JNMES-08-598 - Journal of New Materials for Electrochemical...

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1 UNCORRECTED PROOF 1. INTRODUCTION The Polymer electrolyte membrane (PEM) fuel cell is consid- ered to be one of the most promising clean and efficient alternative energy technologies of the 21 st century when it is used with sus- tainable hydrogen source. With increased interest in developing light and portable electronic systems, technological research was driven towards the use of integrated and small regeneration power sources. In recent years, PEM based miniature fuel cells have been adopted in portable electronic products, such as laptops, cellular phones, PDAs, etc. Silicon is an ideal material for constructing future micro fuel cell, because the silicon based micro fuel cells can be mass produced at a low cost via existing MEMS technol- ogy. This advantage has attracted several studies on the fabrica- tion of the silicon based micro fuel cells [1-10]. In its early devel- opment, the anode and cathode structures (e.g. current collectors, flow fields, fuel reservoir, etc.) were micro-fabricated using silicon wafer followed by stacking them with Nafion ® membranes. How- ever, Nafion ® is polymer and, unlike silicon, is not compatible with conventional MEMS technology. To mitigate this problem, there have been attempts to replace this polymer membrane with acid functionalized inorganic membrane. A pioneer work by Pichonat et al. demonstrated that the use of porous silicon filled with Nafion ® can replace a bulk Nafion ® membrane as a proton exchange membrane in fuel cells [11]. In general, the porous silicon membrane is fabricated by anodiz- ing a silicon wafer in a hydrofluoric solution. This fabrication process produces long narrow channels with a typical diameter of 30 nm. These channels need to be functionalized with acid groups in order to conduct protons. However, due to the long channels with very small diameter of porous membrane, it is almost impos- sible to wet the entire channel surfaces with these acid-functional- group solutions. For example, if the silicon porous membrane is functionalized with Nafion ® by filling the channels with Nafion ® solutions, only the top and bottom portions of each channel would be filled with Nafion ® due to high surface tension. In addition, Nafion ® filled inside the channels will swell to crack the walls when the porous silicon membrane is hydrated. Therefore, we report here a different way of preparing porous silicon membrane using a KOH anisotropic etching process. This new process provides a porous membrane with the V-shaped (or inverse pyramid shaped) channels, which is advantageous for avoiding aforementioned surface tension and swelling problems. *To whom correspondence should be addressed: Email: [email protected] Phone: 1-509-335-3786 Preparation of a New Proton Conducting Silicon Membrane for Miniature Fuel Cells Yi-Tang Chen 1 , Sean S.-Y. Lin 2 , Sung-O Kim 3 and Su Ha *,2 1 Department of Photonics, Institute of Electro-optical Engineering, National Chiao Tung University, Hsinchu, Taiwan 2
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This note was uploaded on 11/03/2010 for the course ECE 999 taught by Professor Sok during the Spring '10 term at Clemson.

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JNMES-08-598 - Journal of New Materials for Electrochemical...

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