Improvements in performance, reliability and durability as well as reductions in production costs, remain critical prerequisites for the commercialization of proton exchange membrane fuel cells. In this thesis, a computational framework for fuel cell analysis and optimization is presented as an innovative alternative to the time consuming trial-and-error process currently used for fuel cell design. The framework is based on a two-dimensional through-the-channel isothermal, isobaric and single phase membrane electrode assembly (MEA) model. The model input parameters are the manufacturing parameters used to build the MEA: platinum loading, platinum to carbon ratio, electrolyte content and gas diffusion layer porosity. The governing equations of the fuel cell model are solved using Netwon's algorithm and an adaptive finite element method in order to achieve quadratic convergence and a mesh independent solution respectively. The analysis module is used to solve two optimization problems: i) maximize performance; and, ii) maximize performance while minimizing the production cost of the MEA. To solve these problems a gradient-based optimization algorithm is used in conjunction with analytical sensitivities. The presented computational framework is the first attempt in the literature to combine highly efficient analysis and optimization methods to perform optimization in order to tackle large-scale problems. The framework presented is capable of solving a complete MEA optimization problem with state-of-the-art electrode models in approximately 30 minutes. The optimization results show that it is possible to achieve Pt-specific power density for the optimized MEAs of 0.422 $g_{Pt}/kW$. This value is extremely close to the target of 0.4 $g_{Pt}/kW$ for large-scale implementation and demonstrate the potential of using numerical optimization for fuel cell design.

Improvements in performance, reliability and durability as well as reductions in production costs, remain critical prerequisites for the commercialization of proton exchange membrane fuel cells. In this thesis, a computational framework for fuel cell analysis and optimization is presented as an innovative alternative to the time consuming trial-and-error process currently used for fuel cell design. The framework is based on a two-dimensional through-the-channel isothermal, isobaric and single phase membrane electrode assembly (MEA) model. The model input parameters are the manufacturing parameters used to build the MEA: platinum loading, platinum to carbon ratio, electrolyte content and gas diffusion layer porosity. The governing equations of the fuel cell model are solved using Netwon's algorithm and an adaptive finite element method in order to achieve quadratic convergence and a mesh independent solution respectively. The analysis module is used to solve two optimization problems: i) maximize performance; and, ii) maximize performance while minimizing the production cost of the MEA. To solve these problems a gradient-based optimization algorithm is used in conjunction with analytical sensitivities. The presented computational framework is the first attempt in the literature to combine highly efficient analysis and optimization methods to perform optimization in order to tackle large-scale problems. The framework presented is capable of solving a complete MEA optimization problem with state-of-the-art electrode models in approximately 30 minutes. The optimization results show that it is possible to achieve Pt-specific power density for the optimized MEAs of 0.422 $g_{Pt}/kW$. This value is extremely close to the target of 0.4 $g_{Pt}/kW$ for large-scale implementation and demonstrate the potential of using numerical optimization for fuel cell design.

A presente pesquisa foi desenvolvida para avaliar as potencialidades das células de combustível como tecnologia em si, inclusive os beneficios econômicos que se podem ter por meio do suprimento de energia elétrica se comparada com o aproveitamento da mesma por meio da rede pública. Além de uma parte descritiva do estado de arte da tecnologia, a presente dissertação foi focada em duas partes: a primeira trata de um estudo experimental onde uma célula, a membrana polimérica, foi conectada a um inversor, permitindo assim de fornecer energia elétrica na rede pública. Na segunda parte foi realizada uma avaliação engenhero-econômica com uma Célula de Combustível de Ácido Fosfórico para o aproveitamento da energia elétrica com cogeração de calor para as condições de mercado brasileiro. O primeiro estudo mostrou como seja possível abastecer uma célula (neste caso alimentada por hidrogênio) para fornecer continuamente energia elétrica na rede, onde necessário ou onde seja impossível para o usuário se conectar a rede pública. O segundo estudo, por sua vez, mostrou que atualmente a células de combustível de média temperatura de Ácido Fosfórico (PAFC) não é uma tecnologia ainda madura e que é viável economicamente somente em aplicações de nicho, por exemplo setores indústriais eletro-intensivos e com necessidade de energia termica também. Todavia, projeções futuras baseadas em curvas de aprendizados e a queda do preço do gás natural mostram como a expansão da tecnologia e a possibilidade de acessar um combustível barato podem abrir futuro para a PAFC mundialmente. / This Masters dissertation aims to study technical potentialities of Fuel Cell technology, including the economical benefits that can provide compared with public grid as well. Thus, the dissertation has been focused in two main parts: the first concerns in an experimental approach to supply electrical power to the public grid using a Polymer Electrolyte Membrane Fuel Cell (PEMFC), while the second one presents a global (from an engineering and economic point-of-view) assessment of a Phosphoric Acid Fuel Cell (PAFC) for the co-generation of heat with electrical energy in Brazil. The first study has been accomplished connecting a PEMFC with a power inverter to the public grid. It has been proved experimentally that Fuel Cell is an alternative device that, as long as fuel is fed, may provide electrical energy continuously and more efficiently than traditional devices. The second study has been focused in the so-called Phosphoric Acid Fuel Cell (PAFC) that, being a Medium Temperature Fuel Cell, beyond to supply electrical energy, may be used for co-generation of thermal energy. Through this study it has been showed that, at the current state-of-art, PAFC is is not already a mature technology and it becomes economically viable only for niche market applications, represented by the industrial sectors with high base load power and continuous thermal energy demand. However, accumulated knowledge expressed by learning curve and natural gas shock price caused by possible LNG supplying and shale gas recovery are the two main factors that may turn investment in PAFC profitable worldwide.

