In Situ Observation of Triple-Phase Interface during Electrocatalytic CO 2 Reduction

The solid–liquid–gas triple-phase interface in the CO 2 electro-reduction reaction (CO 2 RR) is pivotal for determining catalytic activity and selectivity, as it influences both the kinetics and thermodynamics of the reactions. However, observing this interface in situ is challenging because it forms at the interface among the solid catalyst, the flowing electrolyte, and the turbulent CO 2 . To address the issues, we achieved unobstructed in situ Raman observations at the microscale by developing a straightforward catalyst-integrated gas diffusion electrode (GDE). This monolithic GDE, featuring a biomimetic hydrophobic structure, fully releases the triple-phase interface─an essential prerequisite for enabling the in situ detection. Characterizations reveal that the microenvironment at the triple-phase interface significantly enhances multicarbon (C 2+ ) selectivity. Furthermore, using advanced in situ 3D Raman tomography, we successfully visualized the spatial distribution of the triple-phase interface with high precision. The integration of in situ Raman spectroscopy with computational modeling has provided invaluable insights into the evolution of species within the microenvironment, elucidating a high local pH and rapid CO 2 mass transfer at the triple-phase interface.