In situ and operando transmission electron microscopy for the synthesis, fundamental understanding and catalytic applications of nanoalloys

In line with the paradigm of nanoscience, developing functional nanoalloys for catalytic applications requires a thorough understanding of the correlations between their synthesis, structure, properties, and performance. Over the last two decades, the progresses of in situ and operando transmission electron microscopy (TEM) has revolutionized the way to meet this challenge by providing unparalleled observations of nanomaterial dynamics in their formation and application media. The atomic scale resolution and chemical sensitivity of TEM analyses in liquid or gaseous media of controlled composition and temperature are shedding new light on nanoalloys' nucleation and growth mechanisms, the simultaneous kinetic and thermodynamic effects that dictate their structural evolution and their transformations under catalytic conditions. Through this review, we show the opportunities and challenges of in situ/operando TEM in rationalizing the synthesisand understanding the complex structural properties and associated performance of nanoalloys for catalysis and electrocatalysis. We also discuss how future developments will extend the impact of TEM analyses in optimizing the full life cycle of functional nanoalloys.