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Thesis advisor: Dunwei Wang / Due to the increasing energy demand from human activities, efficient utilization of renewable energy, such as wind, solar and geothermal energies, becomes necessary and urgent. Photoelectrochemical water splitting offers a great example to convert solar energy and storage it in the term of chemical bond. Seeking suitable photoanode materials becomes the research focus of my study, because the development of photoanode materials significantly lags that of robust photocathode (such as Si). The main challenge is to fabricate an efficient and stable photoanode material which can deliver high photocurrent and sufficient photovoltage which can match well with those of photocathode when made into tandem cell configuration. Hematite (α-Fe2O3) represents a promising metal oxide photoanode material, with a suitable band gap (2.1 eV), low cost and toxicity. Applying nanostructures and appropriate surface modification layers help address existing research challenges. As a result, a much lower turn on potential and greater photocurrent density is achieved. Another photoanode material attracts our attention is tantalum nitride (Ta3N5), with a similar band gap to hematite but much better light absorption properties, shows a poor stability in aqueous electrolyte. For both photoanode materials, thermodynamic and kinetic aspects are studied in details when tested in water splitting devices. These works provide new ideas and insights on the future studies. / Thesis (PhD) — Boston College, 2015. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Chemistry.

O trabalho apresentado nessa dissertação concentra-se na área de espectroscopia de íons lantanídeos com possível aplicação tecnológica e biotecnológica, e foi desenvolvido por meio da síntese hidrotermal e pirólise de aerossol de partículas inorgânicas, fosfato de lantânio dopadas com íons Pr3+ ou Pr3+/Gd3+ para estudos morfológicos e de conversão de energia. A busca por novos materiais inorgânicos dopados com íons lantanídeos é uma demanda constante. Devido às propriedades luminescentes intrínseca desses íons que são capazes de emitir fótons na faixa do UV-Vis-IV, além de participar de processos de conversão de energia via mecanismos de downconversion ou upconversion. A estabilidade física e química de matrizes inorgânicas também chama atenção. Desta forma, esses materiais podem ser aplicados em diferentes áreas, como, laser, display, fibras óticas, células solares, bioimagiamento, cintiladores, entre outros. Seria de grande interesse que um único material consiga englobar várias dessas aplicações. E foi nessa direção que esse trabalho se concentrou. Síntese de um material cuja capacidade luminescente, propriedades físicas e químicas possibilite sua aplicação em diversas áreas. Com a finalidade de estudar a variação morfológica dos materiais inorgânicos foram realizados dois métodos de síntese, no qual um via hidrotermal houve uma variação do pH do meio reacional e com ela uma variação da morfologia, de nanoagulhas para aglomerados. Para o método de pirólise de aerossol as partículas obtidas foram ocas e esféricas. A fase cristalina obtida para os materiais após o tratamento térmico a 1000°C foi a monoclínica sendo, confirmada por diversas técnicas de caracterização estrutural. Na caracterização espectroscópica, os materiais dopados com íons lantanídeos exibiram emissão ao longo de todo o espectro, do ultravioleta ao infravermelho. Emissões características dos níveis excitados 3PJ do íon Pr3+ foram observadas na região do visível e do infravermelho. Para o íon Gd3+ emissão proveniente do nível 6P7/2 foi observada na região do ultravioleta. Também foram caracterizadas emissões oriundas do nível 4f5d quando o material foi excitado no ultravioleta do vácuo e as energias do band gap da matriz bem como do nível 4f5d para o íon Pr3+. Nesse sentido a matriz LaPO4:Pr3+ ou Pr3+/Gd3+ obtida nesse trabalho apresenta-se apta para diferentes aplicações como luminóforos para UVC, visível ou infravermelho / The study presented in this dissertation focuses on the lanthanide ion spectroscopy area with possible technological and biotechnological application. The study was carried out through hydrothermal synthesis and spray pyrolysis of inorganic particles, lanthanium phosphate doped with Pr3+ or Pr3+ / Gd3+ ions for morphological and energy conversion studies. The search for new inorganic materials doped with lanthanide ions is a constant demand due to the intrinsic luminescent properties of these ions that are able to emit photons in the UV-Vis-IR range, besides participating in energy conversion processes via downconversion or upconversion mechanisms. The physical and chemical stability of inorganic matrices also drag significant attention. Therefore, these materials can be applied in different areas, such as, laser display, optical fibers, solar cells, bioimaging, scintillators and others. It would be of great interest that a single material could comprise several of such applications. This study focused on the synthesis of a material which luminescent, physical and chemical properties would make possible its application on several areas. In order to study the morphological variation of the inorganic materials two synthesis methods were performed, in which a hydrothermal path varying the pH of the reaction medium and morphology of nanofibrils to agglomerates. Hollow and spherical particles were obtained with the spray pyrolysis method. The crystalline phase obtained after the heat treatment at 1000 ° C was monoclinic, which was confirmed by several techniques of structural characterization. In the spectroscopic characterization, the doped materials with lanthanide ions have shown emission along the entire spectrum, from ultraviolet to infrared. Characteristic emissions of the 3PJ excited levels of the Pr3+ ion have been observed in the visible and infrared regions. On the other hand, the Gd3+ ion emission from the 6P7/2 level has been observed only the ultraviolet region. Emissions from level 4f5d were also characterized when the material was excited in vacuum ultraviolet and matrix band gap energies as well as level 4f5d for the Pr3+ ion. Therefore, the LaPO4: Pr3+ or Pr3+/Gd3+ matrices obtained in this study are suitable for different applications as UVC, visible or infrared luminophores

