Thermodynamic and Kinetic Influence of Oxygen Vacancies on the Solar Water Oxidation Reaction of α-Fe₂O₃ Photoanodes

To reveal the role of oxygen vacancies in the solar water oxidation of α-Fe2O3 photoanodes, the kinetic and thermodynamic properties that are closely related to the water oxidation reaction of the α-Fe2O3 photoanode containing oxygen vacancies were investigated. Compared with the pristine α-Fe2O3 photoanode, the presence of surface oxygen vacancies can improve the water oxidation activity and stability of the α-Fe2O3 photoanode simultaneously, but the bulk oxygen vacancies have a negative effect on the water oxidation performance of the α-Fe2O3 photoanode. In thermodynamics, our investigations revealed that the presence of surface oxygen vacancies narrows the space charge region width of the α-Fe2O3 photoanode, which could boost the charge separation and transfer efficiency of the α-Fe2O3 photoanode during water oxidation. Because the surface property and hydrophilicity of α-Fe2O3 are modified owing to the presence of surface oxygen vacancies, the water oxidation kinetics of the α-Fe2O3 photoanode with surface oxygen vacancies is obviously boosted. Our findings in the present work provide comprehensive understanding of the thermodynamic and kinetic differences for α-Fe2O3 photoanodes with and without oxygen vacancies for solar water oxidation.