Proton exchange membrane (PEM) electrochemical cell having an integral electrically-conductive, resiliently compressible, porous pad
View Patent ↗Electrolysis cell comprises, in one embodiment, a proton exchange membrane (PEM), an anode positioned along one face of the PEM, and a cathode positioned along the other face of the PEM. An electrically-conductive, compressible, spring-like, porous pad for defining a fluid cavity is placed in contact with the outer face of the cathode. The porous pad comprises a mat of carbon fibers bound together with one or more, preferably thermoplastic, resins, the mat having a density of about 0.2-1.5 g/cm 3 . Cell frames are placed in peripheral contact with the metal screen and the compression pad for peripherally containing fluids present therewithin. Electrically-conductive separators are placed in contact with the metal screen and the compression pad for axially containing fluids present therewithin. A plurality of the cells may be arranged in series in a bipolar configuration without requiring a separate compression pad between cells (for gas pressure differentials up to about 400 psi or greater). The invention is also directed to a fuel cell wherein the pad replaces the carbon fiber paper or carbon fiber cloth in contact with the cathode or anode.
1. An electrochemical cell comprising:
(a) an anode;
(b) a cathode;
(c) a proton exchange membrane, the proton exchange membrane having a first face and a second face, the proton exchange membrane being positioned between the anode and the cathode, with the anode being electrically coupled to the first face of the proton exchange membrane and the cathode being electrically coupled to the second face of the proton exchange membrane; and
(d) a compression pad for use in defining a cathodic fluid diffusion cavity, the compression pad being electrically-conductive, resiliently compressible and porous, the compression pad consisting of a unitary random mat of carbon fibers bound together using at least one binder.
2. The electrochemical cell as claimed in claim 1 wherein said compression pad has a density of about 0.2-1.5 g/cm 3 .
3. The electrochemical cell as claimed in claim 2 wherein said compression pad has a density of about 0.35-0.77 g/cm 3 .
4. The electrochemical cell as claimed in claim 3 wherein said compression pad has a density of about 0.55-0.77 g/cm 3 .
5. The electrochemical cell as claimed in claim 1 wherein said compression pad has a density of about 0.77 g/cm 3 .
6. The electrochemical cell as claimed in claim 1 wherein at least one of said at least one binder is a thermoplastic binder.
7. The electrochemical cell as claimed in claim 6 wherein said thermoplastic binder is a polyvinylidene fluoride (PVDF).
8. The electrochemical cell as claimed in claim 6 wherein said thermoplastic binder is a combination of a PVDF and polytetrafluoroethylene (PTFE).
9. The electrochemical cell as claimed in claim 1 wherein said at least one binder consists of a PVDF.
10. The electrochemical cell as claimed in claim 1 wherein said at least one binder consists of a combination of a PVDF and PTFE.
11. The electrochemical cell as claimed in claim 1 wherein said carbon fibers have a length in the range of about 100 microns to one inch with a diameter in the range of about 4 to 12 microns.
12. The electrochemical cell as claimed in claim 11 wherein said carbon fibers consist of a combination of chopped carbon fibers having a length of about one-eighth of an inch and a diameter of about 4-12 microns and milled carbon fibers having a length of about 200 microns and a diameter of about 4-12 microns.
13. The electrochemical cell as claimed in claim 9 wherein said PVDF constitutes about 5-40 wt % of said compression pad.
14. The electrochemical cell as claimed in claim 13 wherein said PVDF constitutes about 10-25 wt % of said compression pad.
15. The electrochemical cell as claimed in claim 1 wherein said compression pad, after being compressed to pressures up to about 12,000 psi, has an uncompressed thickness of at least 70% of its original, pre-compressed thickness.