Catalyst coated membrane (CCM) and catalyst film/layer for alkaline membrane fuel cells and methods of making same
Alkaline membrane fuel cells designed with silver cathode catalysts include a catalyst layer comprising silver metal nano-particles and an anion-conducting ionomer. The silver nano-particles are mixed with a solution of the ionomer to form a catalyst ink that is applied to an alkaline membrane to form an ultra-thin cathode catalyst layer on the membrane surface.
1. A catalyst coated membrane (CCM) for use in an alkaline membrane fuel cell (AMFC) comprising:
an anion conducting alkaline membrane; and
a catalyst layer applied adjacent the membrane, wherein the catalyst layer comprises:
(a) a metal nano-powder; and
(b) an ion conducting ionomer.
2. The CCM of claim 1 wherein the metal nano-powder comprises silver-containing nano-particles.
3. The CCM of claim 1 wherein the metal nano-powder has an effective density of about 0.25 g/cm 3 .
4. The CCM of claim 1 wherein the ionomer comprises a polymer with a poly(arylene) backbone.
5. The CCM of claim 2 wherein the weight ratio of the ionomer to the silver nano-particles is about 0 to 10%.
6. The CCM of claim 2 wherein the silver-containing nano-particles comprise a silver alloy.
7. The CCM of claim 2 wherein the silver nano-particles form an open nano-powder structure.
8. The CCM of claim 2 wherein the volume ratio of ionomer:silver is in a range of about 1:0.7 to about 1:1.5.
9. The CCM of claim 8 wherein the volume ratio is in a range of about 1:0.9 to about 1:1.1.
10. The CCM of claim 2 wherein the silver-containing nano-particles are mixed with the ion conducting ionomer to form an ink which is applied to the anion conducting membrane by spraying.
11. The CCM of claim 10 wherein the membrane is positioned during ink application on a heated vacuum table.
12. The CCM of claim 11 wherein the dry membrane is exposed to a solvent, the solvent selectively swelling the membrane surface to promote catalyst layer bonding to the membrane surface.
13. The CCM of claim 1 wherein the metal nano-powder and ionomer are applied to the anion conducting alkaline membrane by screen printing onto the membrane.
14. The CCM of claim 2 wherein the silver-containing nano-powder and ionomer are mixed to form an ink and are applied to a Teflon®-coated film blank, the blank serving as a platform to:
(a) support the metal nano-metal and ionomer and;
(b) transfer the ink to the membrane surface.
15. The CCM of claim 10 wherein the ink is comprised of a mixture of silver containing nano-particles and a solution of an OH-ion conducting ionomer in a solvent.
16. The CCM of claim 15 wherein the OH-ion conducting ionomer is selected from among poly(arylenes) with tetra-alkyl ammonium hydroxide functional groups of functional group densities between 1.5 and 3.5 milli-equivalents per gram, the selecting being based on the ability to absorb liquid water to increase ionic conductivity and to retain hydration in the cathode catalyst layer.
17. The CCM of claim 2 wherein the silver-containing particles are a size from about 5 nm to about 50 nm in diameter.
18. The CCM of claim 17 wherein the silver-coating particles have a void powder factor over about 90%.
19. A method of making a catalyst coated membrane (CCM), composing the steps of:
(a) providing a source of silver-containing nano-particles;
(b) providing a source of hydroxide ion OH-conducting ionomer material;
(c) adding the silver-containing nano-particles to a solution of the OH-ionomer material to form a catalyst ink;
(d) applying the catalyst ink to a cathode side surface of an alkaline membrane; and
(e) applying one or more of heat and pressure to catalyst ink and membrane to secure the ink to the membrane.
20. A cathode catalyst layer for use in a catalyst coated membrane (CCM) in an alkaline membrane fuel cell (AMFC) comprising:
(a) a metal nano-powder; and
(b) an ion conduction ionomer.
21. The cathode catalyst layer of claim 20 wherein the metal nano-powder comprises silver-containing particles.