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<p>Research on the unique properties of metal nanocrystals sparked the advent of powerful
nanomaterial-based technologies that improve the performance of catalysts, electronics,
and cancer therapies, to name a few. Due to their promise, extensive progress has
been made in tailoring the properties of metal nanocrystals by controlling their size,
shape, composition, and structure. However, these nano-scaled materials remain largely
within the confines of research laboratories. One of the biggest hindrances to the
widespread use of metal nanocrystals is cost. Precious metals such as Ag and Au exhibit
compelling properties in the nano scale, yet the astronomical cost of bulk materials
and low throughput of synthetic methods make them impractical for applications that
require more than a few milligrams of nanocrystals. This work addresses this issue
by furthering our knowledge of Cu nanocrystal synthesis and presenting synthetic methods
that lower the cost of its production.</p><p>Cu is significantly cheaper and more
abundant compared to other metals, and much like Au and Ag nanocrystals, Cu nanocrystals
exhibit conductive and catalytic properties. In this work, we present efforts to increase
the impact of Cu nanowires by first developing a multigram-scale synthesis of stable
Ag-coated Cu nanowires (Cu-Ag nanowires). The two-step process starts with the production
of 4.4 g of Cu nanowires in 1 h, followed by a Ag-coating procedure that yields 22
g of Ag-coated Cu nanowires (Cu-Ag nanowires) in 1 h. Due to the large diameters of
Cu nanowires (≈240 nm) produced by this synthesis, a Ag:Cu mol ratio of 0.04 is sufficient
to coat the nanowires with a protective, oxidation-resistant shell. This multigram
synthesis of Cu and Cu-Ag nanowire production process enabled the development of the
first nanowire-based conductive polymer composite for 3D printing with a resistivity
of 0.002 Ω cm, which is >100 times more conductive than commercially available graphene-based
3D printing filaments. Furthermore, a felt-like material consisting of Cu-Ag nanowires
was also used to create a stretchable conductor that has a conductivity of 1000 S/cm
and is stretchable up to 300%. Finally, Cu nanowires were annealed to create a porous
flow-through electrode (FTE). Compared to other commercially available FTEs, Cu nanowires
are significantly thinner, resulting in a 15x increase in surface area compared to
carbon paper. This translates to a 4.2x increase in the productivity of an electroorganic
intramolecular cyclization reaction. </p><p>We also developed a self-heating synthesis
of Cu nanowires, which produced shorter, thinner nanowires than was previously possible.
Self-heating is accomplished through NaOH dilution and glucose degradation, which
allows us to tune the length of the Cu nanowires in the range of 1.0 to 5.5 µm by
simply changing the concentration of glucose, and thereby the temperature of the reaction.
The self-heating aspect of this synthesis decreases the energy cost associated with
producing Cu nanowires, simplifies the reaction procedure, as well as increases its
scalability. </p><p>Finally, we employed single-crystal electrochemistry to elucidate
the growth mechanism of Cu nanoplates. Cu nanoplates have also been used in electronic
and catalytic applications, yet their growth is not as well-understood as Cu nanowires.
Thus, before they can be produced at quantities similar to that of Cu nanowires, we
need to understand how they grow. Single-crystal electrochemistry allows us to replicate
the crystal structure on the surfaces of Cu nanoplates using single crystal electrodes.
The current density (jmp) of Cu(111) and Cu(100) single crystal electrodes were measured
in the nanoplate growth solution, which showed that Cu reduction is 2.6x higher on
Cu(100) compared to Cu(111) in the presence of iodide ions (I-) in a solution containing
a CuCl2 precursor and hexadecylamine (HDA). Increasing the concentration of I- results
in a higher ratio jmp(100)/jmp(111), which alludes to the passivation of the {111}
basal surfaces of Cu nanoplates, resulting in lateral growth. This work clarifies
the role of halide ions on the growth of Cu nanoplates, giving us insight into how
size-control can be achieved. </p><p> As a whole, this work aims to increase the impact
of Cu nanocrystal-based innovations by increasing throughput, simplifying reaction
procedures, and achieving control over the size and dimensions of the synthesized
product.</p>
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