Abstract
Fuel cell anodes operate in a reducing atmosphere, whereas cathodes operate under strongly oxidizing conditions, in difficult electrolytic environments. Electrochemical corrosion can limit the working cathode potential, hence fuel cell operating efficiency, as well as fuel cell lifetime. The four principal classes of electrolyte are aqueous alkali, aqueous acid, and two high temperature, CO2-rejecting systems: molten alkali carbonates (∼650 C) and solid oxide ionic conductors (1000 C). For the aqueous electrolytes, thermodynamically stable cathode materials include some of the noble metals and a range of passive oxides (restricted to Nb and Ta oxides in acid media). However, various kinetically stable carbons permit the possibility of inexpensive cathode construction materials and catalyst supports that are stable to 80 C and to over 200 C in alkaline and acid fuel cells, respectively. The corrosion rates of these cathode components (and those of the supported platinum catalyst in acid media) ultimately limit fuel cell life and performance. In contrast, the high temperature cells show few corrosion problems, provided that the electronically conducting parts in contact with both anode and cathode atmospheres are protected by suitable dielectric coatings to prevent a direct ionic pathway between anodic and cathodic sites.
