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Fast Operando Spectroscopy Tracking in Situ Generation of Rich Defects in Silver Nanocrystals for Highly Selective Electrochemical CO2 Reduction
X. Wu, Y. Guo, Z. Sun, F. Xie, D. Guan, J. Dai, F. Yu, Z. Hu, Y.-C. Huang, C.-W. Pao, J.-L. Chen, W. Zhou*, and Z. Shao*
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.

利用清潔的電能將二氧化碳電化學轉化為有價值的化學品是緩解日益嚴重的溫室效應的有效手段。高效的催化劑在此過程中扮演至關重要的角色,瞭解催化劑及其活性位元點在真實反應狀態下的資訊為催化劑的開發設計提供了指導。我們報導了一種原位形成的納米銀催化劑,其催化二氧化碳轉化為一氧化碳的選擇性接近100%,穩定性可持續120 h以上,在流動反應池中可達到180 mA cm-2的電流密度。我們利用強大的快速原位同步輻射吸收譜技術(TPS 44A),對該催化劑原位演化過程中的電子結構和晶體結構資訊進行採集和分析。我們發現,反應開始後,原始材料中的銀氧鍵快速斷裂,同時伴隨著新的銀銀鍵的快速生成,最終在幾分鐘之內便形成了有缺陷結構的納米銀催化劑,這種缺陷結構在後續的電催化反應中可以穩定存在於催化劑中。結合實驗和理論模擬計算,我們認為該催化劑中存在的具有合適缺陷濃度的結構可以優化反應中間體的吸附能,進而優化目標產物的選擇性。我們的研究不僅報導了一種高效的二氧化碳電還原催化劑,而且證明了快速原位技術在電催化領域中的重要作用。