Assemblies for electrochemical devices

• US 20070148517A1
• Filed: 12/27/2006
• Published: 06/28/2007
• Est. Priority Date: 12/28/2005
• Status: Active Grant

• Current Assignee: Solvay Solexis SPA (Solvac SA)
• Original Assignee: Solvay Solexis SPA (Solvac SA)
• Inventors: Arcella, Vincenzo, Merlo, Luca, Chielmi, Alessandro
• Granted Patent: US 7,943,267 B2
• Time in Patent Office: Days
• US Class Current: 429/483
• CPC Class Codes: H01M 2008/1095 Fuel cells with polymeric electrolytes
• CPC Class Codes: H01M 4/921 Alloys or mixtures with metallic elements
• CPC Class Codes: H01M 4/926 on carbon or graphite
• CPC Class Codes: H01M 8/0271 Sealing or supporting means around electrodes, matrices or membranes
• CPC Class Codes: H01M 8/0273 with sealing or supporting means in the form of a frame
• CPC Class Codes: H01M 8/0276 Sealing means characterised by their form H01M8/0273 takes precedence
• CPC Class Codes: H01M 8/1004 characterised by membrane-electrode assemblies [MEA] H01M8/12 takes precedence
• CPC Class Codes: H01M 8/1023 having only carbon, e.g. polyarylenes, polystyrenes or polybutadiene-styrenes
• CPC Class Codes: H01M 8/1039 halogenated, e.g. sulfonated polyvinylidene fluorides
• CPC Class Codes: H01M 8/1067 characterised by their physical properties, e.g. porosity, ionic conductivity or thickness
• CPC Class Codes: Y02E 60/50 Fuel cells
• CPC Class Codes: Y02P 70/50 Manufacturing or production processes characterised by the final manufactured product

Abstract

Assemblies or MEA devices (Membrane Electrode Assembly) comprising a membrane and two electrocatalytic layers on each side thereof, wherein: the area of each of the two electrocatalytic layers is lower than that of the membrane; on each of the two sides of the ionomeric membrane there is at least one subgasket, applied on the MEA non catalyzed area; the edges of the ionomeric membranes being enclosed among said subgaskets.

Claims

1. Assemblies or MEA device (Membrane Electrode Assembly) comprising a membrane and, on each side two electrocatalytic layers, wherein:

the area of each of the two electrocatalytic layers is lower than that of the membrane;

on each of the two sides of the ionomeric membrane there is at least one subgasket, applied on the MEA non catalyzed area;

the edges of the ionomeric membranes being enclosed among said subgaskets.

2. Assemblies according to claim 1, wherein two or more subgaskets can be present on one or both sides of the membrane.

3. Assemblies or MEA devices according to claim 1, in form of 3-layers, 5-layers or 7-layers.

4. Assemblies according to claim 1, wherein a 3-layer MEA comprises, see FIG. 4:

an active area (1), formed of the two electrocatalytic layers positioned on each side of the membrane, the area of the electrocatalytic layers is lower than that of the membrane;

the ionomeric membrane and the electrocatalytic layers form the 3-layer MEA;

the active area (1) is not coated by subgasket;

an area (2) (see FIGS. 5 and 6) representing the ionomeric membrane surface coated by the subgasket;

(3) (see FIGS. 5 and 6) represent the overlapping of the subgaskets enclosing the membrane edges.

5. Assemblies according to claim 4, wherein on each side of the two electrocatalytic layers, not in contact with the membrane, of a 3-layer MEA a gas microdiffusion layer is applied to obtain a 5-layer MEA.

6. Assemblies according to claim 5, wherein on each side of the two microdiffusion layers, not in contact with the electrocatalytic layer, of a 5-layer MEA a gas macrodiffusion layer is applied to obtain a 7-layer MEA.

7. Assemblies according to claim 1, wherein the membrane and the electrocatalytic layers are obtainable by using (per) fluorinated ionomers with sulphonic groups in —

SO₃H acid or salified form, having equivalent weight from 380 g/eq to 1,600 g/eq, preferably from 500 to 1,200 g/eq, still more preferably 750-950 g/eq.

8. Assemblies according to claim 7, wherein the ionomers comprise the following units:

(A) monomeric units deriving from one or more fluorinated monomers containing at least one ethylenic unsaturation;

(B) fluorinated monomeric units containing —

SO₂F sulphonyl groups in amounts such that the ionomer has the equivalent weight in the above range, transformation of the —

SO₂F groups in acid —

SO₃H or salified form.

9. Assemblies according to claim 7, wherein the ionomers are homopolymers formed of monomeric units (B), the ionomers containing the sulphonic groups in acid —

SO₃H or salified form being obtainable by hydrolysis of the —

SO₂F groups.

