Voltage Losses in Fuel Cell Cathodes

A model of the air diffusion electrode used in fuel cells was developed which accounts for the diffusion of oxygen in the gas‐filled pores as well as diffusion into the liquid‐filled pores, electrochemical reaction, and electrical conduction. The model was applied to a PTFE‐bonded, platinum‐on‐carbon cathode in acid electrolyte to evaluate the relative contribution of these effects. Gas diffusion contributed 38% and ohmic loss in the electrolyte contributed 48% to the voltage loss other than activation. Knudsen diffusion was found to be as important as molecular diffusion. Diffusion of dissolved oxygen and ohmic conduction produced small voltage losses. Diffusion contributes to the utilization loss, especially at high oxygen utilizations, but ohmic effects do not.