Self-supporting hierarchical Co₃O₄-nanowires@NiO-nanosheets core-shell nanostructure on carbon foam to form efficient...

Designing cost-effective and robust bifunctional electrocatalysts for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) is highly desired in hydrogen production from overall water splitting, but still suffers great challenges due to the sluggish catalytic OER/HER kinetics. In this paper, a surface/defect engineering strategy is developed to synthesize three-dimensional (3D) carbon foam (CF)-supported unique hierarchical Co₃O₄ nanowires@NiO nanosheets core-shell nanostructured catalyst (NiO@Co₃O₄/CF) with rich oxygen-vacancies as a novel bifunctional catalyst for alkaline water splitting electrolysis. Benefited from the synergy of the 3D hierarchical core-shell structure and rich oxygen vacancies, the as-obtained NiO@Co₃O₄/CF shows both excellent OER (η₂₀₀ = 325 mV, η₅₀₀ = 374 mV) and HER (η₁₀ = 104 mV) activities with low Tafel slopes (64.26 mV dec^-1 for OER and 109.14 mV dec^-1 for HER, respectively) and outstanding stability. A simple overall water splitting electrolysis cell assembled by this bifunctional NiO@Co₃O₄/CF as both OER and HER catalysts requires only a cell voltage of 1.53 V to obtain the current density of 10 mA cm^-2 and displays a long-term stability. This work has successfully developed an approach for rational design and novel synthesis of metal oxide hybrids as bifunctional electrocatalysts with high activity and stability for overall water splitting.