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

Abstract

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.

Metal-support interaction boosts the stability of Ni-based electrocatalysts for alkaline hydrogen oxidation

“…ICP-MS results suggest that Ni and Ti dissolutions are negligible in 0.1 M NaOH. Yet, Mo is found to dissolve from the top surface of Ni 4 Mo particles (Supplementary Table S4 ), in good agreement with previously reported Mo dissolution on NiMo alloys 51 – 54 . The TiO 2 support does not exhibit an inhibitive effect on Mo dissolution.…”

Insights into the Confinement Effect of NiMo Catalysts toward Alkaline Hydrogen Oxidation

“…In the past decade, the alkaline HOR activity of Ni catalysts has been optimized through various elaborate designs such as doping, interface engineering, and alloying. ,− Among the state-of-the-art Ni-based catalysts, NiMo alloys have been extensively studied and exhibit significantly promoted performance due to the positive regulation from Mo decoration. − Serov et al reported the carbon-supported NiMo alloys as the anodic catalysts of AEMFC, which outputted a record power density of 120 mW cm –2 at that time from the single-cell tests. The high activity was attributed to the weakened hydrogen binding energy (HBE) of the Ni sites by adjacent Mo.…”

Construct of an Electrodeposited Cobalt–Molybdenum Film and Evaluation of Its Efficiency in Hydrogen Evolution

“…Because Co (d7) has a low hydrogen adsorption strength and Mo (d5) has a high hydrogen adsorption strength, the two alloys can draw on each other’s strengths to increase hydrogen adsorption strength and catalytic activity. − In addition, binary catalysts consisting of Mo and Co elements have been used as cathodes for hydroelectrolysis. They have demonstrated good catalytic properties due to either crystalline structure modification − or electronic formation. − Besides, the self-supporting electrode allows for better contact between the catalyst and the reactant on the surface. − …”