Interfacial Electron Transfer Involving Vanadium and Graphene Quantum Dots for Redox Flow Battery

ABSTRACTAmong energy storage devices, the redox flow batteries are important for variety of applications such as for grid storage. In this class of batteries a large number of redox couples have been examined in the past. The vanadium redox couple, although is attractive for this application, suffers from a) poor charge transfer characteristics b) electrode degradation and c) deteriorating performance. We wish to report here that all these deficiencies have been overcome by using a graphene quantum dot electrodes. This electrode has the advantage of large surface area, high electrical and thermal conductivity. The cell voltage of 1.5 V and power density of about 120 mW/cm2 and coulombic efficiency of 90% can be achieved as the redox couples, V(IV)/V(V) and V(III)/V(II) undergo fast electron transfer at the interface of the quantum dots and solution resulting in higher reversibility. The cyclic voltammetric experiments carried out with quantum dots in the solutions during the oxidation of V(IV) show enhanced currents, due to the movements of the dots which is conducive for power gain in the battery operation. The electrochemical degradation is absent with the quantum dot electrode. The charge/discharge cycles have been reproducible.