Synergistic effects of Ni³⁺–Cu0/+ dual sites for efficient and stable hydrogen production in AEM water electrolysis

Achieving efficient and stable hydrogen evolution reaction (HER) with low-cost and earth-abundant electrocatalysts is pivotal for sustainable alkaline water electrolysis. Here, we report on an oxygen vacancy (Ov)-rich Cu₂O/NiO heterostructure with interfacial charge transfer from NiO to Cu₂O that creates Ni³⁺–Cu0/+ dual sites of exceptional catalytic activity through the synergistic promotion of water dissociation and hydrogen adsorption. The Cu₂O/NiO heterostructure exhibits a low overpotential of 19.7 mV at 10 mA cm⁻² with Tafel slope of 36 mV dec⁻¹, outperforming most of the reported catalysts. We also employed the Cu₂O/NiO electrode in an anion exchange membrane (AEM) electrolyzer, achieving 1 A cm⁻² at 1.78 V with stability for >200 hours in continuous operation. To elucidate this unique behavior, thorough characterizations involving HRTEM, STEM(HAADF), XPS, EPR, XANES and DFT calculations were employed which proved the interfacial charge transfer dynamics in Cu₂O/NiO heterostructure and their link with the HER mechanism, offering a new paradigm for rational design of noble metal-free HER electrocatalysts for practical AEM electrolyzers.