A water collecting and recycling structure for silicon-based micro direct methanol fuel cells

An air-breathing micro direct methanol fuel cell (μDMFC) with a water collecting and recycling cathode structure is presented in this paper. The mechanism of water generation in cathode and water collection from the cathode is studied. The capillary channels with hydrophilic surface are designed along the ribs of the air-breathing cathode window to collect excessive water. The collected water is then released via an exhaust pipe. Microfabrication techniques, including double-side lithography and KOH etching, are used to fabricate the anode and cathode plates of the μDMFC on the same silicon wafer simultaneously. The silicon plate surface is treated by low temperature oxygen plasma to improve the hydrophilicity. The μDMFC with the water collecting and recycling structure and the regular one without, both with an active area of 7.8 × 7.8 mm2, are assembled and characterized. Experimental results show that the maximum power density and current density of the both μDMFCs are more than 10 mW cm−2 and nearly 100 mA cm−2 at room temperature, respectively. After both μDMFCs operate at 0.15 V (about 60 mA cm−2 at room temperature) for 1 h, the outputs of the prototype with water collecting and recycling structure decrease to about 9.7 mW cm−2 and 95 mA cm−2 only, while that of regular one decrease to 9 mW cm−2 and 75 mA cm−2. The water is collected by the exhaust pipe in evidence. As such, it would be possible to recycle the water from cathode to anode.