| dc.description.abstract |
<p>The realization of an energy future based on safe, clean, sustainable, and economically
viable technologies is one of the grand challenges facing modern society. Electrochemical
energy technologies underpin the potential success of this effort to divert energy
sources away from fossil fuels, whether one considers alternative energy conversion
strategies through photoelectrochemical (PEC) production of chemical fuels or fuel
cells run with sustainable hydrogen, or energy storage strategies, such as in batteries
and supercapacitors. This dissertation builds on recent advances in nanomaterials
design, synthesis, and characterization to develop novel electrodes that can electrochemically
convert and store energy.</p><p>Chapter 2 of this dissertation focuses on refining
the properties of TiO2-based PEC water-splitting photoanodes used for the direct electrochemical
conversion of solar energy into hydrogen fuel. The approach utilized atomic layer
deposition (ALD); a growth process uniquely suited for the conformal and uniform deposition
of thin films with angstrom-level thickness precision. ALD’s thickness control enabled
a better understanding of how the effects of nitrogen doping via NH3 annealing treatments,
used to reduce TiO2’s bandgap, can have a strong dependence on TiO2’s thickness and
crystalline quality. In addition, it was found that some of the negative effects on
the PEC performance typically associated with N-doped TiO2 could be mitigated if the
NH3-annealing was directly preceded by an air-annealing step, especially for ultrathin
(i.e., < 10 nm) TiO2 films. ALD was also used to conformally coat an ultraporous conductive
fluorine-doped tin oxide nanoparticle (nanoFTO) scaffold with an ultrathin layer of
TiO2. The integration of these ultrathin films and the oxide nanoparticles resulted
in a heteronanostructure design with excellent PEC water oxidation photocurrents (0.7
mA/cm2 at 0 V vs. Ag/AgCl) and charge transfer efficiency. </p><p>In Chapter 3, two
innovative nanoarchitectures were engineered in order to enhance the pseudocapacitive
energy storage of next generation supercapacitor electrodes. The morphology and quantity
of MnO2 electrodeposits was controlled by adjusting the density of graphene foliates
on a novel graphenated carbon nanotube (g-CNT) scaffold. This control enabled the
nanocomposite supercapacitor electrode to reach a capacitance of 640 F/g, under MnO2
specific mass loading conditions (2.3 mg/cm2) that are higher than previously reported.
In the second engineered nanoarchitecture, the electrochemical energy storage properties
of a transparent electrode based on a network of solution-processed Cu/Ni cores/shell
nanowires (NWs) were activated by electrochemically converting the Ni metal shell
into Ni(OH)2. Furthermore, an adjustment of the molar percentage of Ni plated onto
the Cu NWs was found to result in a tradeoff between capacitance, transmittance, and
stability of the resulting nickel hydroxide-based electrode. The nominal area capacitance
and power performance results obtained for this Cu/Ni(OH)2 transparent electrode demonstrates
that it has significant potential as a hybrid supercapacitor electrode for integration
into cutting edge flexible and transparent electronic devices.</p>
|
|
