Abstract
Electrochemical CO2 reduction (ECR) is highly attractive to curb global warming. The knowledge on the evolution of catalysts and identification of active sites during the reaction is important, but still limited. Here, we report an efficient catalyst (Ag-D) with suitable defect concentration operando formed during ECR within several minutes. Utilizing the powerful fast operando X-ray absorption spectroscopy, the evolving electronic and crystal structures are unraveled under ECR condition. The catalyst exhibits a ~100% faradaic efficiency and negligible performance degradation over a 120-hour test at a moderate overpotential of 0.7 V in an H-cell reactor and a current density of ~180 mA cm−2 at −1.0 V vs. reversible hydrogen electrode in a flow-cell reactor. Density functional theory calculations indicate that the adsorption of intermediate COOH could be enhanced and the free energy of the reaction pathways could be optimized by an appropriate defect concentration, rationalizing the experimental observation.
Highlights
Electrochemical CO2 reduction (ECR) is highly attractive to curb global warming
The Ag oxidation states were measured by X-ray photoelectron spectroscopy (XPS)
Fast operando X-ray absorption spectroscopy (XAS) measurements and ex situ scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images revealed that massive defects are efficiently created at the initial stage of ECR
Summary
Electrochemical CO2 reduction (ECR) is highly attractive to curb global warming. The knowledge on the evolution of catalysts and identification of active sites during the reaction is important, but still limited. The use of clean carbon-neutral fuel systems, CO2 sequestration, and CO2 transformation into high value−added products are several strategies for inhibiting continuous increases in or even reducing the CO2 concentration in the atmosphere[6] Among these techniques, electrochemical CO2 reduction (ECR) driven by clean and renewable electricity sources (e.g. solar energy) is promising[7,8], and can synthesize a wide variety of chemicals, such as formic acid, carbon monoxide (CO), alcohol and methane, along with the elimination of CO29–13. Advanced operando X-ray, optical and electron-based characterizations may provide useful information about defect generation under real reaction conditions[28,29,30,31] Among these methods, X-ray absorption spectroscopy (XAS) probes atomspecific structural details of catalysts[12,32,33]. Fast XAS technique with excellent time−resolution should be pursued to understand the mechanism and the formation process of active sites in catalysts during the electrochemical reaction, which is vital for the rational design of new catalysts[36,40,41]
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