Half-Wave Potential or Mass Activity? Characterizing Platinum Group Metal-Free Fuel Cell Catalysts by Rotating Disk Electrodes

There are challenges in comparing catalyst performance. The most common method is to compare half-wave potentials (E_1/2). This metric has been helpful since it has allowed the platinum-group metal-free (PGM-free) catalyst community to show that the half-wave potential of PGM-free catalysts can compete with platinum catalysts. However, the issue with this metric can be observed in that E_1/2 increases as the rotating disk electrode (RDE) catalyst loading increases. Furthermore, comparisons between catalysts by half-wave potential are biased towards studies that used higher loading, and loading dependence complicates comparing studies of different loadings. Hence, we propose a shift to focusing on mass activity for PGM-free catalysts.