A Method for Evaluating Soluble Redox Couple Stability Using Microelectrode Voltammetry

Abstract

Soluble, redox-active organic materials hold promise as charge-storage species for flow batteries; however, chemical stability during extended operation remains a key challenge. While a number of spectroscopic and electrochemical techniques are currently used to probe these complex and often ill-defined decay pathways, these techniques have limitations, including lack of accessibility and potentially cumbersome preparatory steps. Here, we use microelectrode voltammetry to observe nonaqueous flow battery electrolytes directly, simultaneously identifying the rate of self-discharge (reversible material loss) and material decay (irreversible material loss). We validate this technique using ferrocene as a stable model redox couple, examine and address sources of error, and, finally, demonstrate its capability by assessing the decay of a well-studied and moderately-stable substituted dialkoxybenzene [2,5-di-tert-butyl-1,4-bis(2-methoxyethoxy)benzene]. These results suggest that microelectrodes may have utility for rapid assessment of redox electrolyte state-of-charge and state-of-health, both in operando and post mortem.