugar derivatives, and cellulose derivatives.

[0105] Non-limiting specific examples of hydrophilizing agents which are suitable for the purposes of the present invention include alkyl sulfates, alkyl sulfonates, alkyl ether sulfates, polyalkylene glycols and polyalkylene glycol mono- and diethers (e.g., based on C-ι-₆ alkylene glycols such as, e.g., di- tri- and tetraethylene glycol, di- tri and tetrapropylene glycol and polyethylene/propylene glycol, preferably having a weight %4rk^ι q§BSΪkάiι\W^"Wι§k%f not more than about 1,000), homo- and copolymers oτ acrylic acid, optionally in partly or completely neutralized form (e.g., copolymers of acrylic acid and one or more of maleic acid and methacrylic acid), monomeric polycarboxylic acids and salts thereof (e.g., the alkali and alkaline earth metal salts, particularly the Na and K salts) such as, e.g., oxalic acid, succinic acid, sulfosuccinic acid, glutaric acid, and adipic acid, etc., oxy-acids (e.g., monocarboxylic acids) and salts thereof (e.g., the Na and K salts), polyols such as, e.g., glycerol, pentaerythritol and trimethylolpropane, hydroxyacids and salts thereof such as, e.g., lactic acid, dimethylolpropionic acid, citric acid, malic acid and tartaric acid, aminoalcohols and salts thereof such as, e.g., mono- di- and triethanolamine, sugars such as, e.g., glucose, fructose, xylose, sorbose, sucrose, maltose, lactose and galactose, sugar alcohols such as, e.g., sorbitol, xylitol, mannitol, maltitol, lactitol, galactitol and erythritol, sugar derivatives such as, e.g., sugar acids (e.g., gluconic acid) and cellulose derivatives such as, e.g., carboxymethyl cellulose and salts thereof (e.g., the Na salt). The hydrophilizing agents can be employed individually or as combination of two or more thereof.

[0106] In a preferred aspect of the anode assembly of the present invention which incorporates feature (a), when the anode that has been subjected to one or more hydrophilization treatments is immersed in 6.6 M aqueous KOH of room temperature (about 25⁰C) for 10 minutes, the real component of the impedance (Z') of the anode (as determined, for example, according to the procedure set forth in the Examples below) is not larger than about 50 %, e.g., not larger than about 40 % of Z' of the anode without the hydrophilization treatment(s). After 20 minutes of immersion, Z' preferably is not larger than about 75 %, e.g., not larger than about 65 % of Z' of the untreated anode. Also, after 30 minutes of immersion, Z preferably is not larger than about 80 %, e.g., not larger than about 70 % of Z' of the untreated anode.

[0107] In another preferred aspect, Z' of the hydrophilized anode of the present invention after 10 minutes of immersion in 6.6 M KOH of room temperature is not larger than about 3 Ohm-cm², e.g., not larger than about 2.5 Ohm cm², and/or is not larger than about 2 Ohm cm² after 20 minutes, or even after 15 minutes of immersion in 6.6 M KOH.

[0108] In yet another preferred aspect, the anode is substantially completely wetted (e.g., at least about 98 % wetted) by 6.6 M KOH of room temperature within not more than about 60 minutes, e.g., within not more than about 45 minutes. The degree of wetting is determined by comparing the actual value of Z'_act with the final value of Z'_nn ifteV^ofrlpIte^ltiliM^fe^rding to d_wet = Z'_fin IZOA- "Completely wetted" in the present context means a degree of saturation that is achieved at an infinitely long period of time. [0109] In one aspect of the anode assembly of the present invention, the side of the anode which is intended to contact a liquid electrolyte (opposite the side that is intended to contact the liquid fuel), i.e., side b in Fig. 19, may show the above-discussed feature (b) of the anode assembly of the present invention, i.e., it may be (substantially completely) covered with a (preferably polymeric) material that is capable of substantially preventing hydrogen gas to pass through the anode. A corresponding embodiment is schematically illustrated in Fig. 20, which shows gas blocking layer 20 on that side of the anode 3 which faces electrolyte chamber 5 (side b in Fig. 19). Anode 3 can be covered with the polymeric material for the gas blocking layer 20 either before or after the hydrophilization treatment.

Example 1 (comparative)

[0110] A conventional DLFC of the type shown in Fig. 1 with the following parameters was employed for testing:

Area of anode and cathode = each 45 cm² (62 mm x 73 mm);

Thickness or width of electrolyte chamber = 4 mm;

Volume of electrolyte in the electrolyte chamber = 18 cm³;

Thickness or width of fuel chamber = 20 mm; and

Volume of fuel in the fuel chamber = 90 cm³.

[0111] The DLFC was filled with a borohydride fuel and tested under the following conditions:

Full time of test = 20 hours; Unloading regime = open circuit.

[0112] In this test, the maximum gas productivity was 15 cm³/min. As can be seen from Fig. 4, the generation of hydrogen begins to decrease after about 60 minutes, but continues over the full 20 hours of the test.

