Fuel methanol micro

Tominaka S, Ohta S, Obata H, Momma T, Osaka T (2008) On-chip fuel cell micro direct methanol fuel cell of an air-breathing, membraneless, and monolithic design. J Am Chem Soc 130 10456-10457... 

Today, ammonia plants are built with capacities up to more than 3000 metric tons per day (MTPD) and methanol plants are being considered at capacities of 10000 MTPD. This corresponds to the size of synthetic fuel plants based on FT synthesis (35,000 bpd). At the same time, as plants become bigger, there is a trend to minituarise chemical process plants and take advantage of mass production, the economy of numbers competing with the economy of scale. This is one of the key issues in the hydrogen economy and the application of fuel cells. Micro-structured... 

The schematic cross sectional view of the direct methanol micro fuel cell developed by Manhattan Scientific Inc., is shown in Fig. 4. 

The catalytic combustor provides heat for the endothermic reforming reaction and the vaporization of liquid fuel. The endothermic reforming reaction is carried out in a parallel flow-type micro-channel of the reformer unit. It is well known that the methanol steam reforming reaction for hydrogen production over the Cu/ZnO/AbOs catalyst involves the following reactions [10]. Eq. (1) is the algebraic summation of Eqs. (2) and (3). 

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. 

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). 

Lu GQ, Wang CY, Yen TJ, Zhang X. 2004. Development and characterization of a silicon-based micro direct methanol fuel cell. Electrochim Acta 49 821-828. 

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. 

Yao, S.C., Tang, X., Hsieh, C.C., Alyousef, Y, Vladimer, M., Redder, G.K., Amon, C.H., 2006. Micro-electro-mechanical systems (MEMS)-based micro-scale direct methanol fuel cell development. Energy 31 636-649. 

Chin et al. [31] studied Pd/ZnO catalysts for methanol steam reforming, heading for a 10-50 W micro structured fuel processor. The catalysts under investigation contained 4.8, 9.0 and 16.7 wt.% Pd deposited on ZnO powder by impregnation. The catalysts were thoroughly characterized by thermogravimetry (TG), TPR, XRD and TEM. 

Sintering as a micro structuring (see the section above) and bonding technique was applied by Schuessler et al. [85] of Ballard for their compact methanol fuel processor (see Figure 2.94). The stack of plates and the endplate are connected in a single bonding step. 

Enzymes have been considered in bio fuel cells as anode electrocatalysts since their use avoids the problem of poisoning the anode with carbon monoxide present in reforming gas, allowing the use of cheap hydrogen-containing fuels such as methanol. Even though enzymatic fuel cells have been reported to have power output and stability limitations, some of them are currently being used to produce electricity to power small electrical devices with power demands in the order of micro- and milh- Watts as power output limitations are overcome. 

Micro fuel cells intended for use, e.g., with portable electronics, will be mentioned below in section 3.6, as they are often based on direct methanol fuel. Direct methanol fuel cells are also PEM fuel cells, as they are based on the transport of hydrogen ions through a solid polymer electrolyte. 

Figure 4.14. Laptop computer powered by a direct methanol fuel cell. The methanol cartridge is at the back. (From Y. Kubo, NEC Corp., (2004). Micro fuel cells for portable electronics. In Proc. 15 World Hydrogen Energy Conf., Yokohama. OlPL-22, Hydrogen Energy Soc. Japan. Used with permission.)...

One of several recently presented prototypes of a notebook personal computer powered by a micro-DMFC is shown in Fig. 4.14. A replaceable methanol cartridge is placed behind the computer, and the 280-cm DMFC is placed under the laptop keyboard. The fuel cell produces 14 W at 12 V, and if the methanol volume is 30 cm (judged from photo), then the storage capacity is 142 Wh. This would allow the computer to be operated for 14 h at an average consumption of 10 W. Many computer manufacturers, notably in Japan, have recently demonstrated similar DMFC notebook prototypes, including some with a more elegantly integrated methanol container than the one on the early model shown in Fig. 4.14. 

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