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Visualizing Core-Shell Formation by in situ Liquid Cell TEM

The three-stage growth of Pt3Ni-Ni(OH)2 core-shell structures at the gas-liquid interface was observed using in situ liquid cell transmission electron microscopy (TEM).

Recently, platinum-containing core-shell structures with tunable magnetic and catalytic properties have attracted attention due to the potential for a wide range of applications. To date, their synthetic routes are mostly based on galvanic replacement, co-reduction, thermal decomposition and seed-mediated methods.

However, the detailed formation mechanisms of core-shell structures in solution, especially at the gas-liquid interface, are still not completely clear, and most knowledge thus far is based on post-reaction studies or ex situ characterizations. Due to the lack of direct observation with high spatial resolution, some intermediate states may be easily missed. In this regard, it is worthwhile to directly visualize the complicated and delicate dynamic processes.

This year, a group of researchers from Xiamen University observed the three-stage growth of Pt3Ni-Ni(OH)2 core-shell structures at the gas-liquid interface using in situ liquid cell TEM. The stages consist of a thermodynamically driven Pt3Ni alloy core by the monomer attachment, an Ni shell formation due to the depletion of the Pt salt precursor, and the oxidation of the Ni shell into Ni(OH)2 flakes. They also reported the observation of nucleation and growth of the Ni(OH)2 flakes on an existing layer either at the middle part or at the step edge.

More interestingly, the dynamic transformation among the Pt3Ni alloy, Ni clusters and Ni(OH)2 flakes was also imaged even at a high electron dose rate. The scientists believe their findings provide an atomic insight on the rational design of metal-2D core-shell structures and could be also extended to investigate the growth and dynamic processes of other microstructure systems. The study was published in Science China Chemistry[APBN]

Source: Zhang, J. et al. (2020). Tracking the atomic pathways of Pt3Ni-Ni (OH) 2 core-shell structures at the gas-liquid interface by in-situ liquid cell TEM. Science China Chemistry63(4), 513-518.