Electrospun sulfonated silica-based proton exchange membranes for pem fuel cells

Official URL: https://risc01.sabanciuniv.edu/record=b2767339_(Table of contents)

Proton exchange membrane fuel cells (PEMFCs) are considered as the most promising alternative systems for fossil fuel-based devices due to their outstanding characteristics such as high efficiency and applicability in a wide range of sectors. Nevertheless, the materials characteristics and system designs with promising performance, durability, and cost-effectiveness still need to be improved for their commercialization. In this regard, a growing amount of research has been conducted to enhance the properties of their various parts, particularly the membrane as the heart of a PEMFC which serves numerous vital functions. Nafion® membranes are commonly used as the membrane material in PEMFCs due to their several advantages but they suffer mainly from insufficient proton conductivity at low relative humidity (RH) and elevated temperatures as well as high-cost production cost. To overcome the disadvantages of Nafion® membranes, in the present thesis two different strategies were used to synthesis and fabrication of proton conductive membranes with a promising performance at low humidity operation conditions. In the first approach, for substitution of Nafion® membranes sulfonated silica/ poly (vinylidene fluoride-co trifluoroethylene)-based (P(VDF-TrFE)) and sulfonated silica/ poly (vinylidene fluoride)-based (PVDF) hybrid membranes were prepared via single electrospinning method where sulfonated silica (S-SiO2) nanoparticles were used as proton conductive additives and PVDF or P(VDF-TrFE) as the carrier polymers. Hybrid S-SiO2/P(VDF-TrFE) membranes showed a superior proton conductivity (102 mS/cm) at 80°C and 100% RH than the S-SiO2/ PVDF membranes (43 mS/cm) at the same conditions. These iv superior results are due to the P(VDF-TrFE) polymer in the hybrid membrane structure that creates larger micro-channels for proton conduction. In the second approach, modification of Nafion® membranes were investigated by incorporation of sulfonated silica (S-SiO2) network into the Nafion®/PVDF or Nafion®/P(VDF-TrFE) fibrous mats. For this purpose, a single-step dual-electrospinning and sol-gel method were combined for the preparation of composite membranes as a fast and scalable technique. In this part of the thesis, the P(VDF-TrFE)-based membranes showed higher proton conductivity than PVDF-based ones (132 vs. 79 mS/cm at 80°C and 100% RH). Moreover, composite membranes exhibit superior cell performance especially at lower applied humidity conditions. The maximum power density is at 344 mW/cm2 60% RH, and this value is higher than the PVDF-based membranes which are 190 mW/cm2 at the same conditions. These observations suggest that P(VDF-TrFE)-based membranes can be considered as promising alternative membranes for PEMFC applications operating at low humidity conditions.