Micro fuel cells assembling

A representative process for the substrate and electrode preparation is given in Fig. 2. The exploded view of the micro fuel cell assembly developed by Manhattan Scientific Inc., is shown in Fig. 3. 

Fig. 3 Exploded view of the micro fuel cell assembly.

Figure 7-10. Assembling of micro fuel cells - MEA to anodic current collector...

As outlined above, the segmentation of MEA electrodes is a key process to implement the concept of integrated fabrication of micro fuel cells which consists of merely three foils. Figure 7-15 shows the electrical characterisation of the serial interconnected three cell demonstrator. Approximately 40 mA can be drained at 1.5 V. To illustrate the importance of MEA patterning a fuel cell has been assembled with three serial interconnected current collector structures according to Figure 7-9 but with a continuous piece of MEA. 

Figure 17. Assembled polymeric micro fuel cell, after [55], (a) open view and (b) assembled view.

Chu KL et al (2006) A nanoporous silicon membrane electrode assembly for on-chip micro fuel cell applications. J Microelectromech Syst 15(3) 671... 

Morikawa, H., Mitsui, T., Hamagami, J. and Kanamura, K. (2002) Fabrication of membrane electrode assembly for micro fuel cell by using electrophoretic deposition process. Electrochemistry 70, 937-939. 

Chu, K.-L., Gold, S., Subramanian, V., Lu, C., Shannon, M.A., Masel, R.l. (2006) A nanoporous silicon membrane electrode assembly for on-chip micro fuel cell applications. Journal of Microelectromechanical Systems, 15, 671-677. 

Conventional fuel cell stack mainly comprises of (a) membrane electrode assemblies (MEAs) for achieving the electrochemical energy conversion process, (b) bipolar plates for the supply of reactant (fuel and oxidant) gases to MEAs in addition to providing cell to cell electronic conduction path and removal of heat and (c) auxiliary components for the reactant supply and product removal. Table 1 provides some of the essential differences between DMFC and micro fuel cell. 

Chan et al. (2005), have realised micro fuel cells through an approach that combines thin film materials with MEMS (micro-electro-mechanical system) technology. The membrane electrode assembly was embedded in a polymeric substrate (PMMA) which was micromachined through laser ablation to form gas flow channels. The micro gas channels were sputtered with gold to serve as current collectors. This cell utilized the water generated by the reaction for the humidification of dry reactants (H2 and O2). The peak power density achieved was 315 mW cm (901 mA cm" at 0.35 V) for the H2-O2 system with 20 ml min" O2 supply and H2 at 10 psi in dead ended mode of operation. A Y shaped microfluidic channel is depicted in Fig. 21. 

No smart solution is available to store the gaseous hydrogen used in miniature fuel cell (PEMFC) and hence DMFC is receiving enormous interest due to system simplicity. However, specialised air-breathing DMFC components have to be developed. New materials have to be developed in addition to optimisation of structure and operating conditions to take care of performance decay modes. New membrane/electrode assemblies appropriate for the microscale to be developed exploiting the enhanced heat and mass transfer on the microscale for improved performance, and developing microfluidic components for micro fuel cells. 

Sol-gel techniques have been successfidly applied to form fuel cell components with enhanced microstructures for high-temperature fuel cells. The apphcations were recently extended to synthesis of hybrid electrolyte for PEMFC. Although die results look promising, the sol-gel processing needs further development to deposit micro-structured materials in a selective area such as the triple-phase boundary of a fuel cell. That is, in the case of PEMFC, the sol-gel techniques need to be expanded to form membrane-electrode-assembly with improved microstructures in addition to the synthesis of hybrid membranes to get higher fuel cell performance. 

Bieberle-Hutter, A., Santis-Alvarez, A.J., Jiang, B. et al. (2012) Syngas generation from n-butane with an integrated MEMS assembly for gas processing in micro-solid oxide fuel cell systems. Lab Chip, 12, 4894-4902. 

Min K, Tanaka S, Esashi M (2003) Silicon-based micro-poljnner electrolyte fuel cells. In IEEE intemational conference on micro electro mechanical systems, Kyoto Min K, Tanaka S, Esashi M (2006) Fabrication of novel MEMS-based polymer electrolyte fuel cell architectures with catalytic electrodes supported on porous Si02- J Micromech Microeng 16 505-511 Miu M, Danila M, Ignat T, Craciunoiu F, Kleps I, Simion M, Bragam A, Dinescu A (2009) Metallic-semiconductor nanosystem assembly for miniaturized fuel cell applications. Superlatt Microstmct 46 291-296... 

Mocoteguy P, Ludwig B, Scholia J, Nedellec Y, Jones DJ, Roziere J (2010) Long-term testing in dynamic mode of HT-PEMFC H3PO4/PBI Celtec-P based membrane electrode assemblies for micro-CHP applications. Fuel Cells 10(2) 299-311... 

In the two preceding chapters (2 and 3), different aspects of state-of-the-art catalysts and membranes as well as new approaches for these two components were discussed. Starting with the central part of low temperature fuel cells, adjacent to the membrane electrode assembly (MEA) is the gas difiusion media, which ensures a uniform distribution of reactant ses and the transport of products away from the electrodes on a micro- and millimeter scale. The fuel cell is then accomplished by the flow field which is required for a uniform distribution of the reactant across the whole electrochemically active area The chapter starts with a discussion of gas diftiision media and their impact on performance. Different flow field stmctures and requirements for stable and long-term operation of fuel cells are presented. The chapter concludes with an introduction to system-level aspects and overall considerations of system efficiency including other components such as humidifiers and cooling strategies. 

The transport of energy, mass, and charge is at the heart of proton exchange membrane fuel cell (PEMFC) operation. The porous layers in modern membrane electrode assemblies (MEAs) lie at the Interface between the macroscopic phenomena occurring in the flow channels and the micro- and nanoscopic processes in the catalyst layers (see Figure 5.1). These layers must deliver the reactants and remove the products from the electrochemical reactions at the fuel cell electrodes. They must also provide connections to the current collecting plates with minimal thermal and electrical resistances. 

Fuel cell power systems contain an assembly of electrochemical cells, which oxidize a fuel to generate direct current electricity. Balance-of-plant subsystems may include controls, thermal management, a fuel processor, and a power conditioner. Some fuel cell power systems may contain additional power generating equipment such as steam generators, gas turbine generators, or micro-turbine generators. The net power output and all the fuel input to the system shall be taken into account in the performance test calculations. 

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