Abstract
The electrochemical CO2 reduction reaction (CO2RR) represents a very promising future strategy for synthesizing carbon-containing chemicals in a more sustainable way. In spite of great progress in electrocatalyst design over the last decade, the critical role of wettability-controlled interfacial structures for CO2RR remains largely unexplored. Here, we systematically modify the structure of gas-liquid-solid interfaces over a typical Au/C gas diffusion electrode through wettability modification to reveal its contribution to interfacial CO2 transportation and electroreduction. Based on confocal laser scanning microscopy measurements, the Cassie-Wenzel coexistence state is demonstrated to be the ideal three phase structure for continuous CO2 supply from gas phase to Au active sites at high current densities. The pivotal role of interfacial structure for the stabilization of the interfacial CO2 concentration during CO2RR is quantitatively analysed through a newly-developed in-situ fluorescence electrochemical spectroscopic method, pinpointing the necessary CO2 mass transfer conditions for CO2RR operation at high current densities.
Highlights
The electrochemical CO2 reduction reaction (CO2RR) represents a very promising future strategy for synthesizing carbon-containing chemicals in a more sustainable way
Our findings show that in three-phase contact (TPC) systems, the electrochemical CO2RR efficiency at large current densities is greatly influenced by the CO2 concentration at interfaces, which is fundamentally determined by the efficiency of CO2 mass transfer over wettability-controlled interface structures
This architecture is crucial as rapid transport of gaseous CO2 from the bulk gas phase to the surface of the Au/C NPs through the porous electrode was required to achieve a stable interfacial CO2 concentration when operating at high current densities (Fig. 1e, f)
Summary
The electrochemical CO2 reduction reaction (CO2RR) represents a very promising future strategy for synthesizing carbon-containing chemicals in a more sustainable way. TPC systems offer many advantages for electrochemical CO2RR, for example allowing the use of high pH electrolytes (that cannot readily be applied in DPC systems) to promote CO2RR electron transfer kinetics[23,24,25] By this approach, efficient CO2 electrolysis to valuable products (e.g. CO, formic acid) can be achieved at high current densities, the use of the latter being an essential requirement for potential industrial scale applications[26,27,28]. Variations of wettability over three-phase interfaces can dramatically alter the interfacial transportation behaviour of gaseous reactants/products and the contact between catalytic sites and ions in electrolyte, influencing gas diffusion and electron transfer processes as the rate determining steps in electrochemical reaction kinetics[41]
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