Amorphous Nickel Hydroxide Nanosheets with Ultrahigh Activity and Super-Long-Term Cycle Stability as Advanced Water Oxidation Catalysts

Abstract

Good conductivity is conventionally considered as a typical reference standard in terms of selecting water electrolysis catalysts. Electrocatalyst research so far has focused on crystal rather than amorphous due to poor conductivity. Here, we demonstrate that the amorphous electrocatalyst made of 3D honeycomb-like amorphous nickel hydroxide (Ni­(OH)₂) nanosheets synthesized by a simple, facile, green, and low-cost electrochemistry technique possesses ultrahigh activity and super-long-term cycle stability in the oxygen evolution reaction (OER). The amorphous Ni­(OH)₂ affords a current density of 10 mA cm^–2 at an overpotential of a mere 0.344 V and a small Tafel slope of 46 mV/dec, while no deactivation is detected in the CV cycles even up to 5000 times. We also establish that the short-range order, i.e., nanophase, of amorphous creates a lot of active sites for OER, which can greatly promote the electrochemical performance of amorphous catalysts. These findings show that the conventional understanding of selecting electrocatalysts with conductivity as a typical reference standard seems out of date for developing new catalysts at the nanometer, which opens a door ever closed to applications of amorphous nanomaterials as advanced catalysts for water oxidation