Degradation of quinone-based flow battery electrolytes: Effect of functional groups on the reaction mechanism

Organic redox flow batteries are a promising technology for grid-scale energy storage from renewable energy resources. However, the chemical instability of the organic electrolytes prohibits wide-scale commercial implementation as energy storage materials. Therefore, understanding their chemical degradation is essential to develop new and resilient electrolyte materials. In this article, we comparatively studied the chemical degradation pathways of 4,5-dihydroxybenzene-1,3-disulfonic acid (BQDS) and 3,6-dihydroxy-2,4-dimethylbenzenesulfonic acid (DHDMBS) employing potential energy surface exploration. Both the acid-catalyzed and base-catalyzed pathways have been considered. Density functional theory was used to compare the energetics of the reaction paths. The role of functional groups was investigated to get insight into why BQDS is prone to degradation and DHDMBS is much more stable. Furthermore, we studied the effect of the functional groups on the correlation of free energy of degradation and the reduction potential of the quinones.