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Over the past three decades, the steady decrease in fossil energy resources, combined with a sustained increase in the demand for clean energy, has led the scientific community to develop new ways to produce energy. As is well known, one of the main challenges to overcome with fossil fuel-based energy sources is the reduction or even elimination of pollutant gases in the atmosphere. Although some advances have helped to slow the emission of greenhouse gases into the atmosphere (e.g., electric cars and more fuel-efficient gas-burning automobiles), most experts agree that it is not enough. Proton Exchange Membrane (PEM) fuel cells have been widely recognized as a potentially viable alternative for portable and stationary power generation, as well as for transportation. However, the widespread commercialization Proton Exchange Membrane Fuel Cells (PEMFCs) involves a thorough understanding of complex scientific and technological issues. This study investigated the various structure-property relationships and materials durability parameters associated with PEMFC development. First, the correlation between perfluorinated ionomer membranes and processing/performance issues in fuel cell systems was investigated. As confirmed by small-angle X-ray scattering data, impedance analysis, and dynamic mechanical analysis, solution processing with mixed organic-inorganic counterions was found to be effective in producing highly arranged perfluorinated sulfonic acid ionomer (PFSI) membranes with more favorable organization of the ionic domain. Moreover, thermal annealing was shown to enhance the proton mobility, thereby facilitating reorganization of the polymer backbone and the hydrophilic region for improved crystallinity and proton transport properties. This research also confirmed an increase in water uptake in the solution-processed membranes under investigation, which correlated to an increase in proton conductivity. Thus, annealing and solution-processing techniques were shown to be viable ways for controlling morphology and modulating the properties/performance of PFSI membranes. Second, this study investigated the role of the morphology on water and proton transport in perfluorinated ionomers. When annealed at high temperatures, a significant decrease in water uptake and an increase in crystallinity were observed, both of which are detrimental to fuel cell performance. Additionally, controlling the drying process was found to be crucial for optimizing the properties and performance of these membranes, since drying at temperatures close or above the α-relaxation temperature causes a major reorganization within the ionic domains. Third, although many investigations have looked at key PEMFC components, (e.g., the membrane, the catalyst, and the bipolar plates), there have been few studies of more "minor" components—namely, the performance and durability of seals, sealants, and adhesives, which are also exposed to harsh environmental conditions. When seals degrade or fail, reactant gases leak or are mixed, it can degrade the membrane electrode assembly (MEA), leading to a performance decrease in fuel cell stack performance. This portion of the research used degradation studies of certain proprietary elastomeric materials used as seals to investigate their overall stability and performance in fuel cell environments with applied mechanical stresses. Additionally, characterization of the mechanical and viscoelastic properties of these materials was conducted in order to predict the durability based on accelerated aging simulations as well. Continuous stress relaxation (CSR) characterization was performed on molded seals over a wide range of aging conditions using a customized CSR fixture. The effects of temperature, stress, and environmental conditions are reported in terms of changes in momentary and stress relaxations, chain scission and secondary crosslink formation. Aging studies provided insights on how anti-degradants or additives affect the performance and properties of sealing materials, as well as how a variety of environmental considerations might be improved to extend the lifetime of these elastomers. / Ph. D.

Master of Science / Department of Architectural Engineering and Construction Science / Fred Hasler / Data center space and power densities are increasing as today’s society becomes more dependent on computer systems for processing and storing data. Most existing data centers were designed with a power density between 40 and 70 watts per square foot (W/SF), while new facilities require up to 200W/SF. Because increased power loads, and consequently cooling loads, are unable to be met in existing facilities, new data centers need to be built. Building new data centers gives owners the opportunity to explore more energy efficient options in order to reduce costs. Fuel cells are such an option, opposed to the typical electric grid connection with UPS and generator for backup power. Fuel cells are able to supply primary power with backup power provided by generators and/or the electric grid. Secondary power could also be supplied to servers from rack mounted fuel cells. Another application that can benefit from fuel cells is the HVAC system. Steam or high-temperature water generated from the fuel cell can serve absorption chillers for a combined heat and power (CHP) system. Using the waste heat for a CHP system, the efficiency of a fuel cell system can reach up to 90%. Supplying power alone, a fuel cell is between 35 and 60% efficient. Data centers are an ideal candidate for a CHP application since they have constant power and cooling loads. Fuel cells are a relatively new technology to be applied to commercial buildings. They offer a number of advantages, such as low emissions, quiet operation, and high reliability. The drawbacks of a fuel cell system include high initial cost, limited lifetime of the fuel cell stacks, and a relatively unknown failure mode. Advances in engineering and materials used, as well as higher production levels, need to occur for prices to decrease. However, there are several incentive programs that can decrease the initial investment. With a prediction that nearly 75% of all 10 year old data centers will need to be replaced, it is recommended that electrical and HVAC designer engineers become knowledgeable about fuel cells and how they can be applied to these high demand facilities.