Example 2

[0113] A DLFC comprising an anode assembly comprising feature (c) of the present invention of the type shown in Fig. 2 with the following parameters was employed for testing:

Area of anode and cathode = each 45 cm² (62 mm x 73 mm); ^electrolyte chamber = 4 mm;

Volume of electrolyte in the electrolyte chamber = 18 cm³;

Thickness or width of fuel chamber = 20 mm;

Volume of fuel in the fuel chamber = 90 cm³;

Thin film Teflon frame-seal thickness = 50 μm;

Stainless steel capillary needle length = 7 mm, Inside Diameter = 320 μm;

Stainless steel micromesh special membrane with cells = 53 μm; and

Polypropylene wattled net spacer material with cells of 2 mm x 3 mm and with a thickness = 1 mm.

[0114] The DLFC was filled with a borohydride fuel and tested under the following conditions:

Full time of test = 20 hours; Unloading regime = open circuit.

[0115] In this test, the time until the space between anode 3 and special membrane 8 was filled was 45 seconds. As can be seen from Fig. 5, the generation of hydrogen began to decrease after about 45 seconds, and stopped after about 3 minutes, i.e., the fuel decomposition stopped after about 3 minutes.

[0116] It is to be noted that the exemplary and preferred dimensions of the various elements of the DLFC described above apply particularly to fuel cells for portable devices, e.g., for fuel cells which have dimensions of an order of magnitude which is suitable for portable devices (e.g., laptops, cell phones etc.). Examples of corresponding dimensions are given in the Examples herein. For fuel cells which are considerably smaller or larger than those which are suitable for portable devices, the preferred dimensions given herein may not always afford the desired result to the fullest possible extent. One of ordinary skill in the art will, however, be able to readily ascertain the most suitable dimensions for any given size of fuel cell.

[0117] As used herein, a "hydrophilic" material is a material that has an affinity for water. The term includes materials which can be wetted, have a high surface tension value and have a tendency to form hydrogen-bonds with water. It also includes materials which have high water vapor permeability.

[0118] As used herein, a "hydrophobic" material is a material which repels water.

The term includes materials which allow for the passage of gas therethrough but which substantially prevent the flow therethrough of water and similar protic and/or polar liquids. jδfiy

Examples 3 to 5 illustrate the production of anodes which are coated with polyethylene glycol-crosslinked vinyl alcohol homo- and copolymers (aspect (b) of the anode assembly of the present invention). The anodes are composed of the following materials:

(1) Ni mesh (58 mesh, wire diameter 0,14 mm, thickness about 500 μm) with an active layer of 85 % by weight of carbon black catalyst and 15 % by weight of polytetrafluoroethylene (made by wet technology);

(2) Ni mesh (40 mesh, wire diameter 0.14 mm, thickness about 400 μm) with an active layer of 80 % by weight of carbon black catalyst and 20 % by weight of polytetrafluoroethylene (dry technology).

The coating materials used in Examples 3 to 5 are as follows: Polyvinylalcohol (PVA, Merck): M_w = 72,000

Polyethylene glycol (PEG, Aldrich): M_n = 300

Vinyl alcohol/ethylene copolymer (VAE, Aldrich): ethylene content 27 mol-%

Example 3

[0120] A solution is prepared by dissolving 7.31 g of PVA and 4.69 g of PEG in 88 g of de-ionized water under stirring and heating the mixture at 70 ⁰C for 2 hours. One ml of the solution is applied onto one surface of the anode (20 cm²) and is then dried in air at ambient temperature for 20 min. Then 1 ml of the same solution is applied onto the first layer, whereafter the anode is transferred to an oven and dried at 120 ⁰C for 2 hours.

[0121] The resistivity of the resultant coated anode is 0.8 Ohm-cm², and the gas- blocking efficiency thereof is 99 %.

Example 4

[0122] A solution is prepared by dissolving 0.6 g of VAE and 0.4 g of PEG in 29 g of n-propanol/water (1 :1) under stirring and heating the mixture at 70 ⁰C for 2 hours. One ml of the solution is applied onto one surface of the anode (20 cm²) and then dried in air at ambient temperature for 20 min. Then 1 ml of the solution from Example 3 is applied onto the first layer, whereafter the anode is transferred to an oven and dried at 90 ⁰C for 2 hours.

[0123] The resistivity of the resultant coated anode is 0.99 Ohm-cm², and the gas- blocking efficiency thereof is 94 %. [0124] One ml of the solution from Example 4 is applied onto one surface of the anode (20 cm²) and is dried in air at ambient temperature for 20 min. Then 1 ml of the same solution is applied onto the first layer and the resultant coated anode is transferred to an oven and dried at 90 ⁰C for 2 hours.

[0125] The resistivity of the resultant coated anode is 0.88 Ohm-cm², and the gas- blocking efficiency thereof is 89 %.

[0126] The resistivity of the coated anodes in the above Examples may be determined as follows:

Method basics

[0127] The method is based on a DC applied to an ionic conductor in a porous object and a simultaneous measurement of the potential difference of the electrolyte across the object in the thickness direction thereof. A four-electrode cell is used for measurements. Two of the electrodes are "current source" auxiliary electrodes and the two others are identical "potential sense" reference electrodes.

