Operating system optimization, fuel cell performance

The critical issues in designing a vehicular fuel cell power system are the selection of an optimal operating pressure, oxidant flow rate and the choice of an adequate control strategy. Computer models have been developed to simulate fuel cell performance under various operating conditions. 

Mathematical models predicting the performance of a fuel cell can assist system development. Seeking for the optimal operating conditions, these mathematical models can effectively substitute expensive experimental runs. Many questions of practical importance such as the excess air requirement and fuel flow rates can be answered using state of the art numerical models. Moreover, simple mathematical models such as a zero dimensional polarization models help to understand the influence of various electrochemical parameters on fuel cell performance [76,78,83]. 

No exemplary simulation results are presented here. Anyway, these would only be applicable for a certain MCFC system and under certain conditions, and they would not be representative for the broad range of available models. Nevertheless, MCFC models have been applied for various purposes Toshiba et al. [5] compared different flow configurations, Koh and Kang [10] predicted the impact of pressurized operation on fuel-cell performance, Park et al. [14] and Heidebrecht and Sundmacher [56] applied MCFC models to evaluate the effect of the reforming process on the fuel cell and to optimize it, and Bosio et al. [8] studied the application of nonuniform gas distributions with regard to the temperature distribution in MCFCs. 

Microfabrication processes have been used successfully to form micro-fuel cells on silicon wafers. Aspects of the design, materials, and forming of a micro-fabricated methanol fuel cell have been presented. The processes yielded reproducible, controlled structures that performed well for liquid feed, direct methanol/Oj saturated solution (1.4 mW cm ) and direct methanol/H O systems (8 mA cm" ). In addition to optimizing micro-fuel cell operating performance, there are many system-level issues to be considered when developing a complete micro power system. These issues include electro-deposition procedure, catalyst loading, channel depth, oxidants supply, and system integration. The micro-fabrication processes that have... 

In conclusion, all of these observations indicate that there is still much room to improve ADAFC performance by developing novel materials and, on the other hand, by optimizing the operational conditions of the fuel cell. Future work should look into a wider range of potential low-cost materials and composites with novel structures and properties, presenting catalytic activity comparable to that of noble metals. The development of new catalyst systems is more likely in alkaline media because of the wide range of options for the materials support and catalyst, as compared to acidic media which offer more limited materials choice. Moreover, efforts have to be addressed to meet the durability targets required for commercial application. More work is needed to optimize the operational fuel cell conditions, by achieving suitable chemical (OH concentration, hydroxyl/alcohol ratio in the fuel stream) and physical (temperature, pressure, flow rate) parameters. 

The main preparation methods for H2 technical electrodes for low temperature fuel cells have been examined. It has been demonstrated that the electrochemical behavior of the electrodes depends on their fabrication, thus affecting the fuel cell operation. The preparation of the catalyst of the active layer also influences its physical properties and electrochemical performance. Different electrochemical approaches to study HOR on model, as a first approximation, and technical electrodes, are exhaustively analyzed and their kinetic parameters are discussed to evaluate their performance and system modelling. The existence of a gap between the knowledge obtained from studies on model electrodes and technical electrodes is emphasized. To optimize the performance of practical fuel cell electrodes, the preparation of high surface area catalysts with the same characteristics as those shown at the atomic level then seems necessary. In this sense, mechanistic studies are fimdamental to... 

Fuel cell systems are composed of several components. Each component contains different parameters, which influence not only the performance of the particular component, but also the performance of the complete system. Fuel cell process engineering deals with the optimized design of fuel cell systems, including the optimized operation of each component in the system. This demands a characterization tool covering not only the influence of each individual parameter on the target values defined by the requirements of the special application, but also the influence caused by parameter interactions. One possible solution is to use the statistical approach discussed in the previous section. 

The purpose of this section is to describe the chemical and thermodynamic relations governing fuel cells and how operating conditions affect their performance. Understanding the impacts of variables such as temperature, pressure, and gas constituents on performance allows fuel cell developers to optimize their design of the modular units and it allows process engineers to maximize the performance of systems applications. 

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