Ni/Co-based nanosheet arrays for efficient oxygen evolution reaction

Efficient oxygen evolution reaction (OER) catalysts composed of earth-abundant elements are crucial to the development of practical and environmentally friendly water splitting systems. Herein, NiCoO₂/CoO/Ni₃N nanosheet arrays (NiCoON NSAs/NF) are fabricated in situ on the 3D nickel foam. In the alkaline solution, the NiCoON nanocomposite has excellent catalytic OER properties such as a small overpotential of 247 mV (at 10 mA cm⁻²) and Tafel slope of 35 mV dec⁻¹, which are better than those of Ni_xCo_3-xO₄ and most Ni- and Co-based catalysts. There are more active sites with oxygen vacancies on NiCoON NSAs after the treatment with NH₃ and the face-centered cubic NiCoO₂ enhances the formation of active Ni-Co layered hydroxide/oxyhydroxide species (NiOOH) in comparison with spinal Ni_xCo_3-xO₄ during the electrochemical process. In addtion, the Ni³⁺-rich surface together with Co incorporation facilitates the formation of β-NiOOH. Our study reveals that control of active species on NiCoON NSAs/NF leads to high activity and stability in OER catalysis.