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

[Display omitted] •Well-dispersed Sb-doped SnO2 nanoparticle is used to modify carbon paper.•Two-step electrodeposition and in-situ oxidation are used to modify electrode.•Modified electrode is outstanding at active site, conductivity and hydrophilicity.•Modified electrode exhibits superior kinetics for both vanadium redox reactions.•Carbon paper as bifunctional electrode enhances VRFB performance greatly. 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 CP-SnO2/Sb showed a 9% increase in energy efficiency compared to pristine cell (64.5%) at 150 mA cm−2.