Quasi-operando Transmission Electron Microscopy Diagnostics for Electrocatalytic Processes in Liquids.

The need to relate the mechano-physico-chemical phenomena in liquid-based electrocatalysts to the stages of start-up, operation, and shut-down phases is one of the major challenges that the energy community is facing. Understanding these phenomena will pave the way for the tailor-made design of efficient, commercially viable electrocatalytic systems. Transmission electron microscopy plays an important role in the investigation of local electrocatalytic effects, complementing other operando characterization techniques. Herein, after attempting to define the meaning of operando methodologies in relation to electron microscopy studies, the progress in the field is reviewed in terms of the knowledge gained about the catalysts, the solid-liquid interfaces, and the solid-liquid-gas interfacial phenomena for several electrocatalytic reactions. Finally, the parameters that require consideration in operando ec-LPTEM studies of electrocatalytic systems are discussed.