In Situ Transmission Electron Microscopy of Electrocatalyst Materials: Proposed Workflows, Technical Advances, Challenges, and Lessons Learned.

In situ electrochemical liquid phase transmission electron microscopy (LP-TEM) measurements utilize micro-chip three-electrode cells with electron transparent silicon nitride windows that confine the liquid electrolyte. By imaging electrocatalysts deposited on micro-patterned electrodes, LP-TEM provides insight into morphological, phase structure, and compositional changes within electrocatalyst materials under electrochemical reaction conditions, which have practical implications on activity, selectivity, and durability. Despite LP-TEM capabilities becoming more accessible, in situ measurements under electrochemical reaction conditions remain non-trivial, with challenges including electron beam interactions with the electrolyte and electrode, the lack of well-defined experimental workflows, and difficulty interpreting particle behavior within a liquid. Herein a summary of the current state of LP-TEM technique capabilities alongside a discussion of the relevant experimental challenges researchers typically face, with a focus on in situ studies of electrochemical CO conversion catalysts is provided. A methodological approach for in situ LP-TEM measurements on COR catalysts prepared by electro-deposition, sputtering, or drop-casting is presented and include case studies where challenges and proposed workflows for each are highlighted. By providing a summary of LP-TEM technique capabilities and guidance for the measurements, the goal is for this paper to reduce barriers for researchers who are interested in utilizing LP-TEM characterization to answer their scientific questions.