Single atom tungsten doped ultrathin α-Ni(OH)₂ for enhanced electrocatalytic water oxidation

Electrocatalytic water oxidation is a rate-determining step in the water splitting reaction. Here, we report one single atom W⁶⁺ doped Ni(OH)₂ nanosheet sample (w-Ni(OH)₂) with an outstanding oxygen evolution reaction (OER) performance that is, in a 1 M KOH medium, an overpotential of 237 mV is obtained reaching a current density of 10 mA/cm². Moreover, at high current density of 80 mA/cm², the overpotential value is 267 mV. The corresponding Tafel slope is measured to be 33 mV/dec. The d⁰ W⁶⁺ atom with a low spin-state has more outermost vacant orbitals, resulting in more water and OH- groups being adsorbed on the exposed W sites of the Ni(OH)₂ nanosheet. Density functional theory (DFT) calculations confirm that the O radical and O-O coupling are both generated at the same site of W⁶⁺. This work demonstrates that W⁶⁺ doping can promote the electrocatalytic water oxidation activity of Ni(OH)2 with the highest performance.