SYNTHESIS AND CHARACTERIZATION OF SULFONATED CHITOSAN MEMBRANE FOR DIRECT METHANOL FUEL CELL (DMFC) APPLICATIONS

• Main Author: Suhartini
• Format: Theses
• Language: Indonesia
• Subjects: Kimia
• Online Access: https://digilib.itb.ac.id/gdl/view/38295
• Institution: Institut Teknologi Bandung

Chitosan is a product of chitin deacetylation that is easily obtained, soluble in acidic solvent, non-toxic, environmentally friendly, hydrophilic, biocompatible, and biodegradable. Chitosan is widely used in various aspects of life. One of the applications currently developed is the use of chitosan as an electrolyte membrane in fuel cells especially for direct methanol fuel cell (DMFC). Chitosan has been applied as membrane in DMFC but its proton conductivity is still low. Therefore, in this study, chitosan has been modified by the insertion of polar groups in order to increase proton conductivity and decrease methanol permeability. Chitosan was obtained from shrimp shells through deproteination, demineralization, and deacetylation stages. The deacetylation degree of chitosan obtained was 77.05% based on the baseline method of Domszy and Robert and its molecular mass was 4.11 x 104 kDa based on viscometry method. The modification of chitosan membrane has been carried out by sulfonation method using sulfuric acid with a variation of its concentration ranging from 0.1 M to 5 M. The temperature of sulfonation has also been varied. The characterization of sulfonated chitosan has been done using functional group analysis with Fourier Transform Infrared (FTIR) spectrophotometer. The peaks at 864 cm-1, 1062 cm-1 and 1011 cm-1 indicates the vibration of C-O-S and O=S=O, while the peak at 1655 cm-1 shows the vibrational streching of C=O amide. The characterization of sulfonated chitosan membrane was done by swelling degree, ion exchange capacity, proton conductivity, methanol permeability, mechanical properties, and morphology measurement. The sulfonation of chitosan membrane using a 3 M H2SO4 solution resulted in highest proton conductivity that was equal to 0.1153 S.cm-1. This concentration was then used for the study of the effects of sulfonation temperature on the membrane characteristics. The temperature used was 35 °C, 45 °C, 55 °C and 65 °C and the resulting membranes were labelled as KS-35, KS-45, KS-55 and KS-65 respectively. The swelling degree of the resulting membranes showed that its binding water ability increased with increasing sulfonation temperature. The highest swelling degree was 34.03 ? 3.61% for KS-65 and the lowest was 3,57 ? 0,42% for KS-35. The ion exchange capacity was also increased with increasing sulfonation temperature. The highest of ion exchange capacity was 1.65 ? 0.0028 meq.g-1 for KS-65 and the lowest was 1.29 meq.g-1 for KS-35. The proton conductivity of sulfonated chitosan membrane tend to decrease at higher sulfonation temperature. The highest value was 0.8666 S.cm-1 for KS-35. The increase of sulfonation temperature up to 55 °C decreased the permeability of methanol up to 5.54 x 10-7 cm2.s-1. Based on the selectivity coefficient value, it was found that KS-45 showed the best selectivity which value was 1.21 x 106 S.cm-3. The tensile strength measurement showed the increase of sulfonation temperature up to 55 °C could improve the mechanical properties of the membrane. This result was supported by SEM micrograph which showed that the membrane surfaces were denser at higher sulfonation temperature. It can be concluded that sulfonated chitosan membranes are good candidates as electrolyte membranes for DMFC application.