(71g) Flow Battery Electroanalysis:Electron-Transfer Kinetics of Aqueous Fe(III/II) at Noble Metal and Carbon Electrodes | AIChE

(71g) Flow Battery Electroanalysis:Electron-Transfer Kinetics of Aqueous Fe(III/II) at Noble Metal and Carbon Electrodes


Sawant, T. - Presenter, University of Pittsburgh
McKone, J. R., University of Pittsburgh
Energy demand is continuously increasing, but our current energy system is environmentally unsustainable. Not only is the supply of fossil fuels limited, but their continued use pollutes the environment by releasing greenhouse gases. In order to meet future energy needs, we must harness and use renewable energy on a massive scale. Due to the intermittent nature of renewable energy, storage plays a crucial role. The redox flow battery (RFB) is a promising technology to store and use renewable energy on a continuous basis. However, recent research progress in RFBs has been hampered by conflicting reports of RFB kinetics even for well-established battery chemistries. This presentation will discuss recent work in our lab to resolve the ambiguity in the research literature by applying the tools of electroanalysis to accurately characterize flow battery kinetics in the long-term pursuit of efficient RFB energy storage systems.

Our initial work in this area involved critically assessing the use of rotating disk electrode (RDE) voltammetry to obtain electron transfer kinetics for Fe-based RFB electrolytes. We used model electrode systems of Pt and Au with low concentrations of Fe salts and found the kinetics of Fe3+/2+ reaction to be facile, likely due to the known catalytic effect of adsorbed anions. However, we also found that the Pt and Au surfaces needed to be routinely refreshed to obtain reproducible results. This is important because such cleaning cycles cannot be readily applied in a practical RFB. We then applied the same protocol to carbon electrodes and found that the electron transfer kinetics heavily depended on the surface pretreatment. While several studies have suggested that the overall degree of carbon surface oxidation controls electron transfer kinetics, we attributed our results to the presence of specific surface functional groups that catalyze the inner-sphere redox chemistry of Fe-aquo complexes. We further applied this approach to high concentrations of active species to further assess the suitability of RDE for characterizing flow battery kinetics under more device-relevant conditions. We found an unexpected decrease in the apparent catalytic activity of Pt electrodes as the concentration of Fe was increased. These results collectively suggest that the ideal electroanalytical technique for measuring electron-transfer rates in flow batteries must closely resemble a functional device. This presentation will therefore focus on current work in our lab toward the integration of precise kinetics characterization tools directly into the flow loop of a functional RFB.