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<blockquote><div><div>Methods and techniques for tailoring the surface morphology of metallic surfaces are determined in part by the complex behavior of elemental interactions in conjunction with electrochemical reactions. In this work, we show how the surface morphology can be predicted based on experimental data resulting from polarization curves and compositional differences of Fe- and Ni-based superalloys. Electrochemical treatments utilizing NaCl as the electrolyte were adapted using parameters such as the pitting resistance equivalent (PRE) number and polarization curves to obtain both rough and smooth surfaces. Utilizing these metrics, we electrochemically etched Inconel 600, SS304, Inconel 718 and Inconel 625 obtaining average surface roughness values that ranged from 0.05 to 57.4 μm indicating the success of tailoring the technique to obtaining rough and smooth surfaces. The effect of current density, current pulsing, and temperature were varied to elucidate roughness and pitting behavior, and strong correlations to the PRE number and polarization curve properties of the alloy were observed. Heat treatments and subsequent evolution to the microstructure in the form of grain growth and precipitation altered the etching behavior. These techniques can be used in preventing corrosion failure and enhancing electrochemical machining</div></div></blockquote>

Hydrogen fuel cells are devices used to generate electricity from the electrochemical reaction between air and hydrogen gas. An attractive advantage of these devices is that their byproduct is water, which is very safe to the environment. However, hydrogen fuel cells still lack some improvements in terms of increasing their life time and electricity production, decreasing power losses, and optimizing their operating conditions. In this thesis, the cathode part of the hydrogen fuel cell will be considered. This part mainly consists of an air gas channel and a gas diffusion layer. To simulate the fluid dynamics taking place in the cathode, we present two models, a general model and a simple model both based on a set of conservation laws governing the fluid dynamics and chemical reactions. A numerical method to solve these models is presented and verified in terms of accuracy. We also show that both models give similar results and validate the simple model by recovering a polarization curve obtained experimentally. Next, a shape optimization problem is introduced to find an optimal design of the air gas channel. This problem is defined from the simple model and a cost functional, $E$, that measures efficiency factors. The objective of this functional is to maximize the electricity production, uniformize the reaction rate in the catalytic layer and minimize the pressure drop in the gas channel. The impact of the gas channel shape optimization is investigated with a series of test cases in long and short fuel cell geometries. In most instances, the optimal design improves efficiency in on- and off-design operating conditions by shifting the polarization curve vertically and to the right. The second primary goal of the thesis is to analyze mathematical issues related to the introduced shape optimization problem. This involves existence and uniqueness of the solution for the presented model and differentiability of the state variables with respect to the domain of the air channel. The optimization problem is solved using the gradient method, and hence the gradient of $E$ must be found. The gradient of $E$ is obtained by introducing an adjoint system of equations, which is coupled with the state problem, namely the simple model of the fuel cell. The existence and uniqueness of the solution for the adjoint system is shown, and the shape differentiability of the cost functional $E$ is proved.

Hydrogen fuel cells are devices used to generate electricity from the electrochemical reaction between air and hydrogen gas. An attractive advantage of these devices is that their byproduct is water, which is very safe to the environment. However, hydrogen fuel cells still lack some improvements in terms of increasing their life time and electricity production, decreasing power losses, and optimizing their operating conditions. In this thesis, the cathode part of the hydrogen fuel cell will be considered. This part mainly consists of an air gas channel and a gas diffusion layer. To simulate the fluid dynamics taking place in the cathode, we present two models, a general model and a simple model both based on a set of conservation laws governing the fluid dynamics and chemical reactions. A numerical method to solve these models is presented and verified in terms of accuracy. We also show that both models give similar results and validate the simple model by recovering a polarization curve obtained experimentally. Next, a shape optimization problem is introduced to find an optimal design of the air gas channel. This problem is defined from the simple model and a cost functional, $E$, that measures efficiency factors. The objective of this functional is to maximize the electricity production, uniformize the reaction rate in the catalytic layer and minimize the pressure drop in the gas channel. The impact of the gas channel shape optimization is investigated with a series of test cases in long and short fuel cell geometries. In most instances, the optimal design improves efficiency in on- and off-design operating conditions by shifting the polarization curve vertically and to the right. The second primary goal of the thesis is to analyze mathematical issues related to the introduced shape optimization problem. This involves existence and uniqueness of the solution for the presented model and differentiability of the state variables with respect to the domain of the air channel. The optimization problem is solved using the gradient method, and hence the gradient of $E$ must be found. The gradient of $E$ is obtained by introducing an adjoint system of equations, which is coupled with the state problem, namely the simple model of the fuel cell. The existence and uniqueness of the solution for the adjoint system is shown, and the shape differentiability of the cost functional $E$ is proved.

