(51g) From Ex Situ to in Situ: Understanding and Manipulating Nanocrystal Surface Structures with Multi-Dimensional Imaging

Precise control of nanocrystal surface structures and fundamental insights into their stabilization during reactions are crucial for the development of effective catalysts toward long-term practical applications. Comprehensive analysis of complex shapes and dynamics of nanocrystals requires high-scale characterization techniques with real-time imaging capability. However, current imaging techniques are either limited by dimensionality (e.g., 2D projections for transmission electron microscopy, TEM) or temporal resolution (e.g., stationary samples for electron tomography).

In this talk, I will introduce multi-dimensional imaging of metal nanocrystals to uncover their structural and compositional change during chemical reactions. The insights are further used to guide the design and synthesis of nanocrystals with well-defined surface structures and improved catalytic performance. I will first introduce the combination of high-resolution TEM with controlled surface oxidation in realizing surface roughening and stabilization of Cu nanocrystals toward high C₂₊ selectivity in electrochemical CO₂ reduction. Stepping from ex situ to in situ, I will then introduce 4D liquid-phase electron tomography, an integration of liquid-phase TEM with electron tomography, to resolve the 3D shape evolution of core-shell nanocrystals during oxidative etching with nanometer resolution. Core-shell nanocrystals with tunable compositions hold great promise as cost-effective catalysts, while susceptible to external stimuli such as corrosive solvents and high-potential biasing. 3D reconstructions provide us with detailed surface structures, local etching rates, and their interrelation at different time intervals, unveiling the asymmetric etching process and underlying etching preference that is inaccessible to 2D projections. By integrating with kinetic Monte Carlo simulation, we highlight the crucial factors shaping the outcome of nanoparticle transformation, including their intrinsic structures and distance to reaction equilibrium. The development of multi-dimensional characterization platform is anticipated to provide us with comprehensive understanding of nanoscale reactions, guiding the rational design of catalytic nanomaterials with novel structures, high performance, and long-term stability.