| Micro Direct Methanol Fuel Cell is the ideal power source for portable electronic devices and electric vehicle in the future because it offers many advantages such as high energy density, environment friendliness, convenience in fuel storage and transportation. As one of the essential components of μDMFC, the flow field plate has functions of distributing materials, collecting and conducting current and separating single battery in cell stack, etc. It has direct influence on the performance of μDMFC. Based on the idea of gas-liquid separative transportation, a novel μDMFC anode flow field with hydrophilic and superhydrophobic micro channels has been designed and fabricated in this thesis. The single batteries performances were tested after being assembled by these new flow field plates.Nickel film with micro-nano binary structure was coated on SS316L substrate by using electrodeposition techniques, this nickel film shows good hydrophilic properties. However, the film turns into superhydrophobic after being modified by FAS and the static contact angle would be higher than160°when the current density between5A/dm2to9A/dm2. The superhydrophobic surfaces prepared in this study possess both high PH stability in strong acid/alkaline solutions and good durability in ambient air. After100hours immersion in HCL (PH=2) or NaOH (PH=13) solution, the samples can still keep superhydrophobic property with the water contact angle higher than150°. Perfect stability of the superhydrophobic samples also can be observed in a durability test lasting for more than1year. The water contact angle of the samples which was exposed to the air for413days only has a slight change (from166°to164.8°).Novel flow field plates with parallel, single-channel serpentine, multi-channel serpentine and spiral structures were designed. The width and depth of gas-liquid channels as well as the best encapsulation pressure were determined through the calculation and simulation on opening ratio, contact resistance and assembly stress. Lithography technical and wet etching process on SS316L surface were studied, the four flow field plates were successfully fabricated with optimum parameters. Subsequently, the flow field plates were modified by electro-deposition and selective fluorination. Finally, the novel anode flow field plates with hydrophilic and superhydrophobic micro channels were successfully achieved. The battery testing platform was set to test the performance and the fuel channel’s pressure drop of μDMFC. According to different anode flow field plates, eight μDMFC were assembled and they had the same cathode flow field plates. The result shows that the novel flow field plates can obviously improve the output performance of μDMFC. The peak power density of parallel, single-channel serpentine, multi-channel serpentine and spiral flow field plates was separately improved by20%、61.5%、13.6%、16.7%, and the limited current density was separately improved by8.2%、59.4%、13.2%、3.4%. Meanwhile, the average pressure drop and pressure drop amplitude significantly reduced inside the novel anode flow field plates. The pressure drop of parallel, single-channel serpentine, multi-channel serpentine and spiral flow field plates was separately reduced by56.3%、25.6%、0%、16.9%, and the amplitude was separately reduced by51.4%,37.1%、33.3%、55.7%.Single-channel serpentine and spiral flow field plates with hollowed liquid channels were used to do the visualization research on fluid transport properties inside the fuel cell. It is found that the superhydrophobic channels in the novel anode flow field plates will timely discharge the CO2bubble, and the fuel distribution will be more uniform while the performance will be more enhanced. |
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