Highly Active Water-Splitting Electrocatalyst Developed by the Creation of Oxygen Vacancies in a Perovskite Oxide

Abstract

Using both experimental and computational approaches, we have demonstrated a major enhancement of electrocatalytic activity for both half-reactions of water splitting, i.e., the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in alkaline conditions, through the incorporation of oxygen vacancies in the perovskite oxide La₂FeNiO₆ (LaFe_0.5Ni_0.5O₃). Density functional theory (DFT) calculations predicted that the incorporation of oxygen vacancies would lead to the reinforcement of several electronic parameters, namely, the proximity of the d-band center to the Fermi level, closer separation between p and d bands, and greater hybridization of those bands, all of which are known to be descriptors of electrocatalytic properties. Therefore, DFT simulations predicted that the electrocatalytic activity should be enhanced due to the presence of oxygen vacancies. This was thoroughly confirmed by the experiment, where the reduced material containing oxygen vacancies, termed LaFe_0.5Ni_0.5O₃-R, showed remarkably lower overpotentials for both HER and OER. This was particularly notable for OER, where the overpotential decreased by nearly 100 mV, reaching η₁₀ = 330 mV, comparable to those of noble metal catalysts such as IrO₂ and RuO₂. In addition, for both HER and OER, the mass activity and reaction kinetics were enhanced upon the creation of oxygen vacancies. Furthermore, a significant increase in turnover frequency (TOF), by nearly 8-fold, was achieved. In addition, electrochemical impedance spectroscopy indicated that the charge-transport properties were enhanced, leading to facile electron transfer for both HER and OER. The excellent match between computational predictions and experimental results is notable.