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Since the introduction of microchemical systems (MCS) in the last decade, it has been recognized that one of the most crucial challenges is the implementation of an appropriate control strategy. A novel study in realizing a controllable miniature chemical plant for a small-scale hydrogen source for fuel cells is presented. Catalytic steam reforming (SR) reaction of a methanol–water mixture was the model reaction studied. A microscaled reactor, sensors and actuators, were successfully prepared and integrated by using microelectromechanical systems (MEMS) technology. Microfabricated system components were then interconnected with a comprehensive control algorithm which could form the basis for an eventual autonomous, self-contained system. MCS represent a concept wherein precisely microfabricated fluid passages and reaction zones are integrated with sensors and actuators. Having an appropriate control strategy for the entire system of MCS is therefore a significant technical challenge. Although numerous MEMS-based examples of sensors and actuators exist for control of pressure, temperature and flow, there are few cases where these components have been combined with chemical reaction units and control algorithms into MCS. In this study, control of temperature and flow allows the hydrogen production rate to be modulated in a suitable fashion to support proton exchange fuel cell operation as a model. The reaction characteristics with temperature and flow changes, cold start-up behavior and the response to rapid changes in hydrogen demand were investigated. The control scheme implemented showed potential for autonomous control of fuel processing and other microchemical processing applications.

We have successfully fabricated hydrogen–air micro proton exchange membrane fuel cells (PEMFC) on silicon and polydimethylsiloxane (PDMS) base substrates. A complete fuel cell system was fabricated consisting of a PDMS substrate with micro flow channels upon which the membrane electrode assembly was vertically stacked. The PDMS microreactor was fabricated by soft lithography techniques. The membrane electrode assembly (MEA) consisted of electrodes and catalyst deposited on both sides of the Nafion membrane using conventional microfabrication approaches. We have been able to register open circuit voltage in excess of 0.790 V while the peak power of 0.282 mW at 0.375 V was obtained from this fuel cell. The current–voltage (V–I) characteristics for the fuel cell were measured at different temperatures ranging from room temperature to 80 °C. The oxidation of hydrogen was characterized for conversion on different catalyst materials by measuring the composition of product gases.

We have successfully developed miniature hydrogen-air proton exchange membrane (PEM) fuel cells (FC) on silicon and poly-dimethylsiloxane (PDMS) base substrates using conventional and non-conventional microfabrication technologies. Prototype base substrates were fabricated by using well-known micromachining technologies, such as photolithography, deep reactive ion etching, and soft lithography. Sputtering, a physical vapor deposition method, was used to deposit catalysts and electrodes directly on the surface of the Nafion PEM. This paper describes the novel microfabrication approaches employed to selectively deposit electrodes and catalyst materials on the membrane with improved morphology and structure of electrodes. The aim was to reduce precious metal catalyst loadings, ohmic (iR) losses, and to improve structural support for the thin-film FC with concurrent reduction in fabrication complexity.

The booster plate in NAND flash memory cells gives numerous advantages: the reduction of program, erase and pass voltages, zero program disturbance and increased cell current. At the same time, it is simple to integrate the technology to the conventional fabrication processes. It is expected that the booster plate technology will become one of the key technologies for achieving high density memories such as 256 Mbit and 1 Gbit NAND flash.