Considerations of Liquid-Phase Transmission Electron Microscopy Applied to Heterogeneous Electrocatalysis

Abstract

Liquid-phase transmission electron microscopy (LPTEM) is an essential tool for studying the dynamics of materials interactions at the nanoscale, in and/or with their operational environment. Microfabricated SiNx membrane cells further allow the integration of thin-film electrodes that opens the technique to studies of heterogeneous electrocatalysts under relevant electrochemical conditions. However, experiments remain challenging and the characteristics of the dedicated electrochemical cells and of the interactions of the electron beam with the liquid electrolyte demand careful interpretation of the results. Herein, we discuss important aspects that concern the implementation of electrochemical LPTEM (ec-LPTEM). We first consider the range of information that can be accessible with the technique for electrocatalytic applications and we detail the influence of the thickness and flow of liquid electrolytes using membrane-based microcells. Further, we provide guidelines pertinent to the electrochemical configuration of the substrate working, reference, and counter electrodes. We validate these considerations by experimentally demonstrating the application of ec-LPTEM for the CO2 reduction reaction (CO2RR), the oxygen reduction reaction (ORR), and the oxygen evolution reaction (OER). The probed effects in metallic and oxide catalysts are directly related to the applied electrochemical stimuli and corroborate the representativity of the processes under investigation following the considerations described herein.