Understanding the Effect of Drying Techniques on the Microstructure of the Catalyst Layer of Polymer Electrolyte Membrane Fuel Cell

Kurzfassung

Fuel cell technologies can be considered as clean and reliable alternatives to fossil fuel, which are potentially equipped to be used as promising solutions of many problems arising due to the limited energy resources. Polymer electrolyte membrane fuel cell utilizes hydrogen and ambient air as reactants to produce electrochemical energy and the main emission of this energy conversion system is water. In prospect, this technology would fulfill the pressing hunger of humanity to find alternative method of power generation and utilization, and at the same time protect the environment by lowering the amount of adverse emissions. However, further promulgation of this technology is impeded by some drawbacks, which still need to be surpassed such as the high cost of commercialization, issues related with durability, water management and performance of fuel cell. Catalyst layer (CL) is one of the most important components, especially cathode due to the limiting oxygen reduction reaction and mass transport limitations, which could potentially enhance the stability as well as the performance of the cell if designed properly. Understanding the consequences of the catalyst suspension, coating technique and the drying conditions on the microstructure of the catalyst layer and to identify the processes which govern the final output is the fundamental goal of this study. This thesis focuses the experimental analysis of the influences of different drying techniques namely freeze drying, vacuum drying and oven drying on the microstructure of CL, which optimizes the performances according to the variation of micro-structural properties. A wide range of characterizations were conducted to evaluate the electrochemical performances of the MEAs as well as to investigate the structural properties such as porosity and pore size distribution in the cathode CL. In addition, simulations have been carried out with a transient 2D polymer electrolyte membrane fuel cell model to further investigate the performance limitations. Both the experimental and numerical data emphasize the fact that the catalyst layer attained through the freeze-drying technique ensured high porosity, diffusivity and Pt utilization efficiency, better ionomer distribution as well as reduction in local ionomer resistance in CL and mass transport resistance. Overall, the sublimation drying technique improves the performance and water management properties by utilizing better oxygen transport and proton conductivity in the MEA.