Improving the performance of vanadium redox flow batteries for large - scale energy storage

Recently, vanadium redox flow batteries (VRFBs) have received significant attention due to their potential as large-scale electric energy storage devices. Indeed, they have been trialed or adopted commercially for load levelling and related applications worldwide. The VRB employs vanadium ions, V (II)/V (III) and V (IV)/V (V) redox couples, to store energy in negative and positive electrolytes, respectively. Electrical balance is achieved by the migration of proton across a membrane separating the electrolytes. VRBs use only one element (vanadium) in both tanks, exploiting vanadium’s ability to exist in several states. By using one element in both tanks, VRBs can overcome cross-contamination degradation, a significant issue with other RFB chemistries that use more than one element. The performance of VRFBs still needs to be improved in terms of their voltage efficiency (VE) and energy efficiency (EE) to afford long-term and low-cost operation of the cells. In this work, the importance of operational variables on the performance of a unit VRB cell is investigated. Therefore, in order to optimize the operating conditions which can reduce the crossover and maintain the long-term stability of the electrolyte, it is necessary to evaluate the electrolyte, for instance optimum electrolyte can hold more than 70% more vanadium ions or by using graphen-modified-graphite (GMG) electrode, electrochemical activity of the VRBs can be increased about 30% compare to those of pristine graphite. In addition in order to optimize the operating condition which can reduce the crossover and maintain the long-term stability of the electrolyte, it is necessary to evaluate the ion exchange membrane for VRB system.