Real-Time Analysis of CO₂ Reduction Product Distribution by Synchrotron Vacuum Ultraviolet Photoionization Mass Spectrometry

Understanding the transient physicochemical properties at the cathode/catholyte interface is a prerequisite to shedding light on the complex electrochemical CO₂ reduction reaction (CO₂RR) mechanism as well as to steering the product distribution toward precise CO₂ valorization. Herein, we report a flow-cell-based synchrotron vacuum ultraviolet photoionization mass spectrometric approach to resolve the dynamic interfacial species evolution during Cu-catalyzed CO₂RR. By optimizing the photoionization energy, characteristic molecular ions of 8 volatile reduction products, together with the CO₂ reactant, have been precisely captured for both potential step and linear sweep voltammetric measurements. The soft photoionization with fine-tuned energy avoids complicated mass signal deconvolution in conventional quadrupole mass spectrometry with electron impact ionization, while orders of magnitude higher temporal resolution has been demonstrated for this spectroelectrochemical technique as compared to headspace gas chromatography analysis on gaseous effluent from the CO₂RR, providing a feasible way to resolve complex interfacial (electro)chemistry in real time.