Bacteria in nature predominantly grow as biofilms on living and non-living surfaces. The development of biofilms on non-living surfaces is significantly affected by the surface micro/nano topography. The main goal of this dissertation is to study the interaction between microorganisms and nanopatterned surfaces. In order to engineer the surface with well-defined and repeatable nanoscale structures, a new, versatile and scalable nanofabrication method, termed Spun-Wrapped Aligned Nanofiber lithography (SWAN lithography) was developed. This technique enables high throughput fabrication of micro/nano-scale structures on planar and highly non-planar 3D objects with lateral feature size ranging from sub-50 nm to a few microns, which is difficult to achieve by any other method at present. This nanolithography technique was then utilized to fabricate nanostructured electrode surfaces to investigate the role of surface nanostructure size (i.e. 115 nm and 300 nm high) in current production of microbial fuel cells (MFCs). Through comparing the S. oneidensis attachment density and current density (normalized by surface area), we demonstrated the effect of the surface feature size which is independent of the effect on the surface area. In order to better understand the mechanism of microorganism adhesion on nanostructured surfaces, we developed a biophysical model that calculates the total energy of adhered cells as a function of nanostructure size and spacing. Using this model, we predict the attachment density trend for Candida albicans on nanofiber-textured surfaces. The model can be applied at the population level to design surface nanostructures that reduce cell attachment on medical catheters. The biophysical model was also utilized to study the motion of a single Candida albicans yeast cell and to identify the optimal attachment location on nanofiber coated surfaces, thus leading to a better understanding of the cell-substrate interaction upon attachment. / Ph. D. / Formation of surface associated multicellular communities of microorganisms known as biofilms is of concern in medical settings as well as in industries such as oil refineries and marine engineering. It has been shown that micro/nanoscale surface features can highly regulate the process of biofilm formation and the attached cell activities. In this dissertation, we study the interaction between surface nanoscale structures and bacterial adhesion by experiments and biophysical modelling. We develop the Spun-Wrapped Aligned Nanofiber (SWAN) lithography, a versatile, scalable, and high throughput technique for masterless nanopatterning of hard materials. Using this technique, we demonstrate high fidelity whole surface single step nanopatterning of bulk and thin film surfaces of regularly and irregularly shaped 3D objects. SWAN lithography is used to texturize the electrode surface of microbial fuel cells (MFCs), which are envisioned as an alternative sustainable energy source. Compared to the non-patterned electrodes, the electrodes with 115 nm surface patterns facilitate larger biofilm coverage and 40% higher current production. We also develop a biophysical model to optimally texturize the surface of central venous and uretic medical catheters to prevent biofilm formation by fungal pathogen, Candida albicans. We show that the surface structures that result the highest cell total energy retained the least C. albicans. Furthermore, the adhesion behaviour of a single yeast cell is also experimentally studied in conjunction with the developed model.

