Palladium Based Micro-Membrane Hydrogen Gas Separator-Reactor in a Miniature Fuel Processor for Micro Fuel Cells
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Palladium based micro-membrane hydrogen gas separator-reactor in a miniature fuel processor for micro fuel cells. Sooraj V. Karnik*, Miltiadis K. Hatalis*, Mayuresh V. Kothare** * Department of Electrical and Computer Engineering, **Department of Chemical Engineering, Lehigh University, Bethlehem, PA 18015, USA. ABSTRACT A novel palladium-based micromembrane has been fabricated and tested which has the potential to be used for carbon monoxide shift reaction and hydrogen gas separation in a miniature fuel processor for micro fuel cells. The micromembrane structure is built in silicon substrate, using standard MEMS microfabrication processes. The four layers, viz., copper, aluminum, spin-on-glass (SOG) and palladium form the composite micromembrane. Copper, aluminum and SOG serve as a structural support for the palladium film. Copper also acts as a catalyst in the shift reaction that converts unwanted carbon monoxide gas into hydrogen, which in turn is separated by the palladium micro-membrane. For a particular combination of thicknesses for various layers, the composite micro-membrane withstands a pressure gradient up to 1 atm. The micromembrane separates hydrogen from a 20% hydrogen balance nitrogen gas mixture at room temperature. INTRODUCTION Micro-electro-mechanical systems (MEMS) have been used in microfluidics to allow fluid handling in microscale channels and chambers etched in silicon substrates. Such microfluidic systems [1] have been primarily used for chemical analysis and sensor design where they offer the advantages of significantly smaller reagent volumes - at least 104 times less (and correspondingly lower costs) [2] and faster analysis times (at least 10-100 times faster) [3]. The concept of using microfluidic systems equipped with active catalyst sites for developing microreaction systems is a more recent development [4]. By employing recently developed microfabrication techniques, it is now conceivable that microchannel reactors with integrated heaters, sensors/actuators, valves and control electronics could be built in a single unit for improved process monitoring and control. Micromachined chemical reactor systems offer in-line chemical production for safer operation without storage and transportation hazards. Microchannels offer rapid heat and mass transfer because of inherent large surface area to volume ratios. Sputtering or chemical vapor deposition can be used to develop catalytic films in the microreactor channels with precise structure. Accurate control of reaction conditions with respect to effective mixing, heating, quenching and maintaining a desired temperature profile can be accomplished. Micro fuel cells are currently being considered as alternative energy sources for high-end portable devices such as cellular phones and laptop computers [5, 6]. Therefore, the field of building a miniature fuel microreactor for in situ hydrogen production is of particular interest for these fuel cells. Fuel cells, in general, transform the chemical energy of the reactants directly into a DC current. T
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