Performance enhancement of alkaline organic redox flow battery using catalyst including titanium oxide and Ketjenblack

Carbon felt (CF) doped by catalyst including titanium oxide and ketjen black (TiO₂/KB-CF) is used as negative electrode to enhance the redox reactivity of napthoquinone (NQSO) and thus the performance of aqueous organic redox flow batteries (AORFBs). The redox reactivity of NQSO is better with TiO₂/KB-CF than with pristine CF (anodic current density of 13.3 and 19.8 mA·cm⁻², and cathodic current density of −15.7 and −21.9 mA·cm⁻² with pristine CF and TiO₂/KB-CF), while the reaction reversibility of NQSO is also enhanced in TiO₂/KB-CF (ratio of peak current density is 0.84 and 0.9 with pristine CF and TiO₂/KB-CF). These results are due to the hydrophilic and conductive properties of the TiO₂/KB catalyst. TiO₂ can hold many hydroxyl groups that are hydrophilic and electro-active group, while KB is a conductive material that induces a fast electron transfer. With these benefits, the charge transfer resistance of the electrode is reduced from 1.8 Ω with pristine CF to 1.5 Ω with TiO₂/KB-CF. In AORFB tests using NQSO and potassium ferrocyanide under alkaline supporting electrolyte, energy efficiency increased from 58% (pristine CF) to 61% (TiO₂/KB-CF) with a low capacity loss rate of 0.006 Ah·17⁻¹ per cycle and the cross-over rate of active materials during cycling of AORFB was very low.