Microstructured Hydrogen Fuel Cells

Microstructured Hydrogen Fuel Cells, Fig. 1 Operating principle and cross-section schematic of a hydrogen fuel cell... 

Microstructured Hydrogen Fuel Cells, micromachined diffusion media with porous coating for... 

Microfabrication therefore appears to be a viable approach to monohthically integrate the electrolyte with the electrodes, gas diffusion, water management structures, and the flow fields. Based on examples of other microelectrome-chanical systems, the microfabrication approach may lead to cost-effective manufacturing in large volumes of microstructured hydrogen fuel cells. 

Microstructured Hydrogen Fuel Cells, Figure 2 Examples of microstructures for hydrogen fuel cells (a) microchannel flow field (b) silicon microma-chined diffusion media with porous coating for water management (c) silicon pillars as electrode stnjctures (d) porous silicon as a membrane support... 

Kreuer et al. [25] investigated the membrane properties, including water sorption, transport (proton conductivity, electro-osmotic water drag and water diffusion), microstructure and viscoelasticity of the short-side-chain (SSC) perfluorosulfonic acid ionomers (PFSA, Dow 840 and Dow 1150) with different lEC-values. The data were compared to those for Nafion 117, and the implications for using such ionomers as separator materials in direct methanol and hydrogen fuel cells discussed. Tire major advantages of PFSA membranes were seen to be (i) a high proton conductivity. 

FIGURE 21.17 Schematic representation of the microstructures of (a) Nafion and (b) an s-PEEK illustrating the less pronounced hydro-phobic/hydrophilic separation of the latter compared to the forma-. (Reprinted from J. Membr. Sci., On the development of proton conducting polymer membranes for hydrogen and methanol fuel cells, 185, 2001, 29, Kreuer, K.D. et al. With permission from Elsevier Kreuer, K.D., J. Membr. ScL, 185,29,2001.)... 

Men, Y., Kolb, G., Zapf, R. et al. (2008) A complete miniaturized microstructured methanol fuel processor/fuel cell system for low power applications. International Journal of Hydrogen Energy, 33, 1374-1382. 

For different applications, the power needed from the fuel cells varies from less than 1W for small applications such as sensors and mobile phones to over 100 kW for automobiles and stationary applications. With microreactors, hydrogen flows capable of producing power in the range from 0.01 W to 50 kW have been achieved [3]. Numerous applications of fuel conversion in microstructured devices have dealt with the combination with fuel cells to yield a power supply for microelectric devices and microsensors and as an alternative to a conventional battery. Thus, the resulting power output of the fuel cell has been in the low watts area, from 0.01 Wto a few watts, as in the integrated methanol fuel processors built by companies such as Casio and Motorola [4]. PNNL has developed various low-power portable fuel processor systems, from lower than 1W [5-7] to systems that could provide 15 W, such as a portable and lightweight system for a soldier portable fuel cell [8,9]. In the range of... 

A rapidly increasing number of publications deal with steam reforming of fossil and renewable fuels in microstructured reactors. In most cases, the appUcation standing behind this work is the generation of hydrogen for portable, mobile and small-scale stationary fuel cell systems as future distributed source of electrical energy. 

Figure 24.11 shows a microstructured coupled diesel steam reformer/catalytic afterburner developed by Kolb et al. [27], which was operated at temperatures exceeding 800 ° C. The reactor, which was coated with catalyst from Johnson-Matthey Fuel Cells, had separate inlets for anode off-gas and for air supply to the burner. Full conversion of the diesel fuel was achieved for a total operation time of 40 h with this reactor, which had a power equivalent of 2 kW thermal energy of the hydrogen produced. 

V. Cominos, V. Hessel, C. Hofmann, et at Selective oxidation of carbon monoxide in a hydrogen-rich fuel cell feed using a catalyst coated microstructured reactor. Catal. Today 2005, 110, 140-153. 

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