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The modernized world is over-consuming low-cost energy sources that strongly contributes to pollution and environmental stress. As a consequence, the interest for environmentally friendly alternatives has increased immensely. One such alternative is the use of solar energy and water as a raw material to produce biohydrogen through the process of photosynthetic water splitting. In this work, the relation between H2-production and photosynthesis in the green algae Chlamydomonas reinhardtii was studied with respect to three main aspects: the establishment of prolonged H2-production, the involvement of PSII in H2-production and the electron pathways associated with PSII during H2-production. For the first time, this work reveals that PSII plays a crucial role throughout the H2-producing phase in sulfur deprived C. reinhardtii. It further reveals that a wave-like fluorescence decay kinetic, before only seen in cyanobacteria, is observable during the H2-producing phase in sulfur deprived C. reinhardtii, reflecting the presence of cyclic electron flows also in green algae.

The field of solar energy conversion has experienced resurgence in recent years due to mounting concerns related to fossil fuel consumption. The sheer quantity of available solar energy and corresponding opportunity for technological improvement has motivated extensive study of novel light-absorbing semiconductors for solar energy conversion. Often, these studies have focused on new ways of synthesizing and altering thin film semiconductor materials with unique compositions and morphologies in order to optimize them for higher conversion efficiencies. In this dissertation, we discuss the synthesis and electrochemical characterization of a variety of candidate semiconductor materials exhibiting promising characteristics for photoelectrochemical solar energy conversion. Three specific methods of thin film deposition are detailed. The first is a physical vapor deposition technique used to independently tune the morphology and composition of hematite (α-Fe2O3) based materials. Because of hematite’s poor electronic properties, these modifications were able to significantly improve its performance as a photoanode for water oxidation. The second technique is electrodeposition, which was employed to deposit the novel ternary metal oxide, CuBi2O4. The study of these films, along with those prepared by physical vapor deposition, provided insight into the factors limiting the ability of this photo-active material to function as a photocathode for hydrogen evolution from water. The third technique is chemical spray pyrolysis, which was employed to deposit and optimize films of the bismuth chalco-halides BiOI and BiSI. These studies were used to obtain previously unknown properties of these materials relevant to their utilization in photoelectrochemical cells. The manipulation of deposition temperature had significant effects on these properties and dictated the films’ overall photoconversion performance. / text

Resumo: Neste trabalho efetua-se análises técnica e econômica de um reformador a vapor de etanol para a produção de 0,7 Nm3/h de hidrogênio, capacidade esta suficiente para acionar uma célula de combustível do tipo PEMFC de 1 kW. A análise técnica abrange análises físico-química e termodinâmica (que envolve inclusive análise exergética), que consiste em fornecer as faixas de temperatura e pressão necessárias à reforma a vapor, e na determinação dos volumes de reagentes consumidos (neste caso, etanol e água). Foi possível obter informações sobre os principais produtos da reforma a vapor (hidrogênio e dióxido de carbono) e o grau de avanço da reação de reforma do etanol. As informações necessárias para o início da modelagem foram obtidas da literatura. A análise exergética permitiu avaliar as melhores condições (temperatura e pressão) para a reforma, baseando-se nos níveis de irreversibilidades. Finalmente, através da análise econômica, avaliou-se os custos de produção de hidrogênio em função do custo de investimento, operação e manutenção no reformador e acessórios. Foram selecionadas quatro fontes de calor para o processo (gás natural, gás liquefeito de petróleo, álcool e eletricidade). Conclui-se que a reforma a vapor de etanol é tecnicamente viável, podendo colocar o hidrogênio combustível no rol dos insumos energéticos alternativos e renováveis. Do ponto de vista econômico, o kWh de hidrogênio produzido por reforma de etanol apresenta o menor valor (numa faixa de 0,06471 a 0,10863 US$/kWh), devido ao alto custo de investimento e ao pequeno volume de produção de reformadores de etanol. Estes custos energéticos do hidrogênio poderão ser mais baixos, desde que haja uma maior produção em escala de reformadores de etanol. / Abstract: In this work the technical and economic analysis of a steam reformer of ethanol is made. The objective is the production of 0.7 Nm3/h of hydrogen to be used in a 1 kW powered PEMFC. The technical analysis consists in physical and chemical, and thermodynamic studies (including the exergetic analysis). These analysis provide informations as temperature and pressure ranges for steam reforming and the volume of the used reactants (in this case, ethanol and water). Through a mathematic modeling, it’s possible to get informations as the products of reforming (the hydrogen and carbon dioxide are the principal products) and the advance degree of the reaction. The useful informations for the modeling were got in the literature. Also about the technical analysis, an exergetic analysis was carried out, permitting obtain the best conditions (temperature and pressure) for the reforming based in the lowest irreversibilities level for the process. Finally, through the economic analysis, the costs of hydrogen production as a function of investment, operation and maintenance costs was made. Four heat sources for the process (natural gas, liquefied petroleum gas, ethanol and electricity) were considered for this analysis. This study has indicated that the steam reforming of ethanol is technically feasible, for the production of hydrogen as one of the alternative and renewable fuel. Economically, the hydrogen produced by steam reforming of ethanol presents the lowest cost, but expensive (at a range from 0,06471 to 0,10863 US$/kWh) because the high cost of investment and the small production of ethanol reformer. / Orientador: José Luz Silveira / Coorientador: Maria Isabel Sosa / Banca: Diovana Aparecida dos Santos Napoleão / Banca: Celso Eduardo Tuna / Mestre

