(307c) Nanoscale Management of CO Diffusion in the Microenvironment for CO2 Electroreduction: Boosting C2+ Faradaic Efficiency Via Spatial Arrangement of Tandem Catalysts

The performance of the electrocatalytic CO₂ reduction reaction (CO₂RR) is highly dependent on the microenvironment around the cathode. Despite efforts to optimize the microenvironment by modifying nanostructured catalysts or microporous gas diffusion electrodes, their inherent disorder can present a significant challenge to understanding how interfacial structure arrangement governs transport as well as the microenvironment for CO₂RR. To this end, we will discuss the fundamental role of activity for CO₂, CO, and H₂O and the interplay with the arrangement of tandem Cu-Ag catalysts in the cathode.

To this end, we discuss how control of CO localization and CO diffusion are vital for promoting the formation of multicarbon products. However, the management of CO localization and CO diffusion remains underexplored. Herein, we design a three-dimensional tandem catalyst electrode with silver nanoparticles (Ag NPs) to generate CO as an intermediate product at the bottom of a copper (Cu) nanoneedle array. This design is shown to enhance the conversion of the intermediate product, CO. Via this nanostructured design, CO₂ reduces to C₂₊ products with a high Faradaic efficiency (FE_C2+) of 68.4% in a H-cell and 70% in a flow cell with a current density of 350 mA cm^-2 are achieved in the absence of other strategies.

More importantly, we employed in-situ Raman spectroscopy and finite-element method calculations to elucidate the origins of the enhanced selectivity. Together, these approaches reveal the crucial role of prolonging the CO diffusion path length in improving CO utilization during CO₂ conversion with tandem catalyst systems. The favorable CO₂RR selectivity and current density to C₂₊ products in two distinct environments (H-cell and flow cell reactors) further corroborate that this effect is not limited to a particular reactor environment. Overall, this study provides a valuable strategy for designing tandem catalysts for improved selectivity to C₂₊ products in CO₂RR.