EP2070148A1

EP2070148A1 - A fuel cell or a reactor based on fuel cell technology and having a proton conductive membrane as well as methods for making them

Info

Publication number: EP2070148A1
Application number: EP07808875A
Authority: EP
Inventors: Alf Larsson; Olof Dahlberg
Original assignee: Morphic Technologies AB
Current assignee: Morphic Technologies AB
Priority date: 2006-10-06
Filing date: 2007-09-11
Publication date: 2009-06-17
Also published as: CN101589500A; SE530458C2; SE0602127L; WO2008041922A1; TW200935651A; JP2010506357A

Abstract

In the mounting of a membrane (13) in a fuel cell, there is a great risk of damages to the membrane and problems in the sealing between membrane and electrodes occur easily. These problems have been eliminated by in situ moulding of the membrane (13) in the cell. For a cell of DMFC type, a monomer such as acrylamide can be admixed with a sulfonic acid, preferably p-chlorobenzene sulfonic acid. As a cross-linking agent, N, N' -methylene-bis- acrylamide is suitably used in combination with N,N,N',N'- tetramethylene diamine and the setting reaction is initiated by a peroxo salt, suitably ammonium persulfate. As an alternative, the membrane (13) is moulded from a soda glass melt, after which the the soda is dissolved out by acid. The membrane (13) can also be moulded from water glass admixed with titanium dioxide and after the neutralisation of the mixture the water is removed, whereby the molecules arrange themselves to form a silica net, a silica gel.

Description

A FUEL CELL OR A REACTOR BASED ON FUEL CELL TECHNOLOGY AND HAVING A PROTON CONDUCTIVE MEMBRANE AS WELL AS METHODS FOR MAKING THEM

DESCRIPTION

TECHNICAL FIELD

The present invention relates to a fuel cell or a reactor based on fuel cell technology, having at least one cell comprising an anode, a cathode and an intermediate proton conductive membrane.

The invention also relates methods for the manufacturing of a fuel cell or a reactor based on fuel cell technology, having at least one cell comprising an anode, a cathode and an intermediate proton conductive membrane.

In the present context, the terms anode and cathode are used for the respective electrodes also when there is no voltage over them.

By proton conductive membrane is in this context meant a membrane having the ability on its one side to receive protons/hydroxonium ions and on its other side to emit a corresponding number of protons. When a proton enters the membrane from one side, another one is pushed out from the other side. The membrane will furthermore not allow for passage of electrons in the opposite direction and the passage of other ions than H⁺/H₃O⁺ is not desired.

By DMFC is in this context further understood a fuel cell driven by liquid methanol (Direct Methanol Fuel Cell), which fuel cell comprises an anodic side having an anode and a catalyst for the anodic reaction, a cathodic side having a cathode and a catalyst for the cathodic reaction, as well as an intermediate membrane that separates the anodic and cathodic sides from each other.

PRIOR ART

Fuel cells driven by direct methanol are previously known, see for example Alexandre Hacquard, Improving and Understanding Direct Methanol Fuel Cell (DMFC)

Performance, (Thesis submitted to the faculty of Worcester Polytechnic Institute) published on http ://www. wpi.edu/Pubs/ETD/Available/etd-051205 - u C< ⁾RD COPY - TRANSLATIOM s Rute 114) 151955/unrestricted/A.Hacquard.pdf. Among attainable advantages can be mentioned that the fuel is liquid, thus enabling fast fuelling, that both the fuel cell, that can be given a compact design, and the methanol, can be produced at low costs, and that the fuel cell can be designed for a number of different stationary or mobile/portable applications. Fuel cells of DMFC type are furthermore environmentally friendly, only water and carbon dioxide are discharged; no sulfur or nitrogen oxides are formed.