Made available in DSpace on 2014-06-11T19:30:10Z (GMT). No. of bitstreams: 0 Previous issue date: 2005-02Bitstream added on 2014-06-13T19:39:27Z : No. of bitstreams: 1 souza_acc_me_guara.pdf: 1178727 bytes, checksum: 36f6a2063176d1106a7c533e016baa05 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Universidade Estadual Paulista (UNESP) / Neste trabalho efetua-se análises técnica e econômica de um reformador a vapor de etanol para a produção de 0,7 Nm3/h de hidrogênio, capacidade esta suficiente para acionar uma célula de combustível do tipo PEMFC de 1 kW. A análise técnica abrange análises físico-química e termodinâmica (que envolve inclusive análise exergética), que consiste em fornecer as faixas de temperatura e pressão necessárias à reforma a vapor, e na determinação dos volumes de reagentes consumidos (neste caso, etanol e água). Foi possível obter informações sobre os principais produtos da reforma a vapor (hidrogênio e dióxido de carbono) e o grau de avanço da reação de reforma do etanol. As informações necessárias para o início da modelagem foram obtidas da literatura. A análise exergética permitiu avaliar as melhores condições (temperatura e pressão) para a reforma, baseando-se nos níveis de irreversibilidades. Finalmente, através da análise econômica, avaliou-se os custos de produção de hidrogênio em função do custo de investimento, operação e manutenção no reformador e acessórios. Foram selecionadas quatro fontes de calor para o processo (gás natural, gás liquefeito de petróleo, álcool e eletricidade). Conclui-se que a reforma a vapor de etanol é tecnicamente viável, podendo colocar o hidrogênio combustível no rol dos insumos energéticos alternativos e renováveis. Do ponto de vista econômico, o kWh de hidrogênio produzido por reforma de etanol apresenta o menor valor (numa faixa de 0,06471 a 0,10863 US$/kWh), devido ao alto custo de investimento e ao pequeno volume de produção de reformadores de etanol. Estes custos energéticos do hidrogênio poderão ser mais baixos, desde que haja uma maior produção em escala de reformadores de etanol. / In this work the technical and economic analysis of a steam reformer of ethanol is made. The objective is the production of 0.7 Nm3/h of hydrogen to be used in a 1 kW powered PEMFC. The technical analysis consists in physical and chemical, and thermodynamic studies (including the exergetic analysis). These analysis provide informations as temperature and pressure ranges for steam reforming and the volume of the used reactants (in this case, ethanol and water). Through a mathematic modeling, it s possible to get informations as the products of reforming (the hydrogen and carbon dioxide are the principal products) and the advance degree of the reaction. The useful informations for the modeling were got in the literature. Also about the technical analysis, an exergetic analysis was carried out, permitting obtain the best conditions (temperature and pressure) for the reforming based in the lowest irreversibilities level for the process. Finally, through the economic analysis, the costs of hydrogen production as a function of investment, operation and maintenance costs was made. Four heat sources for the process (natural gas, liquefied petroleum gas, ethanol and electricity) were considered for this analysis. This study has indicated that the steam reforming of ethanol is technically feasible, for the production of hydrogen as one of the alternative and renewable fuel. Economically, the hydrogen produced by steam reforming of ethanol presents the lowest cost, but expensive (at a range from 0,06471 to 0,10863 US$/kWh) because the high cost of investment and the small production of ethanol reformer.

