Real-time Monitoring of the Reversible Capture and Release of CO2 on Anthraquinone and Riboflavin-Modified Graphitic Electrodes using ATR-SEIRAS

Electrochemically mediated carbon capture (EMCC) offers a promising alternative to thermochemical carbon capture methods due to its higher energy efficiency and the ability to operate under standard conditions. Graphitic electrodes functionalized with redox-active organic (RAO) capture agents offer a unique opportunity for an inexpensive, abundant, and easily scalable system for direct EMCC. However, the mechanistic understanding and observation of intermediate capture states on carbon surfaces using spectroscopic signatures remains unexplored. Herein, we present in situ monitoring of the reversible capture and release of carbon dioxide (CO2) from graphene-on-gold electrodes modified with grafted anthraquinone (AQ) and a synthesized riboflavin derivative, 10-ethyl-3-methyl flavin derivative (MFD). These electrodes conveniently enable the use of surface-enhanced infrared absorption spectroscopy in an attenuated total reflectance configuration (ATR-SEIRAS). We successfully decouple the spectral responses of the CO2 reduction reaction (CO2RR) and CO2 capture processes by characterizing AQ- and MFD-modified electrodes under argon and CO2 atmospheres. Continuous polarization of the electrode to generate the reduced forms of AQ also generates carbonate (CO32-) peaks at 1640 cm-1 and 1380 cm-1 that overshadow the spectral responses of AQ-bound CO2. Conversely, reducing AQ or MFD under inert atmosphere, followed by introducing CO2 with no applied potential (i.e. at open circuit) results in the growth of distinct spectral features ~1710-1630 cm-1. The release of CO2 was observed through the regeneration of an intense carbonyl stretch at ~1660 cm-1 upon electrooxidation, corresponding with CV observations for AQ and MFD. Preliminary CO2 capture experiments using a two-electrode flow cell device with AQ- and MFD-modified YP-50 porous carbon electrodes indicate that MFD systems perform on par with AQ systems. This work highlights relevant considerations for performing CO2 capture studies under continuous polarization conditions, illuminates key surface intermediates during carbon capture, and demonstrates the ability of our platform to screen novel RAO capture agents.