A nickel alloy with high chrome and molybdenum content was found to form a highly resistive and passive oxide layer. The donor density and mobility of ions in the oxide layer has been determined as a function of the electrical potential when alkaline water layers are on the alloy surface in order to account for the relative inertness of the nickel alloy in corrosive environments.

Water management is a serious issue that affects the performance and durability of PEM fuel cells. It is known, from previous experimental investigations, that surface wettability has influence on water behaviour and fuel cell performance. This finding has lead researchers to develop numerical tools for further investigation of the liquid water behaviour in gas channels. The Volume-of-Fluid (VOF) method has been used in a wide range of studies for its advantage of showing the multi-phase interface in a Computational Fluid Dynamics (CFD) simulation to understand liquid water behaviour in gas channels. In this thesis, numerical study has been carried out to examine the behaviour of liquid water in gas channels. The dynamic movement of the liquid water in the channel and the associated pressure drop, water saturation and water coverage of the GDL have been investigated. Firstly, flow diffusion into the GDL was examined to determine its effect on liquid droplet behaviour in a small section of a gas channel. Furthermore, the effects of the percentage of flow diffusion, GDL wettability, pore size, and water inlet velocity were investigated. Fluid diffusion into GDL found to have insignificant impact on liquid water behaviour so further investigations has been carried with a solid GDL surface. Secondly, gas channel geometry effect on liquid water behaviour was studied. Square, semicircle, triangle, trapezoid with a long base and trapezoid with a short base were compared to find suitable cross section geometry to carry wall wettability investigations. Among the examined geometries, the square cross section showed reasonable results for both scenarios of geometry design, fixed Reynolds number and fixed GDL interface. The effect of wall wettability was assessed by comparing nine different wall/GDL wettability combinations for straight and bend channels. Wall wettability found to have an impact on liquid water behaviour but not as much as GDL wettability. It affects liquid water saturation in the channel by a great deal by accumulating water in the channel edges affecting water behaviour. This was also proven in the last test case of a long channel where water accumulation was investigated by running the calculation until the percentage of water saturation is stabilized. It is also concluded that changing wall wettability from hydrophobic to hydrophilic doubles the percentage of channel occupied by liquid water and increases the time to reach steady state.

A novel electrochemical method to generate nm-scale bubbles at the tips of CNTs can temporarily block the membrane. A 92% blocking efficiency is achieved when the bubbles are stabilized in 30-60 nm diameter „wells‟ at the tips of CNTs. This well is formed by the electrochemical oxidation of the conductive CNTs partially into the polymer matrix of the membrane. Meanwhile, the nanoscale bubbles can be removed with 0.004 atm pressure to recover the transport through the CNT membrane. The CNT membrane with nanoscale bubble valve system was used to demonstrate electrochemical energy storage. Uniform ultrathin Pt films were electrodeposited onto an aligned array of carbon nanotubes (CNTs) for high-area chemically stable methanol fuel cell anodes. Electrochemical treatment of the graphitic CNT surfaces by diazonium benzoic acid allowed for uniform Pt electroplating. The mass activity of the Pt thin film can reach 400 A/g at a scan rate of 20 mV/s and in a solution of 1 M CH3OH/0.5 M H2SO4. A novel programmed pulse potential at 0 V was also seen to nearly eliminate the effects of carbon monoxide poisoning on catalyst Pt. Furthermore, the Pt monolayer was deposited on buckypaper by replacing the precursor Cu monolayer coated on CNTs by the underpotential deposition. The electrochemical surface modification of graphite CNTs by fluorinated benzoic acid was critical to coordinate Cu ions for monolayer formation. The mass activity of the monolayer can be improved to the record value of 2711 A/g. This is about 13 times higher than that of the ~10 nm thick Pt film coated on MWCNTs. Besides the high mass activity, the Pt monolayer coated on buckypaper can be used as catalyst for fuel cells with several advantages such as low cost, high surface area, flexibility, mechanical robustness and enhanced pressure flow. Finally, a new strategy has been developed toward electrochemical water oxidation with Ir complexes catalyst, which was grafted on buckypaper by direct binding to enhance catalyst activity. The TOF (turn over frequency) of the Ir catalyst for water splitting was 7.9 s-1 at the constant potential of 1.4 V vs Ag/AgCl.