JCAP Seminar

An understanding of how materials grow and transform in their working environments is essential to the design of functional materials for various applications. In this talk, I will first present our study of colloidal nanocrystal growth in liquids by the development and applications of in situ transmission electron microscopy (TEM). Nanocrystal shape control is a significant topic since nanoparticle catalytic and other surface-enhance properties are highly dependent on their shape. However, due to the lack of direct observation how facets develop during growth is largely unknown. Using in situ liquid cell TEM, we have been able to identify growth mechanisms of nanocrystals and have discovered rules applied to bulk systems break down at the nanoscale. For instance, the facet development of Pt nanocubes during growth drastically differs from what is predicted by the widely accepted surface energy minimization rule, i.e., Wulff construction. We found that the growth rates of the {100}, {110} and {111} facets are similar until the {100} facets stop growth. Subsequently, the {110} facets are eliminated when two adjacent {100} facets meet. Eventually, the growth of {111} facets fills the corners to complete a nanocube. Theoretical calculation suggests oleylamine ligand mobility on the facet is likely responsible for the arresting of the {100} growing facets. In the second part of my talk, I will present the in situ study of electrochemical processes using both in situ TEM and X-ray absorption spectroscopy. Dissolution-deposition at the electrode-electrolyte interfaces including phase transformations of the precipitates during charge cycles in a Li-S system will be discussed. Lastly, I will briefly introduce our development of photon induced colloidal synthesis and advanced characterization of transition metal hydroxides as efficient electrocatalysts for oxygen evolution reaction (OER).