Sb-doped SnO2 nanoparticle-modified carbon paper as a superior electrode for a vanadium redox flow battery

Herein, we proposed a facile strategy for preparing well-distributed Sb-doped SnO2 nanoparticles on carbon paper (CP) via electrodeposition and in-situ oxidation as bifunctional electrodes for vanadium redox flow batteries. SnO2 and Sb-doped SnO2 modified carbon paper (CP-SnO2 and CP-SnO2/Sb) was respectively obtained by electrodepositing metals (Sn and Sn/Sb) nanoparticles, followed by a conversion to metal oxides with in-situ oxidation. CP-SnO2 exhibited better electrochemical performance toward V3+/V2+ and VO2+/VO2+ redox reactions than CP. This is because SnO2 increases active sites and hydrophilicity, which accelerates electrochemical kinetic and mass transfer for vanadium redox reactions. CP-SnO2/Sb had better electrochemical activity than CP-SnO2, because smaller Sb-doped SnO2 nanoparticles more effectively disperse through carbon fibers, producing more active sites. Furthermore, Sb doping improved conductivity of SnO2. Briefly, CP-SnO2/Sb exhibited excellent hydrophilicity, abundant active sites, and good conductivity, resulting in superior electrochemical activity. We next employed CP-SnO2/Sb as bifunctional electrodes in cell. The cell using CP-SnO2/Sb had better cycling stability and more capacity retention during a 50-cycle charge-discharge test at 50 mA cm(-2). CP-SnO2/Sb reduced the electrochemical polarization of cell at higher current density. Overall, the cell using CPSnO2/Sb showed a 9% increase in energy efficiency compared to pristine cell (64.5%) at 150 mA cm(-2).