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

Abstract 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.