WO2009116103A1

WO2009116103A1 - Electro-chemical device with optimized electrode insulation

Info

Publication number: WO2009116103A1
Application number: PCT/IT2008/000192
Authority: WO
Inventors: Angelo D'anzi
Original assignee: Exergy Fuel Cells S.R.L.
Priority date: 2008-03-21
Filing date: 2008-03-21
Publication date: 2009-09-24

Abstract

An electro-chemical device (1) with optimized insulation of the electrodes (2), comprising at least one pair of collectors (3) which are intended to feed and convey the reagent gases toward respective electrodes (2) which face them and are proximate thereto and between which a membrane (5) is interposed which is impermeable to the gases, and a sealing gasket (6) which is intended to separate the two electrodes (2) to prevent the exchange of gases between them. The perimetric edge (7) of the membrane (5) protrudes with respect to the perimetric frame (8) of the electrodes (2) between which it is interposed and the sealing gasket (6) covers the protruding edge (7) of the membrane (5), coming into contact with the surface of the perimetric edge (7) of the electrodes (2).

Description

ELECTRO-CHEMICAL DEVICE WITH OPTIMIZED ELECTRODE

INSULATION

Technical Field

The present invention relates to an electro-chemical device with optimized electrode insulation: in particular, reference is made to fuel cells and to electrolyzers. Background Art

Electrolyzers are devices which allow electric power applied to the device to be converted into chemical energy contained in a fuel and an oxidizer.

The most common devices are those in which the flow of electric current generates the electrolysis of water to form hydrogen and oxygen in the gaseous phase. The water, anode side, is reduced in the catalytic interface regions with the addition of electric power from an external circuit, the generated protons pass through the electrolyte and oxidize into gaseous hydrogen on the cathode side, while gaseous oxygen is generated on the anode side.

The fuel cell is an electro-chemical device in which, in principle, the chemical energy contained in a fuel and an oxidizer is converted into electric power. A fuel (typically hydrogen or other fuels which include it among its components) and an oxidizer (oxygen or air) enter the cell and

DC electric current, water and heat are obtained from them. The cells are similar to batteries and therefore like other voltaic elements a fuel cell is formed substantially by two electrodes, the cathode and the anode, and an electrolyte which allows ion migration.

Differently from ordinary batteries, in the fuel cell the active material is renewed continuously and therefore the DC electric current can be delivered indefinitely if the supply of fuel and oxidizing gases is maintained. The fuel (hydrogen) and the oxidizing gases (oxygen provided simply by air) strike respectively the anode and the cathode (on the faces that lie opposite the ones in contact with the electrolyte). In view of the porosity of the electrodes, the fuel oxidation reactions and the oxidizer gas reduction reactions are thus fed continuously. Normally, in fuel cells the interface regions between the electrodes and the electrolyte are provided with at least one layer of catalytic material, which allows the oxidizer reduction reactions (cathode side) and fuel oxidation reactions (anode side) to occur with the desired ratio. The electrolyte is intended to conduct the ions produced proximate to one of the electrodes and used proximate to the other electrode. Such ion passage is accompanied by a passage of electrons from the anode to the cathode through an external circuit. Each individual cell thus composed is coupled in electrical series to the next one by interposing a layer of electrically conducting material, which normally acts also as a flow field for the reagents.

The electro-chemical transformation is accompanied by the generation of heat, which has to be extracted in order to keep the operating temperature of the cell within values which allow its regular operation.

A fundamentally important aspect for the application of fuel cells is that the effluents (spent gases and water), which must be removed from the cell continuously, do not contain pollutants.