Due to the environmental problems caused by the steadily increasing usage of fossil fuels, the interest for renewable sources of energy has amplified significantly. Among the several possibilities, hydrogen gas is considered to be one of the most promising fuels forof the future. IfOnce formed from water via photocatalysis it is a desirable, convenient and green improvement in the field of energy. During this work, we have tried to contribute to this important field. 4wt.% Au/TiO2 synthesized by deposition-precipitation with urea was the main photocatalysts used in this project. Other noble metal-loaded (Pt and Ag) titanium dioxide materials were synthesized by deposition precipitation with urea and other methods such as sol gel and sol immobilization. These catalytic systems were studied and their activity compared for hydrogen production from water/methanol mixtures. Sets of monometallic Au, Ag, Pt and bimetallic Au-Pt and Au-Ag supported titanium dioxide were synthesized and tested. Au/TiO2 photocatalysts synthesized by deposition precipitation with urea was were the best in terms of hydrogen production compared to other photocatalysts. In the evaluation of possible sacrificial molecules, isopropanol was less efficient than methanol. Through the formation of bi-metallic Ag-Au/TiO2 and Pt-Au/TiO2 catalysts, the hydrogen production could be further improved. Finally, Ir supported Al2O3 was investigated for the first time as a heterogeneous catalyst for hydrogen production by photocatalytic dehydrogenation of aqueous p-formaldehyde and photoreduction of carbon dioxide.

The energy consumptions worldwide have increased simultaneously with the growth of the population and of the economy. Nowadays, finding an alternative way to satisfy the energy demand is one of the great challenges for the future of humanity, especially due to the limitation of fossil fuels and their effect on global warming. Hydrogen, as an alternative fuel for the future, is very attractive. Compared to traditional methods, such as the steam reforming of natural gas or coal gasification, photocatalytic water splitting (PWS) is considered to be the most sustainable alternative for producing hydrogen as a future fuel. PWS usually relies on semiconductor material that can transform the absorbed solar photon into photogenerated electrons and holes, creating a photopotential which can drive the electrochemical production of molecular hydrogen from the reduction of water. Despite its promising application, semiconductor-based PWS usually suffers from low carrier mobility and short diffusion length. Furthermore, the recombination of photogenerated electrons and holes might occur, especially if there are no suitable reaction sites available on the surface of the semiconductor. In order to facilitate the catalytic reactions on the surface of the semiconductor, the presence of a cocatalyst is necessary in order to obtain more efficient PWS processes. To this day, noble metals such as Pt, Pd, RuO2 and IrO2 are still the benchmark cocatalysts for PWS. Nevertheless, due to their high cost and limited supply, it is mandatory to develop a suitable strategy and to identify more efficient materials. Therefore, within the framework of this dissertation, novel cocatalysts and strategies that can improve the efficiency of the photocatalytic water splitting processes have been developed. Firstly, we developed a cocatalyst combining noble metals and semiconductors by means of partial galvanic replacement of the Cu2O nanocrystal with Au. The deposition of this cocatalyst on TiO2 was studied for the photocatalytic H2 production in order to explore the synergistic effect of the plasmonic resonance from the Au nanoparticles and pn-junction between Cu2O and TiO2. Additionally, the plasmonic effect of the Au films was also studied and utilized in order to improve the PWS. Secondly, the nanoscaling of cocatalysts was studied in order to improve the efficiency thereof and to reduce the cost of the cocatalyst materials. Moreover, it is sought to explore the quantum size effect on the properties of the cocatalyst and their effect on the photocatalytic reaction. Atomically precise Au and Ni nanoclusters were employed in these studies. Au nanoclusters were studied in relation to the cocatalysts in the photocatalytic water splitting, and Ni nanoclusters were studied in relation to the cocatalysts in the electrocatalytic water oxidation. The results of these studies will provide new insights in relation to the strategy used in order to develop efficient cocatalysts for the purpose of photocatalytic water splitting.

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