Electrochemical Deposition of Bismuth on Graphite Felt Electrodes: Influence on Negative Half-Cell Reactions in Vanadium Redox Flow Batteries

In this paper, bismuth (Bi) was successfully deposited on graphite felts to improve the electrochemical performances of vanadium redox flow batteries. Modified graphite felts with different Bi particle loadings were obtained through electrochemical deposition at voltages of 0.8 V, 1.2 V and 1.6 V in 0.1 M BiCl3 solution for 10 min. The optimal Bi particle loading was confirmed by scanning electron microscopy (SEM), single cells and electrochemical tests. The SEM images revealed the deposition of granular Bi particles on the fiber surface. The Bi-modified felts which were electro-chemically deposited at 1.2 V (Bi/TGF-1.2V) showed excellent electrochemical performances in cyclic voltammetry curves and impedance spectroscopy. Meanwhile, the single cells assembled with Bi/TGF-1.2V as negative electrodes exhibited higher voltage efficiencies than the others. The optimized Bi particle loading induced better catalysis of the V3+/V2+ reaction and hence significantly improved the cell performances. In addition, the prepared Bi-modified felts showed stable cell performances and slower charge–discharge capacity declines than the other electrodes at current densities between 20 mA/cm2 and 80 mA/cm2. Compared with the pristine felt, the voltage efficiency of the vanadium redox flow battery assembled with Bi/TGF-1.2V graphite felt was 9.47% higher at the current density of 80 mA/cm2. The proposed method has considerable potential and guiding significance for the future modification of graphite felt for redox flow batteries.