Characterization and properties of sulfonated chitosan membrane for direct methanol fuel cell

Abstract

This dissertation examines the structure and properties of chitosan membranes regarding their applicability in fuel cells. The objective of this work is to synthesize a polymer membrane with improved properties such as high proton conductivity, low water uptake, low methanol permeability, and high efficiency. Membranes made of synthetic polymeric materials with enhanced functionality have been developed to compensate for Nafion® deficiency. Polymeric membranes have numerous benefits, including an excellent mechanism for pore-forming control, high mechanical strength, low cost, and greater flexibility. The membrane properties such as identification of functional groups using Fourier Transform Infrared (FTIR), physical properties using Scanning Electron Microscope (SEM), water uptake, Ion Exchange Capacity (IEC), proton conductivity, methanol permeability, and tensile strength were evaluated. Silica is used as a filler, and it was synthesized through Sol-gel and Stober methods and was calcinated for 2h and 24h. Synthesized silica particles were categorized as pure and sulfonated. The membranes showed successful modification with silica. It was found that the water uptake and proton conductivity of the unmodified and modified silica/chitosan membrane increase with an increase in filler content. The s-SiO2/Cs membranes show improvement in membrane properties, particularly, the 4% s-SiO2/Cs (Sol-gel 24h) which has superior proton conductivity of 0.238 Scm−1 which is higher than that of Nafion® of 1.43 x 10-2 Scm−1. However, this membrane has a methanol permeability of 0.97 × 10−7 cm2s−1 which is higher than 2.83 x10-6 cm2s−1 of Nafion®. The selectivity of the fabricated membrane is 1.269 x 105 S.s/cm-3 which is higher compared to that of Nafion® of 3.71 x 104 S.s/cm-3. It was found that the incorporation of silica particles successfully improves the chitosan membrane’s proton conductivity while suppressing its methanol permeability. The recommended synthesis method of silica is by Sol-gel, and it is significant to introduce sulfonic groups in the silica as to improve its suitability as a membrane filler.