[0128] Fig. 15 shows a schematic cross section view of a cell for measuring the electric resistivity of an object. A cell 7 is filled with electrolyte 8. The cell is provided with "current source" electrodes 11, 11' (working electrode and counter electrode) and "potential sense" electrodes 10, 10' (sense electrode and reference electrode). The object 23 whose resistivity is to be measured is arranged inside the cell 21 so as to be in contact with the electrolyte 22 on both major surfaces thereof. [0129] The resistance of a porous object impregnated with an electrolyte is determined as resistance difference between capillaries of the "potential sense" electrodes with and without the object under measurement. The resistance R is calculated according to equation (1):

R = R₁ - R₀ = (AE₁ - AE₀)/!, (1)

where Ri and AE₁ are resistance and potential difference, respectively with object, and Ro and ΔE₀ are resistance and potential difference without object. I is the source current. Two measurements are carried out: one for electrolyte without object and another one with object impregnated with electrolyte. Ro also includes an empiric temperature correction: R₀(t₂) = Ro(ti)*[1 - 0.017(t₂ - U)] (for the temperature range of

20 - 27 ⁰C). rήd^iitfliiistifily'^'llϊlηy^'object (anode) is calculated according to equation (2):

P = R S (2)

where S is the object surface area. [0130] Equipment and materials

1. Potentiostat/galvanostat, current range +100 mA, current accuracy of 0.1%, voltage measurement accuracy of 0.01 mV;

2. Measurement cell with two "source" electrodes;

3. Two "potential sense" electrodes : Hg/HgO electrodes (Koslow, Radiometer Analytical) filled with 6.6M KOH.

[0131] Procedure

1. Assemble cell without the anode to be measured.

2. Fill cell with electrolyte (6.6 M KOH) using holes for the "source" electrodes up to 2/3 of the height; insert "source" electrodes. Measure electrolyte temperature.

3. Insert two Hg/HgO "potential sense" electrodes (filled with 6.6M KOH).

4. Connect "source" electrodes to Work Electrode and Counter Electrode wires of potentiostat; connect "potential sense" electrodes to Reference Electrode and Sense Electrode wires.

5. By means of control interface select galvanostatic mode of operation and program the following steps:

[0132] The duration of each step is 1 s (total duration 10 s). The potential read-out frequency is 0.2 s. Start program, print data table, plot ΔE (mV) vs. I (mA). Approximate branches of E(I) by linear lines for positive and for negative current values. Absolute values of slopes are equal to the resistance Ro-

6. Disconnect wires of potentiostat, pull out all electrodes, empty and disassemble cell, rinse with distilled water.

7. Assemble cell with anode to be tested. Repeat steps 2. - 6. under the same temperature condition and determine R-i.

8. Calculate the resistance of the electrolyte in the anode using eq. (1), calculate resistivity of anode using eq. (2). The resistivity of the electrolyte is taken from reference data, S = 4 cm², thickness of anode is measured separately.

[0133] The gas-blocking efficiency (E GBL ) of the gas-blocking layer (GBL) of the coated anodes of the above Examples may be determined as follows. E GBL is calculated according to equation (3):

So₈₆ = IOO -(I --^) (3)

where V_GBL is the volume of hydrogen gas that penetrates into the electrolyte chamber, and V is the total volume of hydrogen gas that is produced at the anode/in the fuel chamber.

[0134] In order to determine E _GBL, it is necessary to generate hydrogen gas at a constant pre-determined rate and to measure its flow from the side of the GBL. For this purpose, a triple-chamber cell, shown in Fig. 17, may be used.

[0135] With reference to Figure 17, the cell 12 is produced from alkali-resistant plastic

Delrin™ and is equipped with standard 4 cm² electrodes 13, 15. It is assembled using bolts and is leak-proofed by rubber O-rings. A Ni plate serves as counter electrode 15; a porous polypropylene membrane 14 (Celgard™) which is glued in a standard electrode frame is used as separator. The anode 13 with the GBL to be tested is arranged in the cell 12. The cell is filled with 4M KOH solution; the level thereof must be the same in all three chambers of the cell 12. The anode 13 to be tested must be totally immersed in electrolyte.

[0136] Cell 12 is connected to a test assembly as shown in Fig. 16. The negative terminal of a DC current source (in series with an ammeter) is connected to anode 13 and the positive terminal is connected to Ni counter-electrode 15. Hydrogen gas is generated at a constant rate under a constant current load at anode 13, and oxygen is .IEJU rode 15. Membrane 14 which is arranged between me electrodes 13, 15 separates the flows of hydrogen and oxygen. [0137] E GB_L is calculated as the volume of hydrogen gas that enters the central chamber of the cell 12 divided by the known total volume of generated hydrogen gas. [0138] A gas outlet of the central chamber of cell 12 is connected to a water-filled Drexel bottle 16 (equipped with thermometer 19) by a silicon rubber tube. The hydrogen gas from the central chamber pushes water from Drexel bottle 16 into a beaker 18 placed on balance 17. The volume of hydrogen gas per time unit from the central chamber of cell 12 is obtained from the weight change of beaker 18 with time. [0139] Equipment and materials

1. Cell

2. Laboratory DC power supply (model GPC-3020)

3. Ammeter (Fluke 45 Multimeter)

4. Drexel bottle (250 ml) with built-in thermometer

5. Laboratory balance A&D GX-400, resolution 0.001g

6. PC with RSkey software [0140] Measurement procedure

1. Fill cell with 4M KOH.

2. Fill Drexel bottle with water and connect to cell.

3. Position outlet tube of Drexel bottle above opening in bottle cover so that it does not touch the cover.

4. Turn on PC and start RSkey software to read out the balance data.

5. Turn on DC power supply and set constant current of 100 mA/cm²; record data in MS Excel format (one point per minute) for one hour.

