Nanoscale Management of CO Diffusion in CO2 Electroreduction: Boosting Faradaic Efficiency to Multicarbon Products Via Nanostructured Tandem Electrocatalysts

Abstract

Tandem catalysis presents a promising strategy to improve the selectivity toward multicarbon products in the electrocatalytic carbon dioxide reduction reaction (CO2RR). For this reaction, it is well-known that CO is a critical intermediate for producing multicarbon products. Thus, 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 (FEC2+) of 68.4% in a H-cell and 70% in a flow cell with a current density of 350 mA cm-2 are achieved,. These figures-of-merit are currently among the top reports within the known literature for flow cells with partial current density >200 mA cm-2 to C2+ products. 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.