Reductive Annealing Assisted Enhanced Oxygen Vacancies in MgGa2O4 Spinel towards Improved OER and HER Electrocatalysis

Abstract

This study explores the synthesis and electrochemical performance of MgGa2O4-based catalysts as potential electrocatalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). X-ray powder diffraction (XRD) confirmed the phase purity and spinel structure of the synthesized material, with magnesium occupying tetrahedral sites and gallium at octahedral sites, exhibiting partial inverse spinel characteristics. Fourier-transform infrared (FTIR) and Raman spectra further supported the material's structural features. Positron annihilation lifetime spectroscopy (PALS) revealed the presence of significant oxygen vacancies in the reduced sample (MGO-R), enhancing electrochemical activity. X-ray photoelectron spectroscopy (XPS) analysis showed a higher proportion of oxygen vacancies in MGO-R, corroborating the PALS results. Electrochemical evaluations in 1M KOH demonstrated that MGO-R outperforms MGO-A in both HER and OER, exhibiting superior catalytic activity with lower overpotentials and faster kinetics. MGO-R achieved a hydrogen production current density of 380 mA cm⁻² at -0.8 V vs. RHE and exhibited a high Faradaic efficiency of 98%. Additionally, MGO-R showed excellent OER performance, with a low onset potential of 1.62 V vs. RHE and a Faradaic efficiency of 87%. Stability tests confirmed the durability of MGO-R, with minimal degradation over 200 cycles. These results highlight MGO-R's promising potential as an efficient and stable bifunctional electrocatalyst for overall water electrolysis. This work lays the foundation for further development of highly active and durable electrocatalysts for sustainable energy conversion.