The cell substantially has a three-layer structure, in which the central layer, comprised between the cathode and the anode, constitutes or contains the electrolyte. In practice, the facing surfaces must have an area which is sufficient to achieve current intensities which are adequate for the requirements of the application. It is thus possible to arrive, as a function of the application and of the arrangement of cells, to surfaces of even more than one square meter. The individual cells (characterized by voltages comprised between one half of a volt and one volt, according to the technology used, the operating conditions and the electrical load applied to it) are mutually superimposed, connecting them in series so as to obtain a total voltage of the chosen value. The stacking of cells thus obtained forms the so-called stack, which represents the base of the electro-chemical section. Generally, a fuel cell plant is composed not only by the power module (which contains the electro-chemical section) but also by a current converter (inverter) and a transformer, which convert the direct current generated by the stack into alternating current at the chosen voltage and frequency.

Among all the possible electro-chemical devices, cells and electrolyzers with polymeric membrane known as PEFC (polymer electrolyte fuel cell) are the ones that comprise a so-called MEA (membrane electrode assembly) and two current collectors also known as current carrying plates.

The mating of such components is often complex, since the passage of current (of the scattering type) between the two facing electrodes entails a heavy increase in losses (and therefore a corresponding reduction in the conversion efficiency of the cell).

In these embodiments, production of current occurs by using as electrolyte a polymeric membrane (a perfluorinated sulfonic one, for example) with high proton conductivity, through which protons pass from the anode to the cathode. At the same time, the membrane is extremely impermeable to gases, preventing the two reagents from coming into direct mutual contact.

The gases are then distributed onto the surface of the membrane electrode assembly (MEA) by circulating within suitable channels provided on the current collectors: the collectors are also entrusted with the task of collecting the current that circulates on the sides of the membrane electrode assembly (MEA).

It is important that no gas leaks occur between the membrane electrode assembly (MEA) and the plates: for this purpose, a sealing gasket is interposed between such components but must absolutely not come into contact with the electrode. The electrode is in fact made of porous material and would cause the escape of gas.

In order to avoid this contact, it is known to adopt a solution of the type disclosed in EP- 1241724, in which the membrane electrode assembly

(MEA) is embedded in the sealing gasket so that the sealing gasket itself can penetrate between the porosities of the electrodes, avoiding possible contaminations.

This is possible because the sealing gasket is obtained by injecting material onto the other components.

However, this embodiment does not ensure completely the elimination of mutual contamination of the reagent gases, since adhesion to the porous surfaces of the electrodes is not always ideal: even small leaks can cause evident malfunctions of the electro-chemical device. Disclosure of the Invention

The aim of the present invention is to provide an electro-chemical device with optimized electrode insulation which is independent of the adhesion of the insulating material to the surface of said electrodes.

Within this aim, an object of the present invention is to provide an electro-chemical device with optimized electron insulation of a particularly efficient type even if the electrodes are not porous.

Another object of the present invention is to provide an electrochemical device with optimized electrode insulation which has low costs, is relatively simple to provide in practice and is safe in application. This aim and these and other objects which will become better apparent hereinafter are achieved by the present electro-chemical device with optimized electrode insulation, of the type which comprises at least one pair of collectors which are intended to feed and convey the reagent gases toward respective electrodes which face them and are proximate thereto and between which a membrane is interposed which is impermeable to said gases, and a sealing gasket which is intended to separate the two electrodes to prevent the exchange of gases between them, characterized in that the perimetric edge of said membrane protrudes with respect to the perimetric frame of the electrodes between which it is interposed and in that said sealing gasket covers said protruding edge of said membrane, coming into contact with the surface of said perimetric frame of said electrodes. Brief description of the drawings

Further characteristics and advantages of the invention will become better apparent and evident from the following detailed description of a preferred but not exclusive embodiment of an electro-chemical device with optimized electrode insulation, illustrated by way of non-limiting example in the accompanying drawings, wherein:

Figure 1 is a sectional side view, taken along a plane which is perpendicular to its end faces, of an electro-chemical device with optimized electrode insulation according to the invention;

Figure 2 is a sectional side view, taken along a plane which is perpendicular to its end faces, of a step of the molding of an electrochemical device with optimized electrode insulation according to the invention. Ways of carrying out the Invention

With reference to the figures, the reference numeral 1 generally designates an electro-chemical device with optimized insulation of electrodes 2.

