In situ electron microscopy of catalyst nanoparticles

In situ electron microscopy offers great opportunities for the study of catalyst nanoparticle systems. By using micro-electromechanical systems (MEMS)-based TEM specimen holders it is possible to record the atomic and/or electronic structures of materials, including the evolution of their size and shape, in real time during electrochemical reactions and growth processes at elevated temperature and/or in gas or liquid environments.

The Ernst Ruska-Centre has a wide variety of MEMS-based TEM specimen holders, including DENSsolutions single and double tilt heating and biasing holders, a combined heating and cooling holder and a combined gas reaction and heating holder. The DENSsolutions “Climate” in situ TEM gas and heating holder provides a high pressure (1 bar) gas environment at temperatures of up to 1000 K inside a nano-reactor, enabling atomic resolution characterization of solid-gas reactions in real time.

For example, thermal aging experiments on octahedral Pt-Ni catalyst nanoparticles were carried out in situ in the electron microscope. Originally, the slightly concave octahedral nanoparticles exhibited Pt-rich corners and Ni-rich {111} facets. It was shown that thermal annealing at up to 500 °C results in a surface diffusion of Pt atoms from the corners to the concave Ni-rich {111} facets, resulting in an atomically smooth facet with a Pt-rich surface that is favorable for the catalytic properties. The method of thermal annealing can thus contribute to the optimization and stabilization of the Pt-Ni nanoparticles under acidic ORR conditions.

For more details please refer to the papers:

L. Gan, M. Heggen, C. H. Cui, P. Strasser, Thermal Facet Healing of Concave Octahedral Pt–Ni Nanoparticles Imaged in Situ at the Atomic Scale: Implications for the Rational Synthesis of Durable High-Performance ORR Electrocatalysts, ACS Catalysis 6, 692–695 (2016)

Contact:

Dr. Marc Heggen
Phone: +49 2461 61-9479
E-Mail: m.heggen@fz-juelich.de