Micro fuel cells miniaturization

For micro fuel cells, miniaturization of the fuel-cell system is a key issue. Research in this area includes developing passively operating fuel cells in order to reduce the peripheral spends and the parasitic energy losses and minimize the system complexity. Development must also focus on low-cost production materials such as silicon or thermoplastics, and fabrication techniques such as MEMS technology or injection molding. 

In addition to the design of the solid-gas contactor device, the yield of a desulfurization process directly depends on the physicochemical properties of the used adsorbent crystallite size of the active phase, specific surface area, and porous texture. In the case of a microporous membrane, if the gas flow is forced across the microporosity, it can be expected that the retention will be highly efficient. In return, the low amount of adsorbent restricts the potential applications to the elimination of traces in high-purity gas or to the design of integrated filters for miniaturized devices like micro fuel cells. 

Micro fuel cells are miniature electrochemical energy conversion devices that generate... 

In general, future micro fuel cell design should forego heavy bolts and thick BPs in order to miniaturize the system. The other components, such as the GDL and MEA, are negligible in volume and weight As a result, the material selection for the BPs becomes very important. Thin sheets that are stiff enough to achieve uniform low-contact resistance between MEA, flow field and current collector are needed. The bolts for the stack compression can be replaced by, for example, clamps, straps, or coiling techniques [9]. 

Miniaturization of fuel cells (FC) can offer a possibility in the field of small energy sources. Many silicon-based technologies can be used to perform micro-fuel cells and, in particular, porous silicon. In this chapter, after general consideration on fuel cells, we describe the state of the art of porous silicon integration in micro-fuel cells. In particular, we show how porous silicon has arisen as a promising material to perform many functions necessary to the core fuel cell such as proton exchange membrane, gas diffusion layer and catalyst support or flow fields. The performances of the several final devices reported in the literature are discussed. 

Portable electronic devices need very low power for their operation, often milliwatts, or at most a few watts up to 10 W. Small low-power fuel cells designed as power supplies for portable devices have been named micro-fuel cells or mini-fuel cells, the latter term being preferred. The term of a miniaturization of fuel cells is also current. The power needed for most electric vehicles and other mobile apphcations is about some tenth of a kilowatt. 

A micro fuel cell is a compact miniaturized fuel cell with sizes ranging from a few square millimeters to 1000 mm. They are used as a portable power source for cell phones, laptop computers, personal digital assistants, and other portable low-power electronic devices. The power densities of miniature FCs range from a few tens of microwatts per square centimeter up to several hundreds of milliwatts per square centimeter. Miniature fuel cells... 

Typically, micro fuel cells use methanol as fuel alfhough hydrogen-fed micro fuel cells have also been developed. The choice of the type of fuel cell to use in portable devices may be limited to low-temperature fuel cells such as PEMFC (proton exchange membrane fuel cell/polymer electrolyte membrane fuel cell) and DMFC. However, micro reformed methanol fuel cells and miniature SOFCs have also been developed. 

Since the electrochemical reaction, heat transfer etc. are surface phenomena significant improvements in power density and efficiency is expected to be achieved due to orders of magnitude increase in the surface to volume ratio in micro fuel cells. Correspondingly, however, new iimovations are required to offset miniaturization penalties such as high pressure drops in small channels and high electrical resistance through thin-film current collectors/conductors. 

No smart solution is available to store the gaseous hydrogen used in miniature fuel cell (PEMFC) and hence DMFC is receiving enormous interest due to system simplicity. However, specialised air-breathing DMFC components have to be developed. New materials have to be developed in addition to optimisation of structure and operating conditions to take care of performance decay modes. New membrane/electrode assemblies appropriate for the microscale to be developed exploiting the enhanced heat and mass transfer on the microscale for improved performance, and developing microfluidic components for micro fuel cells. 

The micro fuel cell technology is progressing at such an astonishing rate that its commercial breakthrough is only a matter of time. It is anticipated that miniature fuel cells will be power source of choice for a wide range of consumer/portable electronic produces in the near future. 

One of the technological ways to miniaturize fuel cells is to have recourse to standard microfabrication techniques mainly used in microelectronics and more especially the fabrication of micro- and nano-electro-mechanical systems (MEMS/NEMS). Actually more and more papers show the interest in developing MEMS-based fuel eells, either directly with silicon substrates (fig. 2), or adapting the methods to other substrates such as metals or polymers. These techniques enable notably mass fabrication at low cost (very large number of devices on a very small area) and then eould lead to the reduetion of the global cost of the miniature fuel cells. 

Miniaturization limits for single-chamber micro solid oxide fuel cells with coplanar electrodes. J. Power Sources, 194 (2), 941-949. 

Park, B Y. and Madou, M.). (2006) Design, fabrication, and initial testing of a miniature PEM fuel cell with micro-scale pyrolyzed carbon fluidic plates. J. Power Sources, 162 (1), 369-379. 

Min K, Tanaka S, Esashi M (2003) Silicon-based micro-poljnner electrolyte fuel cells. In IEEE intemational conference on micro electro mechanical systems, Kyoto Min K, Tanaka S, Esashi M (2006) Fabrication of novel MEMS-based polymer electrolyte fuel cell architectures with catalytic electrodes supported on porous Si02- J Micromech Microeng 16 505-511 Miu M, Danila M, Ignat T, Craciunoiu F, Kleps I, Simion M, Bragam A, Dinescu A (2009) Metallic-semiconductor nanosystem assembly for miniaturized fuel cell applications. Superlatt Microstmct 46 291-296... 

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