6. Write down temperature of gas in Drexel bottle.

7. Turn off power supply.

[0141] Example of measurement and calculation of E _GBL

Fig. 18 demonstrates plotted data obtained on anode #328 from Trumem composite.

The slope of the line in the weight - time coordinates corresponds to the rate of water replacement and is equal to the hydrogen gas leaving the central chamber of the cell

12. V_GBL = 0.294 ml/min.

[0142] The total hydrogen gas generation rate V under a total current of I = 0.4 A (0.1

A/cm²- 4 cm²) taking into account the temperature correction at t = 25⁰C is equal to: - _τ 22400 ' 6D 273 + ? . ..

V = I (4)

IF 273

F = 96500 Coulombs/mol is Faraday's number.

_τ. _Λ . 22400- 60 273 + 25 . . ... . . . . ._.

V = 0.4 — = 3.0410«// mm) (5)

2- 96500 273

E GS_L expressed in percent is equal to:

0 ?94

E _GBL = 100 • I 1 - ^u. I - 90.3% (6) ^GBL ' 3.041

[0143] The following non-limiting Example 6 illustrates the production of a hydrophilized anode (without gas blocking layer), i.e. feature (a) of the anode assembly according to the present invention. The anode is composed of a Ni mesh (40 mesh, wire diameter 0.14 mm, thickness about 400 μm) with an active layer of 80 % by weight of catalyst on activated carbon support and 20 % by weight of polytetrafluoroethylene (dry technology).

Example 6

[0144] A solution is prepared by dissolving 5 g of D-sorbitol in 1000 ml of de-ionized water under stirring. The solution is heated to 70 ⁰C in a glass beaker by means of heating plate; an anode material strip (180 mm x 100 mm) is immersed in the solution and allowed to stay therein for 1 hour. Then the strip is taken out and is transferred to an oven and dried at 90 ⁰C for 1 hour. The amount of sorbitol in anode is 0.06 mg/cm². [0145] The degree of hydrophilization of the resultant anode material is checked by means of electrochemical impedance measurements. The equipment used is an AutoLab Potentiostat/Galvanostat PGSTAT30 (EcoChemie) with Frequency Response Analyzer and 3-electrode glass electrochemical cell. The electrolyte is 6.6 M KOH. The reference electrode is a reversible hydrogen electrode (Hydroflex, Gaskatel). A piece of anode (1 cm x 1 cm) is immersed in the electrolyte. Measurements are taken at room temperature at open-circuit potential, at a frequency of 100 Hz and an AC signal afri^fifidliif/iilFriV-l'fhBi'value real component of the impedance (Z¹) is taKen as a measure of the degree of wetting; the lower the value of Z', the better the wetting. A well wetted anode demonstrates a Z value below 2 Ohm*cm². A plot of the wetting kinetics for hydrophilized and non-hydrophilized anodes is shown in Fig. 21. It is seen that the hydrophilized anode becomes well wetted already during the first few minutes of immersion in the KOH solution. In the case of the non-hydrophilized anode it takes more than 80 minutes to afford satisfactory wetting.

[0146] It is noted that the foregoing examples have been provided merely for the purpose of explanation and are in no way to be construed as limiting of the present invention. While the present invention has been described with reference to an exemplary embodiment, it is understood that the words that have been used are words of description and illustration, rather than words of limitation. Changes may be made, within the purview of the appended claims, as presently stated and as amended, without departing from the scope and spirit of the present invention in its aspects. Although the invention has been described herein with reference to particular means, materials and embodiments, the invention is not intended to be limited to the particulars disclosed herein. Instead, the invention extends to ail functionally equivalent structures, methods and uses, such as are within the scope of the appended claims.

Claims

et-Aϊrøis¹

1. An anode assembly for a liquid fuel cell, wherein the assembly comprises at least two of (a), (b) and (c):

(a) an anode wherein at least a part of a side of the anode which is intended to contact a liquid fuel has been subjected to a hydrophilization treatment;

(b) a polymeric material which substantially completely covers a side of the anode which is intended to contact an electrolyte, which polymeric material prevents at least about 80 % of hydrogen gas that is generated at the anode to pass through the anode into the electrolyte;

(c) at least one membrane arranged on the side of the anode which is intended to contact a liquid fuel, the at least one membrane being structured and arranged to allow gas which is formed on or in a vicinity of the side of the anode which is intended to contact the liquid fuel to accumulate adjacent to the anode at least to a point where the accumulated gas substantially prevents the liquid fuel from contacting the anode.

2. The anode assembly of claim 1 , wherein the assembly comprises (a) and (b).

3. The anode assembly of claim 1 , wherein the assembly comprises (a) and (c).

4. The anode assembly of claim 1 , wherein the assembly comprises (b) and (c).

5. The anode assembly of claim 1 , wherein the assembly comprises (a), (b) and (c).

6. The anode assembly of any one of claims 1 to 5, wherein the anode comprises a catalytically active metal on a support.

7. The anode assembly of claim 6, wherein the catalytically active metal comprises at least one of Pt, Pd, Rh, Ru, Ir, Au and Re.

