Role of Cation Deficiency and the Inductive Effect in Ti-Doped NiO for Developing Superior Electrocatalysts for the Oxygen Evolution Reaction

Abstract

Developing efficient, stable, and economical catalysts is crucial for the oxygen evolution process. Herein we report cation-vacant Ti-doped NiO as a promising catalyst for the oxygen evolution reaction (OER). Nonprecious titanium dopant is incorporated into the cation vacant cubic rock-salt Ni_1–2x Ti_x V_x^″O (0 < x < 0.1; V_x^″ = Ni²⁺ cation vacancy) via a facile sol–gel method. We utilized the concept of an inductive effect through doping with more electronegative/Lewis acidic Ti⁴⁺ in the NiO to adjust the redox energy of the active Ni²⁺/Ni³⁺ redox couple to enhance the electrocatalytic OER activity in the basic electrolyte. Doping of tetravalent Ti in NiO lattice generates cation vacancy, which promotes higher OER activity by creating lattice vacancies on the surfaces for better adsorption of water molecules. Among the compositions investigated, Ni_0.9Ti₀.₀₅O is the most active as it exhibits excellent electrocatalytic activity with a low overpotential of 304 mV at the current density of 10 mA cm^–2 compared to the commercial RuO₂ benchmark catalyst. This work presents a design principle by coupling cation vacancies along with the inductive effect of neighboring cations to alter redox energies to provide effective electron transfer required for the electrocatalytic OER by utilizing the inductive effect and cationic vacancy.