Spanos, Pol D.2017-08-012018-05-012017-052017-02-02May 2017Liu, Mingyang. "Role of Vacancies and Electrochemical Applications of Facet-Controlled Synthetic Superlattice Nanomaterials." (2017) Diss., Rice University. <a href="https://hdl.handle.net/1911/96052">https://hdl.handle.net/1911/96052</a>.https://hdl.handle.net/1911/96052The design and fabrication of functional materials is a critical issue in numereous studies. Hence, strategies for material fabrication are particularly important. This thesis focuses on the morphology and crystal-facet-controlled fabrication of catalytic materials which is one of the most appealing methods for enhancing the catalytic activity of target materials. In the related experiments, these materials were incorporated as counter electrodes (CE) of a dye-sensitive solar cell (DSSCs) system. Further, since vacancies change the electronic structures of materials, and greatly influence their physical and chemical properties, it is important that the identification and quantification of vacancies’ types be characterized. In this context, types and concentrations of vacancies were identified, and the correlation between types and concentration of vacancies and transient photocurrent properties were investigated. The first section of the thesis focuses on the synthesis of high performance noxious materials for CE of DSSCs. In the process, it was intially found that the zeta potential is one of the key factors for improving the power conversion efficiency (PCE). The synthesis of {211} faceted Bi2S3 microspheres that possess a negative zeta potential showed remarkable PCE with the assistance of graphene, which possess better catalytic performance than platinum as a CE. In the second part of the work, the correlation between types and concentration of vacancies and the photocurrent properties of noxious materials were investigated. The synthetic {211} faceted Bi2S3 microspheres and the synthesis of {131} faceted 3D SnS were made film devices through calcination at different temperatures, the extent of which was from 350 °C to 450 °C. Based on analysis of positron annihilation spectra, the {211} faceted Bi2S3 possess different types of vacancies or different vacancy concentrations of {131} faceted SnS are changed by increased the temperature. Further, a facile solvo-thermal route to synthesize {211} and {130} faceted Bi2S3 microspheres by nanorod or nanowire assembly grown on reduced graphene oxides was reported. The positron annihilation spectra revealed that {130} faced Bi2S3 microspheres possess sextuple vacancies which exceed triple vacancy with exposed {211} facets. The measurement results confirmed the experimental results of photo-responsive properties. All of the results were found to be consistent with theoretical calculation through density functional theory. In closure，the crystal-facet-controlled fabrication is a promising strategy for the synthesis of high performance nanomaterials. Further, it is believed that through investigation of the crystal structure and catalytic properties of target materials, and especially investigation of the correlation between types and concentration of vacancies and the photocurrent properties, the performance of these materials can be optimized.application/pdfengCopyright is held by the author, unless otherwise indicated. Permission to reuse, publish, or reproduce the work beyond the bounds of fair use or other exemptions to copyright law must be obtained from the copyright holder.Bi2S3 microspheresSnS microspheresBi2S3 microspheres grown on rGOdefects/vacanciespositron annihilation spectrometrytransient photocurrent.Thesis2017-08-01