8. The anode assembly of any one of claims 6 and 7, wherein the support comprises at least one of activated carbon, carbon black, graphite and carbon nanotubes. &. f H'e" "afhbd€ iiss'e'hϊβly of any one of claims 6 to 8, wherein the anode further comprises a binder.

10. The anode assembly of any one of claims 1 to 3 and 5 to 9, wherein in (a) at least a side of the finished anode which is intended to contact a liquid fuel has been subjected to a hydrophilization treatment.

11. The anode assembly of any one of claims 1 to 3 and 5 to 10, wherein in (a) the hydrophilization treatment comprises a treatment with a hydrophilizing agent.

12. The anode assembly of claim 11 , wherein the hydrophilizing agent comprises at least one substance selected from anionic surfactants, cationic surfactants, non-ionic surfactants, polycarboxylic acids and salts thereof, oxy-acids and salts thereof, sugars, sugar alcohols, sugar derivatives and cellulose derivatives.

13. The anode assembly of claim 11, wherein the hydrophilizing agent comprises at least one substance selected from alkyl sulfates and alkyl sulfonates.

14. The anode assembly of claim 11 , wherein the hydrophilizing agent comprises at least one substance selected from polyalkylene glycols and ethers thereof.

15. The anode assembly of claim 14, wherein the weight average molecular weight of the polyalkylene glycols and ethers thereof is not higher than about 1 ,000.

16. The anode assembly of claim 11 , wherein the hydrophilizing agent comprises at least one substance selected from homopolymers and copolymers of acrylic acid, monomeric polycarboxylic acids and salts thereof.

17. The anode assembly of claim 11, wherein the hydrophilizing agent comprises at least one substance selected from glucose, fructose, xylose, sorbose, sucrose, maltose, lactose, galactose, sorbitol, xylitol, mannitol, maltitol, lactitol, galactitol, erythritol and gluconic acid.

18. The anode assembly of claim 11 , wherein the hydrophilizing agent comprises at least one substance selected from carboxymethyl cellulose and salts thereof. f9f "fWi^o^'Hi-hheWWof claim 11, wherein the anode comprises from about 0.001 to about 5 mg/cm² of hydrophilizing agent.

20. The anode assembly of any one of claims 1 to 3 and 5 to 10, wherein in (a) the hydrophilization treatment comprises cold plasma etching of at least a side of the finished anode which is intended to contact the liquid fuel.

21. The anode assembly of any one of claims 1 to 3 and 5 to 20, wherein in (a) a real component of an impedance after 10 minutes of immersion of the anode in 6.6 M aqueous KOH is not larger than about 50 % of a real component of an impedance of the same anode that has not been subjected to the hydrophilization treatment.

22. The anode assembly of any one of claims 1 to 3 and 5 to 21 , wherein in (a) a real component of an impedance after 20 minutes of immersion of the anode in 6.6 M aqueous KOH is not larger than about 75 % of a real component of an impedance of the same anode that has not been subjected to the hydrophilization treatment.

23. The anode assembly of any one of claims 1 to 3 and 5 to 22, wherein in (a) a real component of an impedance of the anode after 10 minutes of immersion in 6.6 M KOH is not larger than about 3 Ohm-cm².

24. The anode assembly of any one of claims 1 to 3 and 5 to 23, wherein in (a) the anode is substantially completely wetted by 6.6 M KOH of 25⁰C within not more than about 60 minutes.

25. The anode assembly of any one of claims 1 , 2 and 4 to 24, wherein in (b) at least about 90 % of the hydrogen gas is prevented from entering the electrolyte.

26. The anode assembly of any one of claims 1 , 2 and 4 to 25, wherein in (b) a resistivity of a combination of the anode with the polymeric material thereon is not larger than about 1 Ohm-cm².

27. The anode assembly of any one of claims 1 , 2 and 4 to 26, wherein in (b) the polymeric material comprises one or more layers of polymeric material and the one or more layers have a total thickness of from about 25 μm to about 200 μm. 2^'jg.

of any one of claims 1, 2 and 4 to 27, wherein in (b) the polymeric material comprises at least one polymer with a hydrophilic group.

29. The anode assembly of claim 28, wherein the hydrophilic group is selected from one or more of OH, COOH and SO₃H groups.

30. The anode assembly of claim 28, wherein the at least one polymer with a hydrophilic group comprises at least one of a homopolymer and a copolymer of vinyl alcohol.

31. The anode assembly of claim 28, wherein the at least one polymer with a hydrophilic group comprises a vinyl alcohol/alkene copolymer.

32. The anode assembly of any one of claims 28 to 31, wherein the at least one polymer with a hydrophilic group is at least partially crosslinked with at least one crosslinking agent which comprises a polymer that has at least one functional group which is capable of reacting with a functional group of the hydrophilic polymer.

33. The anode assembly of any one of claims 28 to 32, wherein the at least one polymer with a hydrophilic group comprises a polymer having OH groups and the at least one crosslinking agent comprises at least one polymer selected from polyethylene glycol, polyethylene oxide, a homo- or copolymer of acrylic acid and combinations of two or more thereof.

34. The anode assembly of any one of claims 32 and 33, wherein the crosslinking agent comprises at least one of a polyethylene glycol with a number average molecular weight of from about 300 to about 10,000 and a polyethylene oxide with a number average molecular weight of from about 35,000 to about 200,000.