10. Assemblies according to claim 7, wherein the fluorinated monomers (A) are selected from the following:

vinilydene fluoride (VDF);

C₂-C₈ perfluoroolefins, preferably tetrafluoroethylene (TFE);

C₂-C₈ chloro- and/or bromo- and/or iodo-fluoroolefins as chlorotrifluoroethylene (CTFE) and bromotrifluoroethylene;

CF₂═

CFOR_f1, (per)fluoroalckylvinylethers (PAVE), wherein Rf₁ is a C₁-C₆ (per)fluoroalkyl, for example trifluoromethyl, bromodifluoromethyl, pentafluoropropyl;

CF₂—

CFOX perfluoro-oxyalkylvinylethers, wherein X is a C₁-C₁₂ perfluoro-oxyalkyl having one or more ether groups, for example perfluoro-2-proxpoxy-propyl;

fluorovinylethers (MOVE) of general formula CFX_AI═

CX_AIOCF₂OR_AI(A-I), wherein R_AI is a linear, branched C₁-C₆ (per)fluoroalkyl group or C₅-C₆ cyclic, or a linear or branched when possible C₁-C₆ (per)fluoro-oxyalkyl group containing from one to three oxygen atoms;

when R_AI is fluoroalky or fluorooxyalkyl as above it can contain from 1 to 2 atoms, equal or different, selected from the following;

H, Cl, Br, I;

X_AI═

F, H, preferably F;

preferably (MOVE 1) CF₂═

CFOCF₂OCF₂OCF_3,, (MOVE 2) CF₂=CFOCF₂OCF₂OCF₃, (MOVE 3) CF₂═

CFOCF₂OCF₃.

11. Assemblies according to, claim 7, wherein, alternatively to monomers (B), for preparing the ionomers having equivalent weight as reported for sulphonic ionomers, monomers (B′

) are used containing precursor groups which are transformed by hydrolysis into —

COOH acid groups, and optionally in their corresponding salts, optionally monomers (B′

) are used in admixture with monomers (B).

12. Assemblies according to claim 1, wherein the ionomers contain from 0.01% to 2% by moles of monomeric units deriving from a bis-olefin of formula:

R₁R₂C═

CH—

(CF₂)_m—

CH═

CR₅R₆

wherein;

m=2-10, preferably 4-8;

R₁, R₂, R₅, R₆, equal to or different from each other, are H or C₁-C₅ alkyl groups, preferably H.

13. Assemblies according to claim 1, wherein the membranes and the electrocatalytic layers contain perfluorinated ionomers obtainable from ionomers comprising:

monomeric units deriving from TFE;

monomeric units deriving from CF₂═

CF—

O—

CF₂CF₂SO₂F.

14. Assemblies according to claim 1, wherein the ionomers are crosslinked or crosslinkable.

15. Assemblies according to claim 1, wherein the electrocatalytic layers comprise an ionomer and a catalyst, preferably Pt or a mixture of Pt with one or more metals, preferably Ru, Rh, Mo, said catalyst being finely dispersed and preferably supported on carbon powder.

16. Assemblies according to claim 15, wherein the ratio by weight between catalyst and ionomer in each of the two electrocatalytic layers ranges from 0.5 to 4, preferably between 0.5 and 2.5.

17. Assemblies according to claim 15, wherein the ratio mg of metal catalyst/cm² of electrocatalytic layer ranges from 0.01 to 2.

18. Assemblies according to claim 1, wherein the subgaskets can be thermoplastics or elastomeric polymers, hydrogenated or fluorinated.

19. Assemblies according to claim 1, wherein the subgaskets have the following geometrical characteristics:

an empty area (7), see FIG. 7-1, inside the subgasket, corresponding to the active area (1) of FIG. 4, delimited by the perimeter of (7) or internal perimeter of the subgasket;

an external perimeter (9), larger than that (10) of the ionomeric membrane, see FIG. 7-4;

the perimeter of the openings (11) (see FIG. 7-6) in the subgasket is lower than that of the openings (12) (see FIG. 7-3) in the membrane.

20. A process for preparing the assemblies according to claim 1, comprising a step whereby at least two subgaskets are used, by applying at least one subgasket sheet on each side of the membrane, the subgasket edges of the two subgasket sheets being in contact with each other and not with the membrane except the ones of the internal subgasket perimeter.

21. A process for preparing MEA devices according to claim 20, wherein the electrocatalytic layer is applied prior or after the application of the subgasket.

22. A process according to claim 20, wherein the application of the subgasket to the MEA is carried out by hot pressing, or calendaring adhesivized subgaskets or injection molding.

23. A process according to claim 22, wherein the subgasket application to the MEA is carried out by hot pressing by using adhesivized subgaskets on one side with a holt melt adhesive.

24. Electrochemical devices comprising the assemblies according to claim 1.

25. Fuel cells comprising the assemblies according to claim 1.

26. Use of the assemblies according to claim 1 in electrochemical devices, in particular in fuel cells.