Operando Heating and Cooling Electrochemical 4D-STEM Probing Nanoscale Dynamics at Solid–Liquid Interfaces

Operando/in situ methods have revolutionized our fundamental understanding of molecular and structural changes at solid–liquid interfaces and enabled the vision of “watching chemistry in action”. Operando transmission electron microscopy (TEM) emerges as a powerful tool to interrogate time-resolved nanoscale dynamics, which involve local electrical fields and charge transfer kinetics distinctly different from those of their bulk counterparts. Despite early reports on electrochemical or heating liquid-cell TEM, developing operando TEM with simultaneous electrochemical and thermal control remains a formidable challenge. Here, we developed operando heating and cooling electrochemical liquid-cell scanning TEM (EC-STEM). By integrating a three-electrode electrochemical circuit and an additional two-electrode thermal circuit, we can investigate heterogeneous electrochemical kinetics across a wide temperature range of −50 to 300 °C. We used Cu electrodeposition/stripping processes as a model system to demonstrate quantitative electrochemistry from −40 to 95 °C in both transient and steady states in aqueous and organic solutions, which paves the way for investigating energy materials operating in extreme climates. Machine learning-assisted quantitative 4D-STEM structural analysis in cold liquids (−40 °C) reveals a distinct two-stage growth of nanometer-scale mossy Cu nanoislands with random orientations followed by μm-scale Cu dendrites with preferential orientations. This work benchmarked electrochemistry in the three-electrode EC-STEM and systematically investigated the temperature and pH dependence of the Pt pseudoreference electrode (RE). At room temperature, the Pt pseudo-RE shows a reliable potential of 0.8 ± 0.1 V vs the standard hydrogen electrode and remains pH-independent on the reversible hydrogen electrode scale. We anticipate that operando heating/cooling EC-STEM will become invaluable for understanding fundamental temperature-controlled nanoscale electrochemistry and advancing renewable energy technologies (e.g., catalysts and batteries) in realistic climates.