35. The anode assembly of any one of claims 28 to 34, wherein the at least one polymer with a hydrophilic group comprises a polymer having OH groups and the at least one crosslinking agent comprises a polymer comprising a monomeric unit having at least one of a carboxylic acid and a sulfonic acid group. 36 Th"e" 'atfόde" -a^'s^'s'e'rnbly of claim 35, wherein the monomeric unit comprises an ethylenically unsaturated carboxylic acid.

37. The anode assembly of claim 36, wherein the ethylenically unsaturated carboxylic acid is selected from acrylic acid, methacrylic acid, maleic acid and any combinations thereof.

38. The anode assembly of claim 35, wherein the at least one crosslinking agent comprises a homo- or copolymer of acrylic acid.

39. The anode assembly of claim 35, wherein the at least one crosslinking agent comprises polyacrylic acid.

40. The anode assembly of claim 39, wherein the polyacrylic acid has a weight average molecular weight of from about 2,000 to about 250,000.

41. The anode assembly of claim 38, wherein the crosslinking agent comprises a copolymer of acrylic acid and maleic acid.

42. The anode assembly of claim 41 , wherein the crosslinking agent has a weight average molecular weight of from about 2,000 to about 5,000.

43. The anode assembly of claim 28, wherein the at least one polymer with a hydrophilic group is at least partially crosslinked with at least one crosslinking agent selected from a silicate, a pyrophosphate, a sugar alcohol, a polycarboxylic acid and an aldehyde.

44. The anode assembly of claim 43, wherein a weight ratio of the at least one polymer with a hydrophilic group and the crosslinking agent is from about 2:1 to about 1 :2.

45. The anode assembly of any one of claims 43 and 44, wherein the crosslinking agent comprises sulfosuccinic acid. 46: TfiS"anadl""d'ssέιfi^'biy of any one of claims 1, 2 and 4 to 45, wherein in (b) the side of the anode that is covered with the polymeric material has been subjected to a surface treatment prior to covering the side with the polymeric material.

47. The anode assembly of claim 46, wherein the surface treatment comprises a hydrophilization treatment.

48. The anode assembly of claim 47, wherein the hydrophilization treatment comprises a treatment with a hydrophilizing agent.

49. The anode assembly of claim 48, wherein the hydrophilizing agent comprises at least one substance selected from anionic surfactants, cationic surfactants, non-ionic surfactants, polycarboxylic acids and salts thereof, oxy-acids and salts thereof, sugars, sugar alcohols, sugar derivatives and cellulose derivatives.

50. The anode assembly of any one of claims 1 and 3 to 49, wherein in (c) the at least one membrane comprises a single layer of material.

51. The anode assembly of any one of claims 1 and 3 to 50, wherein in (c) the at least one membrane comprises a hydrophilic material.

52. The anode assembly of claim 51 , wherein the hydrophilic material comprises at least one of a metal and a metal alloy.

53. The anode assembly of any one of claims 51 and 52, wherein the hydrophilic material comprises stainless steel.

54. The anode assembly of any one of claims 1 and 3 to 50, wherein in (c) the at least one membrane comprises a hydrophobic material.

55. The anode assembly of claim 54, wherein the hydrophobic material comprises an organic polymer.

56. The anode assembly of any one of claims 54 and 55, wherein the hydrophobic material comprises one or more of a polyolefin, a polyamide and polyacrylonitrile. "57. Tf)§"a'i1odS ''asTe'ffibϊy of any one of claims 1 and 3 to 56, wherein in (c) the at least one membrane comprises one or more of a non-woven material, a composite material, a laminate material, a composite/laminate material, a foam material, a porous paper material, a cloth material, a carbon/graphite material, a sintered metal material, a ceramic material, and a polymer material.

58. The anode assembly of any one of claims 1 and 3 to 57, wherein in (c) the at least one membrane comprises one or more of a mesh and a foam.

59. The anode assembly of any one of claims 1 and 3 to 58, wherein in (c) the at least one membrane comprises a stainless steel micromesh.

60. The anode assembly of claim 59, wherein the micromesh comprises cells having a size of up to about 0.5 mm.

61. The anode assembly of any one of claims 59 and 60, wherein the mesh has a thickness of from about 0.01 mm to about 5 mm.

62. The anode assembly of any one of claims 1 and 3 to 57, wherein in (c) the at least one membrane comprises one or more of a polymer mesh and a porous polymer layer.

63. The anode assembly of claim 62, wherein the polymer mesh or porous polymer layer has a thickness of from about 0.02 mm to about 2 mm.

64. The anode assembly of any one of claims 62 and 63, wherein the polymer mesh has a cell size of from about 0.01 mm to about 0.1 mm and the porous polymer layer has a pore size of from about 0.01 μm to about 0.1 mm.

65. The anode assembly of any one of claims 1 and 3 to 64, wherein in (c) the at least one membrane is in contact with a side of the anode which is intended to contact the liquid fuel.

66. The anode assembly of claim 65, wherein the at least one membrane is at least one of attached and bonded to the surface of the anode. ^"67.

of any one of claims 1 and 3 to 64, wherein in (c) the fuel cell further comprises one or more of a free space and a spacer structure arranged between the at least one membrane and the anode.

68. The anode assembly of claim 67, wherein the fuel cell comprises a spacer structure comprised of a spacer material having a free space therein.

