Quinone voltammetry for redox-flow battery applications

The electrochemical behaviour of octafluoro-9,10-anthroquinone is reported, motivated by the use of this lipophilic quinone as the negative electrode couple (anolyte) in redox flow battery applications. At low concentrations, the reduction mechanism is found to follow the classic EE process, expected for quinones in aprotic solution and both anionic species are stable on the voltammetric timescale. The reduction process is, however, strongly influenced by a number of factors, including the identity of the electrolyte cation. The dianion is also unstable on longer timescales, with a disproportionation mechanism affecting the stability of reduced products, even at potentials above the reduction potential of the mono-anion. An insoluble film is shown to form on the electrode surface, which gradually degrades the voltammetric response. Conclusions from the electrochemical data are supported by in situ EPR and ex situ NMR spectroscopy.