Preparation And Characterization Of SPEEK/HPW And Its Surface-Modification For Proton Exchange Membranes

As the heart of pronton exchange membrane fuel cells (PEMFCs), proton exchange membranes (PEMs), play an important role in affecting the performance of fuel cells. Commercial membranes, such as Nafion, although it has high proton conductivity and chemical stability, the properties of high fuel permeability and dramatically reduced proton conductivity at high temperature, make it hard to satisfy the needs of operation under high temperature and low humidity, let alone its high cost. Sulfonated poly (ether ether ketone)(SPEEK) is a kind of material with low cost, high thermostability and good water absorption. However, the proton conductivity and swelling ratio of SPEEK are high comparing with other sulfonated materials at the same sulfonation degree. Therefore, it is a challenge for SPEEK material with high proton conductivity as well as lower swelling ratio.In order to improve the proton conductivity of SPEEK, HPW was introduced into SPEEK matrixs to prepare SPEEK/HPW hybrid membranes. The leakage of HPW would be found as HPW was water-soluble, which would reduce the performance of fuel cells. Furthermore, we prepared composite membranes by in-situ polymerization of aniline and pyrrole on the surface of SPEEK/HPW to reduce the leakage of HPW.SPEEK/HPW hybrid membranes with different weight ratio of HPW to SPEEK matrix were prepared firstly. The proton conductivity of SPEEK/HPW-5was71.82mS/cm at25℃,2.28times of the value of SPEEK membrane and3.6%higher than the value of SPEEK membrane at80℃; the water absorption was up to57.01%～92.04%,1.5times of the value of SPEEK at25℃; the weight loss ratio was44.57%at80℃, which was bad for the performance of PEMs.To limit the weight loss ratio of HPW, SPEEK/HPW-PANI composite membranes were prepared by in-situ polymerization with aniline on the surface of SPEEK/HPW hybrid membranes. The proton conductivity of SPEEK/HPW-PANI-5was32.29mS/cm at25℃and91.53mS/cm at80℃,which was higher than SPEEK at the same temperature; the swelling ratio was32.48%at25℃and54.04%at80℃, which was78.27%and79.68%of SPEEK respectively at the same time; the weight loss ratio was1.29%at25℃,62.32%of SPEEK/HPW (2.07%),76.79%of SPEEK (1.68%), the weight loss ratio was19.84%at80℃,68.58%of SPEEK/HPW (28.93%). To reduce the weight loss ratio of HPW, SPEEK/HPW-PPy composite membranes were prepared by in-situ polymerization with pyrrole on the surface of SPEEK/HPW hybrid membranes, as pyrrole was stronger absorption performance than that of aniline. The proton conductivity of SPEEK/HPW-PPy-5was37.22mS/cm at25℃and72.44mS/cm at80℃, which was higher than SPEEK at the same temperature; the swelling ratio was30.87%at25℃and47.98%at80℃, which was74.39%and70.75%of SPEEK respectively at the same time; the weight loss ratio was1.85%at25℃,89.37%of SPEEK/HPW (2.07%), the weight loss ratio was11.35%at80℃,39.23%of SPEEK/HPW (28.93%).It showed that the surface micro-coating on membranes was a functional strategy to reduce the leakage of effective components and enhance the thermal stability of the hybrid membrane.