Conversion of Catalytically Inert 2D Bismuth Oxide Nanosheets for Effective Electrochemical Hydrogen Evolution Reaction Catalysis via Oxygen Vacancy Concentration Modulation

Abstract Oxygen vacancies ( V o ) in electrocatalysts are closely correlated with the hydrogen evolution reaction (HER) activity. The role of vacancy defects and the effect of their concentration, however, yet remains unclear. Herein, Bi 2 O 3 , an unfavorable electrocatalyst for the HER due to a less than ideal hydrogen adsorption Gibbs free energy (Δ G H* ), is utilized as a perfect model to explore the function of V o on HER performance. Through a facile plasma irradiation strategy, Bi 2 O 3 nanosheets with different V o concentrations are fabricated to evaluate the influence of defects on the HER process. Unexpectedly, while the generated oxygen vacancies contribute to the enhanced HER performance, higher V o concentrations beyond a saturation value result in a significant drop in HER activity. By tunning the V o concentration in the Bi 2 O 3 nanosheets via adjusting the treatment time, the Bi 2 O 3 catalyst with an optimized oxygen vacancy concentration and detectable charge carrier concentration of 1.52 × 10 24 cm −3 demonstrates enhanced HER performance with an overpotential of 174.2 mV to reach 10 mA cm −2 , a Tafel slope of 80 mV dec −1 , and an exchange current density of 316 mA cm −2 in an alkaline solution, which approaches the top-tier activity among Bi-based HER electrocatalysts. Density-functional theory calculations confirm the preferred adsorption of H* onto Bi 2 O 3 as a function of oxygen chemical potential (∆ μ O ) and oxygen partial potential ( P O2 ) and reveal that high V o concentrations result in excessive stability of adsorbed hydrogen and hence the inferior HER activity. This study reveals the oxygen vacancy concentration-HER catalytic activity relationship and provides insights into activating catalytically inert materials into highly efficient electrocatalysts.