Ultra-Small Metal Nanoparticles: Aerosol- and Laser-Assisted Nanomanufacturing, Characterization, and Applications

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Yang, Yong
Zachariah, Michael R.
Ultrasmall metal nanoparticles (1-10 nm) are certain to be the building blocks of the next generation of electronic, catalytic, and energy storage devices. Despite their importance, synthesizing these extremely small nanoparticles, at least in sufficient quantities to enable their industrial utility however, is challenging due to their low stability and tendency to agglomerate. Numerous techniques developed thus far typically generate metal nanoparticles in small quantities with a main difficulty in industrial scale-up being poor thermal control. This shortcoming often leads to wide size distributions, inhomogeneous dispersion, and aggregation. Thus, there is a pressing need for developing new strategies for scalable manufacturing of ultrasmall metal nanoparticles towards industrial applications. This dissertation identifies two techniques for scalable manufacturing of ultrasmall metal nanoparticles with tunable size, constituency, microstructure, and other properties: an aerosol droplet mediated approach and an ultrafast laser shock approach. The aerosol droplet mediated approach employs the fast heating and quenching nature of aerosol droplet nanoreactors containing precursor species to produce ultrasmall metal nanoparticles uniformly dispersed in polymer or graphene matrices. The fast heating and quenching nature intrinsic to the aerosol droplets is also employed to fabricate a new type of engineering material, notably high entropy alloy nanoparticles, defined as five or more well-mixed metal elements in near equimolar ratios. As an example of application, I further employ the aerosol droplets to create antimony nanoparticles incorporated carbon nanosphere network and the resulting architecture offered one of the best potassium ion battery anode performances in terms of both capacity and cycling stability. This dissertation also introduces an ultrafast laser shock technique to decorate metal nanoparticles onto carbon nanofibers (CNFs) in-situ with kinetically tunable size and surface density. A shorter laser shock enables the formation of metal nanoclusters with higher number densities and smaller sizes while longer laser shock leads to the further growth of metal nanoclusters and the achievement of their equilibrium shape. The catalytic performance towards electrocatalytic hydrogen evolution was greatly enhanced for CNF supported metal nanoclusters with a smaller size and higher number density.