Spatiotemporal visualization of CO2 electrolysis

Abstract We report here an electrolysis optical coherence tomography (eOCT) platform to visualize the chemical reactions occurring in a CO 2 electrolyzer. The eOCT platform was designed to capture three dimensional images and videos at high spatial (~1 µm) and temporal (<1 µs) resolutions. We captured 12 h of footage of an electrolyzer, containing a porous electrode separated by a membrane, converting a continuous feed of liquid KHCO 3 to reduce CO 2 into CO at applied current densities of 50-800 mA cm −2 . This video resolved the nucleation and formation of CO 2 in the cathode compartment upon reaction of HCO 3 – with H + delivered through the membrane, the formation of CO at the cathode|electrolyte interface, and H 2 throughout the cathode compartment. The video captured the strikingly dynamic movement of the cathode and membrane components during electrolysis, and linked CO production to regions of the electrolyzer in which CO 2 were in direct contact with both the membrane and the catalyst layers. This visualization enabled us to correlate the decrease in CO production to a buildup of CO 2 , CO, and H 2 , and (bi)carbonate salts at the cathode layer. The statistical analysis of phase distribution images allowed us to understand the competition between main (CO 2 reduction) and side (hydrogen evolution) reactions in both time and space domains. We also show how a pulsing current liberates these residual bubbles and (bi)carbonates to recover CO production. These results highlight the power of using an eOCT platform to temporally and spatially resolve CO2RR electrolysis.