Semimetallic hydroxide materials for electrochemical water oxidation

Searching for catalyst materials with high intrinsic activity for water oxidation holds the key to numerous clean energy technologies. Hydroxide semiconductors are electrochemically active to drive oxygen evolution reaction (OER), but suffer from poor electronic conductivity, restricting their intrinsic electrocatalytic activity. Here, a semimetallic hydroxide material was designed as efficient OER catalyst with both improved electronic conductivity and intrinsic electrocatalytic activity. By cationic doping and anionic vacancy manipulation, the NiFe layered double hydroxide (LDH) semiconductor was turned into semi-metallic with two orders of magnitude lower resistivity. Consequently, the semi-metallic LDH (SM LDH) array electrode exhibited an intrinsically improved OER activity with a low overpotential of 195 mV at 10 mA cm−2 and a low Tafel slope of 40.9 mV dec−1 in alkaline medium, outperforming commercial RuO2 catalysts (316 mV, 99.6 mV dec−1) under the same test condition. In-depth Raman and first-principles calculations demonstrated that the enhanced OER intrinsic activity of SM LDH was associated with the high electronic conductivity, which promoted the formation and stabilization of high-valence metal sites in oxyhydroxide intermediates. These finding suggest semi-metallic hydroxides as an advanced electrode material with both fascinating electric and catalytic properties.