Tungsten oxide/fullerene-based nanocomposites as electrocatalysts and parasitic reactions inhibitors for VO(2+)/VO(2)(+) in mixed-acids

The relatively high cost of all-vanadium redox flow batteries (VRFBs) limits their widespread deployment. Enhancing the kinetics of the electrochemical reactions is needed to increase the power density and energy efficiency of the VRFB, and hence decrease the kWh cost of VRFBs. In this work, hydrothermally synthesized hydrated tungsten oxide (HWO) nanoparticles, C(76), and C(76)/HWO were deposited on carbon cloth electrodes and tested as electrocatalysts for the VO(2+)/VO(2)(+) redox reactions. Field Emission Scanning Electron Microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDX), high-resolution transmission electron microscope (HR-TEM,), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), and contact angle measurements were used to characterize the electrodes’ material. The addition of the C(76) fullerene to HWO was found to boost the electrode kinetics towards the VO(2+)/VO(2)(+) redox reaction, by enhancing the conductivity and providing oxygenated functional groups at its surface. A composite of HWO/C(76) (50 wt% C(76)) was found to be the optimum for the VO(2+)/VO(2)(+) reaction, showing a ΔE(p) of 176 mV, compared to 365 mV in the case of untreated carbon cloth (UCC). Besides, HWO/C(76) composites showed a significant inhibition effect for the parasitic chlorine evolution reaction due to the W-OH functional groups.