(668g) Progress Toward a Standardized Electrode/Electrolyte Benchmarking Approach for Redox Flow Batteries

To advance environmental sustainability, there is a need to improve the penetration of renewable energy technologies, as they are environmentally friendly and globally abundant. Due to the spatial and temporal intermittency of many renewables, large-scale electrochemical energy storage is likely to play an important role for their expanded use. The redox flow battery (RFB) is a promising approach for storing renewable energy for use when and where it is needed.

Recent research progress on RFBs has been hampered by conflicting reports of electron-transfer kinetics even for well-established electrolyte chemistries. We are working to resolve some of the conflicting data by developing standardized, reproducible approaches for characterizing the interfacial electron transfer kinetics of RFB electrode-electrolyte combinations. We have therefore developed a method for benchmarking the kinetics on RFB electrode-electrolyte combinations using established electroanalytical protocols comprising rotating-disk electrode voltammetry combined with careful electrode surface pre-treatments. We compared kinetics data for a range of model electrode surfaces including platinum, gold and glassy carbon. Using aqueous Fe(3+/2+) electrolytes modeled after the positive electrolytes in Fe/Cr RFBs, we found that electron-transfer rates depended heavily on the type of surface pretreatment, which we attribute to the presence of specific surface functional groups that catalyze the inner-sphere redox chemistry of Fe aquo complexes. Based on the precision and internal consistency of our results, we contend that this approach can be used to good effect to understand the electrokinetic properties of a wide range of RFB electrode-electrolyte combinations.