Insights on designing non-PGM catalyst layers at low humidity

Abstract

Non-precious group metal (non-PGM) catalysts offer the opportunity to significantly reduce fuel cell costs. However, owing to its low volumetric activity, non-PGM electrodes are made an order of magnitude thicker than platinum-based electrodes. Thicker electrodes increase transport losses making it critical to optimize electrode composition. In most studies, non-PGM electrodes are tested with fully humidified O2/air to maximize the proton conductivity. However, the fully humidified inlet gas makes non-PGM electrodes more prone to water flooding which can cause long-term performance degradation. In the present study, a single-phase, non-isothermal model was used to investigate the structure-performance relationships of the non-PGM electrodes operated at low relative humidity. Our modeling study reveals that high porosity is not necessarily required for non-PGM electrodes operating at low relative humidity. Instead, high solid and electrolyte phase volume fractions are desired. Our proposed strategy is to reduce the thickness of the non-PGM electrode while keeping the mass loading of the non-PGM catalyst consistent.