Hydrogen fuel cells are devices used to generate electricity from the electrochemical reaction between air and hydrogen gas. An attractive advantage of these devices is that their byproduct is water, which is very safe to the environment. However, hydrogen fuel cells still lack some improvements in terms of increasing their life time and electricity production, decreasing power losses, and optimizing their operating conditions. In this thesis, the cathode part of the hydrogen fuel cell will be considered. This part mainly consists of an air gas channel and a gas diffusion layer. To simulate the fluid dynamics taking place in the cathode, we present two models, a general model and a simple model both based on a set of conservation laws governing the fluid dynamics and chemical reactions. A numerical method to solve these models is presented and verified in terms of accuracy. We also show that both models give similar results and validate the simple model by recovering a polarization curve obtained experimentally. Next, a shape optimization problem is introduced to find an optimal design of the air gas channel. This problem is defined from the simple model and a cost functional, $E$, that measures efficiency factors. The objective of this functional is to maximize the electricity production, uniformize the reaction rate in the catalytic layer and minimize the pressure drop in the gas channel. The impact of the gas channel shape optimization is investigated with a series of test cases in long and short fuel cell geometries. In most instances, the optimal design improves efficiency in on- and off-design operating conditions by shifting the polarization curve vertically and to the right. The second primary goal of the thesis is to analyze mathematical issues related to the introduced shape optimization problem. This involves existence and uniqueness of the solution for the presented model and differentiability of the state variables with respect to the domain of the air channel. The optimization problem is solved using the gradient method, and hence the gradient of $E$ must be found. The gradient of $E$ is obtained by introducing an adjoint system of equations, which is coupled with the state problem, namely the simple model of the fuel cell. The existence and uniqueness of the solution for the adjoint system is shown, and the shape differentiability of the cost functional $E$ is proved.

Hydrogen fuel cells are devices used to generate electricity from the electrochemical reaction between air and hydrogen gas. An attractive advantage of these devices is that their byproduct is water, which is very safe to the environment. However, hydrogen fuel cells still lack some improvements in terms of increasing their life time and electricity production, decreasing power losses, and optimizing their operating conditions. In this thesis, the cathode part of the hydrogen fuel cell will be considered. This part mainly consists of an air gas channel and a gas diffusion layer. To simulate the fluid dynamics taking place in the cathode, we present two models, a general model and a simple model both based on a set of conservation laws governing the fluid dynamics and chemical reactions. A numerical method to solve these models is presented and verified in terms of accuracy. We also show that both models give similar results and validate the simple model by recovering a polarization curve obtained experimentally. Next, a shape optimization problem is introduced to find an optimal design of the air gas channel. This problem is defined from the simple model and a cost functional, $E$, that measures efficiency factors. The objective of this functional is to maximize the electricity production, uniformize the reaction rate in the catalytic layer and minimize the pressure drop in the gas channel. The impact of the gas channel shape optimization is investigated with a series of test cases in long and short fuel cell geometries. In most instances, the optimal design improves efficiency in on- and off-design operating conditions by shifting the polarization curve vertically and to the right. The second primary goal of the thesis is to analyze mathematical issues related to the introduced shape optimization problem. This involves existence and uniqueness of the solution for the presented model and differentiability of the state variables with respect to the domain of the air channel. The optimization problem is solved using the gradient method, and hence the gradient of $E$ must be found. The gradient of $E$ is obtained by introducing an adjoint system of equations, which is coupled with the state problem, namely the simple model of the fuel cell. The existence and uniqueness of the solution for the adjoint system is shown, and the shape differentiability of the cost functional $E$ is proved.

