Experiment Study On Micro Direct Methanol Fuel Cell With Non-equipotent Flow Field

Micro direct methanol fuel cell (μDMFC) receives people's concerns extremely, because it offers many advantages such as quick activation rate, convenience in fuel handling and low cost etc. The flow field structure affects whether the electrodes get uniform and adequate fuel and whether the reaction products can move successfully. To find a more excellent flow field structure, this paper studied characterizations of the pressure drop and the removal of CO₂ bubbles in anode flow fields ofμDMFCs, respectively equipped with non-equipotent serpentine flow field (NESFF) and conventional equipotent serpentine flow field (ESFF).To tackle with the blockage of CO₂ bubbles, a NESFF with 400μm at inlet width and 757μm at depth and an ESFF with the same characteristic parameters were designed. The semi-activeμDMFCs with transparent cover were assembled, and the MEA active area was 14mmxl4mm. The test system forμDMFCs established by the research group was used to test the performance ofμDMFCs and the pressure drop between the inlet and outlet of the flow field, and shoot the removal of CO₂ bubbles in anode side.Effect of two flow field structures on the pressure drop and removal of CO₂ bubbles was studied at constant currents (20mA, 60mA and 100mA) under the same operation conditions such as methanol concentration and flow rate etc. The change amplitude and cycle of pressure drops of two flow fields showed almost the same laws at the current of 20mA. When the current was increased to 60mA and 100mA, the change amplitude and cycle of pressure drops of NESFF were smaller, and the average value and cycle of pressure drops of the latter one were respectively twice and five times bigger than those of the former one at 100mA. At the bigger currents, the phenomenon that CO₂ bubbles blocked flow channels was obviously existed in ESFF, but the removal of the bubbles were relatively smooth in NESFF, and the phenomenon the channel was filled with bubbles did not appeared. The peak power ofμDMFC with NESFF was improved by 15%, compared with that of ESFF.Flow field on the PMMA substrate with 135μm at the inlet width and 200μm at the depth was fabricated using hot embossing technology to further study the effect of micro NESFF on the performance ofμDMFC and the batch replication of polymer flowfield plates. For densely patterned and high-depth channels, replication and demolding were very difficult. Experimental results showed with the increasing of hot embossing temperature, pressure and the thickness of substrate, the replication accuracy increased. And thicker polymer substrate needed higher demolding temperature. When the 2mm thickness substrate was embossed at hot embossing temperature of 120℃,pressure of 600Kg and demolding temperature of 100℃, the average absolute errors of channel bottom width and average absolute errors of channel depths were respectively 2.3% and 3.6%. On the basis, the flowfield plate fabricated by hot embossing was used to assemblyμDMFC, the peak power of which was 15.6mW.