Electrochemically Mediated Carbon Capture on Surface-Confined Quinone: Unveiling Interfacial Pathways via Surface-Enhanced Spectroscopy

High Resolution Image Download MS PowerPoint Slide Electrochemically mediated carbon capture (EMCC) offers a promising route for energy-efficient CO 2 separation by leveraging redox-active sorbents such as quinones. While recent efforts have increasingly focused on immobilizing quinones onto electrode surfaces, the mechanistic pathway for surface-confined EMCC remains largely unresolved. In this work, the interfacial redox behavior and CO 2 reactivity of anthraquinone (AQ) grafted onto gold electrodes is investigated, using cyclic voltammetry, attenuated total reflectance surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS), and density functional theory (DFT). Voltammetric analysis revealed two well-defined, reversible one-electron reduction waves under anhydrous and inert conditions, closely resembling solution-phase behavior. ATR-SEIRAS further showed the reversible evolution of vibrational fingerprints corresponding to the radical anion (RAQ) and dianion (DAQ) species. Under CO 2 -saturated conditions, SEIRAS spectra and complementary DFT calculations revealed persistent RAQ signatures, with no evidence of RAQ–CO 2 adduct formation. CO 2 binding was observed only after the second electron transfer, resulting in the formation of a mono(carbonate) DAQ–CO 2 complex. These findings support an alternative EEC mechanism, in contrast to the previously assigned ECEC and EECC pathways for strong CO 2 -binding anthraquinone sorbents, suggesting that the observed behavior is likely governed by interfacial factors such as charge delocalization and steric constraints within the multilayer grafted film. This work underscores the critical role of interfacial spectroelectrochemistry in elucidating chemically-coupled surface-confined redox processes and demonstrates that conventional solution-phase models may not fully capture the mechanistic nuances of immobilized EMCC systems.