When considering organic redox couples as active charge storage materials in redox flow batteries, several characteristics are important, including redox potential, solubility, and stability. Although redox potentials can be reliably estimated using density functional theory calculations, predicting solubility and stability remains a significant challenge, especially when considering the charged states of a material. The majority of reports on the solubility of organic materials have been limited to the uncharged (often neutral) forms of redox couples. Stability is usually probed using electrochemical techniques (e.g. cyclic voltammetry and bulk electrolysis) and with flow cell cycling. Although some instances of in situ spectroscopic analysis of flow cell electrolytes has been reported, for the most part, experimental determination of the failure mechanisms of an organic redox couple has been attempted via post-mortem analysis of an electrolyte after cycling. In none of these experiments is the charged form analyzed separately from components beyond the electrolyte salt and solvent – such as electrode surfaces, membranes, and potential fields – that may lead to decomposition. My group is interested in characterizing the charged forms of organic molecules using methods that allow us to determine the sources and mechanisms of decomposition. Thus, in addition to the standard electrochemical methods and cycling studies, we have focused on the generation and isolation of charged species using chemical means. By isolating the charged species, we are able to measure solubility and analyze stability in controlled environments, choosing when to introduce any component that is not the active species itself. Here I will give an overview of the methods we have used to generate, isolate, and characterize charged organic molecules, as well as and what we have learned, both independent of and complementary to electrochemical methods for analysis.
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