69. The anode assembly of any one of claims 67 and 68, wherein the spacer structure comprises a layer of spacer material having a thickness of up to about 3 mm.

70. The anode assembly of claim 69, wherein the layer of spacer material has a thickness of from about 0.5 mm to about 1.5 mm.

71. The anode assembly of any one of claims 68 to 70, wherein the spacer material comprises a hydrophobic material.

72. The anode assembly of claim 71 , wherein the hydrophobic material comprises a polymeric material.

73. The anode assembly of claim 72, wherein the hydrophobic material comprises one or more of an olefin homopolymer, an olefin copolymer, ABS, polymethylmethacrylate, polyvinyl chloride, and polysulfone.

74. The anode assembly of claim 72, wherein the hydrophobic material comprises one or more of polyethylene, polypropylene, polytetrafluoroethylene, and ABS.

75. The anode assembly of any one of claims 71 to 74, wherein the at least one membrane comprises a hydrophilic material.

76. The anode assembly of any one of claims 67 to 75, wherein the spacer structure comprises a net.

77. The anode assembly of claim 76, wherein the net comprises a wattled net.

78. the anode" assέiti'biy of any one of claims 76 and 77, wherein the net comprises openings of from about 1 mm to about 50 mm.

79. The anode assembly of any one of claims 67 to 78, wherein the fuel cell comprises a spacer structure comprised of a frame seal which is arranged on the side of the anode which is intended to contact the liquid fuel.

80. The anode assembly of claim 79, wherein the frame seal comprises a hydrophobic material.

81. The anode assembly of claim 80, wherein the hydrophobic material comprises a polymer.

82. The anode assembly of claim 81, wherein the polymer comprises a fluorinated polymer.

83. The anode assembly of any one of claims 79 to 82, wherein the frame seal has a thickness of from about 0.02 mm to about 0.05 mm.

84. The anode assembly of claim 67, wherein the spacer structure comprises both a spacer material having a free space therein and a frame seal which is arranged on the side of the anode which is intended to contact the liquid fuel.

85. The anode assembly of any one of claims 1 and 3 to 84, wherein in (c) the anode assembly comprises at least a first membrane adjacent to the anode and a second membrane on a side of the first membrane which is intended to contact the liquid fuel, at least the first membrane being structured and arranged to allow gas which is formed on or in the vicinity of the side of the anode which comes into contact with the liquid fuel to accumulate adjacent to the anode at least to a point where the accumulated gas substantially prevents the liquid fuel from contacting the anode.

86. The anode assembly of claim 85, wherein the second membrane is structured and arranged to filter solids from the liquid fuel, protect the first membrane, or both. #7: The anode ^"asse'm^'5ly" of any one of claims 85 and 86, wherein the first membrane and the second membrane form an integral structure.

88. The anode assembly of any one of claims 85 to 87, wherein the second membrane comprises one or more of a material that is different from that of the first membrane, a thickness that is different from that of the first membrane, and a pore size or cell size that is different from that of the first membrane.

89. The anode assembly of any one of claims 85 to 88, wherein the second membrane comprises one or more of a material that is substantially the same as that of the first membrane, a thickness that is substantially the same as that of the first membrane, and a pore size or cell size that is substantially the same as that of the first membrane.

90. The anode assembly of any one of claims 85 to 89, wherein at least the first membrane comprises a polymer mesh or porous polymer layer having a thickness of between about 0.02 mm and 2 mm and a cell size of from about 0.01 mm to about 0.1 mm or a pore size of from about 0.01 μm to about 0.1 mm.

91 The anode assembly of any one of claims 85 to 90, wherein at least the first membrane comprises a stainless steel mesh having a thickness of from about 0.01 mm to about 5 mm.

92. The anode assembly of any one of claims 85 to 91, wherein the first membrane is one or more of bonded to and in contact with the side of the anode that is intended to contact the liquid fuel.

93. The anode assembly of any one of claims 85 to 91, wherein the fuel cell further comprises one or more of a free space and a spacer structure arranged between the first membrane and the anode.

94. The anode assembly of any one of claims 1 to 93, wherein the anode is one or more of fixed within a fuel cell case and in sealing engagement with a fuel cell case.

95. A liquid fuel cell comprising the anode assembly of any one of claims 1 to 94. ^■§£. ^:?rte"fϋel cell of claim 95, wherein the fuel cell comprises at least one of a metal hydride and a metal borohydride compound in a fuel chamber thereof.

97. The fuel cell of any one of claims 95 and 96, wherein an electrolyte chamber thereof comprises a liquid electrolyte.

98. The fuel cell of claim 97, wherein the liquid electrolyte comprises aqueous solution of one or more metal hydroxides.