In the above mentioned publication, the anode and the cathode in the disclosed fuel cell consist of graphite and are both provided on their respective one side with a channel system or the like, at the anode for supply of a liquid methanol- water mixture and at the cathode for supply of oxygen, neat or air oxygen. Between the anode and the cathode there is a proton conductive membrane and between the membrane and the anode and the cathode, respectively, there is what is called a gas diffusion layer. Moreover, the gas diffusion layers or the membrane on the anodic side carries a catalyst of Pt and Ru and on the cathodic side a catalyst of solely Pt. The gas diffusion layers consist of carbon cloth or carbon paper. On the anodic side, the gas diffusion layer receives the CO₂ formed in connection with the oxidation of the methanol on the anodic catalyst and allows it to diffuse up to an upper end surface where CO₂ bubbles are formed. On the cathodic side, the supplied oxygen gas passes through the gas diffusion layer and reacts with electrons and protons passing through the membrane, to form water. Similar to membranes for other fuel cells driven by direct methanol, the membrane here consists of Nafion™, a sulfonated polymer of PTFE type. The catalysts are applied on the gas diffusion layers or on the membrane in the form of an ink of an organic solvent, finely powdered catalyst particles and a solution of Nation™, after which the solvent is allowed to evaporate. It is stated to be essential to have a network of Nafion™ for efficient transport of protons to the membrane. The thus prepared gas diffusion layers are furthermore used as electrodes.

It has however been shown that Nafion™ does not have the desired methanol resistance but starts to dissolve already when exposed to 2 M (about 6 %) methanol. Known fuel cells of DMFC type have moreover had too low a power density, due to the slow electrochemical oxidation of methanol at the anode, and that methanol has been able to migrate through the PEM membrane (Polymer Electrolyte Membrane) to the cathode where the methanol has oxidised. This results not only in fuel loss, but also in that the platinum catalyst used at the cathode is poisoned by formed carbon monoxide, which leads to decreased efficiency. The complexity of the reactions has made it difficult to achieve a satisfying yield. US-B 1-6,444,343 (Prakash et al.) reviews a number of different PEM membranes, starting already at 1959 when it was suggested to manufacture such membranes for H₂/O₂ fuel cells by condensation of phenol sulfonic acid and formaldehyde. For membranes in H₂/O₂ fuel cells it was also possible to use partially sulfonated polystyrene, and the membranes could also be manufactured from a cross-linked styrene-divinylbenzene with an inert fluorocarbon matrix followed by sulfonation or from homopolymers of α,β,β-trifluorostyrene-sulfonic acid. Considering the drawbacks mentioned for such materials, especially in connection with the use of fuel cells of DMFC type, it is suggested in '343 to manufacture the membrane from a cross-linked polystyrene sulfonic acid within an inert matrix of poly(vinylidene fluoride).

In all cases there is a risk of damage to the membrane in connection with the positioning of the same in the cell, and problems in the sealing between membrane and electrodes occur easily.

BRIEF ACCOUNT OF THE INVENTION

The primary object of the present invention is to achieve a fuel cell or a reactor based on fuel cell technology, in which the problems with risks of damages to the membrane and sealing problems have been eliminated.

This object is achieved for the fuel cell or the reactor based on fuel cell technology mentioned in the introduction by the membrane being moulded in situ between the anode and the cathode in said at least one cell.

In a first embodiment of the method mentioned in the introduction, the object is achieved by admixing a suitable monomer with sulfonic acid, after which a cross- linking agent is added, the actual polymerisation is initiated by addition of a setting agent and the achieved mixture is moulded in situ to form a membrane between the anode and the cathode in said at least one cell. By the in situ moulding, the problems mentioned above have been completely eliminated.

The monomer is preferably acrylamide. Thereby, the membrane will consist of by sulfonic acid modified polyacrylamide and a proton conductive membrane is achieved that in cells of DMFC type is not attacked by the reactants and that is essentially impermeable to ions other than protons/hydroxonium ions. Sulfonic acids have a low pKa that allows for translation of protons/hydroxonium ions through the gel, while essentially preventing passage of other ions.

All sulfonic acids can be used that can be coupled to amide nitrogen, but e.g. 1- chlorotetrafluoroethylene sulfonic acid is costly and chlorosulfonic acid can form a product that is not completely stable. Hence, the sulfonic acid is preferably constituted by p-chlorobenzene sulfonic acid.

