Research Of Polymer Electrolyte Membrane For Fuel Cell Applications

Proton exchange membrane (PEM), which is one of the core components of proton exchange membrane fuel cells (PEMFC), has bifunctional effects of proton transfer, oxidant and the barrier between fuel. The performance and cost of the fuel cells are strongly dependent on the characteristics and price of the membranes. Although the widely used perfluorosulfonated acid (PFSA) membranes, such as Nafion series products, have good electrochemical properties, mechanical properties, chemical and thermal stabilities, fuel cell performances and long life span. The PFSA membranes existed two major shortcomings:(1) High cost;(2) because of the water absorbed by PEM evaporation at high temperature (>80℃), there is a sharp drop in proton conductivity. And thus, high temperatuer operation of PEMFC with PFSA membranes is not practical. However, fuel cells that can operate above100℃offer many benefits, including fast electrode kinetics, simplified water/thermal management and significantly resolved the poisoning problem of CO on the anode catalyst surface. Therefore, development of novel PEMs with low cost and high-temperature resistance is very necessary.Firstly, Poly (styrenesuflonic) acid (PSSA) and poly (vinylidene fluoride)(PVDF) composite membranes have been prepared by free radical polymerization. By analysising the relationship of the reaction-time and the characteristics of micro-structural, electrochemistry and physical properties of PVDF/PSSA Composite Membranes by SEM, EDX, EIS and TG, it is found that both the water content and proton conductivity of PVDF/PSSA membrane did increase if the hot-pressing time was extended. When the hot-pressing reactive time approached to8hour, the water content reached4.4%at the room temperature, the proton conductivity reached the maximum (0.375S/cm) and the resisting strength reached to32.1MPa at the optimum values. Which shows that the conductivity of the SIPN composite membrane can be improved clearly while keeping the better mechanical and thermo property by Interpenetrating Networks methods.Secondly, Poly(tetrafluoro ethylene)(PTFE) and Poly(styrenesuflonic) acid (PSSA) have been prepared and evaluated as proton exchange membrane electrolytes in Semi-Interpenetrating polymer network process. SEM was used to characterize the structures of the PTFE/PSSA membranes. The results show that the effects of divinylbenzene (DVB) contents on thermo-stability and proton conductivity were investigation. The proton conductivity obtained for PTFE/PSSA membrane reached another maximum and1S/cm, when the ratio of the styrene-divinyl approached the optimum values at6%. The conductivity of the PTFE/PSSA composite membrane was improved clearly while holding the better mechanical property and thermo property.Finally, Sulfonated polystyrene (SPS) and Poly(tetrafluoro ethylene)(PTFE) have been prepared and evaluated as proton exchange membrane electrolytes in brush coating process. By reading the degree of sulfonation and the characteristics of microstructural, physical and electrochemistry properties of SPS/PTFE Composite Membranes by FI-IR, SEM, EDX, EIS and TG. It is found that both the water content of SPS/PTFE membrane and proton conductivity did increase if the concentrations of H2SO4were increased. When the concentrations of H2SO4approached the optimum values at20%, the water content reached51.5%at the room temperature, the proton conductivity reached the maximum (0.031S/cm) and the resisting strength reached to327.3MPa, which shows that the proton conductivity of the SPS/PTFE composite membrane can be improved clearly while holding the good mechanical and thermo property by brush coating process.