The deal of this thesis is study of the influence of LiOH added to electrolyte on Ni-Cd batteries. In theoretical part are analyzed properties of Ni-Cd accumulators in strong alkaline surroundings, especially with emphasis on structure changing of NiOH2 and NiOOH. In the second part of theoretical are also described methods for depositing Ni layers. In practical part electro-chemical spectrum and mass changing on Quartz crystal microbalance are measured by cyclic voltammetry method during charge/discharge process. The process of cation integration to the positive electrode structure in KOH, NaOH and CsOH electrolyte including related structural changes are observed.

The aim of the present project was to investigate the possibilities of using a Zr55Cu30Ni5Al10 Bulk Metallic Glass (BMG) alloy as articulating surface in an artificial hip joint. In order for a material to be used in human body as an implant, the foremost requirement is the acceptability by the human body. The implantations should not cause diseases or other complications for the patients. Moreover, the biomaterials should possess sufficient mechanical strength, high corrosion and wear resistance in harsh body environment with varying loading conditions. There have been extensive research on the properties of stainless steel, Co-Cr-Mo alloys and Ti alloys regarding their bio-compatibility and they are currently being used as orthopedic implants, however less information is available for bulk metallic glasses. So, understanding the corrosion properties of BMGs is one of the key issues to evaluate their potential as biomaterials. In the first phase of the project there was an attempt to develop a Zr-based BMG from pure elements in a vertical resistance furnace and quenching in liquid nitrogen. Afterwards, samples were examined by X-Ray diffraction and microscopically to investigate the presence of crystalline phases.  The second phase was electrochemical measurements to study the passivation behavior and the susceptibility to pitting corrosion for the crystalline Zr55Cu30Ni5Al10, amorphous Zr55Cu30Ni5Al10 BMG (received from Japan) and comparing the result with stainless steel and Co-Cr-Mo (F75). Investigations on corrosion properties were made in phosphate-buffered saline (PBS) with and without the addition of albumin fraction V, at a room temperature of 20 °C and body temperature (37°C) and in different pH values of 7.4 and 5.2. Running the experiment in lower pH shows the behavior of the implant against any probable inflation in the patient body. The last phase was to investigate the interaction between the protein and surface of materials. For this purpose, FTIR spectroscopy and Electrochemical Impedance Spectroscopy (EIS) were carried out.

Fuel cells are expected to play a major role in the economy of this century and for the foreseeable future. The use of hydrogen and fuel cells can address critical challenges in all energy sectors like commercial, residential, industrial, and transportation. Fuel cells are electrochemical devices that convert energy of a chemical reaction directly into electrical energy by combining hydrogen fuel with oxygen from air. If hydrogen is used as fuel, only byproducts are heat and water. The objective of this thesis is to investigate the effect of operating temperature and relative humidity (RH) of reactant gases on proton exchange membrane (PEM) fuel cell performance by adjusting the operation temperature of the fuel cell and humidification temperature of the reactant gases. In this study, the effect of the different operating parameters on the performance of single proton exchange membrane (PEM) fuel cell have been studied experimentally using pure hydrogen on the anode side and air on the cathode side. Experiments with different fuel cell operating temperatures, different air and hydrogen humidification temperatures have been carried out. The experimental results are presented in the form of polarization curves, which show the effects of the various operating parameters on the performance of the PEM fuel cell. The polarization curves data have been fit to a zero dimensional model, and the effect of the fuel cell operation and humidification temperatures on the kinetic parameters and the cell resistance have been determined. The fuel cell has been operated with 1.2 and 2 stoichiometry ratio for hydrogen and air, respectively. Fuel cell performance was detected at different fuel cell operation temperatures changing from 60 to 80 &ordm / C, and relative humidity of the entering gases changing from 20 to 100 % for air and 50 % and 100 % for hydrogen. Tests were performed in a PEM fuel cell test station. The highest performance of 275 mA/cm2 at 0.6 V and 650 mA/cm2 at 0.4 V was obtained for 50 % RH air with a constant 100 % relative humidity of hydrogen for working at atmospheric pressure and 60 oC fuel cell temperature. However, the highest performance of 230 mA/cm2 at 0.6 V for 50 % RH of air with a constant 100 % relative humidity of hydrogen and the highest performance of 530 mA/cm2 at 0.4 V for both 70 % RH and 100% RH air with a constant 100 % relative humidity of hydrogen was obtained for working at atmospheric pressure and 70 oC fuel cell temperature. Besides, the highest performance of 200 mA/cm2 at 0.6 V and 530 mA/cm2 at 0.4 V was obtained for 100 % RH air with a constant 100 % RH of hydrogen for working at atmospheric pressure and 80 oC fuel cell temperature.