In recent decades, the use of fossil fuels has increased exponentially with a corresponding sharp increase in the pollution of the environment. The need for clean and sustainable technologies for the generation of power with reduced or zero environment impact has become critical. A number of attempts have been made to address this problem; one of the most promising attempts is polygeneration. Polygeneration technology is highly efficient and produces lower emissions than conventional methods of power generation because of the simultaneous generation of useable heat and electrical power from a single source of fuel. The overall efficiency of such systems can be as high as 90%, compared to 30-35% for conventional single-product power plants. A number of different technologies are available for polygeneration, such as micro gas turbines, sterling engines, solar systems, and fuel cells. Of these, fuel cell systems offer the most promising technology for polygeneration because of their ability to produce electricity and heat at a high efficiency (about 80%) with either low or zero emissions. Various fuel-cell technologies can be used in polygeneration systems. Of these, solid oxide fuel cells (SOFCs) are the most suitable because they offer high system efficiency for the production of electricity and heat (about 90%) coupled with low or zero emissions. Compared to other types of fuel cells, SOFCs have fuel flexibility (direct operation on hydrocarbon fuels, such as biogas, bio-ethanol, bio-methanol, etc.) and produce high-quality heat energy. The development of polygeneration systems using SOFCs has generally followed one of two approaches. The first approach involves the design of a SOFC system that operates at a temperature of 850 oC and uses natural gas as a fuel. The second approach uses low-temperature (generally 400-600 oC) SOFC (LTSOFC) systems with biomass, e.g., syngas or liquid fuels, such as bio-methanol and bio-ethanol. The latter systems have strong potential for use in polygeneration. High-temperature SOFCs have obvious disadvantages, and challenges remain for lowering the cost to meet commercial interest. The SOFC systems need lower operating temperatures to reduce their overall costs. This thesis focuses on the development of nanocomposites for advanced fuel-cell technology (NANOCOFC), i.e., the next generation SOFCs, which are low-temperature (400-600 oC), marketable, and affordable SOFCs. In addition, new concepts that pertain to fuel-cell science and technology—NANOCOFC (www.nanocofc.com)—are explored and developed. The content of this thesis is divided into five parts: In the first part of this thesis (Papers 1-5), the two-phase nanocomposite electrolytes, viz. ceria-salt and ceria-oxide, were prepared and studied using different electrochemical techniques. The microstructure and morphology of the composite electrolytes were characterised using XRD, SEM and TEM, and the thermal analysis was conducted using DSC. An ionic conductivity of 0.1 S/cm was obtained at 300 ºC, which is comparable to that of conventional YSZ operating at 1000 ºC. The maximum output power density was 1000 mW/cm2 at 550 oC. A co-doped ceria-carbonate was also developed to improve the ionic conductivity, morphology, and performance of the electrolyte. In the second part of this thesis (Papers 7-9), composite electrodes that contained less or no nickel (Ni) were developed for a low-temperature SOFC. All of the elements were highly homogenously distributed in the composite electrode, which resulted in high catalytic activity and good ASOFC performance. The substitution of Ni by Zn in these electrodes could reduce their cost by a factor of approximately 25. In the third part of this thesis (Papers 10), an advanced multi-fuelled solid-oxide fuel cell (ASOFC) with functional nanocomposites (electrolytes and electrodes) was developed. Several different types of fuel, such as gaseous (hydrogen and biogas) and liquid fuels (bio-ethanol and bio-methanol), were tested. Maximum power densities of 1000, 300, 600, and 550 mW/cm2 were achieved with hydrogen, bio-gas, bio-methanol, and bio-ethanol, respectively, in the ASOFC. Electrical and total efficiencies of 54% and 80%, respectively, were achieved when the single cell was used with hydrogen. The fourth part of this thesis (Papers 11) concerns the design of a 5 kW ASOFC system based on the demonstrated advanced SOFC technology. A polygeneration system based on a low-temperature planar SOFC was then designed and simulated. The efficiency of the overall system was approximately 80%. The fifth part of this thesis (Paper 12) describes a single-layer multi-fuelled electrolyte-free fuel cell that is a revolutionary innovation in renewable-energy sources. Conventional fuel cells generate electricity by ion transport through the electrolyte. However, this new device works without an electrolyte, and all of the processes occur at particle surfaces in the material. Based on a theoretical calculation, an additional 18% enhancement of the fuel cell’s efficiency will be achieved using this new technology compared to the conventional technologies. Our developed ASOFC systems with functional nanocomposites offer significant advantages in reducing the operational and capital costs for the production of power and heat by using different fuels based on the fuel-cell technology. ASOFC systems can be used for polygeneration with renewable fuels (i.e., biomass fuels) at high efficiency as a sustainable solution to energy generation in our society. The results have been achieved for this thesis work has demonstrated an advanced fuel cell technology. / <p>QC 20111213</p>