The method of manufacturing preferably comprises the use of acrylamide as monomer and the use of p-chlorobenzene sulfonic acid as sulfonic acid. The acrylamide is admixed with p-chlorobenzene sulfonic acid in water and is heated to the boiling point while stirring, after which the solution is allowed to slowly cool and the cross-binder is added when the solution has reached room temperature. The polyacrylamide modified by p-chlorobenzene sulfonic acid solves the problem that higher contents of methanol can attack membranes of other polymeric materials and that methanol tends to migrate through the membrane and thereby impair the efficiency of the cell. If there is liquid on the other side of the membrane, as in cells of our DMFC type, the spontaneous diffusion of methanol through the membrane of said modified polyacrylamide can be almost completely eliminated, which means that this type of membrane is particularly well suited for cells that have liquid in both cell halves. Acrylamide is furthermore cheap to purchase.

As a cross-linking agent N,N'-methylene-bis-acrylamide is preferably used in combination with N,N,N',N'-tetramethylene diamine, which will give the final polymer a stable spatial configuration, and as the setting agent that initiates the actual polymerization a peroxo salt is used, such as sodium percarbonate, sodium perbenzoate etc., but preferably ammonium persulfate (CAS No. 7727-54-0) is used.

The moulding, which accordingly can be made in situ in the cell, can be done in a short time, about 40 sec. In comparison with individually manufactured membranes that are built into a fuel cell or a reactor, this embodiment results in less risk of damages to the thin membrane in connection with the mounting thereof, as well as an improved sealing, and the catalyst will better "creep" into the wall of the membrane as compared to the case in connection with pressing.

In an alternative embodiment of the method, the object is attained by the achievement of a glass melt, the achieved glass melt is moulded in situ to form a thin membrane between the anode and the cathode in said at least one cell, and in an immediately preceding step said at least one cell is, if needed, preheated to a temperature that is high enough not to cause problems with premature solidification of the glass melt during the in situ moulding in the cell. By the in situ moulding, the problems concerning risks of damages to the membrane and sealing problems have been eliminated.

Suitably, the glass melt is achieved by melting of soda and finely divided silica is gradually mixed into the soda melt while stirring whereby the silica is dissolved, and the glass membrane formed in situ in the cell is preferably treated with acid that dissolves the soda out from the glass, such that a matrix remains that essentially consists of silicic acid (silica).

In yet another embodiment of the method the object is achieved by gradually mixing a finely divided titanium dioxide into water glass (sodium metasilicate, CAS No. 6834- 98-0) while stirring, the mixture is moulded in situ to form a thin membrane between the anode and the cathode in said at least one cell, and the mixture is thereafter transformed into a net of silicic acid that contains titanium dioxide. This is a method that is simple and cost efficient.

In both cases, the thin glass membranes achieved have excellent properties in respect of proton conduction and ion- and electron barrier properties and given that they are moulded in situ they are not at risk of being exposed to unevenly acting clamping forces or the like, cracking the membrane, as may be the case in connection with the mounting of prefabricated membranes.

BRIEF DESCRIPTION OF THE ENCLOSED DRAWINGS

In the following, the invention will be described in greater detail with reference to the preferred embodiments and the enclosed drawings.

Fig. 1 is a principle flowchart showing a fuel cell unit of DMFC type, in which liquid methanol is stepwise oxidised in fuel cells to form carbon dioxide and water.

Fig. 2 is a view in cross-section over the fuel cell unit according to Fig. 1, showing a preferred arrangement of electrodes, intermediate membranes and flow channels. Figs. 3-4 are planar views over a couple of different flow patterns in which the reactants can be led inside each unit.

Fig. 5 is a simplified cross-sectional view of a cell that has been prepared for the moulding of a proton conductive membrane between the electrodes.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

In the fuel cell unit of DMFC type shown in the principle flowchart in Fig. 1, liquid methanol is stepwise oxidised in fuel cells to carbon dioxide and water. The shown fuel cell unit comprises three fuel cells 1, 2 and 3 connected flow- wise in series, for conducting the stepwise oxidation in three separate steps. Each fuel cell comprises an anode 11, a cathode 12 and a membrane 13 that separates them from each other. On the anodic side, methanol is oxidised to formaldehyde in the first step 1 , in the second step 2 the obtained formaldehyde is oxidised to formic acid and in the third step 3 the obtained formic acid is oxidised to carbon dioxide. On the cathodic side, freshly supplied hydrogen peroxide is reduced in each step 1-3, to form water. The supply of oxidant to the different steps is suitably controlled such that the reactions on the anodic and the cathodic sides are in stoichiometric balance with each other in every separate step. Thereby, the reactions can be more reliably refined and controlled in order to increase yield.