99. An anode assembly for a liquid fuel cell, wherein the assembly comprises:

(a) an anode wherein at least a part of a side of the anode which is intended to contact a liquid fuel has been subjected to a hydrophilization treatment with a hydrophilizing agent;

(b) a polymeric material which substantially completely covers a side of the anode which is intended to contact an electrolyte, which polymeric material prevents at least about 90 % of hydrogen gas that is generated at the anode to pass through the anode into the electrolyte, the polymeric material comprising least one polymer having a hydrophilic group selected from OH, COOH and SO₃H groups and being at least partially crosslinked with at least one crosslinking agent which comprises a polymer that has at least one functional group that is capable of reacting with a functional group of the hydrophilic polymer;

100. A liquid fuel cell for use with a liquid fuel that is prone to undergo decomposition with generation of hydrogen gas, the fuel cell comprising: a cathode; an anode; an electrolyte chamber arranged between the cathode and the anode; a fuel chamber arranged on a side of the anode which is opposite to a side which faces the electrolyte chamber; one or mo're lasers df polymeric material arranged on a side of the anode which faces the fuel chamber; and at least one membrane arranged on the side of the anode which faces the fuel chamber, wherein the one or more layers of polymeric material prevent an at least substantial portion of the hydrogen gas that is present in the fuel chamber when liquid fuel is present in the fuel chamber from passing through the anode into the electrolyte chamber and wherein the at least one membrane is structured and arranged to allow gas which is formed on or in a vicinity of the surface of the anode which faces the fuel chamber to accumulate adjacent to the anode at least to a point where the accumulated gas substantially prevents the liquid fuel in the fuel chamber from contacting the anode

101. A liquid fuel cell for use with a liquid fuel that is prone to undergo decomposition with generation of hydrogen gas, the fuel cell comprising: a cathode; an anode; an electrolyte chamber arranged between the cathode and the anode; a fuel chamber arranged on a side of the anode which is opposite to a side which faces the electrolyte chamber; and one or more layers of polymeric material arranged on a surface of the anode which faces the fuel chamber, wherein the one or more layers of polymeric material prevent an at least substantial portion of the hydrogen gas that is present in the fuel chamber when liquid fuel is present in the fuel chamber from passing through the anode into the electrolyte chamber, and wherein at least a part of a side of the anode which is intended to contact the liquid fuel has been subjected to a hydrophilization treatment.

102. A liquid fuel cell for use with a liquid fuel that is prone to undergo decomposition with generation of hydrogen gas, the fuel cell comprising: a cathode; an anode; an electrolyte chamber arranged between the cathode and the anode; a fuel chamber arranged on a side of the anode which is opposite to a side which faces the electrolyte chamber; and af Wifoftt'mM&rlne arranged on the side of the anode which faces the fuel cnamber, wherein the at least one membrane is structured and arranged to allow gas which is formed on or in a vicinity of the surface of the anode which faces the fuel chamber to accumulate adjacent to the anode at least to a point where the accumulated gas substantially prevents the liquid fuel in the fuel chamber from contacting the anode, and wherein at least a part of a side of the anode which is intended to contact the liquid fuel has been subjected to a hydrophilization treatment.

103. A liquid fuel cell for use with a liquid fuel that is prone to undergo decomposition with generation of hydrogen gas, the fuel cell comprising: a cathode; an anode; an electrolyte chamber arranged between the cathode and the anode; a fuel chamber arranged on a side of the anode which is opposite to a side which faces the electrolyte chamber; one or more layers of polymeric material arranged on a surface of the anode which faces the fuel chamber; and at least one membrane arranged on the side of the anode which faces the fuel chamber, wherein the one or more layers of polymeric material prevent an at least substantial portion of the hydrogen gas that is present in the fuel chamber when liquid fuel is present in the fuel chamber from passing through the anode into the electrolyte chamber, wherein the at least one membrane is structured and arranged to allow gas which is formed on or in a vicinity of the surface of the anode which faces the fuel chamber to accumulate adjacent to the anode at least to a point where the accumulated gas substantially prevents the liquid fuel in the fuel chamber from contacting the anode, and wherein at least a part of a side of the anode which is intended to contact the liquid fuel has been subjected to a hydrophilization treatment.

104. The fuel cell of any one of claims 100 to 103, wherein the fuel cell is a direct liquid fuel cell.

105. The fuel cell of any one of claims 100 to 104, wherein the fuel cell is portable. ^"106. ?rϊe''fuέl Slff ofariy^one of claims 100 to 105, wherein the fuel cell comprises at least one of a metal hydride and a metal borohydride compound in the fuel chamber.

107. The fuel cell of any one of claims 100 to 106, wherein the fuel chamber is arranged in a cartridge that is at least one of connected to a housing of the fuel cell and removably mounted to a housing of the fuel cell.

108. The fuel cell of any one of claims 100 to 107, wherein the fuel cell further comprises at least one member that allows liquid fuel to pass from the fuel chamber of the cartridge to an area adjacent the anode.

109. The fuel cell of any one of claims 100 to 106, wherein the fuel cell comprises a case which accommodates at least the anode, wherein at least one part of the fuel chamber is arranged outside the case, and wherein the case is connected to the at least one part of the fuel chamber that is arranged outside the case through one or more liquid passageways.

110. The fuel cell of claim 109, wherein the at least one part of the fuel chamber that is arranged outside the case comprises a cartridge.

111. The fuel cell of any one of claims 109 and 110, wherein the at least one membrane is arranged at least one of (a) at or in a vicinity of one or more locations of the case where liquid fuel from the at least one part of the fuel chamber that is arranged outside the case can enter the case, (b) at or in a vicinity of one or more locations of the at least one part of the fuel chamber that is arranged outside the case where liquid fuel can leave the at least one part of the fuel chamber that is arranged outside the case, and (c) at one or more locations inside the one or more liquid passageways.