Acetylacetonate-modified TiO₂ nanoparticles coated on the carbon felt as the negative electrode of vanadium redox flow battery for reducing HER and enhancing V³⁺/V²⁺ redox reactions

The occurrence of the hydrogen evolution reaction (HER) on the surface of the carbon-based negative electrode of the vanadium redox flow battery (VRFB) causes high charge transfer resistance (R_CT) for the desired V³⁺/V²⁺ redox reaction leading to irreversible capacity loss. To this effect, we have synthesized acetylacetonate-modified TiO₂ (SGTA) and unmodified TiO₂ (SGT) coating colloidal solutions as electrocatalysts for enhanced V³⁺/V²⁺ redox reaction on the carbon-felt negative electrodes of VRFB. The SGTA particles exhibit significantly higher homogeneity with sizes of ≤15 nm, in comparison to the severely aggregated SGT particles with diameters of ∼23–75 nm in colloidal solution. When coated on the pristine carbon felt (P-CF), the surface morphology of the SGTA@CF electrode exhibits relatively dense, uniformly coated particles, in comparison to the sparse, non-even coating of aggregated particles on the SGT@CF electrode surface. Consequently, the charge transfer for V³⁺ → V²⁺ reduction reaction and charge storage capacity are determined to be in the order SGTA@CF > SGT@CF > P-CF, confirming that the competitive and irreversible HER was higher on the surface of non-evenly coated fibers and bare carbon felt, respectively.