Ni- and Co-Based Heterogeneous Nanosheet Array As Efficient Electrocatalysts for Oxygen Evolution Reaction from Water

Efficient oxygen evolution reaction (OER) catalysts composed of earth-abundant elements are crucial to the development of practical and environmental-friendly water splitting system. Herein, we present the synthesis of Ni- and Co-based heterogeneous composites and their application in electrocatalytic OER. Using a straightforward two step reaction, the NiCoO2/CoO/Ni3N nanosheet arrays (NiCoON NSAs/NF) are fabricated in situ on the 3D nickel foam. We have controlled the ratio of two metal sources, reaction temperature, and the annealing time to optimize the active surface species, as well as the morphology. 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 NixCo3-xO4 and most Ni- and Co-based electrocatalysts. There are more active sites with oxygen vacancies on NiCoON NSAs after the treatment with NH3 and the face-centered cubic NiCoO2 facilitates the formation of active Ni-Co layered hydroxide/oxyhydroxide species (NiOOH) in comparison with spinal NixCo3-xO4 during the electrochemical process. In addition, the Ni3+-rich surface together with Co incorporation has been shown to favor the formation of β-NiOOH over γ-NiOOH. Our study reveals that the precise control of active species on NiCoON NSAs/NF leads to high activity and stability in OER catalysis.