THESIS
2020
xviii, 93 pages : illustrations ; 30 cm
Abstract
Bi-continuous nanoporous metals, with unique structural characteristics and properties like
high specific surface area and good electrical conductivity, have been applied in a wide range
of applications. The most typical method to fabricate nanoporous metals is dealloying, the
selective dissolution of one or more components from an alloy. The percolation dissolution
mechanism explains the morphology evolution during dealloying. However, the selection of
alloy systems and the preparation of uniform alloy precursors always limit the applications of
dealloying in preparing bi-continuous nanoporous metals.
In my dissertation, I discuss the percolation dissolution of compound precursors to prepare
bi-continuous nanoporous metals. The new method is called reduction-induced decompositi...[
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Bi-continuous nanoporous metals, with unique structural characteristics and properties like
high specific surface area and good electrical conductivity, have been applied in a wide range
of applications. The most typical method to fabricate nanoporous metals is dealloying, the
selective dissolution of one or more components from an alloy. The percolation dissolution
mechanism explains the morphology evolution during dealloying. However, the selection of
alloy systems and the preparation of uniform alloy precursors always limit the applications of
dealloying in preparing bi-continuous nanoporous metals.
In my dissertation, I discuss the percolation dissolution of compound precursors to prepare
bi-continuous nanoporous metals. The new method is called reduction-induced decomposition (RID). First, the RID of AgCl is chosen as an example to show bi-continuous nanoporous Ag
that resembles dealloyed structures can be prepared via RID. The RID also provides high
tunability in its length scales, porosity, and structural hierarchy. Then, based on the AgCl RID
system, we study the kinetics of RID by controlling the rate of reaction through the
concentration of the reductant, NaBH
4. At low concentrations, RID mostly occurs at a constant
and low reaction rate under surface diffusion control, whereas at high concentrations and
relatively high rates, bulk diffusion controls the reactions. At the early stages of the bulk
diffusion-controlled RID, oriented nanoporous Ag evolves at high reaction rates. We identify a
rate threshold and elaborate a model for the evolution of the oriented structure. The better understanding of RID kinetics and the formation mechanism of the oriented structure enables
us to apply RID in flow cells to prepare nanoporous metal electrodes with an interesting
oriented structure. The nanoporous metal electrodes prepared in flow cells have potential in a
variety of flow cell applications.
In the last chapter of the dissertation, we take the preparation of nanoporous Zn as an
example and show the advantage of RID in preparing reactive nanoporous metals. The as-fabricated
monolithic nanoporous Zn served as the Zn anode in a Ni-Zn cell and achieved good
performance.
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