Miniature Fuel Cells

For micro fuel cells, miniaturization of the fuel-cell system is a key issue. Research in this area includes developing passively operating fuel cells in order to reduce the peripheral spends and the parasitic energy losses and minimize the system complexity. Development must also focus on low-cost production materials such as silicon or thermoplastics, and fabrication techniques such as MEMS technology or injection molding. 

Electrochemistry is the basis of many important and modem applications and scientific developments such as nanoscale machining (fabrication of miniature devices with three dimensional control in the nanometer scale), electrochemistry at the atomic scale, scanning tunneling microscopy, transformation of energy in biological cells, selective electrodes for the determination of ions, and new kinds of electrochemical cells, batteries and fuel cells. 

A miniature methanol steam reformer for polymer electrolyte fuel cell... 

In redox mediation, to have an effective electron exchange, the thermodynamic redox potentials of the enzyme and the mediator have to be accurately matched. For biocatalytic electrodes, efficient mediators must have redox potentials downhill from the redox potential of the enzyme a 50 mV difference is proposed to be optimal [1, 18]. The tuning of these potentials is a compromise between the need to have a high cell voltage and a high catalytic current. Furthermore, an obvious requirement is that the mediator must be stable in the reduced and oxidized states. Finally, for operation of a membraneless miniaturized biocatalytic fuel cell, the mediators for both the anode and the cathode must be immobilized to prevent power dissipation by solution redox reactions between them. 

Direct-methanol fuel cells (DMFCs) have attracted considerable attention for certain mobile and portable applications, because of their high specific energy density, low poison emissions, easy fuel handling, and miniaturization [129,130], However, the methanol permeation through electrolyte membranes (usually called methanol cross-over) in DMFCs still is one of the critical problems hindering the commercialization [131,132], Nafion , a... 

J. P. Meyers and H. L. Maynard. Design considerations for miniaturized PEM fuel cells. Journal of Power Sources 109 (2002) 76-88. 

Miniaturizing Microreactors and Fuel Cells 4471 7.1. Present Status 4486... 

Miniaturization of electrochemical power sources, in particular batteries and fuel cells, has been described as a critical—but missing—component in transitioning from in-lab capability to the freedom of autonomous devices and systems. - In top-down approaches, macroscopic power sources are scaled to the microlevel usually by the use of fabrication methods, often in combination with new materials. Power generation schemes that can themselves be microfabricated are particularly appealing, as they can lead to a one-stop fabrication of device/machine function with an integrated power source. 

Fuel cells incorporating lithographic methods and masking/deposition/etching protocols have been fabricated on Si wafers and thereby satisfy two critical needs in a standard fuel cell collection of electrons (current collectors) and controlling the flow field of fuel and oxidant. Kelley et al. produced a miniature direct methanol fuel cell (DMFC) with a current— voltage and fuel utilization performance that matched standard-sized DMFCs prepared in-lab.A working volume for the miniature DMFC of 12 mm was reported, with an operational performance of 822 W h kg at 70 °C. ... 

Finally, there are some miscellaneous polymer-electrolyte fuel cell models that should be mentioned. The models of Okada and co-workers - have examined how impurities in the water affect fuel-cell performance. They have focused mainly on ionic species such as chlorine and sodium and show that even a small concentration, especially next to the membrane at the cathode, impacts the overall fuelcell performance significantly. There are also some models that examine having free convection for gas transfer into the fuel cell. These models are also for very miniaturized fuel cells, so that free convection can provide enough oxygen. The models are basically the same as the ones above, but because the cell area is much smaller, the results and effects can be different. For example, free convection is used for both heat transfer and mass transfer, and the small... 

Extensive review literature exists in the area of biological fuel cells. Notably, Palmore and Whitesides summarized biological fuel cell concepts and performance up to 1992." More recently, Katz and Willner discussed recent progress in novel electrode chemistries for both microbial and enzymatic fuel cells,and Heller reviewed advances in miniature cells.This article does not duplicate these valuable contributions. Instead, we focus on the strengths and weak-... 

For example, the small scale of the device was intended as a demonstration of architecture suitable for implanted applications. Mano et al. demonstrated a miniature fuel cell with bilirubin oxidase at the cathode catalyst that is more active at pH 7 and tolerates higher halide concentrations than does laccase. Additionally, the long-side-chain poly-(vinylpyridine)—Os(dialkyl-bis-imidazole)3 redox polymer discussed above was employed to both lower the anode potential and, via the long side chains, enhance electron transport from the biocatalyst. The cell achieved a current density of 830 at 0.52 V... 

In the future, commercial buildings as well as individual homes may be outfitted with fuel cells as an alternative to receiving electricity (and heat) from regional power stations. Researchers are also working on miniature fuel cells that could replace the batteries used for portable electronic devices, such as... 

Miniature Thin-Film Fuel Cells. In 1990. C.K. Dyer (Bell Communications Research, Morristown. New Jersey ) reported the successful construction of a tiny electrochemical device (unconventional fuel celli... 

A. J., Schmidt, M. A., Jensen, K. F., A suspended-tube microreactor for thermally-effident fuel processing, in Proceedings of the 6th International Conference on Microreaction Technology, IMRET 6 (11-14 March 2002), AIChE Pub. No. 164, New Orleans, 2002,147-158. Tanaka, S., Chang, K.-S., Min, K.-B., Satoh, D., Yoshida, K., Esashi, M., MEMS-based components of a miniature fuel cell/fuel reformer system, Chem. 

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