Fuel cell micro

ISPP imits are not the only micro device imits of interest for space applications micro fuel cells, compact cleanup units for water treatment, portable heating and cooling units and devices for chemical processing and mining are considered [91]. 

Such bimetallic alloys display higher tolerance to the presence of methanol, as shown in Fig. 11.12, where Pt-Cr/C is compared with Pt/C. However, an increase in alcohol concentration leads to a decrease in the tolerance of the catalyst [Koffi et al., 2005 Coutanceau et ah, 2006]. Low power densities are currently obtained in DMFCs working at low temperature [Hogarth and Ralph, 2002] because it is difficult to activate the oxidation reaction of the alcohol and the reduction reaction of molecular oxygen at room temperature. To counterbalance the loss of performance of the cell due to low reaction rates, the membrane thickness can be reduced in order to increase its conductance [Shen et al., 2004]. As a result, methanol crossover is strongly increased. This could be detrimental to the fuel cell s electrical performance, as methanol acts as a poison for conventional Pt-based catalysts present in fuel cell cathodes, especially in the case of mini or micro fuel cell applications, where high methanol concentrations are required (5-10 M). 

Yamazaki Y. 2004. Application of MEMS technology to micro fuel cells. Electrochim Acta 50 663 -666. 

The hnding of very substantial amounts of incomplete oxidation products for methanol and formaldehyde oxidation can have considerable consequences for technical applications, such as in DMFCs. In that case, the release of formaldehyde at the fuel cell exhaust has to be avoided not only from efficiency and energetic reasons, but in particular because of the toxicity of formaldehyde. While in standard DMFC applications the catalyst loading is sufficiently high that this is not a problem, i.e., only CO2 is detected [Arico et al., 1998], the trend to reducing the catalyst loading or applications in micro fuel cells may lead to situations where the formation of incomplete oxidation products could indeed become problematic (see also Wasmus et al. [1995]). For such purposes, one could dehne a maximum space velocity above which formation of incomplete oxidation products may become critical. 

Micro-fuel cells using small tanks of hydrogen could operate mobile generators, electric bicycles and other portable items. Large 250-kW... 

This technique yields a catalyst composed entirely of metal nanoparticles or nanocrystalline thin film, and it allows for control of size and distribution while eliminating the need for a dispersing and supporting medium. The obtained electrodes contained as little as 0.017 mg Pt/cm and performed as well as standard E-TEK electrodes (Pt loading 0.4 mg/cm ). The PLD technique may be of special interest as an alternative to the sputtering process in the production of micro fuel cells. 

The need for different and novel materials as possible DLs has increased substantially in the last few years—especially with the development of new and more complex fuel cell designs. Lurthermore, the interest in small-scale fuel cells to be used as battery replacements in portable electronic devices such as PDAs, laptops, cell phones, music players, etc. has pushed the research for irmovative, inexpensive, and efficient fuel cells further [72,73]. Therefore, it is not surprising that most of the recent new DL materials are being used in micro fuel cells. 

Besides silicon, other materials have also been used in micro fuel cells. Cha et al. [79] made micro-FF channels on SU8 sheets—a photosensitive polymer that is flexible, easy to fabricate, thin, and cheaper than silicon wafers. On top of fhe flow channels, for both the anode and cathode, a paste of carbon black and PTFE is deposited in order to form the actual diffusion layers of the fuel cell. Mifrovski, Elliott, and Nuzzo [80] used a gas-permeable elastomer, such as poly(dimethylsiloxane) (PDMS), as a diffusion layer (with platinum electrodes embedded in it) for liquid-electrolyte-based micro-PEM fuel cells. 

Cha et al. [190] studied the relationship between DL thickness and the dimensions of the FF channels in micro fuel cells. They concluded that, with micro fuel cells, matching the thickness of the DL to the dimensions of the FF channels improves the overall performance and prevents DL damage. 

C. Y. Lee and C. W. Chuang. A novel integration approach for combining the components to minimize a micro fuel cell. Journal of Power Sources 172 (2007) 115-120. 

Because of its lower temperature and special polymer electrolyte membrane, the proton exchange membrane fuel cell (PEMFC) is well-suited for transportation, portable, and micro fuel cell applications. But the performance of these fuel cells critically depends on the materials used for the various cell components. Durability, water management, and reducing catalyst poisoning are important factors when selecting PEMFC materials. 

Technical progress as well as investments in PEMFCs for transportation, stationary, portable, and micro fuel cell applications has been dramatic in recent years. The present view is ophmistic for fuel cell power generation the status is presently at the field trial level, or early commercialization stage, moving into volume commercialization. Although commercially viable, niche PEMFC applicahons exist today, the first commercial mass markets for fuel cells are expected to be for handheld electronic devices, PCs, and other portable devices. 

Fuel cells are currently being intensively developed as they have the potential to provide power in a relatively nonpolluting fashion. Legislation in the United States requires that a percentage of all new vehicles should emit no hydrocarbons or oxides of nitrogen (so-called zero emission vehicle. The current internal combustion engine cannot meet such stringent demands and so alternatives have to be found. The main contenders are electric cars which run on either batteries or fuel cells, or a combination of the two. Current developments now include not only fuel-cell-driven buses and cars, but also power sources for homes and factories. Micro-fuel cells for mobile phones and laptops have been developed. 

Nanotechnology Sees Applications in Fuel Cells and Solar Power—Micro Fuel Cells to Power Mobile Devices... 

Cells and Solar Power—Micro Fuel Cells to... 

Pattekar, A. V., Kothare, M. V., A microreactor for hydrogen production in micro fuel cells, IEEE J. Microelectromech. Syst. 2004, 13, 7-18. 

Keywords polymer electrolyte membrane fuel cell (PEMFC), porous silicon, silicon electrodes, micro fuel cells. 

The authors thank Dr. Ying Wang (MTI Micro Fuel Cells) and Dr. Lisa Xiao (PEMEAS) for reviewing parts of the manuscript and for their valuable comments and suggestions. 

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