Redox flow batteries (RFBs) are extremely promising for their potential to economically store vast quantities of renewable electricity. In this context, our group is interested in integrating flow battery technologies with solar energy converters, either by charging RFBs with the output of photovoltaic cells or through the use of integrated photo-electrochemical flow battery schemes. However, our ability to conceptualize and design these types of devices has been hampered by the remarkable lack of consensus about electron transfer kinetics even for well-known RFB electrolyte chemistries. Several insights regarding RFB electrocatalysis can be gleaned from prior and ongoing work in electroanalytical chemistry, but the conditions under which these measurements are usually executed do not match those under which flow batteries operate, particularly with respect to electrolyte concentration and electrode identity. This leaves open the question of whether canonical experimental methods (i.e., those used for routine electroanalysis and fuel cell characterization) can be used to accurately predict the operational characteristics of practical RFB devices.<br/><br/>Our research group is pursuing applied electroanalysis of aqueous flow battery redox couples; our overaching goal is to use straightforward, replicable lab experiments to explain and predict the performance of practical RFBs. To this end, we have used classical voltammetry methods to study aqueous Fe<sup>3+/2+</sup> electron transfer rates using noble metal and glassy carbon electrodes. Key conclusions from these studies include: (a) electrode pre-treatments have huge effects on reproduciblility and apparent electron-transfer kinetics; (b) noble metal and carbon surfaces exhibit completely different apparent catalytic properties; and (c) electron-transfer rates observed in low concentration (millimolar) electrolytes are characteristically different than those observed at high concentrations (molar). These results lead us to conclude that there is a need for new, purpose-built electroanalytical approaches that can extract reproducible kinetics data under conditions that more closely resemble functional RFB operation.

What is the right way to measure flow battery kinetics?

2019 Spring National Meeting

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