Development of a silicon-based wettability controlled membrane for microscale direct methanol fuel cells

This paper utilizes a unique approach to improve the water and air management at the cathode of a micro Direct Methanol Fuel Cell. Both structural modification and local surface wettability control are utilized. The wettability control of the surface is achieved by depositing a Self-Assembled Monolayer (SAM) on the surface. The technology of SAM has been advanced by coating on selective interior regions of a silicon wafer. This was accomplished using a mask wafer with open slots attached to define the areas that need to be coated. Structure modification such as controlling hole size leads to a magnification of the influence of the surface tension force. A two-inch silicon wafer is formed of alternate strips of hydrophobic and hydrophilic zones with arrays of holes of different sizes. Water will be guided along the hydrophilic wetting zones with large hole openings, while the air goes into the cathode from the hydrophobic dry areas with smaller holes. In this study, a silicon-based membrane is accordingly built to observe the water and air management. Images from a CCD camera showed clearly that the water drained from the big holes without blocking the air passages