(63d) Flow Battery Electroanalysis: Using Continuous Flow Micro-Electrochemistry to Bridge the Gap between Laboratory Analysis and Device Design

Grid-scale energy storage technologies play a crucial role in incorporating intermittent renewable energy resources into the current energy system. Redox flow batteries (RFBs) have garnered significant attention in the recent years for their potential to store large quantities of renewable electricity at low cost. However, commercialization of this technology is significantly inhibited by the design of electrode-electrolyte interfaces that exhibit rapid and stable interfacial electron transfer. Moreover, there do not yet exist reliable tools to elucidate precise and accurate electron-transfer kinetics for current and future generations of RFB electrolytes. To address this challenge, we are developing electroanalytical tools to characterize the kinetics of several representative redox couples under conditions that are similar to practical RFBs.

In prior work, we used rotating disk electrode (RDE) techniques to evaluate interfacial electron transfer kinetics of aqueous Fe-based RFB redox couple at millimolar concentrations. However, these techniques were found to be inadequate when using active species at molar concentrations. Thus, to gain a deeper insight into the mechanistic basis of the observed differences at battery-relevant concentrations, we are now developing an analytical approach based on 3D-printed continuous flow apparatus that incorporates microscopic electrodes of various compositions. Initial results have confirmed that we can replicate prior measurements using this platform and that we can evaluate accurate electron-transfer kinetics at device-level concentrations. This tool is also capable of resolving a comparable range of electron-transfer kinetics to RDE using a much smaller number of individual measurements (as little as one per electrode-electrolyte pair). Moreover, our continuous flow cell could be incorporated into a functioning RFB loop to measure the real time degradation of electrolyte under operation, resulting in opportunities to develop standardized RFB metrology. Thus, we conclude that this analytical approach is well-suited for routine analysis of RFB electron-transfer behavior and will be helpful in the pursuit of electrode-electrolyte pairs that minimize efficiency losses due to sluggish reaction kinetics.