O nitrato nas águas subterrâneas é considerado um dos principais problemas com relação aos padrões de potabilidade estabelecidos pela Portaria MS nº 2914/2011, o limite é de 10 mg NNO3-/L, tendo em vista que a ingestão de altas concentrações de nitrato está associada a doenças como câncer e a metahemoglobinemia. As preocupações com o nitrato devem-se as concentrações insidiosas e persistentes deste íon registradas pela CETESB desde o início do monitoramento das águas subterrâneas em 1990. O presente trabalho propôs a avaliação de um processo alternativo para remoção de nitrato, trata-se de um sistema bioeletroquímico, também conhecido como MFC (Microbial Fuel Cells), que utiliza microrganismos para desnitrificação. Esse tratamento consiste no uso de processos biológicos potencializados pelo processo de eletrólise, aproveitando desta forma, os principais pontos característicos de cada processo de maneira combinada. O sistema foi testado em escala de bancada, e consiste basicamente em uma câmara anódica onde ocorre a oxidação da matéria orgânica e uma câmara catódica onde ocorre o processo de redução do nitrato a N2. Entre as câmaras é utilizada uma membrana de troca iônica de forma a permitir somente a passagem de prótons da câmara anódica para a catódica, além de impedir a difusão de oxigênio para a câmara catódica. O experimento realizou 8 testes variando a taxa de aplicação total de 2,88 a 11,52 L/dia com uma concentração 15 mg N-NO3-/L. Nos últimos dois testes ainda foi aplicada uma tensão externa. O sistema atingiu uma eficiência média de remoção de nitrato de 80,84 ± 16,73 %. As concentrações finais de nitrato permaneceram dentro dos padrões de potabilidade, com valor médio de 1,88 ± 2,03 mg N-NO3-/L, obtendo-se uma taxa de desnitrificação de 0,0498 ± 0,03 kg/m³.dia. O acúmulo de nitrito no sistema teve valor médio de 0,36 ± 0,37 mg N-NO2-/L. / Nitrate in groundwater is considered to be one of the main problems with regard to the potability standards established by Ordinance MS nº 2914/2011, the limit is 10 mg N-NO3-/L, considering that the intake of high concentrations of nitrate Is associated with diseases such as cancer and methemoglobinemia. Concerns with nitrate are due to the insidious and persistent concentrations of this ion recorded by CETESB since the beginning of groundwater monitoring in 1990. The present work proposed the evaluation of an alternative process for nitrate removal. This is a bioelectrochemical system, also known as MFC (Microbial Fuel Cells), which uses microorganisms for denitrification. This treatment consists in the use of biological processes potentiated by the electrolysis process, thus taking advantage of the main characteristic points of each process in a combined manner. The system was tested on a bench scale, and basically consists of an anodic chamber where the oxidation of organic matter occurs and a cathodic chamber where the process of nitrate reduction to N2 occurs. Between the chambers an ion exchange membrane is used in order to allow only the passage of protons from the anode chamber to the cathodic, in addition to preventing the diffusion of oxygen to the cathodic chamber. The experiment performed 8 tests varying the total application rate from 2.88 to 11.52 L/d with a concentration of 15 mg N-NO3-/L. In the last two tests an external voltage was still applied. The system achieved an average nitrate removal efficiency of 80.84 ± 16.73%. The final concentrations of nitrate remained within the potability standards, with an average value of 1.88 ± 2.03 mg N-NO3-/L, obtaining a denitrification rate of 0.0498 ± 0.03 kg/m³.d. The accumulation of nitrite in the system had an average value of 0.36 ± 0.37 mg N-NO2-/L.

Os eletrocatalisadores Pt/C e Pt-Terras Raras/C (terras raras = La, Ce, Pr, Nd, Sm, Tb, Dy, Ho, Er, Tm, and Lu) foram preparados (20% em massa e razão atômica Pt-TR de 50:50) pelo método de redução por álcool, usando H2PtCl6.6H2O (Aldrich) e Terras Raras Cl3.xH2O (Aldrich) como fonte de metais, etileno glicol como solvente e agente redutor e, o carbono Vulcan XC72, como suporte. Os catalisadores foram caracterizados por espectroscopia de energia dispersiva de raios X (EDX), análises de difração de raios X (DRX) e microscopia de transmissão eletrônica (TEM). As análises por EDX mostraram que as razões atômicas dos diferentes eletrocatalisadores Pt-TR/C preparados foram similares às composições nominais de partida. Em todos os difratogramas, observa-se um pico largo em aproximadamente 2 = 25o o qual foi associado ao suporte de carbono Vulcan XC72 e quatro outros picos de difração em aproximadamente 2 = 40o, 47o, 67o e 82o os quais são associados aos planos (111), (200), (220) e (311), respectivamente, da estrutura cúbica de face centrada (CFC) de platina e suas ligas. Para os eletrocatalisadores Pt-TR/C também foram observadas fases nos difratogramas de raios X referentes aos óxidos de terras raras. Foram preparados eletrocatalisadores Pt-La/C com diferentes razões atômicas. Micrografias de transmissão eletrônica apresentaram uma razoável distribuição das partículas de Pt no suporte de carbono com algumas aglomerações, o que está de acordo com os resultados de difração de raios X. O desempenho para a oxidação de CO, metanol e etanol foi investigada através de voltametria cíclica, cronoamperometria e espectroscopia no infravermelho com transformada de Fourier. A atividade eletrocatalítica dos eletrocatalisadores Pt-TR/C, em especial PtLa/C, foram maiores que do Pt/C. A investigação por espectroscopia no infravermelho com transformada de Fourier para a oxidação de etanol com os eletrocatalisadores PtLa/C mostrou que o acetoaldeído e o ácido acético foram os principais produtos formados. O eletrocatalisador PtLa/C (30:70) apresentou melhores resultados para a reação de redução de oxigênio, oxidação de metanol e etanol, e a temperaturas superiores a 30°C para oxidação de monóxido de carbono. / PREPARATION AND CHARACTERIZATION OF PT-RARE EARTH/C ELECTROCATALYSTS FOR PEM FUEL CELLS

