Bimetallic NiM/C (M = Cu and Mo) Catalysts for the Hydrogen Oxidation Reaction: Deciphering the Role of Unintentional Surface Oxides in the Activity Enhancement

Emerging interest in the platinum group metal (PGM)-free electrocatalysts calls for a fundamental understanding of the key factors determining their activity, the latter being critical for the development of efficient catalysts. Ni-based materials show high promises as PGM-free anodes of anion exchange membrane fuel cells (AEMFCs). However, their hydrogen oxidation reaction (HOR) activity can differ by several orders of magnitude, and the factors responsible for this are still being debated. In this work, the effect of unintentional surface oxides in Ni/C and NiM/C (M = Cu and Mo) is revealed by benchmarking either the catalysts conventionally stored under ambient conditions or purposely reduced oxide-free materials. The analysis of electrocatalytic data complemented by detailed material characterization, Monte Carlo simulations, and density functional calculations, underlines the key importance of surface oxides in the HOR catalysis on Ni, NiCu, and NiMo electrodes. These findings underscore the need to measure the HOR activity of Ni-based catalysts in the absence of surface oxides in order to unambiguously interpret the influence of other factors (such as the electronic effect of the second element) on activity enhancement.

Automated summary

This study reveals the significant influence of unintentional surface oxides in nickel-based materials on electrocatalytic reactions, particularly the hydrogen oxidation reaction (HOR) activity. These findings highlight the importance of excluding the effects of surface oxides when evaluating the activity of nickel-based catalysts, in order to accurately interpret the impact of other factors.