Abstract: Nanoparticle-based heterogeneous catalysis is intrinsically surface-confined, and thus it is advantageous to increase the surface area per mass of the nanocatalysts. The surface energy is also directly related to the activity of the nanocatalysts because the binding and detachment of the substrate, intermediates, and the final products require the optimal positioning of the nanoparticle surface energy. In order to enhance the activity, therefore, the design comcepts of nanocatalysts have evolved to encompass the core-shell nanoparticles with lattice mismatch between core and shell, which would dramatically increase the surface energy, well-defined polyhedral nanocrystals with high index crystal facets, alloy nanopartucles with optimal d-band position, and eventually alloy nanoframes. There are pros and cons of these nanoparticles because, in general, very high activity of nanocatalysts is not compatible with the stability of them during catalysis. For example, nanoframes have been developed to maximally profit from the large surface area. However, their catalytic performances might rapidly deteriorate due to the collapse of the nanoframe structure consisting of tenuous connected nanowires. Therefore, we have a daunting task of developing nanocatalyst systems exhibiting all the desired properties of 1) high surface area, 2) high structural robustness, and 3) fine-tuned surface energy.
In this seminar, I will describe our current efforts on development of ideally performing nanocatalysts for electrolytic water splitting and H2 fuel cells, which have received a great attention due to ever increasing environmental problems associated with fossil fuel usages. Specifically I will focus on the synthesis of multiphasic nanoparticles, which exhibit regio-specifically located multiple material phases within a very small nanoparticle domain and eventually evolve into nanoframe catalysts with high surface area, high structural robustness, and fine-tuned surface energy. The nanoscale alloying process and atom exchange process, which is of a paramount importance to the formation of nanoframes with desired structural features, will be described in detail.
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