Os eletrocatalisadores Pt/C e Pt-Terras Raras/C (terras raras = La, Ce, Pr, Nd, Sm, Tb, Dy, Ho, Er, Tm, and Lu) foram preparados (20% em massa e razão atômica Pt-TR de 50:50) pelo método de redução por álcool, usando H2PtCl6.6H2O (Aldrich) e Terras Raras Cl3.xH2O (Aldrich) como fonte de metais, etileno glicol como solvente e agente redutor e, o carbono Vulcan XC72, como suporte. Os catalisadores foram caracterizados por espectroscopia de energia dispersiva de raios X (EDX), análises de difração de raios X (DRX) e microscopia de transmissão eletrônica (TEM). As análises por EDX mostraram que as razões atômicas dos diferentes eletrocatalisadores Pt-TR/C preparados foram similares às composições nominais de partida. Em todos os difratogramas, observa-se um pico largo em aproximadamente 2 = 25o o qual foi associado ao suporte de carbono Vulcan XC72 e quatro outros picos de difração em aproximadamente 2 = 40o, 47o, 67o e 82o os quais são associados aos planos (111), (200), (220) e (311), respectivamente, da estrutura cúbica de face centrada (CFC) de platina e suas ligas. Para os eletrocatalisadores Pt-TR/C também foram observadas fases nos difratogramas de raios X referentes aos óxidos de terras raras. Foram preparados eletrocatalisadores Pt-La/C com diferentes razões atômicas. Micrografias de transmissão eletrônica apresentaram uma razoável distribuição das partículas de Pt no suporte de carbono com algumas aglomerações, o que está de acordo com os resultados de difração de raios X. O desempenho para a oxidação de CO, metanol e etanol foi investigada através de voltametria cíclica, cronoamperometria e espectroscopia no infravermelho com transformada de Fourier. A atividade eletrocatalítica dos eletrocatalisadores Pt-TR/C, em especial PtLa/C, foram maiores que do Pt/C. A investigação por espectroscopia no infravermelho com transformada de Fourier para a oxidação de etanol com os eletrocatalisadores PtLa/C mostrou que o acetoaldeído e o ácido acético foram os principais produtos formados. O eletrocatalisador PtLa/C (30:70) apresentou melhores resultados para a reação de redução de oxigênio, oxidação de metanol e etanol, e a temperaturas superiores a 30°C para oxidação de monóxido de carbono. / PREPARATION AND CHARACTERIZATION OF PT-RARE EARTH/C ELECTROCATALYSTS FOR PEM FUEL CELLS

A new type of fuel cell that combines the advantages of a proton exchange membrane fuel cells and anion exchange membrane fuel cells operated with methanol is demonstrated. Two configurations: one with a high pH anode and low pH cathode (anode hybrid fuel cell (AHFC)),and another with a high pH cathode and a low pH anode (cathode hybrid fuel cell (CHFC)) have been studied in this work. The principle of operation of the hybrid fuel cells were explained. The two different hybrid cell configurations were used in order to study the effect of the electrode fabrication on fuel cell performance. Further, the ionomer content and properties such as the ion exchange capacity and molecular weight were optimized for the best performance. A comparison of the different ionomers with similar properties is carried out in order to obtain the best possible ionomer for the fuel cell. An initial voltage drop was observed at low current density in the AHFC, this was attributed to the alkaline anode and the effect of the ionomers with the new cationic groups were studied on this voltage drop was studied. These ionomers with the different cationic groups were studied in the CHFC design as well. Finally, the use of non platinum catalyst cathode with the CHFC design was also demonstrated for the first time.

Improvements have been made to the fuel cell power module (FCPM) within the SOFC cogeneration simulation code developed under the umbrella of the International Energy Agencies Annex 42 project. The main objective of the improved model developed here is to increase generality and applicability, and to decrease reliance on empirical data. A semi-mechanistic model has been developed to represent a nominal 5 kW tubular SOFC stack power module. This model has been implemented into the building simulation software ESP-r. Results illustrating the FCPM system performance as it relates to the output power required by the building as well as results from a number of different operating scenarios are presented in this study. Actual tests performed on a 5 kW SOFC unit were used to validate the model. The simulation results are found to correlate well with experimental observations. The improved model also allows for manipulation of operational parameters such as fuel utilization, excess air ratio and temperature as well as physical parameters such as cell dimensions and materials. Results from sensitivity and parametric simulations are also presented to demonstrate the enhanced capabilities of the model.

