Micro fuel cells design

Micro fuel cell designs without polymeric membranes can overcome some PEM-related issues such as fuel crossover, anode dry-out or cathode flooding. In these membraneless laminar flow-based fuel cells (LF-EC) two or more liquid streams merge into a single microfluidic channel. The stream flows over the anode and the cathode electrodes placed on opposing side walls within the channel. The reaction of fuel and oxidant takes place at the electrodes while the two liquid streams and their liquid-liquid interface provide the necessary ionic transport [122,123]. 

FOIL TYPE MICRO FUEL CELL DESIGN Planar Design of PEMFC... 

Figure 7-13. Characteristic of PEM micro fuel cells. Design 1 meander anodic flow filed, design 2 parallel rib flow field...

In general, future micro fuel cell design should forego heavy bolts and thick BPs in order to miniaturize the system. The other components, such as the GDL and MEA, are negligible in volume and weight As a result, the material selection for the BPs becomes very important. Thin sheets that are stiff enough to achieve uniform low-contact resistance between MEA, flow field and current collector are needed. The bolts for the stack compression can be replaced by, for example, clamps, straps, or coiling techniques [9]. 

The need for different and novel materials as possible DLs has increased substantially in the last few years—especially with the development of new and more complex fuel cell designs. Lurthermore, the interest in small-scale fuel cells to be used as battery replacements in portable electronic devices such as PDAs, laptops, cell phones, music players, etc. has pushed the research for irmovative, inexpensive, and efficient fuel cells further [72,73]. Therefore, it is not surprising that most of the recent new DL materials are being used in micro fuel cells. 

Figure 3.55. Carbon nanohorn substrates used for catalyst backing in NEC s passive DMFC design. (From Y. Kubo (2004). Micro fuel cells for portable electronics. In Proc. 15 World Hydrogen Energy Conference, Yokohama. Used with permission.)...

In addition to the design of the solid-gas contactor device, the yield of a desulfurization process directly depends on the physicochemical properties of the used adsorbent crystallite size of the active phase, specific surface area, and porous texture. In the case of a microporous membrane, if the gas flow is forced across the microporosity, it can be expected that the retention will be highly efficient. In return, the low amount of adsorbent restricts the potential applications to the elimination of traces in high-purity gas or to the design of integrated filters for miniaturized devices like micro fuel cells. 

Lee, S.-J. Chang-Chien, A. Cha, S.W. O Hayre, R. Park, Y.I. Saito, Y. Prinz, F.B. Design and fabrication of a micro fuel cell array with flip-flop interconnection. J. Power Sources 2002, 112, 410 18. 

Microfabrication processes have been used successfully to form micro-fuel cells on silicon wafers. Aspects of the design, materials, and forming of a micro-fabricated methanol fuel cell have been presented. The processes yielded reproducible, controlled structures that performed well for liquid feed, direct methanol/Oj saturated solution (1.4 mW cm ) and direct methanol/H O systems (8 mA cm" ). In addition to optimizing micro-fuel cell operating performance, there are many system-level issues to be considered when developing a complete micro power system. These issues include electro-deposition procedure, catalyst loading, channel depth, oxidants supply, and system integration. The micro-fabrication processes that have... 

Micro fuel cells are primarily designed for portability. Their size is dictated by the size of the device they power. Consumer products such as laptop PCs, portable electronic video games, video cameras, PDAs, and cellular telephones are several examples of portable electronics where a micro fuel cell could be used to power the device. These fuel cells have been designed on primarily two fuel cell types, DMFC and PEMFC. These fuel cell types provide high power density based on their small size and are suitable for powering small devices. A need for high efficiency, combined with a need for lightweight and small size makes these fuel cell types ideal. 

A same approach has been used by Karnik and co-workers who successfully produced Pd-based membrane via micro-fabrication and used it for hydrogen separation. The authors were able to design and fabricate a micro-reactor that was used for hydrogen separation however, the support (or a part of it) for the micro-membrane is made of copper, which is also active catalyst for WGS reaction. The reactor can be thus used for on-board hydrogen production for micro-fuel cell applications. 

Figure 7. Bipolar design of micro fuel cell, after [29],...

Portable electronic devices need very low power for their operation, often milliwatts or at most a few watts, and no more than 10 W. Small low-power fuel cells designed as a power supply for portable devices are termed micro-fuel cells or mini-fuel cells (mini-FCs), the latter term being preferred. The concept of a miniamrization of fuel cells is also current. 

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