Microscale fuel cell

Fuel cells are electrochemical devices that convert the chemical energy of the fuels directly into electrical energy, and are considered to be the key technology for power generation in stationary, automotive, portable and even microscale systems. Among all kinds of fuel cells, direct methanol fuel cells have really exhibited the potential to replace current portable power sources and micropower sources in the market (Yao et al., 2006). 

Figure 4. Performance of the mesoscale fuel cell and Battelle s microscale methanol processor. (Reprinted with permission from ref 63. Copyright 2001 Elsevier.)...

The most effective mitigation approach is likely a combined system-, device- and material-level approach for a particular application. Fundamental understanding of the degradation mechanisms of the PEM at the nano- and microscale is essential to provide a linkage of the key processes occurring at that scale to the device- and system-level engineering strategies. It will provide the most probable pathway to break the current technical barriers in the PEM fuel cell development. 

Holladay, J. D., Wainright, J. S., Jones, E. O., Gano, S. R., Power generation using a mesoscale fuel cell integrated with a microscale fuel processor, J. Power Sources 2004, 130, 111-118. 

The most complicated way to provide fuel to a microscale fuel cell is the use of reforming technology to process a hydrocarbon into a hydrogen rich stream,... 

To build an efficient, high-quality microscale fuel cell, microfabrication techniques need to be combined with appropriate materials such as Nation based membrane electrode assemblies (MEAs). These techniques must be able to produce three-dimensional structures, allow reactant and product flow into and out of the device, process appropriate materials, and should be of low cost. Fortimately, traditional thin film techniques can be modified for microscale fuel cell fabrication, while maintaining their advantages of surface preparation, sensor integration, and finishing or packaging. In addition, other techniques are also available and are discussed in the following sections. 

Some common ways of fabricating the MEA for microscale fuel cells include hot pressing the membrane onto preformed electrodes or hot pressing a complete MEA onto a substrate, screen printing a membrane onto a substrate and depositing the electrodes on either side, and using spin deposition to deposit the membrane followed by electrode deposition. 

In designing a microscale fuel cell, there are several considerations that need to be accounted for. These include the following is the fuel cell to be completely active or passive will it operate at room temperature or elevated temperatures will the fuel be at atmospheric pressure or elevated pressure will external humidification be required and finally, will the fabrication techniques... 

Morse, J.D. Jankowski, A.F. Graff, R.T. Hayes, J.P. Novel proton exchange membrane thin-film fuel cell for microscale energy conversion. Proceedings of the 46th National Symposium of the American Vacuum Society, 25 October-29 October 1999 J. Vac. Sci. Technol. A Vacuum, Surfaces Films 2000, 18, 2003-2005. 

Mediated enzyme electrodes were also realized on combined microscale and nanoscale supports [300]. Bioelectrocatalytic hydrogels have also been realized by co-assembling electron-conducting metallopolypeptides with bifunctional building blocks [301]. More recently, redox-modified polymers have been employed to build biofuel cells [25, 70, 302, 303]. In 2003, an enzymatic glucose/02 fuel cell which was implanted in a living plant was introduced [147]. 

Control over reagent diffusion is also an important microscale effect. Slow diffusive times can be used to advantage. Yoon et al. have shown that the effects of slow diffusive mixing can be used to advantage when laminar fuel cells are operated [8]. This is a case where a reaction is driven in the mass transfer domain to operate without an electrolyte membrane. 

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