Competitive Halogen Adsorption Governs Alkaline Hydrogen Oxidation Activity and Stability of Ni‐Based Electrocatalysts

Nickel-based catalysts exhibit only 1-2% of the activity of noble metal catalysts for the hydrogen oxidation reaction (HOR) in alkaline environments. The underlying mechanism remains unclear, posing significant challenges for developing high-activity nickel-based catalysts. Here, the effect of anion adsorption (OH^-, Br^-, Cl^-, and SCN^-) on the HOR mechanism of Ni-based catalysts is investigated through experimental analysis. Results indicate that the preferential adsorption of Br^- and Cl^- not only accelerates hydrogen transfer, increasing the HOR limiting current, but also inhibits OH^- adsorption, thereby preventing nickel oxidation. Through anion adsorption, the HOR activity of the NiMoO_x catalyst is enhanced by 13% and the onset potential for Ni oxidation is delayed by 40 mV. In contrast, pseudohalogen anions (SCN^-), owing to their strong coordination with Ni, penetrate the electric double layer interface to adsorb on the catalyst surface, thus poisoning the Ni-based catalyst. Consequently, alkaline anion exchange membrane fuel cells catalyzed by Cl^--modified NiMoO_x achieve a peak power density of 234.3 mW cm^-2, exceeding that of unmodified NiMoO_x by a factor of 1.24.