Cation-induced formation of highly active γ -NiFeOOH for efficient oxygen evolution reaction

Abstract

The oxygen evolution reaction (OER) activity of Ni-based oxyhydroxides greatly hinges on their phase structures, which are mainly γ and β phases: the former has higher intrinsic activity than the latter. However, it is still a grand challenge to purposefully generate γ phase, rather than β phase. Here, we propose a cation-doping strategy to generate γ phase by taking Zn-doped NiFeP/N-doped C (Z-NFP/N-C) precatalyst as a model. In contrast to the case of NFP/N-C that can only be reconstructed into β-NiFeOOH, Zn dopant will induce the formation of γ-NiFeOOH during an electrochemical process. Specifically, the doped Zn cation will promote the dissolution of NiFeP and redeposition of NiFeOOH on the surface. Simultaneously, the cation defects generated by Zn leaching will force the surrounding Ni valence state to rise for charge balance and will attract more K+ in the solution to intercalate into the interlayer of NiFeOOH, resulting in the formation of γ-NiFeOOH. As a result, the γ-NiFeOOH/Z-NFP/N-C exhibits superior OER performance: a low overpotential of 216 mV at 10 mA cm−2 and satisfactory stability (100 h at 17 mA cm−2). Our study offers a practical approach to produce highly active “true catalyst” for efficient water splitting.