Self-Activated Micro Direct-Methanol Fuel Cell (muDMFC) at Near Room Temperature

摘要

This research project was focused on the development and testing of Micro Direct-Methanol Fuel Cells (Micro DMFC). A Si-based Micro DMFC was developed and its electrochemical characteristics studied. The peak power density reached 50 mW/sq cm at 60 deg C. A new MEA design was successfully developed to mitigate MeOH crossover without requiring novel membranes. A Micro DMFC was also fabricated by using photochemically etched stainless steel bipolar plates and the performance was improved to achieve a maximum power density of 100 mW/sq cm at 60 deg C and atmospheric pressure. Water crossover through the membrane was found to be a critical issue to limit direct use of high concentration fuel. A solution using the capillary pressure to push water back from the cathode to anode and a thin membrane such as Nafion 112 has been successfully developed. The net water crossover through the membrane was reduced by a factor of five. This paves the way to directly use concentrated fuel on the anode. An 8-cell air-breathing DMFC stack was developed and demonstrated. Cathode flooding was totally avoided using our newly developed water management strategy. It was found that O2 transport in air-breathing operation is sufficient. Results also demonstrated that it is feasible to finally use pure methanol in a completely passive DMFC. Experimental results proved the degassing ability of sandwiched membrane breather to separate CO2 from aqueous methanol fuel stream in the Micro DMFC, and we determined that the bubble breathing feature can take a more active role in the microfluidic management of the whole system. Since the bubble breathing rate can be much faster than condensing rate of vapor bubble, which led to inefficiency of most reported micro bubble pumps, our degassing technique with hydrophobic porous membrane opened a great opportunity for a self-pumping mechanism to circulate the fuel inside Micro DMFC.