Fabrication And Analyzation Of Proton Exchange Membranes With Short-side-chain PFSA After Annealing Under A Series Of Temperature

Proton exchange membrane fuel cell (PEMFC) is an electrochemical devicewithout emission and with high energy conversion efficiency. Proton exchangemembrane (PEM) is the crucial component of fuel cell, which is not only anelectrolyte but also a separator of the reactant gases. Currently, PEM is made ofperfluorinated sulfonic acid resin (PFSA). However, the proton conductivity and thegas crossover will be influenced by the structure of PFSA. In addition, the structureof PFSA is sensitive to temperature. That means in different temperature the structureof PEM will be different. For those reason, it is necessary to research the thermalproperties of PFSA.Previous researches have demonstrated annealing long-side-chain (LSC) PFSAmembrane could help to increase the proton conductivity and mechanical property ofthe membrane and decrease the humidity-induced stress of the membrane. However,the LSC-PFSA membrane is not suitable for the application of fuel cell under hightemperature and low humidity conditions. So it is very significant to research thethermal properties of short-side-chain (SSC) PFSA which can be used under hightemperature and low humidity conditions. In this thesis, we used SSC-PFSA producedby Solvay to prepare PEM, and analyzed the changes of structures and properties ofPEM after annealing under different temperature. We also discussed the question ofthe changes of the color of the composite membranes when they were annealed. Theconclusions have been drawn as followed:(1) Preparation of a series of SSC-PFSA membrane between140℃-270℃. Itcould be found that the membrane crystallinity would increase with the annealingtemperature increasing. That could promote the formation to a more compact andmore organized molecular structure and also enhances the mechanical strength of themembrane. At the same time, the organized structure of the cluster can provide goodchannels for the transfer of proton and increase the proton conductivity. Additionally,the annealing temperature is higher, the water-uptake of membrane is lower, whichcan reduce the membrane decay caused by the hydration and drying cycles due to the start-up/shut-down of fuel cells.(2) In the procedure of preparation of composite membranes, it is needed to addsome surfactant which can improve the resin-uptake of ePTFE/PFSA compositemembranes. However, after a series of processes, the surfactant in the membrane cannot be totally removed. The residual surfactant would make the H-form membranechange color but would not make the Na-form membrane turn into other color, whenthe membranes are heated. It can be demonstrated that the introduction of Na+willgenerate a static electricity net which makes the side chain of the membrane moveunder an order when the membrane is heated. At the same time, in the inner ofH-form membrane, the side chain will move without any order, and the residualsurfactant will promote this random motion.