TiNb 2 O 7 nanoparticle-decorated graphite felt as a high-performance electrode for vanadium redox flow batteries

A novel, low-cost, safe, highly catalytic, and stable TiNb 2 O 7 nanoparticle-modified graphite felt (TNO-modified GF) electrode was successfully fabricated using a simple solvothermal method for vanadium redox flow batteries (VRFBs). The TNO-modified GF electrode showed the highest electrocatalytic activity toward the VO 2+ /VO 2+ redox couple among all samples measured. According to charging-discharging results, the average energy efficiency of the cell using TNO-modified GF electrode reached 79.06% at 100 mA cm −2 , which is 4.43% and 15.73% higher than the cells constructed with heat-treated GF (HT-GF) and pristine GF (P-GF) electrodes, respectively. Moreover, cycling tests revealed no observable decay in the efficiencies after 100 cycles, indicating that the TNO-modified GF electrode is stable over repetitive cycling. The superior electrochemical performance of the cell with the TNO-modified GF electrode is attributed to the introduction of uniformly distributed TNO nanoparticles. The modification increased oxygen-containing functional groups on the surface of GF, thus making it more hydrophilic. It also lowered the activation barrier for electrochemical reactions within vanadium ions, leading to facilitate the charge transfer process on the surface of GF.