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.