In-Situ Soft X-Ray Spectromicroscopy Characterization of Electrochemical Processes

摘要

Soft X-ray Scanning Transmission X-ray microscopy (STXM) is a synchrotron-based technique which can provide both spectroscopic characterization (near edge X-ray absorption fine structure, NEXAFS) and chemically selective imaging with high spatial resolution (～30 nm). Recently, we have developed in situ flow electrochemical devices which allow control of the electrochemical environment while conducting STXM measurements, thus providing a platform for in-situ studies of electrochemical oxidation and reduction processes. This presentation reports results of in situ flow electrochemical STXM studies on three different systems to demonstrate the present capabilities. First, the ability to rapidly exchange the electrolyte is demonstrated by a STXM Fe 2p and in situ electrochemical study of the ferro/ferricyanide solution redox system. Second Cu and Ag-doped Cu catalysts for CO_2 electrochemical reduction (CO_2R) were successfully prepared using in situ electrodeposition. Third, the electrolyte was changed from CuSO_4 to NaHCO_3 (as substrate for CO_2R) and the cell was operated under electrochemical CO_2 reduction conditions, while monitoring the changes to the Cu deposited layer at various potentials, including -0.5 V where CO_2 reduction is expected. The figure shows a cyclic voltammogram (CV) and color-coded Cu oxidation state maps which were derived from Cu 2p stacks measured under chronoamperometric conditions at the indicated potentials. These results demonstrate that in situ flow electrochemical STXM measurements can be performed in our device under varying electrochemical reaction conditions, enabling visualization of the morphology changes from selective energy imaging, and quantitative tracking of electrochemical transformations from spectromicroscopy. This system will be used for in situ studies of CO_2 electrochemical reduction catalysis with the goal of obtaining mechanistic insights to guide the development of catalysts with improved efficiency and selectivity. In addition, the system will be used to study a variety of material science, chemistry and environmental science related questions associated with oxidation or reduction processes, such as mechanisms of extra-cellular electron transport in marine sediment microbial biofilms.