The three fuel cells 1, 2 and 3 are also electrically connected in series. Two electrons are going from the anode 11₁ in step one to the cathode 12₃ in step three, via a load 15, shown in the form of a bulb; two electrons are going from the anode 11₃ in step three to the cathode 12₂ in step two; and two electrons are going from the anode 11₂ in step two to the cathode \2_\ in step one. In all three cells 1, 2 and 3, formed protons/hydroxonium ions are going from the anode 11, through the membrane 13, to the cathode 12.

Fig. 2 is a view in cross-section over the fuel cell unit according to Fig. 1, showing a preferred arrangement of electrodes 11, 12, intermediate membranes 13 and flow channels 16. The anodes 11, the cathodes 12 and the membranes 13 are formed by thin plates or sheets that are attached to each other in order to form a package or a pile. In conventional fuel cell units, the joining can be mechanical, e.g. by not shown connecting rods, or alternatively not shown joints of a suitable glue, e.g. of silicone type, are used in order to hold the plates/sheets together. Between the membrane 13 and the anode 11 and between the membrane 13 and the cathode 12, a surface structure 16 is arranged that will give an optimised liquid flow over essentially the entire side of the plates. The flow lines shown in Fig. 1, between the individual fuel cells 1, 2 and 3, are constituted by flow connections that are formed in the plate package/pile but also by externally positioned flow connections shown in Fig. 2.

According to the invention, the membrane 13 is constituted by a thin sheet that is moulded in situ between the anode 11 and the cathode 12 in the fuel cell. By the in situ moulding, the risk of damaging the membrane 13 in connection with the mounting of the same in the cell is avoided, and neither will there be problems with the sealing between the membrane 13 and the electrodes 11, 12.

According to a first embodiment, the membrane moulded in situ consists of a polymeric material that allows for migration of protons/hydroxonium ions from one side of the membrane 13 to the other.

As is further described below, the polymeric material advantageously consists of by sulfonic acid modified polyacrylamide. The modification by sulfonic acid of the polyacrylamide will not to any appreciable extent destroy the stability of the polymer; it will withstand attacks by many solvents and also by hydrogen peroxide. Also in terms of electricity, the material has beneficial properties such as high resistance (against electrons), high proton permeability and the ability to withstand high voltages. Sulfonic acids have a low pKa that allows for translation of protons/hydroxonium ions through the gel, while essentially preventing passage of other ions. By the modification by sulfonic acid, a proton conductive membrane is accordingly achieved that in cells of DMFC type is not attacked by the reactants and that is essentially impermeable to ions other than protons/hydroxonium ions.

AU sulfonic acids that can be coupled to amide nitrogen can be used, but preferably the sulfonic acid is constituted by p-chlorobenzene sulfonic acid. 1-chlorotetra- fluoroethylene sulfonic acid is for example costly and chlorosulfonic acid can form a product that is not completely stable. Moreover, the by sulfonic acid modified polyacrylamide will essentially stop the passage of other ions and molecules, such as methanol, and it is not electrically conducting, which means that electrons from the cathode 12 cannot pass through the membrane 13 to the anode 11. Accordingly, no appreciable migration of methanol can take place from the anode 11 to the cathode 12, which means that there is no appreciable fuel loss due to migration of methanol and no formation of carbon monoxide at the cathode 12, which could otherwise decrease the efficiency of a platinum catalyst that is optionally used there. According to a second embodiment, the membrane moulded in situ consists of a glass that allows for migration of protons/hydroxonium ions from one side of the membrane 13 to the other. As further described below, the glass may advantageously be manufactured from a soda glass melt out of which the soda suitably has been dissolved after the moulding. The remaining silica matrix withstands attacks by many solvents and also by hydrogen peroxide. Also in terms of electricity, the material has beneficial properties such as high resistance (against electrons), high proton permeability and the ability to withstand high electrical voltages. According to an alternative embodiment, the starting point is water glass into which finely divided titanium dioxide has been mixed. After in situ moulding of the mixture between the electrodes 11, 12, the mixture is neutralized and the water is evaporated, whereby the molecules arrange themselves to form a silica net doped with titanium dioxide, a silica gel, in which the titanium dioxide acts as a catalyst for the desired reaction. Such a membrane has the same properties and advantages as the above glass membrane produced from a melt. Naturally, other and/or additional catalysts can be used instead of titanium dioxide and if desired such catalysts can also be incorporated in the glass melt that the membrane is moulded from.

