Vanadium—Polydopamine Flow Battery

Dopamine (DA) exhibits quinone/hydroquinone redox activity at ∼0.77 V vs SHE. As the potential is sufficiently high, this can be a replacement to the VO 2+ /VO 2 + redox couple (catholyte) of the vanadium redox flow battery. But DA undergoes polymerization into polydopamine (PDA) while cycling in the flow battery. Therefore, a hybrid flow battery was constructed with PDA coated thermally activated graphite felt positive electrode and V 3+ /V 2+ in 3 M H 2 SO 4 anolyte. The vanadium-PDA flow battery exhibits a capacity of ∼275 mAh g PDA −1 in the first cycle. When the battery was subjected to continuous galvanostatic charge-discharge up to 300 cycles, a capacity retention of ∼86% was observed with coulombic efficiency close to > 99%. Besides, energy efficiency of ∼63% at a current density of 5 A g −1 was observed. The peak power density of the battery was found to be ∼8.83 W g −1 at a current density of ∼14.31 A g −1 .