Study On The Key Materials Of MEA And Model & Simulation In Direct Methanol Fuel Cell

Direct methanol fuel cells (DMFC) are a promising power source for various applications. Membrane Electrode Assembly (MEA) is the key unit in direct methanol fuel cells. It is significant for optimizing the strugture of MEA and improving the cell performance in DMFC throuth experiment, model and the simulation study.This purpose of this dissertation is to further research and identify the structure-activity relationship between internal structure of MEA and macro properties of cell. Research is done from the model simulation and experimental two directions. Parameters statistical analysis and optimization management in Direct methanol fuel cell, preparation and characterization of the key materials of MEA, performance of single cell, model and simulation have been studied and discussed respectively and systemic for improving the cell performance, stability and energy efficiency. The expectation of this research is to provide the guidance in designing and optimizing the strugture of MEA and the cell.According to the characteristics, parameters in the direct methanol fuel cell are classified as geometric parameters, physical parameters, working parameters and constant parameters. In order to optimize the parameters of management, Grading Model are established according the cell performance unction partial derivative parameters, and the parameters are divided into primary parameters of level zero parameters, level 1 parameters, level 2 parameters and level 3 parameters. For different level of parameters, we give the corresponding parameter optimizing management strategy. The research work did effective guidance for thesis research direction and helped determing the research work is on MEA parts, and chose the membrane materials as film electrode materials for research.In this study, novel sodium titanate (Na2Ti3O7) nanotube/Nafion(?) composite membranes were prepared by a solution casting method. The properties of these composite membranes were measured to evaluate the applicability of these membranes in DMFCs. It was found that the addition of Na2Ti3O7 nanotubes enhanced the water uptake and reduced the methanol permeability of the composite membranes as high as 10 times. The new composite membrane was found to have significantly 2-5 times higher selectivity than a pure Nation(?) membrane and thus has good potential to outperform Nation(?) in DMFCs. The mechanism is also discussed and analyzed. With new composite membrane materials of 5wt.% Na2Ti3O7/Nafion(?) for proton exchange membrane, Membrane Electrode Assembly (MEA) was prepared using hot-pressing method, and been tested in single direct methanol fuel cell. Operation parameters of cell temperature, cathode humidifying temperature, methanol concentration, methanol flow rate and air flow rate have been employed to study on the effect of direct methanol fuel cells polarization curve. The AC impedance maps were tested and analyzed. The results show that the cell performance of new composite membrane is superior to that of the pure Nafion membrane, which blocked the methanol crossover successfully. The main reason is that the novel composite membrane decreases the charge transfer resistance, and protectes the effect surface in the reduction reactions of Oxgen in cathode.Established a model of single direct methanol fuel, model and numerical simulation method is effective which are validated through the comparison with experimental data. The effect of methanol crossover, anode methanol solution and the cathode oxygen concentration distributions in the MEA are investigated. The Conclusion is cell performance is reduced due to the existence of methanol penetrate. Increase of anode methanol feed concentration will enhance the methanol crossover. The methanol penetrable influence could be reduced through the operating conditions, and thus cell performance also could be improved.