In the embodiment shown in Fig. 2, the anode 11 and the cathode 12 have thicknesses of less than 1 mm and the membrane 13 has a thickness of less than 5 mm, for plastics preferably less than about 2.5 mm and for glass preferably less than about 0.1 mm. The anode 11 as well as the cathode 12 has one planar side and said surface structure 16, that gives an optimised liquid flow over essentially the entire side of the plate, is arranged on the anode 11 as well as on the cathode 12, while both sides of the intermediate membrane 13 are planar. The planar side of the cathode 12i in cell 1 in the fuel cell unit shown in Fig. 1 is then in abutting contact with the planar side of the anode 11₂ in cell 2, and so on. Naturally, the cathode 12][ in cell 1 as well as the anode 11₂ in cell 2 e.g. may consist of a single plate that can be provided with said surface 16 on both sides.

Suitably, the anode 11 as well as the cathode 12 is constituted of thin metal sheets of a material that is electrically conducting and resistant to the reactants, such as stainless steel, with a thickness in the magnitude of from 0.6 mm down to 0.1 mm, preferably 0.3 mm. The surface structure in the anode 11 and the cathode 12 may be formed by channels 16 of waved cross-section. Suitably, the channels 16 have a width in the magnitude of 2 mm up to 3 mm and a depth in the magnitude of from 0.5 mm down to 0.05 mm. The surface structure 16 in the anode and cathode plates 11, 12 is preferably produced by adiabatic forming, also called High Impact Forming. One example of such forming is disclosed in US-B2-6,821,471.

Between the anode 11 and the membrane 13 and between the cathode 12 and the membrane 13, there are thin, porous catalyst carriers 14, preferably in the form of felts of carbon fibre, in which the catalyst adapted for the reaction desired in the cell is applied. In that way the constructing of a compact pile of fuel cells 1, 2, 3 with electrodes 11, 12 of the same thin sheet shape having one planar side and one side with surface structure is facilitated, whereby a high power density can be achieved.

Figs. 3 and 4 show a couple of different surface structures or flow patterns that will give an optimised liquid flow over essentially the entire side of the plate. In Fig. 3, parallel channels 16 have been repeatedly perforated laterally, such that the entire surface structure consists of shoulders arranged in a checked pattern, forming a grating pattern of channels 16. Finally, Fig. 4 shows that meander shaped channels 16 that run in parallel also can be used. In all cases including different possible flow paths one should strive to make them equally long from inlet to outlet.

As is mentioned above, the membrane 13 is according to the invention applied in the cell by in situ moulding between the anode 11 and the cathode 12. This is shown in greater detail in Fig. 5 that is a cross-sectional view of a cell in a fuel cell unit which has been prepared for in situ moulding of the membrane 13 between the anode 11 and the cathode 12. In order better to illustrate the invention, the electrodes 11, 12 and the intermediate space for the membrane 13 to be moulded have been drawn with highly exaggerated thicknesses. In the shown cell in the fuel cell unit, the two electrodes 11, 12 are, on their sides facing each other and facing the space for the membrane, provided with a surface structure 16 in the form of channels. The porous catalyst carrier 14 abuts against the respective sides of the two electrodes 11, 12 that are provided with the surface structure 16, which porous catalyst carrier 14 preferably is in the form of a carbon fibre felt, in which a catalyst that is optimised for the reaction desired in the cell is applied.

