An Amorphous Cobalt Borate Nanosheet-Coated Cobalt Boride Hybrid for Highly Efficient Alkaline Water Oxidation Reaction

We present a simple in situ sodium borohydride (NaBH 4 ) reduction approach to produce amorphous core–shell like cobalt borate nanosheet-coated cobalt boride hybrid (Co-B@Co-Bi). Benefiting from the unique rich amorphous Co-Bi layer, it exhibits extraordinary catalytic activity and good stability toward the oxygen evolution reaction (OER) in 1.0 M KOH, with an overpotential of 291 mV to obtain a current density of 10 mA cm –2, outperforming most of the documented metal–metalloid-based electrocatalysts. This reverse addition strategy might provide a promising pathway for designing various transition metal borate and boride hybrid for more applications.