Studies On The Formation Of Integrated Membrane Electrode Assembly Using Electrohydrodynamic Atomization Deposition For Direct Methanol Fuel Cells

Direct methanol fuel cells (DMFCs) have received increasing attention to be utilized on portable electronic devices such as cell photo and laptop due to their high energy density, simple system configuration, low emissions and operating temperature. Membrane electrode assembly (MEA) which is the most important unit in the DMFC plays an important role in the performance of DMFC. In this work, a structure-graded MEA had been fabricated to improve the structure of MEA and increase the power density of DMFC using Electrohydrodynamic Atomization (EHDA).A long cone-jet mode in which the cone was longer than stable cone-jet mode had been used in the process of deposited Nafion solution using EHDA, and the solution could be deposited on the basic directly with the jet dispersing barely. The length of cone could be increased when the applied voltage was decreased or the flow rate was turned large, and there was no influence with the working distance changing. Several Nafion membranes had been made with different solutions and different atomization parameters in long cone-jet mode. Compared with other membranes, the Nafion membrane deposited at3.5kV applied voltage,2.5×10-10m3s-1flow rate and15mm working distance using EHDA had presented smooth and uniform. What’s more, this membrane had a higher water uptake than Nafion(?)117, which proved a better proton conductivity.A three-layer integrated MEA was prepared by EHDA and Pt and Pt-Ru catalyst loading were0.4mg·cm-2and1mg·cm-2, respectively. It was found that the integrated MEA exhibited close packed structure and the catalyst electrodes had been integrated with the Nafion membrane which was130μm. The DMFC was assembled with three-layer integrated MEA. The methanol crossover test showed that the cell presented higher rate of the increase of methanol crossover between40℃and50℃than other temperature increase steps. The cell performance increased when the temperature rose, and the enhancement level of the cell performance was more significant at lower temperature range than that at higher temperature. The peak power density was4mW·cm-2at70℃. The impedance arcs and its fitting curves showed that the impedance arc became larger and the mass transfer resistance became higher with higher temperature, that is, the gas-phase transport resistance became larger as the temperature rose. After an85h life test, it was observed that the EHDA deposited cathode electrode side of the integrated MEA still present well compact contact feature.At last, a structure-graded and integrated MEA with seven layers was prepared by EHDA deposition. It was found that the MEA exhibited close packed structure with the cathode and anode catalyst electrodes integrated with the Nafion membrane and Pt and Pt-Ru catalyst loading was0.4mg-cm-2and lmg-cm-2, respectively. The DMFC was assembled with structure-graded and integrated MEA to test the performance of MEA. The cell performance increased when the temperature rose. The enhancement level of the cell performance decreased since the temperature beyond60℃. The peak power density of3.1mW·cm-2was obtained at70℃. After a48h life test, it was observed that the EHDA deposited electrode of the MEA still present well compact contact feature.