Defect-Engineered MoO2 Nanostructures as an Efficient Electrocatalyst for Oxygen Evolution Reaction

Abstract

This article presents the experimental and theoretical insights into defect-engineered MoO2 nanostructures (NSs) in terms of oxygen vacancy and OH- occupancy toward oxygen evolution reaction (OER). Two categories of beta-MoO2 NSs are grown on a silicon substrate via a hydrogenation process from pregrown alpha-MoO2 structures. The postgrown MoO2 system gets OH- occupancy after 7 h of annealing (MoO2+OH-). On increasing the annealing duration to 9 hrs, both oxygen vacancies and OH - occupancy have been made into the MoO2 system (MoO2-x+OH-). The as grown materials have been assessed for promising energy conversion applications toward electrocatalytic OER. The as-grown MoO2-x+OH-. very efficiently catalyzes the OER at a lower overpotential and yields a higher current density compared to the as-grown MoO2+OH- and commercial MoO2. Both the oxygen vacancy and OH- occupancy in the MoO2 system play a synergistic role in enhancing the OER properties. The experimental observations are validated theoretically and plausibly explained with the help of a state-of-the-art density study. The simulation calculations reveal that the introduction of oxygen vacancy and OH- occupancy lowers the overpotential of OER The OH- ions act passively on the surfaces of MoO2 that decrease the binding of reaction intermediates and aid in easy desorption of O-2 molecules. Besides, the oxygen defect sites reduce the charge-transfer resistance, which eventually reduces the OER overpotential. Our empirical findings with theoretical supports render a significant shrewdness to the electrocatalytic performances of the defect-engineering MoO 2 systems toward OER applications.