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Wind and solar energy installations will be deployed at an increasing rate in the coming decades due to increasing demand for carbon-free electricity. However, energy from these sources is intermittent and peak production fails to coincide with peak demand. In order for the grid to become completely reliant on renewable energy, energy storage systems must be adjacently deployed to support the grid during low production periods. The redox flow battery (RFB) is one of the most promising new technologies to store and use very large quantities of renewable energy on a continuous basis.

The energy efficiencies of flow batteries are often limited in part by slow electron-transfer reactions, and this challenge is driving new research to develop electrodes and redox couples that exhibit fast electron transfer kinetics. In this context, we are working to understand the influence of electrocatalysis on the practical performance of established and emerging flow battery chemistries. Our prior work focused on critically assessing rotating disk electrode (RDE) voltammetry techniques—which are widely used for kinetics studies in fuel cell research—for measuring electron transfer rates in RFBs. Based on the results, we concluded that the unique characteristics of flow batteries necessitate the development of new experimental techniques that better approximate their operating conditions.

Our current approach employs microelectrodes in a flow cell to eliminate the confounding effects of mass transport and electrical resistance in RFB electrokinetics experiments. Results to date show that microelectrode methods can resolve electron-transfer kinetics at least an order of magnitude faster than conventional RDE experiments. We also found that flowing the electrolyte can mitigate electrode fouling effects in the Pt|FeCl₂||FeCl₃|Pt material system, which yields better estimates of the true electron-transfer kinetics. Ongoing work in our lab is now focused on characterizing the kinetics of several RFB couples at carbon fiber microelectrodes in a channel-flow configuration, since carbon is desirable for use in RFBs due to its low cost.