(Digital Presentation) Kinetic Studies of Aorfb Posolyte on Graphite Micro-Fiber Electrodes

Aqueous organic electrolytes used as posolyte for redox flow battery applications are growing in interest due to their fast kinetics on carbon materials. The determination of their kinetic constants remains a necessity for a better understanding of their overall electrochemical behavior but also for a fine evaluation of the effect of surface activation and possible electrode aging during cycling. However, the studies performed on carbon felts have shown a lack of accuracy due to the macro-porosity and high surface area of these materials, even at very low electrolyte concentrations (10-4 M). Thus, in this study, we propose another system, allowing to shift from the macro to the micro scale: microelectrodes prepared with single fibers extracted from the corresponding graphite porous felt [1-2]. These microelectrodes allow the qualitative study of solutions at higher concentrations (up to 0.5 M in K4[Fe(CN)6]) and a quantitative analysis through EIS and CV modelling for solutions at 10-2 M with the determination of kinetic constants on activated and non-activated single fibers. In addition, the effect of activation treatments of graphite felts, on the oxidation kinetics of ferrocyanide is investigated through cyclic voltammetry. In fact, this method allows to determine optimal treatment conditions of carbon felts for a better performance of the battery. Moreover, the degradation of the activation over time can be also studied, which means that the same method could be applied for the study of the aging of the felt after cycling in the battery. References: [1] L. Landon-Lane, A. T. Marshall, D. A. Harrington, EIS at carbon fiber cylindrical microelectrodes, Electrochemistry Communications, 109 (2019) 106566 [2] L. Landon-Lane, A. J. Downard, A. T. Marshall, Single fibre electrode measurements – A versatile strategy for assessing the non-uniform kinetics at carbon felt electrodes, Electrochimica Acta, 354 (2020) 136709 Acknowledgement: This work has been supported by the European Union under HIGREEW, Affordable High-performance Green Redox Flow batteries (Grant Agreement no. 875613).