Applications of Graphene in Vanadium Redox Flow Batteries

Abstract

Vanadium redox flow batteries (VRFBs) exhibit great promise as easily scalable, long-lasting, modular systems for grid-scale energy storage. However, vanadium crossover and poor reaction kinetics increase their operating costs by requiring frequent system regeneration and reducing energy efficiency, respectively. In this thesis, Nafion membranes were modified with single to few-layer nitrogen/sulfur-doped graphene (NS-graphene) by developing a large area Langmuir film deposition method with the aim of reducing vanadium crossover and potentially improving reaction kinetics. Using this approach, the ability to reduce vanadium permeability through Nafion 117 and Nafion 115 membranes by 75% and 53%, respectively, was demonstrated while maintaining a high enough proton conductivity that the overall selectivity of the membranes was increased by 243% and 65% when compared to the results for bare Nafion. To determine the impact of the intrinsic electrocatalytic activity of graphene on redox flow battery performance, a comparison of NS-graphene, graphene oxide (GO), and reduced graphene oxide (RGO) was carried out using both monolayer electrodes and drop-cast films. Through this work, it was confirmed that the previously established approach developed by Punckt et al. [1] to account for porosity could not be extended to quasi-reversible systems such as that of the VRFB. An alternative data analysis scheme based on Dunn’s Method is proposed, showing mildly promising results, with more work needed in the area to develop strong conclusions.