Theoretical Insights into Designing β-M@Ni(OH)2 Electrocatalysts for Efficient Urea Oxidation

Abstract

Ni-based catalysts show great potential for the urea oxidation reaction (UOR) due to their high activity, low cost, and broad energy and environmental applications. Herein, we investigate two possible mechanisms for N₂ formation on β-Ni(OH)₂ using density functional theory (DFT) and further focus on the dehydrogenation steps of the intramolecular pathway over β-Ni(OH)₂ and β-M@Ni(OH)₂ catalysts (M = Cr, Fe, Co, Cu, Mo, Ru, Rh, Pd, Ir, Pt, and Au). The results show that the intramolecular pathway is energetically favourable on β-Ni(OH)₂, and that the enhanced urea adsorption energy, E_ads (urea), over β-M@Ni(OH)₂ originates from the upshift of the d-band centre, ε_d, which is induced by M-doping. Gibbs free energy analyses identify β-Fe@Ni(OH)₂, β-Co@Ni(OH)₂, and β-Pd@Ni(OH)₂ as promising catalysts with low limiting potentials. Furthermore, the urea adsorption strength shows a linear correlation with the calculated limiting potentials, suggesting that it can serve as an effective descriptor for urea oxidation toward N₂ formation. This study provides theoretical guidance for the screening and design of highly active Ni-based UOR catalysts.