Electrochemical analysis of polymer electrolyte membrane fuel cell operated with dry-air feed

Electrochemical analysis of a commercial polymer electrolyte membrane fuel cell (PEMFC), operated at varying cathode relative humidity (RH) and current density, has been conducted to understand the factors that affect power performance when the PEMFC is operated with a dry-air feed. With a change in the cathode RH from 80 to 4%, the electrochemical area and double-layer capacitance of the cathode are reduced by 9 and 8%, respectively. This indicates that exclusion of the catalyst layer (CL) of the cathode from proton access occurs to some extent at low RH. It does not, however, explain the observed increase in activation loss. For the dry-air feed, the ionic resistances of the membrane and cathode CL are comparable in magnitude. Impedance analyses show that drying of the cathode at low RH and low current density leads not only to an increase in the ionic resistance of the CL, but also to increases in both charge-transfer and mass-transfer resistances. The simultaneous decrease in all the resistance components with decrease in the air permeability of the cathode diffusion layer highlights the importance of cathode design for operation with dry-air feed.