Mapping the Double Layer Using Proton-Coupled Electron Transfer at Functionalized Carbon Electrodes

Abstract

Conductive electrodes functionalized with molecularly well-defined species are emerging as effective active materials for a wide range of applications, from electrocatalytic CO2 and O2 reduction, to high performance lithium-sulfur batteries.1–3 For redox-active species that participate in proton-coupled electron transfer (PCET), the extent of conjugation, applied potential, and distance between the redox center and electrode determine the potential and electric field experienced at the site of electron transfer. This electric field in turn determines the pH-dependent energetics of electron transfer (i.e. Pourbaix behavior) and the rate PCET. We discuss how measurements of PCET to redox-active species functionalized to carbon electrodes can yield insight into the potential and electric field profiles within the electrode-electrolyte double layer. Systematically increasing the distance between the redox-active moiety and the electrode results in the moiety experiencing a progressively weaker electric field, as determined by changes to PCET behavior. Based on these results, we propose strategies to quantify the strength of the electric field as a function of this distance. This work can inform strategies for effective pH modulation at electrified interfaces in ways that can enhance electrocatalytic processes and other applications, such as electrochemical CO2 capture based on pH swing.References Ren, G. et al. Porous Core-Shell Fe3C Embedded N-doped Carbon Nanofibers as an Effective Electrocatalysts for Oxygen Reduction Reaction. ACS Applied Materials and Interfaces 8, 4118–4125 (2016).Zhang, S., Fan, Q., Xia, R. & Meyer, T. J. CO2 Reduction: From Homogeneous to Heterogeneous Electrocatalysis. Accounts of Chemical Research 53, 255–264 (2020).Zhao, C.-X. et al. Semi-Immobilized Molecular Electrocatalysts for High-Performance Lithium–Sulfur Batteries. Journal of the American Chemical Society 143, 19865–19872 (2021).