The electro-chemical device 1 comprises at least one pair of collectors (normally known as pole plates 3), which are intended to feed and convey through suitable surface channels 4 the reagent gases toward the respective electrodes 2: the reagent gases (of which for example one is a fuel and the other one is an oxidizer) can be hydrogen and oxygen or, optionally, methanol and oxygen, depending on the required type of reaction and on the amount of specific energy of the device 1. The pole plates 3 skim the electrodes 2 so that the channels 4 face the outer surface of the electrodes 2.

The electrodes 2, in a particular embodiment, are made of a substantially sponge-like material which is permeable to the gases. A membrane which is impermeable to gases and a sealing gasket 6 are interposed between the electrodes 2, the gasket being designed to separate the two electrodes 2 to prevent the exchange of gases between them: the simultaneous presence of the polymeric membrane 5 and of the sealing gasket 6 ensures the ideal separation and insulation of the electrodes 2 with respect to the gases.

A perimetric edge 7 of the membrane 5 protrudes with respect to a perimetric frame 8 of the electrodes 2 between which it is interposed and the sealing gasket 6 covers the protruding edge 7 of the membrane 5, coming into contact with the surface of the perimetric frame 8 of the electrodes 2: in this manner, the separation of the reagent gases is ensured in an optimum manner, since the perimetric edge extends laterally, constituting an obstacle for the reagent gases; the gasket 6 contributes to maintaining the correct position of the edge 7 and to increasing the mutual insulation of the electrodes 2 with consequent segregation of the reagent gases: for this purpose, the gasket is generally made of polymeric material, particularly with silicone resins.

The use of silicone resins (liquid silicones with more or less rapid cross-linking) for the sealing gasket 6 allows to obtain it by injection, within suitable containment assemblies 9 for the electrodes 2 and the membrane 5 : the silicone resin in the fluid state is injected and the containment assemblies 9 are kept in the locked position until subsequent polymerization occurs.

According to the embodiment shown in Figure 2, the containment assemblies 9 are constituted by two shells which can be arranged mutually opposite, are shaped complementarily and are adapted to form, in a mated configuration, a seat for the electrodes 2 and the membrane 5 and a conveyance cavity for the polymer to be injected during the provision of the gasket 6.

The containment assemblies 9 comprise suitable supporting and positioning means 10 for the perimetric edge 7 of the membrane 5; the supporting means 10 are distributed along the perimetric edge 7 and in particular can be constituted by a plurality of thin distributed stems which are adapted for the point-like support of a portion of the edge 7. The large number and the distribution of such stems ensure the correct and complete support of the perimetric edge 7; the limited diameter instead provides protection as regards the correct insulation that the membrane 5 and the gasket 6 must ensure.

As mentioned, the containment assemblies 9 comprise substantially two jaws or shells, a lower one and an upper one, which are provided with at least one respective slot 11, aligned and proximate to a respective portion of the perimetric edge 7.

Each slot is closed so as to delimit externally the perimetric frame 8 of one of the electrodes 2: in practice, the shape and dimensions of each closed slot 11 are substantially such as to ensure that the perimetric frame 8 can be completely surrounded (from the outside) by the slot 11 or, in other words, when the device 1 is completely assembled, the slot 11 must contain the perimetric frame 8 of the electrodes 2.

The sealing gasket 6 has at least one pair of crests 12, an upper one and a lower one, whose shape and dimensions are complementary to those of the respective slot 11 of the respective jaw of the containment assembly 9 with which it has been provided: each slot 11 represents the mold of the respective crest 12.

Once assembly has occurred, the plates 3 abut with their central portion (the one provided with the channels 4) against the surface of the corresponding electrode 2 and with their perimetric portion against the outer surface of the gasket 6.

