| Proton exchange membrane fuel cells (PEMFCs) and direct methanol fuel cells (DMFCs), are one of priority development of the energy technologies because of their high energy conversion efficiency, high power density, high low emissions and environment friendly,etc. Proton exchange membrane (PEM), is one key component of the PEMFC. Nafion is the current state-of-the-art PEM material. However, several drawbacks of Nafion, such as high methanol permeability, low humidity, a major reduction in conductivity at high temperatures and high cost, have led researchers to investigate promising alternatives.At present, the main method to achive the high performance PEM applied in the PEMFC and DMFC is sythieseing perfect sulftone polymer or modifying the polymer. Poly(ether su ether ketone ketone)(PESEKK), are receiving considerable attention as a kind of promising PEM for their excellent high mechanical properties, thermal stability, oxidation resistance and high proton conductivity.Firstly, a series of PESEKK-g-PSPMA copolymers were successfully synthesized via the chloromethylation of the PESEKK main chain, followed by the ATRP of SPMA monomers onto the backbone of PESEKK. The copolymers with different degree of sulfonation could be modulated simply by the control of ATRP time. The wateruptake, IEC values, and proton conductivity of the copolymers depend on the grafting polymerization time, and the increase of ATRP time lead to the value increase of the above parameters. The methanol permeability of the copolymers membranes increases as the polymerization time increasing, which is much lower than that of Nafion117.And the conductivity of the copolymers membranes is from1.40×10-4s/cm to6.53X10-2s/cm, methanol permeability from1.34×10-7cm2.s-1to2.20×10-7cm2.s-1。Secondly, because Sulfone Poly(ether sulfone) owe much stronge dipole-dipole interactions with water and proton conductivity, we have prepared blend membranes based on aromatic polymers Sulfonate Poly(ether sulfone ether ketone ketone)(SPESEK) and Sulfonate Poly(ether sulfone)(SPES) by using different weight ratios of the two polymers to obtain the most suitable electrolyte for DMFC applications. Morphology of the membranes shows two polymers have good compatibility. Proton conductivity of the composites was found to be higher than that of the pure SPESEKK membrane and increase with the increasing content of SPES. Among the blends membranes prepared in this study, SPESEKK/SPES5:5membrane is more suitable for DMFC application in terms of its proton conductivity, methanol permeability(0.66×10-6cm2.s-1) and mechanical properties values (Tensile strength:52.3MPa). This study reveals the feasibility of preparing low cost SPESEKK/SPES blend membranes having relatively lower methanol crossover comparable to that of Nafion117.At last in this research, we modify SPNB to achieve the good performance. Sulfonate Poly(butoxymethylene norbornene-co-biphenyl oxymethoxy norbornene)(SP(BN/BphN))(defined below as:SPNB) and aminopropyltriethoxysilane (KH550) hybrid crosslinked proton exchange membranes doped with different weight ratio of phosphotungstic acid (PWA) were prepared by a simple sol-gel process. The chemical structures of hybrid membranes were characterized by1H NMR and energy dispersive X-ray spectrometry (EDX). The uniform and homogeneous distributions of KH550and PWA in the crosslinked hybrid membranes proved by scanning electron microscopy (SEM) led to enhanced water uptakes, proton conductivity and stability of the nanocomposites. The effect of the dispersed PWA on the properties of membranes such as thermal stability, water uptake, and proton conductivity was also been studied. The incorporation of PWA has significantly improved the proton conductivity of the hybrid membrane. In particular, the conductivity of SPNB/KH550/PWA25reached the maximum of0.02S cm-1at80℃under the100%relative humidity condition, which is the same order of magnitude of that of Nafion117. And SPNB/KH550/PWA20owes the lowest proton transport activation energy (8.39KJ. mol-1). |
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