Ultrafine NiFe-Based (Oxy)Hydroxide Nanosheet Arrays with Rich Edge Planes and Superhydrophilic-Superaerophobic Characteristics for Oxygen Evolution Reaction.

NiFe-based (oxy)hydroxides are the benchmark catalysts for the oxygen evolution reaction (OER) in alkaline medium, however, it is still challenging to control their structures and compositions. Herein, molybdates (NiFe(MoO 4 ) x ) are applied as unique precursors to synthesize ultrafine Mo modified NiFeO x H y (oxy)hydroxide nanosheet arrays. The electrochemical activation process enables the molybdate ions (MoO 4 2- ) in the precursors gradually dissolve, and at the same time, hydroxide ions (OH - ) in the electrolyte diffuse into the precursor and react with Ni 2+ and Fe 3+ ions in confined space to produce ultrafine NiFeO x H y (oxy)hydroxides nanosheets (<10 nm), which are densely arranged into microporous arrays and maintain the rod-like morphology of the precursor. Such dense ultrafine nanosheet arrays produce rich edge planes on the surface of NiFeO x H y (oxy)hydroxides to expose more active sites. More importantly, the capillary phenomenon of microporous structures and hydrophilic hydroxyl groups induce the superhydrophilicity and the rough surface produces the superaerophobic characteristic for bubbles. With these advantages, the optimized catalyst exhibits excellent performance for OER, with a small overpotential of 182 mV at 10 mA cm -2 and long-term stability (200 h) at 200 mA cm -2 . Theoretical calculations show that the modification of Mo enhances the electron delocalization and optimizes the adsorption of intermediates.