Alkaline hydrogen oxidation reaction on ruthenium-based catalysts: From mechanism insights to catalyst advances

Abstract

Hydrogen has been regarded as one of the most promising alternatives to traditional fossil fuels due to its high energy density, as well as zero carbon emission. Notably, hydrogen fuel cells have been developed into the leading hydrogen energy utilization technology. However, even for the platinum group metal (PGM), the kinetics of anodic hydrogen oxidation reaction (HOR) becomes sluggish with several orders of magnitude decline, when the electrolytes vary from acid to base. More importantly, the fundamental reason for the kinetic pH effect is controversy. Therefore, comprehending alkaline HOR mechanism and exploring high-effective electrocatalysts are significant for the commercialization of fuel cells. Among them, as the cost-effective member of PGM, ruthenium (Ru) has a similar hydrogen binding energy to Pt, which has been extensively explored for alkaline HOR. Accordingly, the recent advancement of Ru-based catalysts for alkaline HOR is summarized in this review. Firstly, the comprehensive analyses are conducted on the reaction mechanism, focusing on the discrepancy and dispute on the crucial influencing factor towards alkaline HOR. Subsequently, guided by the reaction mechanism, the recent high-performance Ru-based catalysts are elucidated from following effects: geometric effect, electronic effect, and support effect. Finally, the challenge and prospect are pointed out for providing inspiration for future Ru-based catalysts and promoting further development of hydrogen fuel cells.