Study of the Kinetics of Redox Active Polymers in Non-Aqueous Media Under High Mass-Transfer Conditions Using Scanning Electrochemical Microscopy

Abstract

We present on the use of Scanning Electrochemical Microscopy (SECM) to quantify the reaction kinetics of redox active polymers with molecular weights between 21 and 318 kDa that have been shown as promising mediators for non-aqueous redox flow cell batteries. [1] The promise of these mediators is that they are highly soluble in cost effective organic solvents, e.g. up to 2.7 M in acetonitrile, have tunable size, and reversible electrochemical behavior. However, it is not well understood how the kinetics of electron transfer, and its mechanisms, might change on these polymers with increasing size and concentration. Experiments have also shown that these polymers produce electroactive films on Pt and C electrodes, therefore elucidating the charge transfer properties of these films is important in evaluating their electrochemical performance under flow conditions. SECM can be used by combing the information obtained from approach curves in the feedback mode with the steady state voltammetry at ultramicroelectrodes of known size to determine the electron transfer rate and other kinetic information. [2] Imaging of polymer films in the feedback mode can also complement with useful information about the heterogeneity of charge transfer and charge transport on working electrodes. Fundamental knowledge of the kinetics of redox active polymers allows for better prediction of the effects of size and functionalization for analogous systems. [1] Gavvalapalli, N.; Hui, J.; Cheng, K.; Lichtenstein, T.; Shen, M.; Moore, J.S.; Rodríguez-López, J. J. Am. Chem. Soc. 2014, 136, 16309-16316 [2] Mirkin, M. V.; Bard, A. J. J. Anal. Chem. 1992, 64, 2293–2302.