High-performance nickel/iron catalysts for oxygen evolution in pH-near-neutral borate electrolyte synthesized by mechanochemical approach

In this work, a novel method of mechanochemistry is used to directly prepare high-performance Ni-Fe based catalysts for oxygen evolution reaction (OER) in an environmental-friendly borate electrolyte with near-neutral pH. Such a procedure is simple, effective, and time-saving. The effect of iron-based raw materials and mechanochemical reaction on OER of catalysts are investigated. It shows that iron nitrate nonahydrate is the best iron resource compared to iron hydroxide and iron oxide due to amorphous iron species in catalysts for strengthening the “Fe inductive effect” and generating active Ni species with high valence. Besides, the grinding time can control the mechanochemical reaction from mixed reaction to solid reaction in the catalyst synthesis process. When the time is 30 min, the catalyst is composed with amorphous Ni(OH)2 and the precursors of NiFe-LDH. This catalyst only needs 413 mV overpotential to reach 1 mA cm−2 in 0.1 M K-Bi (pH=9.2), which is better than precious RuO2. It is proven that the mechanochemical approach is an alternative method for synthesizing superior OER catalysts. [Display omitted] •Mechanochemistry was used for preparing superior Ni-Fe catalysts for OER.•Synthesis process was simple, effective and time-saving.•Improved OER by amorphous phase iron species due to “Fe inductive effect”.•Phase reconstruction of raw materials regulated by grinding time during synthesis.•Superior catalyst composed of amorphous Ni(OH)2 and the precursors of NiFe-LDH.