Improving the efficiency of the electrocatalytic reaction at electrode interface is of great significance to the development of the electrocatalysis science and technology. An in-depth investigation of the structure-activity relationship of the electrocatalyst and the electrocatalytic process at nanoscale is helpful for understanding the catalytic mechanism, and further promotes the rational design of the high-performance electrocatalyst. Due to the characteristics of high spatial resolution and in-situ characterization, electrochemical scanning tunneling microscope (ECSTM) has been widely used in electrocatalysis researches, and has been increasingly recognized as a tool to bridge the gap between the electrocatalysis science and traditional surface chemistry. This presentation aims to introduce our recent efforts on the investigation of the electrocatalysis by ECSTM at the molecular scale. Contents to be covered include: 1. Clarifying the structure-activity relationship of Co-N4 site in ORR. Cobalt porphyrins with distinct substituents CoTPPX4 (X= Cl, H, OCH3) was investigated as the molecular model catalyst. The electrocatalytic performance of the model catalysts were revealed by electrochemical measurements. ECSTM characterizations were performed to investigate the formation of CoTPPX4-O2 complex in ORR. Theoretical simulations demonstrate the limiting energy barrier difference for different model catalysts in the reaction. The O2 adsorption and catalytic conversion process in ORR was revealed by the in-situ ECSTM experiments and ECSTM potential step experiments. This work provides molecular evidence for understanding the structure-activity relationship of Co-N4 site with different electron density in ORR. 2. Revealing the dynamic process of cobalt phthalocyanine (CoPc) catalyzed CO2 reduction reaction. The high contrast CoPc-CO2 complex can be observed in the STM image. The reduction of CoIIPc, the binding of CO2 and the conversion of the CoPc-CO2 complex in the reaction was revealed by the in-situ ECSTM experiments. ECSTM potential step experiments provide the dynamic information of the initial stage of the reaction, which includes the reduction of CoIIPc and the binding of CO2 on active site, and the binding of CO2 on CoIPc is qualitatively determined as the limiting step in this stage. This work provides direct molecular evidence for understanding the mechanism of CoPc catalyzed CO2 reduction reaction.

Molecular insights into electrocatalysis by electrochemical scanning tunneling microscopy

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