Enhanced Hydrogen Evolution Using β-MnO₂ Monolayer on Ni Electrode with Engineered Oxygen Vacancies

Developing cost-effective and high-performance electrodes is critical for advancing hydrogen (H2) production through electrochemical water splitting. In this study, we present a novel electrode design by integrating a β-MnO2 monolayer onto a conventional Ni(100) substrate (MnO2(110)/Ni(100)). This work uniquely explores the influence of oxygen vacancies (OVs) at distinct sites─Osub-top and bridge sites─on both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Our findings reveal that the Osub-top vacancy (OOV-MnO2(110)/Ni(100)) significantly enhances HER activity, achieving a hydrogen Gibbs free energy (ΔGH) of −0.015 eV, which surpasses the performance of noble metals such as Pt/C (−0.082 eV) and Ir (−0.08 eV). Additionally, the cathodic exchange current density (J0,c) of OOV-MnO2(110)/Ni(100) reaches 10–0.774 Acm–2, outperforming Pt/C (10–0.92 Acm–2) and Ir (10–1.44 Acm–2). Electrochemical analysis confirms a cathodic activation overpotential (ηa,c) of 0.141 V at 10 mAcm–2 in a 0.5 M H2SO4 solution, achieving a hydrogen production rate (HPR) of 0.91 mmolh–1cm–2 at an applied voltage (Vapp) of 1.60 V. This study provides the first comprehensive analysis of site-specific oxygen vacancy effects on bifunctional MnO2-based electrodes, demonstrating superior HER activity while maintaining dual functionality for both cathodic and anodic processes. Our results highlight the potential of engineered oxygen vacancies to develop low-cost, high-efficiency electrodes for sustainable hydrogen production, offering a competitive alternative to precious metal-based catalysts.