The effect of platinum on carbon corrosion behavior in polymer electrolyte fuel cells

To assess the catalytic effect of platinum on the corrosion of the high surface area carbon support, single triangular potential sweeps with various upper and lower limits were applied to fuel cells comprising electrodes having different Pt/C compositions. Carbon loss rates in H-2/N-2 and air/air mode were determined by integration of the resulting CO2 concentration peaks in the exhaust gas of the positive electrode. Generally, the contribution of platinum catalyzed carbon corrosion to total CO2 evolution was found to decrease with increasing upper potential limit. Similar carbon loss rates obtained for Pt/C and pure carbon electrodes in case of lower potential limits of 1.0 V indicate that the catalytic activity of platinum is substantially lowered by the formation of a passivating oxide layer on the platinum particles. Changes in corrosion behavior in the potential range below 0.6 V. which cannot be attributed to platinum effects, are suggested to originate from modifications in carbon surface oxide composition. Due to the high oxygen equilibrium potential of approximately 1 V, carbon corrosion in air/air mode is significantly influenced by platinum oxide formation. However, the polarization of the negative electrode and the influence of platinum oxidation on the equilibrium potential results in a passivating effect that is less pronounced than expected from measurements in H-2/N-2 mode. (C) 2011 Elsevier Ltd. All rights reserved.