STEADY-STATE MODEL FOR AN OXYGEN FUEL-CELL ELECTRODE WITH AN AQUEOUS CARBONATE ELECTROLYTE

A mathematical model has been developed to describe the steady-state c onstant-current operation of an oxygen cathode in aqueous carbonate el ectrolyte, as might be used as a component of a direct-methanol fuel c ell. The diffusion and reaction of oxygen in PTFE-bonded Pt-catalyzed porous gas diffusion electrode agglomerates as well as Ohmic and migra tion effects over the catalyst layer were taken into account. The mode l accurately predicts the shape and the oxygen pressure dependence of cathode polarization data for 2 and 4 M K2CO3 electrolyte, using no ad justable parameters. Transport of OH- ions out of the catalyst layer i s shown to be a limiting factor in the operation of these modern fuel cell cathodes, which have been generally optimized for maximum oxygen transport in the electrolyte. The model. indicates that higher catalys t layer porosities and thinner electrodes would yield better cathode p erformance in this electrolyte.