Submitted by Johnny Rodrigues (johnnyrodrigues@ufcg.edu.br) on 2018-03-15T16:40:52Z No. of bitstreams: 1 ALDREANY PEREIRA DO NASCIMENTO - DISSERTAÇÃO PPGEQ 2016..pdf: 4384493 bytes, checksum: 8cf20c9f79749f12b562389c82ec5d3f (MD5) / Made available in DSpace on 2018-03-15T16:40:52Z (GMT). No. of bitstreams: 1 ALDREANY PEREIRA DO NASCIMENTO - DISSERTAÇÃO PPGEQ 2016..pdf: 4384493 bytes, checksum: 8cf20c9f79749f12b562389c82ec5d3f (MD5) Previous issue date: 2016-10-30 / Capes / A crise do petróleo juntamente com a grande necessidade de novas fontes de energias sustentáveis leva ao desenvolvimento de tecnologias mais limpas e eficientes. Neste contexto, as células a combustível aparecem como uma das soluções promissoras para a geração de energia elétrica, tendo como produto da reação, basicamente água e calor. Este trabalho de dissertação consiste na caracterização de uma célula a combustível PEM (Polymer Electrolyte Membrane) alimentada com hidrogênio e ar para a conversão de energia elétrica da energia química contida no gás hidrogênio. A célula a combustível utilizada é de potência nominal de 1 kW, constituída por 72 células ligadas em série com um sistema de controle próprio. A caracterização é feita através da utilização de uma carga resistiva configurável com base num microcontrolador. A partir dos parâmetros registrados (corrente e tensão), a curva de polarização, a densidade de corrente e a eficiência foram calculadas com base nos sistemas de curto circuito ligado e desligado (SCU: ON e SCU: OFF, respectivamente). Os resultados mostram uma potência máxima de saída de aproximadamente 623 W (37,09 V, 16,78 A), e uma densidade de corrente de 209,75 mA/cm2, com uma eficiência operacional em torno de 42 %, com o sistema de SCU: OFF. Para o sistema SCU: ON a potência máxima de saída é em torno de 664 W (39,10 V, 17,81 A) com densidade de corrente de 222,62 mA/cm2 e uma eficiência operacional de 44 %. O sistema de carga variável mostrou-se satisfatório para testar a célula, com um desvio entre a potência nominal e a real inferior a 20 %. Os relativamente baixos valores de eficiência do sistema (<20 %) são explicados pelo tempo de vida da célula. / The use of new sustainable energy sources is dependent on the development of clearer and more efficient technologies. Therefore, the fuel cells appear like a promising solution for the electrical energy generation, since that the reaction products are water and heat. This work plans to characterize a polymer electrolyte membrane fuel cell, feeding with hydrogen and air. The tested 1 kW nominal power fuel cell is constituted by 72 cells connected in serial. The characterization is made using a variable resistive charge system. It comprises 64 resistors (20 W) together with blowers for cooling. From the electrical parameters (voltage and current), the polarization curve, the current density and the efficiency of the fuel cell were calculated, with the short-circuit system on and off (SCU: ON and SCU: OFF). A maximum output power of 623 W (37.09 V and 16.78 A), with a current density of approx. 209.75 mA/cm2 and an efficiency around 42 % are obtained when the SCU is OFF. With the SCU: ON, the values are 664 W (39.10 V and 17.81 A), 222.62 mA/cm2 and 44 %, respectively. The results show that the resistive charge system is appropriate to test this kind of fuel cell. The low global efficiency values (< 20 %) can be explained by the fuel cell age.