Towards reliable assessment of hydrogen oxidation electrocatalysts for anion-exchange membrane fuel cells

Recent advancement of proton exchange membrane fuel cells has led to commercial sales of fuel-cell cars but market barrier exists because this technology heavily relies on platinum catalyst. Given the permission of adopting platinum-group-metal-free catalysts, anion-exchange membrane fuel cell has received notable attention. However, the sluggish kinetics of anodic hydrogen oxidation reaction (HOR) largely limit the cell efficiency. Although many high-performance HOR catalysts have been reported, there are analytical uncertainties in the literature concerning the assessment of the catalyst activity. Here we determine the origin of false HOR currents in the recorded polarization curves and propose a rigorous approach to eliminate them. We unveil experimentally the uncertainties of obtaining exchange current densities (j₀) using Tafel plot from Bulter–Volmer equation and recommend employing the micro-polarization region method. For bulky catalysts that cannot establish a well-defined diffusion layer, we suggest applying external stirring bar to offer certain level of enforced convection and using j₀ to compare the activity.