Multi-high valence state metal doping in NiFe hydroxide toward superior oxygen evolution reaction activity

In this study, we demonstrate multi-high valence 3d transition metal (TM) doping to boost the oxygen evolution reaction (OER) activity and stability of NiFe hydroxide. Self-supported NiFe hydroxides with multiple high valence 3d TM (V⁴⁺, V⁵⁺, Ti³⁺, Ti⁴⁺, Co³⁺, and Cr³⁺) doping are fabricated using a facile Ni-corrosion method at room temperature without the use of any additional oxidizing agent. The high-valence metal dopants effectively tune the electronic structure of Ni. In situ Raman, ex situ electron energy-loss spectroscopy, and density functional theory calculations reveal that Cr is advantageous for the formation of oxyhydroxide with the longest Ni-O bond length, facilitating the decomposition of *OOH intermediate species for the generation of O₂. Additionally, Ti contributes to charge transfer. The optimized NiFe hydroxide with V, Ti, and Cr dopants (FNVTiCr) outperforms the benchmark RuO₂ and reported Ni-based catalyst by exhibiting an overpotential of 240 mV at 100 mA cm⁻² and stability for 70 h. Notably, an alkaline electrolyzer with an FNVTiCr anode and Pt/C cathode is also demonstrated with an ultralow cell voltage of 1.49 V to generate a current density of 10 mA cm⁻², which is stable for 100 h, surpassing the benchmark industrial catalyst. This multi-high valence 3d TM doping approach provides a strategy for designing a low-cost, effective, and stable Ni-based catalyst.