Performance of Surface‐Oxidized Ni 3 B, Ni 2 B, and NiB 2 Electrocatalysts for Overall Water Splitting

The development of efficient and earth‐abundant bifunctional electrocatalysts is of great important for energy conversion and storage technologies. Three surface oxidized nickel borides of Ni−B−O@Ni 3 B, Ni−B−O@Ni 2 B and Ni−B−O@NiB 2 electrocatalysts have been prepared and investigated. Surface oxidation, which is inevitable for the bifunctional nickel borides, promotes the activity for the oxygen evolution reaction (OER), but leads to activity degradation for the hydrogen evolution reaction (HER). Meanwhile, boron is found to play a crucial role in the oxidation of nickel, facilitating the formation of an active intermediate for the OER. Ni−B−O@Ni 3 B turns out to be the best bifunctional electrocatalyst. An alkaline electrolyzer constructed using Ni−B−O@Ni 3 B electrodes as both anode and cathode has achieved a current density of 10 mA cm −2 at 1.58 V for overall water splitting with satisfied durability, rivaling the integrated noble metal electrode.