Robust nanoporous NiMn oxide electrocatalysts for the oxygen evolution reaction through defect engineering

Abstract

The sluggish oxygen evolution reaction (OER) remains a major bottleneck in hydrogen generation through electrolysis, particularly in large current operations. Thus, there is a huge interest in the development of highly active and robust non-noble metal-based OER catalysts. Herein, we report excellent catalytic performance of oxygen vacancy enriched, nano-porous Mn₃O₄/Ni/NiMnO₃ architecture, synthesized in situ over a NiMn substrate through high-rate straining and chemical dealloying. The multiphase active surface exhibits significantly low overpotentials of only 262 mV and 282 mV even at high current densities of 500 mA cm⁻² and 1000 mA cm⁻², respectively. Our first-principles analysis revealed the prevalence of multi-site lattice oxygen-mediated pathways with two parallel mechanisms of direct evolution of O₂, (a) facile cleavage of Ni–O bonds at the NiMnO₃ surface and release of lattice oxygen and (b) activation of under-coordinated Mn–O polyhedra at the Ni/NiMnO₃ interface and cleavage of OH groups by protonation of surface O atoms. The presence of oxygen vacancies leads to electronic reconstruction, further enhancing the adsorption kinetics of reaction intermediates.