Water management in monopolar fuel cells
A monopolar fuel cell stack comprising proton exchange membrane fuel cells supplied with a gaseous anodic reactant, preferably hydrogen, and a gaseous cathodic reactant, preferably air. The monopolar fuel cell stack, forming at least one substantially planar array, includes a liquid water retention barrier disposed over an electrode to retain liquid water within the fuel cells. The barrier is preferably used over the cathode side of each fuel cell and allows excess air flow to cool the fuel cell stack without drying the membrane in each fuel cell. The liquid water retention barrier may be either: (i) a thin, gas permeable, liquid water impermeable membrane; (ii) a thin, porous sheet of material; or (iii) a thin, substantially solid sheet of material except for a plurality of small through-holes that penetrate from one side of the sheet to an opposing side of the same sheet.
1 . A monopolar fuel cell stack comprising:
a plurality of fuel cells placed spatially in a side-by-side arrangement forming at least one substantially planar array, each cell comprising an ion-conducting membrane with an anode and a cathode disposed on opposing sides of the membrane and a gas permeable, liquid water impermeable water retention barrier having a first face secured in intimate contact across the active area of the cathode and a second face exposed to ambient air conditions; and
a substantially planar fluid permeable electronically conducting current collector providing electronic communication between the active area of the anode of a first fuel cell and the active area of the cathode of a second fuel cell adjacent the first fuel cell in the array.
2 . The fuel cell stack of claim 1 , wherein the water retention barrier is electronically non-conducting and extends across the cathodes of two or more of the plurality of fuel cells.
3 . The fuel cell stack of claim 1 , wherein the water retention barrier is secured along the edge of each of the plurality of fuel cells.
4 . The fuel cell stack of claim 1 , wherein the water retention barrier and the current collector are the same structure.
5 . The fuel cell stack of claim 1 , wherein the water retention barrier serves as a secondary current collector.
6 . The fuel cell stack of claim 1 , wherein the cathode comprises a gas diffusion layer, and wherein the water retention barrier is disposed within the gas diffusion layer.
7 . The fuel cell stack of claim 1 , wherein the water retention barrier has a face in full intimate contact with a gas diffusion layer of the cathode.
8 . The fuel cell stack of claim 7 , wherein the water retention barrier is a gas permeable, liquid water impermeable membrane.
9 . The fuel cell stack of claim 8 , wherein the water retention barrier is hydrophobic.
10 . The fuel cell stack of claim 1 , further comprising a means for recovering water from the anode of each fuel cell.
11 . The fuel cell stack of claim 1 , wherein the porous water retention barrier has an average pore size between 20 and 500 nanometers.
12 . The fuel cell stack of claim 1 , wherein the water retention barrier includes a component selected from porous polymer sheet or film, expanded polymer sheet or film, filter paper, perforated polymer film, organic felts, and combinations thereof.
13 . The fuel cell stack of claim 1 , wherein the water retention barrier includes a material selected from porous thermoplastic sheet or film, expanded PTFE, polymer felt, non-halogenated thermoplastic, and combinations thereof.
14 . The fuel cell stack of claim 1 , wherein the water retention barrier includes a non-halogenated thermoplastic selected from polyethylene, polypropylene, polystyrene, polycyclo-pentadiene, nylons, and combinations thereof.
15 . The fuel cell stack of claim 1 , wherein the water retention barrier includes a component selected from perforated metal sheet or foil, micro expanded metal sheet or foil, porous metal fritts, metal felts, and combinations thereof.
16 . A method of operating a monopolar fuel cell stack comprising a plurality of fuel cells, each fuel cell having an anode and a cathode in contact with opposing faces of an ion conducting membrane, comprising:
supplying hydrogen gas to the anode of each fuel cell;
passing ambient air through a gas permeable, liquid water retention barrier covering the cathode of each fuel cell;
withdrawing water vapor from the cathode through the liquid water retention barrier of each fuel cell;
preventing the passage of liquid water through the liquid water retention barrier of each fuel cell; and
allowing liquid water from each cathode to hydrate the membrane in each fuel cell.
17 . The fuel cell stack of claim 16 , further comprising:
maintaining the anode of each fuel cell at a lower temperature than the cathode of each fuel cell.
18 . The fuel cell stack of claim 16 , further comprising:
back diffusing liquid water from the cathode through the membrane to the anode of each fuel cell.
19 . The fuel cell stack of claim 18 , further comprising:
removing liquid water from the anode of each fuel cell.
20 . A subassembly for a monopolar fuel cell stack, comprising:
a gas permeable, substantially liquid water impermeable barrier; and
a layer of particulate filtration material coupled to the barrier.
21 . The subassembly of claim 20 , further comprising:
a hydrophobic coating layer applied to the surface of the particulate filtration material exposed to unfiltered ambient air.
22 . The subassembly of claim 20 , further comprising chemical and/or microbiological abatement or destruction media.