Electrodes functionalized with molecularly well-defined reactive/catalytic species have become attractive for promoting a wide variety of electrochemical energy conversion processes or systems, such as electrocatalytic CO₂ and O₂ reduction, as well as metal-sulfur and redox-flow batteries.^1-3 Critical to the performance of these electrodes is the interaction between the electric field, and the molecular species at the electrical double layer. Nevertheless, elucidating the potential/electric field experienced at the functionalized interface is challenging. We show in this work that the acid-base thermochemical (i.e. Pourbaix) behavior of molecular quinones can vary depending on their mode of covalent attachment to a carbon electrode and ionic strength of the electrolyte, in a manner that sheds light on the experienced interfacial electric field. This work can inform strategies for effective pH modulation at electrified interfaces in ways that can enhance the electrocatalytic processes and systems mentioned above, and enable newer applications such as pH-swing-based electrochemical CO₂ capture using appropriately chemically modified electrodes.⁴

References

1 Ren, G. et al. Porous Core–Shell Fe3C Embedded N-doped Carbon Nanofibers as an Effective Electrocatalysts for Oxygen Reduction Reaction. ACS Applied Materials & Interfaces 8, 4118-4125, doi:10.1021/acsami.5b11786 (2016).

2 Zhang, S., Fan, Q., Xia, R. & Meyer, T. J. CO2 Reduction: From Homogeneous to Heterogeneous Electrocatalysis. Accounts of Chemical Research 53, 255-264, doi:10.1021/acs.accounts.9b00496 (2020).

3 Zhao, C.-X. et al. Semi-Immobilized Molecular Electrocatalysts for High-Performance Lithium–Sulfur Batteries. Journal of the American Chemical Society 143, 19865-19872, doi:10.1021/jacs.1c09107 (2021).

4 Jin, S., Wu, M., Gordon, R. G., Aziz, M. J. & Kwabi, D. G. pH swing cycle for CO2 capture electrochemically driven through proton-coupled electron transfer. Energy & Environmental Science, doi:10.1039/D0EE01834A (2020).