Between the anode 11 and the cathode 12 and in sealing contact therewith, there is in each cell arranged an upwardly open, essentially U-shaped spacing frame 17 that has a thickness that defines the thickness of the membrane 13 to be moulded in situ in the cell. The material of the spacing frame 17 can be chosen from a number of different materials but preferably polyacrylate is used. The pile 11, 12 of electrodes and spacing frames 17 that form the basis for the fuel cell unit can be held together by gluing, but in the embodiment shown in Fig. 5 there is used four through bolts 18 (whereof two are shown), one in each corner of the electrode plates. Accordingly, a space is formed between the two catalyst carriers 14 in a cell, which space is sideways and in depth delimited by the spacing frame 17 and is upwardly open and in which the membrane 13 is to be moulded.

For the moulding, a suitable monomer is admixed with sulfonic acid, after which a cross-linking agent is added, the actual polymerisation is initiated by addition of a setting agent and the obtained mixture is in situ moulded to form a membrane in the upwardly open space between the anode and the cathode 11, 12.

As the person skilled in the art immediately and without any inventive work will realise, a plurality of monomers exists that are suitable to use, among others tetrafluoroethylene can be mentioned and those suggested in the above mentioned US-B 1 -6,444,343

(Prakash et al.), which is incorporated herein by reference, but preferably the monomer is constituted by acrylamide. Thereby, the membrane will consist of by sulfonic acid modified polyacrylamide and a proton conductive membrane is achieved that in cells of DMFC type is not attacked by the reactants and that is essentially impermeable to ions other than protons/hydroxonium ions.

Sulfonic acids have a low pKa that allows for translation of protons/hydroxonium ions through the gel, while essentially preventing passage of other ions. All sulfonic acids that can be coupled to amide nitrogen can be used, but preferably the sulfonic acid is constituted by p-chlorobenzene sulfonic acid. 1-chlorotetrafluoroethylene sulfonic acid is for example costly and chlorosulfonic acid can form a product that is not completely stable.

The method of manufacturing preferably comprises the use of acrylamide as monomer and the use of p-chlorobenzene sulfonic acid as sulfonic acid. The acrylamide is admixed with p-chlorobenzene sulfonic acid in water and is heated the boiling point while stirring, after which the solution is allowed to slowly cool and the cross-binder is added when the solution has reached room temperature. They can however also be added earlier if desired. The polyacrylamide modified by p-chlorobenzene sulfonic acid solves the problem that higher contents of methanol can attack membranes of other polymeric materials and that methanol tends to migrate through the membrane and thereby impair the efficiency of the cell. If there is liquid on the other side of the membrane, as in cells of DMFC type, the spontaneous diffusion of methanol through the membrane of said modified polyacrylamide can be almost completely eliminated, which means that this type of membrane is particularly well suited for cells that have liquid in both cell halves. Acrylamide is furthermore cheap to purchase.

As a cross-linking agent N,N'-methylene-bis-acrylamide is preferably used in combination with N,N,N',N'-tetramethylene diamine, which will give the final polymer a stable spatial configuration, and as the setting agent that initiates the actual polymerization a peroxo salt is used, such as sodium percarbonate, sodium perbenzoate etc., but preferably ammonium persulfate.

After the addition of the setting agent, the mixture is in situ moulded to form a membrane in the fuel cell or in the reactor based on fuel cell technology. The moulding, which accordingly is made in situ in the cell, is done in a short time, about 40 sec. In comparison with individually manufactured membranes that are built into a fuel cell or a reactor, this results in improved sealing as well as elimination of the risk of damages to the thin membrane in connection with the mounting thereof, and the catalyst will better "creep" into the wall of the membrane as compared to the case in connection with pressing.

