Redox flow batteries (RFBs) are an energy storage technology that can provide convenient, versatile energy distribution. They can fulfill growing energy consumption needs while reducing harmful emissions by enabling the use of intermittent renewable energy generation. RFBs can deliver grid-scale energy capacities and feature the unique ability to scale power and capacity independently. These systems store electrical energy as chemical energy in the form of two charged redox-active species in solution. The electrochemical and physicochemical properties of individual redox-active species influence all RFB system performance metrics (e.g., energy densities, power densities, lifespan) and dictate system costs. Although RFBs have entered the commercial market as vanadium RFBs, their affordability remains a major limitation. The pursuit of cost-effective redox-active species with competitive performance characteristics remains a tedious process of individual synthesis, measurement, and evaluation. To expand the material design space, we explored organic species paired with non-aqueous solvents. Careful selection and analysis of redox-active electrolyte libraries can help discern meaningful correlations that will help advance the molecular design of optimal compounds for use in these systems. It should be acknowledged that high-performance redox-active species do not guarantee economic or environmental feasibility, as we show using a hypothetical nitrate-recovery and ammonia-generation system. Using pyridinium salts as model anolytes, we have identified an insightful solubility correlation to dispersion forces (i.e., C-H···π interactions). Furthermore, we discuss that pyridinium solutions demonstrate properties uncommon among other redox-active electrolytes, including low viscosities and high conductivities. Future work in pyridinium development should include exploring physicochemical and electrochemical structure-property relationships to improve molecular design strategies and assess tangential effects of their scaled application.
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