The replacement of internal combustion engines used for transportation by polymer electrolyte membrane fuel cells (PEMFCs) is one goal of the future since they are clean, quiet, energy efficient and capable of quick start-up. At present, fuel cells are receiving much attention at both fundamental research, and technology development levels, but cost is the main factor that hinders the commercialisation of PEMFCs. In order to reduce cost, a better, fundamental description of fuel cell operation than is presently available is required. The operation of PEMFCs simultaneously involves electrochemical reactions, current distribution, fluid mechanics, multicomponent multiphase mixtures, and heat transfer processes. It is important to have a comprehensive mathematical model to provide improved understanding of the interactions between various electrochemical and transport phenomena in PEMFCs in order to aid in the design and optimisation of fuel cells. This thesis describes research at developing such a comprehensive model.

Currently, electrical generation from solid carbon (biomass, coal) is conducted at low efficiency (~35 %) compared to other power sources. The Direct Carbon Fuel Cell (DCFC) is a technology capable of electro-oxidising elemental carbon for the production of electricity at a projected 80 % efficiency. This improvement has significant benefits for the reduction of greenhouse gas emissions. The research status of the DCFC technology is in early stages, with no practical continuous or stacked designs having been established. The sole concept for a continuous anode has been based on particulate carbons, these designs suffer from poor carbon polarisation and a lack of fuel versatility. This work focusses on the development of a continuous, monolithic anode for a direct carbon fuel cell. A monolithic anode has the benefit of acting both as fuel and current collector. This concept achieves improved fuel polarisation and also avoids the pumping of hot molten carbonate mixtures, and the corrosion issues associated with a separate metallic anode. In this regard, a parallel was drawn with the aluminium production industry in the Söderberg electrode. This technology allows for the continuous pyrolysis and extrusion of carbonaceous mixtures into solid carbon anodes. This project simulated the process of Söderberg electrodes through isostatic compression of pine sawdust in a novel, bespoke heated press, designed and built in-house. This apparatus also allowed for the live monitoring of resistance during heating. The formation factors of pyrolysis temperature, applied load and particle size were studied. The anodes formed in these processes were subjected to various characterisation methods and a practicality assessment made. The electrochemical properties of each anode were also assessed in a novel, bespoke DCFC apparatus, again designed and built in-house. It was found that the anodes formed were of a suitable BET surface area (300 – 450 m2 g-1), possessed high microporosity and were of a tensile strength comparable to industrial Söderberg electrodes. Electrochemical tests found the anodes to produce OCV values near the theoretical value for carbon electro-oxidation (1.01 V). A maximal power of 7.87 mW cm-2, at 0.58 V was achieved using an anode formed at 620°C, 12.3 N applied load and with a mixed particle size.

Fei, Fei. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2011. / Includes bibliographical references (leaves 102-106). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese.

The main purpose of this research is to design a thermal energy conversion device, which is aimed to collect unused heat produced by nature. In order to achieve high-efficiency conversion, some novel devices will be studied to convert heat energy into mechanical power. A simple heat exchanger as well as heat engine device is proposed in this study. Dichloromethane is used as an important factor due to its physical properties. Finally, the concept of a tubular linear generator will be adopted to generate electric power. The feature of the proposed simple thermal energy conversion device is that we can use unused heat sources as input, such as solar energy and waste heat from car engines. Besides, the system is capable to work under the condition of low-temperature difference