Structural Self-Reconstruction of Catalysts in Electrocatalysis.

Recent years have witnessed significant development of electrocatalysis for clean energy and related potential technologies. The precise identification toward active sites of catalysts and the monitoring of product information are highly desirable to understand how the materials catalyze a specific electrocatalytic reaction. For a long period, the identification of active sites and the cognition of corresponding catalytic mechanisms are generally based on various ex situ characterization methods which actually could not capture dynamic structure and intermediate information during electrocatalytic processes. With recent developments of in situ and operando characterization techniques, it has been extensively observed that most of the catalysts would undergo structural self-reconstruction as a result of electro-derived oxidation or reduction process of the catalysts at a given potential, often accompanied by the increase or decrease of catalytic activity as well as the change of catalytic selectivity. In fact, such structural self-change in the catalytic process does make it difficult to identify the true catalytically active sites efficiently, thus hindering the understanding of the real catalytic mechanism. Therefore, we believe that understanding the self-reconstruction by the combination of reliable characterization techniques and theoretical calculations holds the key to rational design of advanced catalysts. In this Account, we provide in-depth insights into recent progress regarding structural self-reconstruction of electrocatalysts in several typical electrochemical reactions with the emphasis on fundamental knowledge, structure-property relationships, structural evolution process, and modulation of self-reconstruction. To deliver a clear understanding, it has to be pointed out in advance that these catalysts with drastic structural and activity self-change in electrocatalytic processes are suggested to be called precatalysts under nonreaction conditions. The restructured active components in realistic reaction conditions are true catalysts. The structural self-reconstruction process bridges the precatalysts with true catalysts. To understand the self-reconstruction behavior, the following three critical aspects will be carefully disclosed and discussed in depth. First, fundamental origin of structural self-reconstruction of electrocatalysts is introduced. It is noteworthy that the atomic-level correlations between the self-reconstruction behavior and intrinsic structure of precatalysts are emphasized due to the fact that even if some precatalysts are congeneric, they often exhibit a diverse self-reconstruction phenomenon and catalytic performance. Second, the self-reconstruction process should be monitored by advanced characterization techniques, which is central to precisely unveil the self-reconstruction behavior. In situ or operando characterizations have been considered as judicious methods to track the self-reconstruction, capture dynamic structure and analyze real-time reaction products. Finally, based on the dynamic structure and product information together with comprehensive theory calculations, the enhancement or degradation mechanism of catalytic activities can be unambiguously clarified. With thoughtful studies toward the complete self-reconstruction process of electrocatalysts, some feasible methods to tune the self-reconstruction and improve the performance can be rationally proposed. Based on this progress, we hope to provide new insight into electrocatalysis, particularly the self-reconstruction and true active sites of electrocatalysts, and then to offer guidelines for rational design of advanced electrocatalysts.