Anion doping enabling SnO₂ superior electrocatalytic performances for vanadium redox reactions

SnO2 has been applied in various fields due to its high activity, low cost, variety, and tunable structure. However, the low electrical conductivity of SnO2 hinders its application in electrochemical catalysis. Both cationic and anionic doping can improve the electrical conductivity of SnO2. In this work, doping F was used to optimize the catalysis of SnO2 on the redox reactions for VO2+/VO2+ and V3+/V2+. O2- is replaced by F- with the production of a free electron in SnO2 structure, which increases the electronic conductivity of SnO2. Furthermore, F doping increases the concentration of structural defects in SnO2, such as oxygen vacancies. F doping increases the structural defect of SnO2, such as oxygen vacancy. Therefore, F doping can increase the electrochemical activity of SnO2 by increasing active sites, promoting vanadium ion adsorption and accelerating electron transport. The activity of the VO2+/VO2+ and V3+/V2+ reactions of F doped SnO2 is higher than that of undoped SnO2. The SnO2 at doping mass ratio of 10% (SnO2/F-10) exhibits the best electrochemical performance over 5% and 20%. After SnO2/F-10 modification, the reversibility and electrochemical kinetics of the graphite felt are improved. Cell adopting SnO2/F-10 has larger discharge capacity, higher utilization rate of electrolyte and lower polarization than blank cell. At 150 mA cm(-2), the energy efficiency of cell is increased from 52.3% to 68.7% by using SnO2/F-10. At 50 mA cm(-2), the modified cell also shows good stability during 50 cycles. Overall, this work promotes the application of metal oxides in vanadium redox flow battery.