Quinones: understanding their electrochemistry, chemistry and degradation pathways to tap their full potential in aqueous redox flow batteries

Abstract

Aqueous Organic Redox Flow Batteries (AORFBs) have emerged as a promising alternative for large-scale energy storage. Their advantages include cost-effectiveness due to accessibility of industrial scale quantities of quinone feedstocks, as well as safety and environmental sustainability using aqueous electrolytes. Benzoquinones and related structures such as naphthoquinones and anthraquinones display fascinating chemistry, with biological and redox properties observable in nature, that make them prime candidates for use in AORFBs. A library of quinone-based structures with tuned properties has been studied to this end, however the long-term stability remains a critical challenge, as degradation processes significantly impact the lifetime and overall battery performance. This review is a discussion on the chemistry of quinones including their presence in nature which provides insights into their chemistry, and an analysis of their degradation pathways in AORFBs. Each degradation mechanism contributes to structural decomposition, reducing the amount of redox active material in the RFB system, which presents itself through capacity fade, loss of redox reversibility, and ultimately reducing battery efficiency. Case studies and examples of key degradation pathways are presented to illustrate the main challenges faced in the development of viable AORFBs based on these materials.