Cell applications

Table 2. Minimum Technical Requirements for Fuel Cell Applications ...

Williams, R. II. (1998). Fuel Decarbonization for Fuel Cell Applications and Sequestration of the Separated CO2. In Eco-restrncturmg hnpIic3tions for Sustainible... 

The extent to which anode polarization affects the catalytic properties of the Ni surface for the methane-steam reforming reaction via NEMCA is of considerable practical interest. In a recent investigation62 a 70 wt% Ni-YSZ cermet was used at temperatures 800° to 900°C with low steam to methane ratios, i.e., 0.2 to 0.35. At 900°C the anode characteristics were i<>=0.2 mA/cm2, Oa=2 and ac=1.5. Under these conditions spontaneously generated currents were of the order of 60 mA/cm2 and catalyst overpotentials were as high as 250 mV. It was found that the rate of CH4 consumption due to the reforming reaction increases with increasing catalyst potential, i.e., the reaction exhibits overall electrophobic NEMCA behaviour with a 0.13. Measured A and p values were of the order of 12 and 2 respectively.62 These results show that NEMCA can play an important role in anode performance even when the anode-solid electrolyte interface is non-polarizable (high Io values) as is the case in fuel cell applications. 

For the support material of electro-catalysts in PEMFC, Vulcan XC72(Cabot) has been widely used. This carbon black has been successfully employed for the fuel cell applications for its good electric conductivity and high chemical/physical stability. But higher amount of active metals in the electro-catalysts, compared to the general purpose catalysts, make it difficult to control the metal size and the degree of distribution. This is mainly because of the restricted surface area of Vulcan XC72 carbon black. Thus complex and careM processes are necessary to get well dispersed fine active metal particles[4,5]. 

Rodriguez FJ, Sebastian PJ, Solorza O, Perez R (1998) Mo-Ru-W chalcogenide electrodes prepared by chemical synthesis and screen printing for fuel cell applications. Int J Hydrogen Energy 23 1031-1035... 

Comings, V., Hardt, S., Hessel, V., Kolb, G., Lowe, H., Wichert, M., Zape, R., a methanol steam micro-reformer for low power fuel cell applications, Chem. Eng. Commun. (2003) accepted for publication. 

Min M, Cho J, Cho K, Kim H. 2000. Particle size and alloying effects of Pt-based alloy catalysts for fuel cell applications. Electrochim Acta 45 4211-4217. 

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). 

Finally, we have discussed the effect of incomplete Cj oxidation product formation for fuel cell applications and the implications of these processes for reaction modeling. While for standard DMFC applications, formaldehyde and formic acid formation will be negligible, they may become important for low temperature applications and for microstructured cells with high space velocities. For reaction modeling, we have particularly stressed the need for an improved kinetic data base, including kinetic data under defined reaction and transport conditions and kinetic measurements on the oxidation of Ci mixtures with defined amounts of formaldehyde and formic acid, for a better understanding of cross effects between the different reactants at an operating fuel cell anode. 

Second, sensors are often intended for a single use, or for usage over periods of one week or less, and enzymes are capable of excellent performance over these time scales, provided that they are maintained in a nfild environment at moderate temperature and with minimal physical stress. Stabilization of enzymes on conducting surfaces over longer periods of time presents a considerable challenge, since enzymes may be subject to denaturation or inactivation. In addition, the need to feed reactants to the biofuel cell means that convection and therefore viscous shear are often present in working fuel cells. Application of shear to a soft material such as a protein-based film can lead to accelerated degradation due to shear stress [Binyamin and Heller, 1999]. However, enzymes on surfaces have been demonstrated to be stable for several months (see below). 

The choice of immobilization strategy obviously depends on the enzyme, electrode surface, and fuel properties, and on whether a mediator is required, and a wide range of strategies have been employed. Some general examples are represented in Fig. 17.4. Key goals are to stabilize the enzyme under fuel cell operating conditions and to optimize both electron transfer and the efficiency of fuel/oxidant mass transport. Here, we highlight a few approaches that have been particularly useful in electrocatalysis directed towards fuel cell applications. 

Of direct interest for biofuel cell applications are the reported reduction of O2 by multi-copper oxidases on carbon nanotube electrodes [Yan et al., 2006 Zheng et al., 2006] and the oxidation of H2 by hydrogenase covalently bound to carbon nanotubes [Alonso-Lomillo et al., 2007]. The hydrogenase/nanotube anode is extremely stable (>1 month), and shows 33-fold enhanced enzyme coverage compared with similarly treated graphite of the corresponding geometric surface area. A. vinosum... 

The optical properties of a-Si H are of considerable importance, especially for solar-cell applications. Because of the absence of long-range order, the momentum k is not conserved in electronic transitions. Therefore, in contrast to crystalline silicon, a-Si H behaves as though it had a direct bandgap. Its absorption coefficient for visible light is about an order of magnitude higher than that of c-Si [74]. Consequently, the typical thickness (sub-micrometer) of an a-Si H solar cell is only a fraction of that of a c-Si cell. 

Dalluge, J. J. Mass spectrometry for direct determination of proteins in cells Applications in bitechnology and microbiology Fresenius. J. Anal. Chem. 2000,366, 701-711. 

Fuel cell applications Manganese dioxide as a new cathode catalyst in microbial fuel cells [118] OMS-2 catalysts in proton exchange membrane fuel cell applications [119] An improved cathode for alkaline fuel cells [120] Nanostructured manganese oxide as a cathodic catalyst for enhanced oxygen reduction in a microbial fuel cell [121] Carbon-supported tetragonal MnOOH catalysts for oxygen reduction reaction in alkaline media [122]... 

Of course, the design and the development of new redox couples for solar cell applications is a challenging task because it has to meet several critical requirements ... 

Polybasic carboxylic hydroxy and amino acid aided synthetic routes directed towards obtaining mixed inorganic materials, especially for battery and fuel cell applications, are overviewed. It has been shown that, in spite of enormous number of papers on the subject, significant efforts should be undertaken in order to understand the basic principles of these routes. Possible influence of the structure of reactants employed in the process (acids, poly hydroxy alcohols, metal salts) is put forward, and some directions of future work in the field are outlined. 

DNPT is particularly active in full cavity moulded, precured closed-cell applications with CR, NBR, EPDM and SBR. It is efficient in an extrusion environment. 

Pourier, M. and Sapundzhiev, C., Catalytic decomposition of natural gas to hydrogen for fuel cell applications, Int. J. Hydrogen Energ., 22, 429, 1997. 

Bessel, C. et al., Graphite nanofibers as an electrode for fuel cell applications, /. Phys. Chem., 105, 1115, 2001. 

Muradov, N., Emission-free fuel reformers for mobile and portable fuel cell applications, J. Power Sourc., 118, 320, 2003. 

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