Electrical Properties of Nanoscale Materials for Energy Conversion Applications

Abstract

Materials that show the greatest efficacy, stability and reactivity for energy conversion and storage often have hierarchical structures that range from microscale to nanoscale. There are a diverse number of ways of engineering nanomaterials but those that are from earth abundant materials or are processed from low cost methods are highly sought after. The first section of this thesis focuses on how structuring metal oxide materials can impact their electrochemical properties. Monolayer mesoscopic V2O5 sol gels were prepared using colloidal crystal lithography. The structuring was compared to a thin film material demonstrating the structured surface showed much higher electrochemical activity, as evidenced by the cyclic voltammetry (CV). The charging and discharging was performed at various rates, with the templated structure able to retain higher capacity at rates of 1C compared to the thin film. Over extended cycling the patterned surface was also much more resilient to structural alteration as a result of the open structure. Following from the V2O5 work sol gel MoO3/MoS2 structures were prepared on carbon fiber paper for use as an HER cathodic electrode. Two means of preparing MoS2 from MoO3 was assessed, one prepared by chemical vapor deposition and the other through hydrothermal sulfurization. Polarization curves, corrected for the iR drop, show very promising overpotentials of 172 mV. Calculations performed suggested that the interfacial chemistry of the MoO3/MoS2 is likely the largest contributor to the enhancement however patterning may further show potential with increased mass loading. In the second portion of the thesis self-assembled nanowires from porphyrin monomers were assembled through ionic assembly. The electrical properties of these wires were investigated using a modified scanning probe microscope. The current-voltage characteristics that were measured suggested that the vertical conductive pathway is thickness dependent and the LUMO state is altered as result of the thickness of the wire. As part of this work scanning thermoelectric voltage microcopy was reviewed and the important characteristics were considered. As a proof of concept a modified atomic force microscopy is used to measure the small voltages (from 1 µV-1000 mV) that were produced upon an applied thermal gradient. All noise sources were sufficiently suppressed to provide an appropriate circuit for performing a scanning measurement. A prototype board and power supply was board and power supply was designed to create an ambient pressure, low noise scanning thermoelectric voltage microscope.