Optimising the catalysts for the methanol driven fuel cell unit shown in Fig. 1 will e.g. result in that said first catalyst is formed by 60-94 % Ag, 5-30 % Te and/or Ru, and 1- 10 % Pt alone or in combination with Au and/or TiO₂, preferably at the ratio of about 90:9:1 for the reaction CH₃OH → HCHO + 2 H⁺ + 2 e^" (a) of SiO₂ and TiO₂ in combination with Ag for the reaction

HCHO + H₂O «→ HCOOH + 2 H⁺ + 2 e^" (b) of Ag alone or in combination with TiO₂ and/or Te for the reaction

HCOOH *-» CO₂ + 2 H⁺ + 2 e^" (c) said second catalyst is then formed by e.g. carbon powder (carbon black), anthraquinone and Ag and phenolic resin, for the reaction

H₂O₂ + 2 H⁺ + 2 e^" → 2 H₂O (d)

As is mentioned above, the optimised catalyst for the second step is suitably constituted by SiO₂, TiO₂ and Ag. Anthraquinone (CAS no. 84-65-1) is a crystalline powder that has a melting point of 286⁰C and that is insoluble in water and alcohol but soluble in nitrobenzene and aniline. The catalyst can be produced by mixing carbon powder (carbon black), anthraquinone and silver with e.g. phenolic resin, after which it is moulded and allowed to solidify. The moulded product is then released from its support, is crushed and finely grinded, after which the obtained powder is slurried in a suitable solvent, is applied where desired, after which the solvent is allowed to evaporate.

Example 8 g of acrylamide was admixed with 2 g of p-chlorobenzene sulfonic acid (p-CBSA) in 80 ml water and was heated to the boiling point on an electrical plate, while stirring, after which the solution was allowed slowly to cool on the plate. Hereby, a coupling product was formed between the acrylamide and p-CBSA, via the amide nitrogen in the acrylamide, and HCl was also formed that was degassed during the boiling. When the solution had reached room temperature a cross-linking agent was added, in this case 2 g of N,N'-methylene-bis-acrylamide in combination with 0.5 ml of N,N,N',N'- tetramethylene diamine, which gave the final polymer a stable structure. In order to mould a membrane, a quarter of the obtained product was withdrawn and the actual polymerisation was initiated by a peroxo salt, in this case ammonium persulfate, of which the tip of a spatula was enough. The polymerisation started after 40 sec, which meant that there was plenty of time to transfer the product to the already assembled fuel cell, in which the moulding of the membranes took place in an upright position. The membranes moulded in the fuel cell were shown to give impeccable sealing. It was also shown that the catalyst better "crept" into the wall of the membrane than the case in connection with pressing, and there were no damages to the membrane.

The in situ moulded membrane had excellent function in a fuel cell of DMFC type. The membrane was not dissolved by methanol, the power density was high and there were no problems with fuel loss by migration of methanol through the membrane, which meant that a high efficiency was maintained and that the yield was satisfactory.

Suitably a soda glass melt is used for the manufacturing of an in situ moulded glass membrane. First, soda (Na₂CO₃) is melted and then finely divided silica (SiO₂) is gradually mixed into this during continued heating to make ready the melt. When the melt has been introduced in its intended space in the fuel cell, which may be preheated if needed, it is allowed to cool before the soda is dissolved out from the glass membrane by a weak acid, whereby a silica matrix remains. The remaining silica matrix withstands attacks by many solvents and also by hydrogen peroxide. Also in terms of electricity, the material has beneficial properties such as high resistance (against electrons), high proton permeability and the ability to withstand high electrical voltages.

According to an alternative embodiment, the starting point is water glass into which finely divided titanium dioxide has been mixed. After the in situ moulding of the mixture between the electrodes, the mixture is neutralised and the water is evaporated, whereby the molecules arrange themselves to form a silica net, a silica gel, doped by titanium dioxide. Such a membrane has the same properties and advantages as the above glass membrane produced from a melt.

Although the invention has been described above with reference to the preferred embodiments, it is clear that a person skilled in the art and without any inventive work can come up with a number of modifications of the invention within the scope of the appended claims. The material in the in situ moulded membrane may e.g. need to be modified if the membrane is to be used in a fuel cell or reactor based on fuel cell technology other than one of DMFC type. If desired, it is of course possible to mix one or more suitable catalysts, such as Ag alone or in combination with TiO₂ and/or Te, in the soda glass melt, and when using water glass it is also possible, if desired, to supplement TiO₂ with one or more additional suitable catalysts, such as Ag and/or Te, or to change it to such.

