A Carbon Corrosion Model to Evaluate the Effect of Steady State and Transient Operation of a Polymer Electrolyte Membrane Fuel Cell

A carbon corrosion model is developed based on the formation of surface oxides on carbon and platinum of the polymer electrolyte membrane fuel cell electrode. The model predicts the rate of carbon corrosion under potential hold and potential cycling conditions. The model includes the interaction of carbon surface oxides with transient species like OH radicals to explain observed carbon corrosion trends under normal PEM fuel cell operating conditions. The model prediction agrees qualitatively with the experimental data supporting the hypothesis that the interplay of surface oxide formation on carbon and platinum is the primary driver of carbon corrosion. Carbon is commonly used as material for catalyst supports, gasdiffusion media and bipolar plates in Proton Exchange Membrane (PEM) fuel cells, though it is well-known that carbon is thermodynamically unstable in PEM fuel cell cathode environments. The current PEM fuel cell cathodes typically operate at temperatures in the range of 60 ◦ C–85 ◦ C and potentials in the range of 0.5–0.95 V (vs. RHE), which is significantly more anodic than the equilibrium potential for carbon oxidation to carbon dioxide (0.207 V vs. RHE). However, the kinetics of carbon oxidation under PEM operational conditions is relatively slow. This slow oxidation kinetics makes carbon an appropriate material for PEM electrodes. Carbon corrosion occurs at different rates under various fuel cell operating conditions. A few distinct conditions that can lead to extensive carbon corrosion and catastrophic performance decay in a short period of time have been identified. One such condition occurs during start/stop operations when air leaks into or is present in the anode gas channels and creates potential variation in the planform. 1–3 Another condition that leads to carbon corrosion is fuel starvation induced by flow mal-distribution in the individual cells of the stack. 4 In both cases, undesirable oxygen reduction reaction (ORR) at the anode decreases the potential of ionomer keeping high potential difference between carbon and ionomer (close to equilibrium potential of ORR). That results in high potential difference (∼1.4 V) between carbon and ionomer at the opposite electrode and accelerated carbon corrosion at this potential. 1–4 The corresponding system strategies to mitigate have