Single‐Atom Doping and High‐Valence State for Synergistic Enhancement of NiO Electrocatalytic Water Oxidation
Meng Liu, Yujin Ji, Youyong Li, Pengfei An, Jing Zhang, Junqing Yan, Shengzhong Liu
Abstract
Abstract The NiO‐based electrocatalytic oxygen evolution reaction (OER) of water splitting is recognized as a promising approach to produce clean H 2 fuel. However, the OER performance is still low, and especially, the overpotential is larger than 200 mV at the current density of 10 mA cm −2 . Herein, an Ir@IrNiO sample is prepared with single‐atom (SA) Ir 4+ doping and surface metallic Ir nanoparticles loaded onto the NiO. Owing to the bonding of the loaded Ir with surface‐exposed Ni 2+ , the nearby Ni atoms exist in the + 3 valence state, that is, the surface‐loaded Ir particles behave like a stabilizer for the Ni 3+ sites. Under the synergistic effect of SA Ir 4+ and high‐valance‐state Ni 3+ , the Ir@IrNiO nanostructure effectively reduces the overpotential to 195 mV at a current density of 10 mA cm −2 . Moreover, it gives an Ir‐content‐normalized current density of 0.0457 A mg Ir −1 , 72.1 times higher than that of the best commercialized IrO 2 (6.33 × 10 −4 A mg Ir −1 ), under the condition of 1.5 V versus reversible hydrogen electrode. Operando Raman and X‐ray absorption fine‐structure (XAFS) measurements reveal that there are more surface‐active species of Ni 3+ , which adsorb and activate water molecules to form Ni 3+ –*OH at low voltage, the intermediate of Ni 4+ –•O is then formed at a relatively high bias voltage, and then the •O is transferred to the SA Ir 4+ sites to generate Ir 4+ –O–O with OH at increased voltage. This work can help design more SA‐based highly active OER materials.