Design, Fabrication And Performance Investigation Of Direct Methanol Fuel Cells

Direct methanol fuel cell(DMFC) is one of the proton exchange membrane fuel cell. Due to its unique advantages, such as simpler system structures, facile liquid fuel storage, higher energy densities and environmental benignancy, the DMFC has been identified as one of the most promising power sources for portable and mobile applications. Most of the previous studies have been focused on DMFCs at high temperature. However portable devices such as mobile phones and laptops are working at room temperature. With the goal of optimizing battery performance, this paper studies on the DMFC working at room temperature. In this paper, we report mainly on the structural aspects of DMFCs, such as reactant and product management, design and manufacture of the bipolar plate and methanol crossover inhibition. The main contents of this thesis include:1. Two-phase flow and temperature characteristics of DMFCBased on visualization methods, this chapter provides a detailed investigation on two-phase flow and transport characteristics in the cathode and anode with three common flow fields, including serpentine flow field, parallel flow field and porous flow field, which can provide a theoretical basis for the optimization for DMFC reactant and product management. And then influence of operational parameters(e.g. open-circuit voltage, cyclical dynamic behavior, methanol solution flow rate and discharge current density) on the temperature characteristics of two-phase flow at anode serpentine flow field were studied.2. Fabrication and properties of DMFC with miniature channelsIn order to reduce the cost of materials and manufacturing and improve the performance of DMFC, the miniature channels of graphite bipolar plates are manufactured by multi-tooth tool. The morphology of the miniature channels are characterized by 3D Super Depth Digital Microscope. Especially how the DMFC with miniature channels is affected by various operational parameters(e.g. methanol concentration, methanol flow rate, oxygen flow rate, pressure, ambient temperature) are investigated. In addition, the parameters of the miniature channels are optimized by software of finite element analysis COMSOL Multiphysics and verified by experiment.3. Performance validation of DMFC with serpentine and porous composite flow fieldIn order to find a balance between methanol crossover inhibition and electrochemical performance of the battery, we add an additional porous flow field on the basis of serpentine flow field. A detailed analysis of the functional properties of the porous flow field plate are reported, especially the effects of the PMFSFD structural parameters(assembly types, porosity, thickness and gradient form) on the battery performance are analyzed. Additionally, how the fuel cell with composite flow field is affected by various operational parameters(operational position, a methanol solution temperature, oxygen back-pressure) and how it behaves under the dynamic conditions are also investigated.