The crests 12, in this assembly configuration, are compressed with elastic deformation against the perimetric edge 7 of the membrane 5 in conditions of hermetic clamping of the edge 7 and consequent mutual optimized insulation of the electrodes 2 between which the membrane 5 is interposed.

On said shells of the containment assembly 9, the supporting means

10 for the perimetric edge 7 of the membrane 5 and the facing pairs of slots

11 are not aligned; the supporting means 10 constitute the resting element for a region of the edge 7 which lies proximate to the surface clamped between parts of the sealing gasket 6.

It has thus been shown that the invention achieves the proposed aim and objects.

The invention thus conceived is susceptible of numerous modifications and variations, all of which are within the scope of the appended claims.

All the details may further be replaced with other technically equivalent ones.

In the exemplary embodiments shown, individual characteristics, given in relation to specific examples, may actually be interchanged with other different characteristics that exist in other exemplary embodiments.

Moreover, it is noted that anything found to be already known during the patenting process is understood not to be claimed and to be the subject of a disclaimer. In practice, the materials used, as well as the shapes and the dimensions, may be any according to requirements without thereby abandoning the scope of the protection of the appended claims.

Where technical features mentioned in any claim are followed by reference signs, those reference signs have been included for the sole purpose of increasing the intelligibility of the claims and accordingly such reference signs do not have any limiting effect on the interpretation of each element identified by way of example by such reference signs.

Claims

1. An electro-chemical device with optimized insulation of the electrodes (2), of the type which comprises at least one pair of collectors (3) which are intended to feed and convey the reagent gases toward respective electrodes (2) which face them and are proximate thereto and between which a membrane (5) is interposed which is impermeable to said gases, and a sealing gasket (6) which is intended to separate the two electrodes (2) to prevent the exchange of gases between said electrodes, characterized in that the perimetric edge (7) of said membrane (5) protrudes with respect to the perimetric frame (8) of the electrodes (2) between which it is interposed and in that said sealing gasket (6) covers said protruding edge (7) of said membrane (5), coming into contact with the surface of said perimetric edge (7) of said electrodes (2).

2. The device according to claim 1, characterized in that said sealing gasket (6) is obtained by injecting, within suitable assemblies (9) for containing the electrodes (2) and the membrane (5), material in the fluid state and by subsequent polymerization thereof.

3. The device according to claim 2, characterized in that said containment assemblies (9) comprise suitable supporting and positioning means (10) for said perimetric edge (7) of said membrane (5), said supporting means (10) being distributed along said perimetric edge (7).

4. The device according to claim 2, characterized in that said containment assemblies (9) comprise substantially two jaws, a lower one and an upper one, which are provided with at least one respective slot (11) and are aligned and proximate to a respective portion of said perimetric edge (7), each slot (11) being closed so as to delimit externally the perimetric frame (8) of one of said electrodes (2).

5. The device according to claim 4, characterized in that said sealing gasket (6) has at least one pair of crests (12), an upper one and a lower one, whose shape and dimensions are complementary to those of the respective slot (11) of the respective jaw, each of said slots (11) being the mold of the respective crest (12).

6. The device according to claim 1, characterized in that once assembly has occurred, said plates (9) abut with their central portion against the surface of the corresponding electrode (2) and with their perimetric portion against the outer surface of said gasket (9), said crests (12) being compressed by elastic deformation against the perimetric edge (7) of said membrane (5) in conditions of hermetic clamping of said edge (7) and consequent mutual insulation of the electrodes (2) between which the membrane (5) is interposed.

7. The device according to one or more of the preceding claims, characterized in that on said shells, said supporting means (10) for said perimetric edge (7) of said membrane (5) and said facing pairs of slots (11) are not aligned, said supporting means (10) constituting the support for a region of said edge (7) which lies proximate to the surface clamped between parts of the sealing gasket (6) provided with said crests (12) at said slots (11).