Claims

1. A fuel cell or a reactor based on fuel cell technology, having at least one cell comprising an anode (11), a cathode (12) and an intermediate proton conductive membrane (13), characteri s ed in that the membrane (13) is in situ moulded between the anode (11) and the cathode (12) in said at least one cell.

2. A fuel cell or reactor according to claim 1, characteri s ed in that the membrane (13) consists of a thin plate of by sulfonic acid modified polyacrylamide that allows for migration of protons/hydroxonium ions from one side of the membrane to the other.

3. A fuel cell or reactor according to claim 2, characteri s ed in that the sulfonic acid is p-chlorobenzene sulfonic acid.

4. A fuel cell or reactor according to claim 1 , characteri s ed i n that a soda glass melt has been used for the moulding of the membrane (13), and that the membrane is thin enough to allow for migration of protons/hydroxonium ions from one side of the membrane to the other.

5. A fuel cell or reactor according to claim 4, characteri s ed in that after the moulding, the membrane (13) has been treated by acid that has dissolved out the soda from the glass, such that a matrix remains that essentially consists of silicic acid (silica).

6. A fuel cell or reactor according to claim 1, characterised in that the membrane (13) consists of sodium metasilicate (CAS No. 6834-98-0) that has been doped by finely divided titanium dioxide, and that the membrane is thin enough to allow for migration of protons/hydroxonium ions from one side of the membrane to the other.

7. A method of manufacturing a fuel cell or a reactor based on fuel cell technology, having at least one cell comprising an anode (11), a cathode (12) and an intermediate proton conductive membrane (13), c haracteri s e d in that

- a suitable monomer is admixed with sulfonic acid,

- a cross-linking agent is added, which gives the final polymer a stable spatial configuration,

- the actual polymerisation is initiated by the addition of a setting agent, and - the obtained mixture is in situ moulded to form a membrane (13) between the anode (11) and the cathode (12) in said at least one cell.

8. A method according to claim 7, characteri s e d in that - acrylamide is used as said monomer,

- p-chlorobenzene sulfonic acid is used as said sulfonic acid,

- the acrylamide is admixed with the p-chlorobenzene sulfonic acid in water and is heated to the boiling point while stirring, after which the solution is allowed to slowly cool, and - the cross-linking agent is added when the solution has reached room temperature.

9. A method according to claim 7 or 8, characteri s e d in that N,N'-methylene-bis- acrylamide in combination with N,N,N',N'-tetramethylene diamine is used as said cross-linking agent.

10. A method according to any one of claims 7-9, characteri s e d in that a peroxo salt is used as said setting agent.

11. A method according to claim 10, characteri s ed in that said peroxo salt is ammonium persulfate.

12. A method of manufacturing a fuel cell or a reactor based on fuel cell technology, having at least one cell comprising an anode (11), a cathode (12) and an intermediate proton conductive membrane (13), characteri s e d in that - a glass melt is achieved,

- the obtained glass melt is in situ moulded to form a thin membrane (13) between the anode (11) and the cathode (12) in said at least one cell.

- in an immediately preceding step said at least one cell is, if needed, preheated to a temperature that is high enough not to cause problems with premature solidification of the glass melt during the in situ moulding in the cell.

13. A method according to claim 12, characteris ed in that the glass melt is achieved by the melting of soda and gradually mixing finely divided silica into the soda melt, such that the silica is dissolved.

14. A method according to claim 13, characteri s ed in that the glass membrane (13) formed in situ in the cell is treated by acid that dissolves out the soda from the glass, such that a matrix remains that essentially consists of silicic acid (silica).

15. A method of manufacturing a fuel cell or a reactor based on fuel cell technology, having at least one cell comprising an anode (11), a cathode (12) and an intermediate proton conductive membrane (13), c haracteri se d in that

- finely divided titanium dioxide is gradually mixed into water glass (sodium metasilicate, CAS No. 6834-98-0) while stirring, - the mixture is in situ moulded to form a thin membrane (13) between the anode

(11) and the cathode (12) in said at least one cell, and

- the mixture is thereafter transformed to a silica net that contains titanium dioxide.