O nitrato nas águas subterrâneas é considerado um dos principais problemas com relação aos padrões de potabilidade estabelecidos pela Portaria MS nº 2914/2011, o limite é de 10 mg NNO3-/L, tendo em vista que a ingestão de altas concentrações de nitrato está associada a doenças como câncer e a metahemoglobinemia. As preocupações com o nitrato devem-se as concentrações insidiosas e persistentes deste íon registradas pela CETESB desde o início do monitoramento das águas subterrâneas em 1990. O presente trabalho propôs a avaliação de um processo alternativo para remoção de nitrato, trata-se de um sistema bioeletroquímico, também conhecido como MFC (Microbial Fuel Cells), que utiliza microrganismos para desnitrificação. Esse tratamento consiste no uso de processos biológicos potencializados pelo processo de eletrólise, aproveitando desta forma, os principais pontos característicos de cada processo de maneira combinada. O sistema foi testado em escala de bancada, e consiste basicamente em uma câmara anódica onde ocorre a oxidação da matéria orgânica e uma câmara catódica onde ocorre o processo de redução do nitrato a N2. Entre as câmaras é utilizada uma membrana de troca iônica de forma a permitir somente a passagem de prótons da câmara anódica para a catódica, além de impedir a difusão de oxigênio para a câmara catódica. O experimento realizou 8 testes variando a taxa de aplicação total de 2,88 a 11,52 L/dia com uma concentração 15 mg N-NO3-/L. Nos últimos dois testes ainda foi aplicada uma tensão externa. O sistema atingiu uma eficiência média de remoção de nitrato de 80,84 ± 16,73 %. As concentrações finais de nitrato permaneceram dentro dos padrões de potabilidade, com valor médio de 1,88 ± 2,03 mg N-NO3-/L, obtendo-se uma taxa de desnitrificação de 0,0498 ± 0,03 kg/m³.dia. O acúmulo de nitrito no sistema teve valor médio de 0,36 ± 0,37 mg N-NO2-/L. / Nitrate in groundwater is considered to be one of the main problems with regard to the potability standards established by Ordinance MS nº 2914/2011, the limit is 10 mg N-NO3-/L, considering that the intake of high concentrations of nitrate Is associated with diseases such as cancer and methemoglobinemia. Concerns with nitrate are due to the insidious and persistent concentrations of this ion recorded by CETESB since the beginning of groundwater monitoring in 1990. The present work proposed the evaluation of an alternative process for nitrate removal. This is a bioelectrochemical system, also known as MFC (Microbial Fuel Cells), which uses microorganisms for denitrification. This treatment consists in the use of biological processes potentiated by the electrolysis process, thus taking advantage of the main characteristic points of each process in a combined manner. The system was tested on a bench scale, and basically consists of an anodic chamber where the oxidation of organic matter occurs and a cathodic chamber where the process of nitrate reduction to N2 occurs. Between the chambers an ion exchange membrane is used in order to allow only the passage of protons from the anode chamber to the cathodic, in addition to preventing the diffusion of oxygen to the cathodic chamber. The experiment performed 8 tests varying the total application rate from 2.88 to 11.52 L/d with a concentration of 15 mg N-NO3-/L. In the last two tests an external voltage was still applied. The system achieved an average nitrate removal efficiency of 80.84 ± 16.73%. The final concentrations of nitrate remained within the potability standards, with an average value of 1.88 ± 2.03 mg N-NO3-/L, obtaining a denitrification rate of 0.0498 ± 0.03 kg/m³.d. The accumulation of nitrite in the system had an average value of 0.36 ± 0.37 mg N-NO2-/L.

The subject of this graduation thesis is low-cost alkaline power cells and especially electrodes with alternative catalyst made of MnOx + dopant. The thesis expands the bachelor´s thesis [1] and previous research [4] [12] [13] [14]. Volt-ampere characteristics and power characteristics of the katodes for AFC, subsidized with various dopants, are the outcome of this project. The project presents the optimalisation of preparation process of AFC electrodes. The aim is to prepair several electrodes with identical construction, which varies only with the type of the dopant.

No description available.