Redox-decorated peptides as candidates for flow battery active materials

Replacing vanadium and other inorganic redox couples in redox flow batteries (RFBs) with small molecule organics has been of interest in recent years. Due to their tunability in redox potentials and solubility, they offer a wider design space for optimizing cell performance metrics. A significant problem in this area involves the compatibility of organics with membranes, in particular with respect to crossover. Nafion, which is used in the highly acidic vanadium-based RFB electrolytes, does not prevent the crossover of organics in neutral, basic, and nonaqueous environments, and in fact, no commercial membrane does this effectively. The result is batteries that are half the capacity that could be realized vs. a situation in which crossover of active storage materials is prevented. Our group first investigated phenothiazine-decorated glycol cores for potential alternatives to monomer-based electrolytes. We report on these results as well as the performance of redox couples attached to a peptide backbone in effort to prevent crossover. With TEMPO- and viologen-decorated polymers, we compared crossover and charge/discharge cycling in flow cell batteries compared to small molecule versions.