Template-Assisted Electrodeposition of One-Dimensional Nanostructures for Sensing and Solar Energy Applications
Open Access
- Author:
- Hernandez-Pagan, Emil A
- Graduate Program:
- Chemistry
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- September 23, 2011
- Committee Members:
- Thomas E Mallouk, Dissertation Advisor/Co-Advisor
Thomas E Mallouk, Committee Chair/Co-Chair
Mark Maroncelli, Committee Member
Raymond Edward Schaak, Committee Member
Joan Marie Redwing, Committee Member - Keywords:
- Nanowires
electrodeposition
template - Abstract:
- One-dimensional nanowires and nanotubes offer unique properties that cannot be achieved with bulk materials. High surface area, strain relaxation, quantum confinement, and orthogonal light absorption and charge separation are examples. In this work, conducting polymer nanowires were synthesized by template-assisted electrodepositon. The dimensions of the nanowires could be easily controlled, and arrays or individual nanowires could be obtained. The conducting polymers synthesized were polypyrrole and poly(3,4-ethylendioxythiophene), as well as palladium-polymer and platinum-polymer composites. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) / energy-dispersive X-ray spectroscopy (EDS) were employed for structural characterization. Integration of the nanowires onto test structures was carried through electrofluidic assembly. Once assembled, the electrical properties of individual nanowires were investigated and studied for sensing of various gases. Template-assisted electrodeposition was also employed to synthesize cadmium selenide (CdSe) and copper indium diselenide (CuInSe2) nanowires. The crystal structure and crystallite domain size of the CdSe nanowires was controlled by either direct electrodeposition from an electrolyte that contained both elements or by topochemical cation exchange starting from crystalline t-Se nanowires. This was confirmed by TEM, X-ray Diffraction (XRD), and electron diffraction. CdSe nanowire photoanodes were used to study the effects of crystallite domain size on the photoelectrochemical properties. CuInSe2 nanowires were characterized by SEM, TEM/EDS, XRD, inductively coupled plasma mass spectrometry, Mott-Schottky analysis, and single wire electrical measurements. It was demonstrated that single phase p- and n-type CuInSe2 nanowires could be fabricated by this method. Since micro and nanowire arrays coupled to inexpensive catalysts are promising materials for unassisted-overall water splitting, the viability of membrane-based electrolytic cells was investigated. The challenge is to find conditions under which the cell can operate at solar flux (25 mA/cm2) and near neutral pH without significant series resistance. Potential losses were analyzed with anion exchanger membranes and different buffers. It was discovered that monoprotic buffers gave minimal transmembrane pH gradients because of fast permeation of the membrane by the neutral acid. With these membrane/buffer combinations, it should be possible to separate the products of photoelectrolysis with low series resistance over a broad range of operating pH.