Designing interface structures of nickel with transition metal nitrides for enhanced hydrogen electro-oxidation

Abstract

Alkaline exchange membrane fuel cells are hampered by sluggish kinetics of the anodic hydrogen oxidation reaction (HOR). Recently, heterostructure catalysts show great potential in tailoring the electronic structure to promote catalytic performance. Herein, we systematically studied the alkaline HOR performance of heterostructures of nickel with transition metal nitrides (Ni/TMNs, TMN = δ3−MoN, δ1−MoN, and WN) by density functional theory calculations. The HOR on Ni/TMNs was found to proceed preferentially through the initial H2 dissociation into two adsorbed H*, followed by its recombination with the adsorbed OH* as the rate-determining step. The inter-regulated electronic structure at the interface can improve the degree of energy-level alignment between the d-band of interfacial Ni and the p-band of OH*, thus enhancing the adsorption free energy of OH* (ΔGOH*). Meanwhile, the downward shift of the p-band of interfacial N also weakens the adsorption free energy of H* (ΔGH*), making it more thermo-neutral. The precisely optimized H* and OH* adsorption at heterojunction interfaces substantially accelerates the recombination of H* and OH* in the HOR, resulting in the high HOR activity of Ni/TMNs. Among all considered catalysts, Ni/δ1−MoN shows the optimum HOR activity, resulting from the almost thermo-neutral ΔGH* and the strongest ΔGOH*.