Mapping the kinetics of hydrogen evolution reaction on Ag via pseudo-single-crystal scanning electrochemical cell microscopy

Abstract

AbstractElucidating the structure-activity relationship in electrocatalysis is of fundamental interest for electrochemical energy conversion and storage. However, the heterogeneity in the surface structure of electrocatalysts, including the presence of various facets, poses an analytical challenge in revealing the true structure-activity relationship because the activity is conventionally measured on ensemble, resulting in an averaged activity that cannot be unequivocally associated with a single structural motif. Scanning electrochemical cell microscopy (SECCM) [1] combined with colocalized electron backscatter diffraction (EBSD) offers a direct way to reveal the correlative local electrochemical and structural information. Herein, we measured the hydrogen evolution reaction (HER) activity on Ag and its dependence on the crystal orientation. From the combined EBSD and SECCM mapping, it is found that Ag grains closer to {111} show a higher exchange current density, while those closer to {110} show a lower Tafel slope. The Tafel slope is also found to decrease with the step density increase. The ability to measure the electrocatalytic activity under a high mass-transfer rate allows us to reveal the activity difference at a high current density (up to 200 mA/cm2). The approach reported here can be expanded to other systems to reveal the nature of active sites of electrocatalysis.