Discovery of Materials for Renewable Energy Applications
Open Access
- Author:
- Holder, Cameron
- Graduate Program:
- Chemistry
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- November 06, 2020
- Committee Members:
- Raymond Edward Schaak, Dissertation Advisor/Co-Advisor
Raymond Edward Schaak, Committee Chair/Co-Chair
Ayusman Sen, Committee Member
John B Asbury, Committee Member
Robert Rioux, Outside Member
Philip C Bevilacqua, Program Head/Chair - Keywords:
- Energy
Nanomaterials
Characterization
Electrocatalysis - Abstract:
- The continuous development of new technologies has required the discovery of new materials with specifically tailored properties. Since the function of a material will be in part dictated by its structure, it is imperative that selective synthetic methods and protocols for materials characterization be established to enable materials with the desired structures and properties. In particular, a promising class of materials due to their size-dependent properties and tunable syntheses are nanoparticles. Nanomaterials are of interest for a variety of different applications including but not limited to; catalysis, optoelectronics, and biomedicine. While significant progress has been made towards understanding how to rationally control the kinetics and thermodynamics of synthetic processes, it can still be challenging to consistently obtain high-quality materials with the desired phase and morphology. In this dissertation I highlight my efforts to discover, synthesize, and characterize materials that have applications towards renewable energy. I start by discussing two characterization techniques, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). XRD is commonly used to evaluate the crystalline components in a material while XPS provides information about the elemental composition and chemical states at a material’s surface. Key aspects that may be encountered when utilizing both techniques are highlighted for both bulk and nanomaterials. In regards towards XPS, several collaborations that I provided XPS data for are further discussed to highlight the diversity of information that the technique can provide. Next, I describe efforts to synthesize and evaluate cobalt sulfide nanoparticles for their catalytic activity towards the electroreduction of CO2 to value-added products. The polydisperse cobalt sulfide nanoparticles were synthesized through a colloidal approach and electrocatalytically tested on Ti foils. The observed gaseous and liquid products ranged from one-carbon to four-carbons, though all products had low Faradaic efficiencies. The cobalt sulfide particles were stable electrochemically for up to 24 hours at -0.49 V vs. RHE; however, it appeared that the particles were not structurally stable as the elemental composition post-testing indicated a severe loss of sulfur. Even though small amounts of products were generated, this result was important because it was the first report of a heterogeneous cobalt material that could promote C-C coupling towards C2-C4 products. Finally, I discuss efforts to selectively synthesize three unique phases of cesium cadmium chloride nanoparticles; CsCdCl3, Cs2CdCl4, and Cs3Cd2Cl7. These nanoparticles were all made through similar approaches, though slight synthetic variations included reaction temperatures, injection rates of the cesium oleate precursor, and the starting amounts of the cadmium salt. The observed selectivity was hypothesized to arise from these variables working together to modulate the local concentration of cesium and cadmium ions available to react to form nanoparticles. The bandgaps of the three synthesized phases were evaluated experimentally using diffuse reflectance UV-Vis spectroscopy as well as computationally through DFT modeling done in collaboration with Prof. Ismaila Dabo’s group. The large bandgaps (> 4.70 eV) that were predicted and observed places these phases into a category of materials known as ultra-wide bandgap semiconductors.