Research On The Preparation And Properties Of Functionalized Graphene Oxide Modified Poly(Ether Sulfone)-based Composite Proton Exchange Membranes

Fuel cell is a kind of power generating device which can convert the chemical energy existing in the fuel and the oxidant into electrical energy. Fuel cell has some advantages such as the high energy conversion efficiency, good environmental compatibility and so on. Fuel cells are generally constituted by the electrode, an electrolyte membrane and a collector. In these components, the electroyte membrane is the core part of the fuel cell. Therefore, its property can directly influence the performance of fuel cell. In the fuel cells, the proton exchange membranes have been widely used. As the proton exchange membrane is the core component of the proton exchange membrane fuel cell, using the proton exchange membrane with the better performance is very important. At present, Nafion membrane produced by DuPont is a kind of PEM which is widely used, with high proton conductivity and good chemical stability. Nevertheless, this type of PEM has some disadvantages such as high cost and high methanol permeability, and operating temperature should not exceed 80℃. In the view of these disadvantages, the sulfonated aromatic polymers have been widely used in the fuel cells due to their better thermal stabilities, chemical stabilities and so on. In a variety of the proton exchange membranes, the organic-inorganic composite proton exchange membrane has received extensive attention in recent years, and its advantages are reflected in the adding inorganic particles which can improve the mechanical property, thermal stability and decrease the swelling ratio of the membrane, sometimes also improve the proton transfer etc. In this paper, the study focused on the use of functionalized graphene oxide modified polymer electrolytes to build the organic-inorganic composite proton exchange membranes, and their properties were characterized, mainly including the following two parts:In the first part, we prepared the sulfonated polystyrene brushes grafted graphene oxide, and then introduced to the sulfonated poly (ether sulfone) matrix to build a series of the composite proton exchange membranes by reversible addition fragmentation chain transfer polymerization for the first time. The properties of sulfonated polystyrene brushes grafted graphene oxide and the different functionalized graphene oxide doped composite membranes were studied in details. The results showed that some properties of the composite membranes, such as proton conductivity, thermal stability, mechanical stability and oxidation stability were improved a lot as compared with that of the pristine membrane. At the same time, the methanol permeability of the composite membrane decreased. The proton conductivity of SPES/SPB-FGO-2 is nearly doubled as compared with that of the pristine membrane at 25℃. This result can be attributed to the fact that the SPB-FGO was well-distributed within the SPES membrane matrix and the ion clusters were relatively uniform in size, which made the SPB-FGO fillers create broad ionic pathways through the sulfonic acid groups in polymer brushes via interfacial interactions. Our study demonstrated that the incorporation of an appropriate amount of SPB-FGOs could improve the properties of PEMs, opening up a new design concept to fabricate organic-inorganic composite PEMs.In the second part, we prepared a series of quaternized graphene oxide/sulfonated poly (ether sulfone) ionic crosslinked composite proton exchange membranes. As a result of the interaction between the -SO3H group in SPES and the quaternary ammonium group in QGO, an ionic crosslinking network structure was constructed. Compared with the pristine membrane, the SPES/QGO composite membranes exhibited better oxidation stability and mechanical stability, at the same time, the swelling ratio, water uptake and methanol permeability of the composite membranes decreased. In all the composite membranes with different content of QGO, the swelling ratio and water uptake of SPES/QGO-10 composite membrane was the lowest. In addition, the introduction of QGO made the proton conductivity of the composite membrane decrease a lot, but the proton conductivity at 80℃ of the SPES/QGO-10 could still reach 0.0185 S cm-1. The results of this work showed that the SPES/QGO ionic crosslinked membrane had better comprehensive properties, so it can be used as a potential proton exchange membrane material.