Electrodes for alkaline fuel cells with circulating electrolyte
Fuel cell electrodes are described which comprise a non-woven network of conductive fibers, such as a carbon fleece, nickel foam sheet or stainless steel wool layer, plus additional activated carbon material, carrying one or more catalyst components and at least one polymeric substance as binder and/or repellancy agent to establish three zone interfaces (liquid-solid-liquid) or three phase interfaces (gas-liquid-solid). The electroactive catalyzed material is embedded into the conductive structure by specified deposition processes, such as coating, blading or spraying.
1. A fuel cell electrode comprising:
a non-woven network of conductive fibers, electroactive carbon material carrying one or more catalysts, and at least one polymeric substance selected from the group consisting of a binder and a repellancy agent to establish liquid-solid-liquid zone interface or gas-liquid-solid phase interface,
whereby structure of the electrode is formed upon embedding electroactive carbon material into the network of conductive fibers by a deposition process selected from the group consisting of coating, blading and spraying, and
whereby specific catalyst density of the electrode is within the range of 0.8 mg/cm 3 to 50 mg/cm 3 (per vol.) or 0.1 mg/cm 2 to 2.0 mg/cm 2 (per area) and overall density of the electrode is within the range of 50 mg/cm 2 to 150 mg/cm 2 (per area),
wherein the conductive fibers are selected from the group consisting of a carbon fleece, nickel and stainless steel, and wherein the nickel conductive fibers comprise a nickel foam sheet and the stainless steel conductive fibers comprise stainless steel wool.
2. The fuel cell electrode as claimed in claim 1 , wherein the catalyzed electroactive carbon material is treated with one or more polymeric binders, the polymeric binders being selected to provide a suitable hydrophobic/hydrophilic balance to the electrode, creating an optimum ionic conduction pathway in the electrode.
3. The fuel cell electrode as claimed in claim 2 , wherein the polymeric binders are selected from the group consisting of polytetrafluoroethylene, fluorinated ethylene-propylene copolymers, polyethylene, polypropylene, ethylene-propylene copolymers, polyisobutenes, polysulfones and epoxy resins.
4. The fuel cell electrode as claimed in claim 1 , wherein the electroactive carbon material is steam-activated or CO 2 -activated acetylene carbon black, or a mix with carbon black or graphite, and the one or more catalysts are selected:
a) from one or more noble metal catalysts in the range of 0.1–1.2 mg/cm 2 for anodes; and
b) from the group consisting of a noble metal catalyst in the range of 0.1–1.2 mg/cm 2 , a non-noble metal catalyst, and mixtures thereof for oxygen or air cathodes, wherein the non-noble metal catalyst is selected from the group consisting of spinels, perovskites and Co-porphyrines.
5. The fuel cell electrode as claimed in claim 4 , wherein the electroactive carbon material is steam-activated or CO 2 activated carbon, and 0.2 to 3.0 mass % of a spinel AB 2 O 4 is added to the carbon material to hasten carbon activation and to further stabilize the catalyst, wherein A=Mn, Co, Ni, Cu, or Cd, and B=Al, V, Cr, Ti.
6. The fuel cell electrode as claimed in claim 5 , wherein the electrode is manufactured by filling a conductive metal fiber or carbon fleece structure with the electroactive carbon material by
a) doctor blading of a highly viscous mixture achieved by adding the catalyst-containing electroactive carbon material to a suspension of polymer binder or adding the electroactive carbon material without a catalyst to a suspension of polymer binder and post-catalyzing the electrode;
b) spraying a low viscosity mixture; and
c) rolling, pressing, or rolling and pressing the electrodes to a predetermined electrode thickness, at a predetermined temperature.
7. The fuel cell electrode as claimed in claim 1 , wherein multiple electrodes comprise stacks of various lengths adjusted to provide a predetermined voltage, wherein individual cells comprise either:
a) edge-collecting terminals; or
b) bipolar plates forming bipolar assemblies.
8. The fuel cell electrode as claimed in claim 7 , wherein the fuel cell electrodes comprising cells having edge collecting terminals further comprise fuel channels and oxygen manifolds arranged in pairs.
9. The fuel cell electrode as claimed in claim 7 , wherein the fuel cell electrodes comprising cells having bipolar assemblies comprise bipolar plates formed from molded conductive plastic or corrugated metal plates.
10. A fuel cell electrode comprising:
a non-woven network of conductive fibers, electroactive carbon material carrying one or more catalysts, and at least one polymeric substance selected from the group consisting of a binder and a repellancy agent to establish liquid-solid-liquid zone interfaces or gas-liquid-solid phase interfaces,
whereby structure of the electrode is formed upon embedding electroactive carbon material into the network of conductive fibers by a deposition process selected from the group consisting of coating, blading and spraying, and
whereby specific catalyst density of the electrode is within the range of 0.8 mg/cm 3 to 50 mg/cm 3 (per vol.) or 0.1 mg/cm 2 to 2.0 mg/cm 2 (per area) and overall density of the electrode is within the range of 50 mg/cm 2 to 150 mg/cm 2 (per area), wherein the conductive fibers are selected from the group consisting of a carbon fleece, nickel and stainless steel, and wherein the non-woven network of nickel or stainless steel conductive fibers is partly coated by at least one polymeric substance selected from the group consisting of polytetrafluoroethylene, fluorinated ethylene-propylene copolymers, polyethylene, polypropylene, ethylene-propylene copolymers and polyisobutenes, thereby conferring hydrophobicity to the nickel or stainless steel while still supporting electrical surface conductivity.