Small fuel cells

The fuel processor efficiency is size dependent therefore, small fuel cell power plants using externally reformed hydrocarbon fuels would have a lower overall system efficiency. 

Gardner, K. 3rd Annual International Symposium on Small Fuel Cells and Battery Technologies for Portable Power Applications, Washington, DC, 2001. 

To compete in this arena, biofuel cells must take advantage of inherent biocatalytic properties that cannot be duplicated by conventional technology. Among these key properties are (1) activity at low temperature and near-neutral pH, (2) chemical selectivity, and (3) potentially low-cost production using fermentation and bioseparation technologies. To the extent possible, these properties must be exploited with minimal compromise of power density and stability. This constraint leaves one major class of conventional applications suitable for biofuel cells small fuel cells for portable power. 

In addition to the activity, other important requirements for the catalyst are the capability to start the reaction rapidly without the necessity for previous reduction with hydrogen and to perform effectively with intermittent operation these are essential properties for the catalyst in reformers, especially for portable and small-scale stationary fuel cell applications. In this respect, Dias and Assaf [61] focused on the potential of Pd, Pt and Ir to promote fast and intermittent ignition of methane ATR in Ni/y-Al203. They concluded that the three metals are very good promoters of the reduction of the nickel catalyst with methane, but the lower cost of palladium makes this metal more suitable than Pt and Ir for small fuel cells. 

With respect to fuel cells, Korea is working to build up highly competitive capabilities for manufacturing advanced fuel cell technology. The target for 2012 is to introduce stationary fuel cells (370 MW) into the market. In addition, 10,000 fuel cell vehicles are planned to be running on the road by 2012. Small fuel cells for replacing batteries, either DMFC or PEMFC with a micro fuel processor, are expected to be introduced into the market by private companies in 2006. 

In order to study cathode flooding in small fuel cells for portable applications operated at ambient conditions, Tuber et al.81 designed a transparent cell that was only operated at low current densities and at room temperature. The experimental data was then used to confirm a mathematical model of a similar cell. Fig. 4 describes the schematic top and side view of this transparent fuel cell. The setup was placed between a base and a transparent cover plate. While the anodic base plate was fabricated of stainless steel, the cover plate was made up of plexiglass. A rib of stainless steel was inserted into a slot in the cover plate to obtain the necessary electrical connection. It was observed that clogging of flow channels by liquid water was a major cause for low cell performance. When the fuel cell operated at room temperature during startup and outdoor operation, a hydrophilic carbon paper turned out to be more effective compared with a hydrophobic one.81... 

Nowak, R.J., A DARPA perspective on small fuel cells for the military, in Proceedings Solid State Energy Conversion Alliance (SECA) Workshop, Arlington, VA, 29 March 2001. 

Smaller fuel cells (1 kW and lower) may be used as portable power as well as back-up power (uninterruptible power supply) or as battery chargers. Small fuel cells are also being developed as battery replacement which would enable longer operation time for consumer electronics (such as laptop computers, cell phones, cameras, and music players). There is a wide array of possible fuel cell applications in military battery chargers, telecommunications, navigation systems, soldier power, computers, various power tools,... 

Proton Exchange Membrane (PEMFC) These cells use a perfluorinated ionomer polymer membrane which passes protons from the anode and cathode. They operate at about 80 °C. These are being developed for use in transport applications and for portable and small fuel cells. 

If communities and companies had the ability to generate their own electricity via small fuel cells using renewable energy to make hydrogen, they could fulfill their energy needs locally and would not have to depend as much on imported energy. 

A small fuel cell in this portable breath tester catalyzes the oxidation of ethanol by oxygen in the air. 

Power requirements of portable hydrogen equipment such as cameras, mobile phones or laptop computers currently covered by batteries, typically of lithium ion type, could with a small fuel cell and some 10-20 g of directly or indirectly stored hydrogen prolong operational time by a factor of 5-10. A discussion of such options using direct methanol fuel cells is made in section 4.6. 

Demonstrations of Small Fuel-cell System Prototypes... 

A small fuel cell of about 1-kW in capacity, could cogenerate year-round to provide base-load power and hot water. Larger fuel cells would provide too much heat than a home can use most of the time. The DOE estimates that the optimal size for a residential combined heat and power (CHP) or cogeneration system in the United States is about 0.75-kW for a PEM fuel cell. 

As Appleby and Foulkes observe, it was once widely assumed, on the basis of the early space-related efforts, that small fuel cells (putting out a few kilowatts) for electric vehicles would come first, and that larger units for sta-... 

Christopher Dyer, Replacing the battery in portable electronics, Scientific American, July 1999, p. 88. Dyer s article was one of three in a special report on fuel cells in that issue. The second (A. John Appleby, The Electrochemical Engine for Vehicles ) described the prospects of fuel cells as a power source for vehicles. The third (Alan Lloyd, The Power Plant in Your Basement ) described the outlook for small fuel cells powering homes and other small-scale applications. 

Irving, P. Fuel Processor for Generating Pure Hydrogen for Fuel Cells from Sulfur-Containing Fuels . Proceedings of the 4 Annual Knowledge Foundation s International Symposium, Small Fuel Cells 2002. Washington... 

Most portable electronic devices would require a fuel cell of less than 100 W output, and often considerably less. Here, effort is concentrated on perfecting the DMFC, because of the convenience of methanol as a liquid fuel. Clearly, portable power is a very promising high-value opportunity for small fuel cells, but the outcome would have little impact on overall energy consumption and is not strictly part of the hydrogen energy scene. Nevertheless, many observers believe that volume production of micro fuel cells would be a key technical and economic driver for the entire fuel-cell market. 

The portable application is attractive because the number of possible units is high and the cost limitations seem to be met more easily than for fuel cell systems in mobile or stationary applications [17-20]. This is especially tme for small fuel cells for consumer applications. 

T. Pichonat, B. Gauthier-Manuel, and D. Hauden, A new proton-conducting porous silicon membrane for small fuel cells. Chemical Engineering Journal, 101(1-3) (2004) 107-111. 

M. Muller, C. Muller, F. Gromball, M. Wolfle, and W. Menz, Micro-structured flow fields for small fuel cells. Microsystem Technologies, 9 (2003) 159-162. 

Small fuel cells for portable applications require bipolar plates with surface textures (flow-fields) with partial cross-sections <1.0 mm. This requires a tool technology that allows a complete filling of the mold and the transmission of the structures of the tool onto the bipolar plate material. 

During the 1960s, an American company du Pont de Nemours started to develop a new polymeric ion-exchange membrane marketed as Nation . This had a drastic effect on the further development of fuel cells, particularly for applications of the second type. It was soon obvious that this membrane could help to strongly enhance the characteristics and lifetime of relatively small fuel cells. At the same time, success was achieved toward substantially lower platinum catalyst outlays in such fuel cells. These developments aroused the interest of potential fuel-cell users. 

TABLE 243. Annual Number of Small Fuel Cell Units Installed... 

With respect to fuel-cell technology itself, the small portable units use commercially available membrane electrode assemblies (MEA) and gas diffusion layers (GDL). As the operating temperature of small fuel-cell stacks usually lies below 50 °C, the requirements with respect to material stability of MEA and GDL, but also of sealing gaskets and bipolar plates are comparable lower than for other applications. For example, it is well known that metallic bipolar plates show significantly lower corrosion below 50 °C than at typical operation temperature of 80 °C [6,7], so that a sufficient lifetime for portable applications can be achieved with stainless steel. 

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