Study On Proton Exchange Membranes And Micro Fuel Cells Based On MEMS

The proton exchange membrane (PEM), a key component of proton exchange membrane fuel cells (PEMFC), has dual functions of proton conduction and separation of the anode from the cathode. So far, only perfluorinated sulfonic acid ionomer membranes have been used in practical fuel cells, and their costs are the highest among different components of a fuel cell. The high cost of the perfluorinated membrane is one of the most important factors for retarding the commercialization of PEMFC. It is obvious that the PEMFC steadily working at an elevated temperature can resolve the poisoning problem of CO on the catalyst surface. Operating of PEMFC at the mode of non-humidification of the reactant gases is advantageous for simplifying the PEMFC system. Micro fuel cell based on Micro-Electro-Mechanical System is promising for practically applications.In this dissertation, much work was focused on the following projects: the structure and performance of perfluorinated proton exchange membranes (Nafion, Aciplex, Flemion, and Shanghai); the preparation, characterization and application of recast Nafion membrane, degradation mechanism of polystyrene sulfonic acid membrane and application of its composite membranes in fuel cells, operation of PEMFC at the mode of non-humidification of reactant gases and its application at Micro Fuel Cell based on Micro-Electro-Mechanical System (MEMS). The aim of this work is to explore preparation technology of PEM, to reduce its cost, to simplify or eliminate humidification sub-system of PEMFC, and to explore the application of Micro fuel cell. Some of original research results are summarized asfollows: It is found that for thick proton exchange membranes mass transport limitation in the high current density range is mainly originated from the limitation of proton transport due to a long-distance diffusion. Given the same chemical composition, thickness, and equivalent weight of PEM, membrane preparation technology is nearly independent of membrane performance. At the process of preparation of recast-Nafion by solution-cast method, replacing low-boiling-point solvent by high-boiling-point one and preparing membrane under appropriate temperature are two decisive factors for high-quality recast -Nafion membrane. The PEMFC with Nafion / ZrH(PO4)x(SO4)y blend membrane can steadily work at a temperature of 110℃. The degradation of the PSSA membrane mainly takes place at the cathode side of the cell. A new kind of the PSSA - Nafion composite membrane, where the thinner Nafion membrane is bonded with the PSSA membrane and located at the cathode side of the cell, is designed to overcome the degradation process of the PSSA membrane in fuel cells. This kind of composite membrane is promising to be used on the PEMFC due to its reduced cost. A micro fuel cell on silicon wafers has been successfully fabricated using micro-electronic fabrication techniques including spin coating, photolithography, dry and wet etching, chemical and physical vapor deposition. It is found sputtering a Cu / Au composite layer on the top of the silicon wafer can reduce its resistance as a current collector. The micro fuel cell with smaller size channels gives better performance than the state-of-the-art fuel cell with larger size channels at the diffusion-limiting current region. The micro fuel cell operated on dry H2 / O2 is promising for a practically compact fuel cell system in the low power range.