SYNTHESIS AND CHARACTERIZATION OF CHITOSAN BASED MEMBRANES IN FUEL CELL APPLICATION

• Main Author: Ledyastuti (NIM 205 05 014), Mia
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/6461
• Institution: Institut Teknologi Bandung

ABSTRACT: <br /> <br /> Fuel cells are often considered to be attractive in modern applications for their high efficiency and potentially CO2 emission free, in contrast to currently more common combustion engine using petroleum and natural gas that emit C)2. Like a combustion engine, a fuel cell uses some sort of chemical fuel as its energy source, howeber the chemical energy is directly converted to electrical energy similar to battery without any inefficient combustion steps. The primary components of a fuel cell are an ion conducting electrolyte, a cathode, and an anode. Among the various types of fuel cells, the Polymer Elecrolyte Membrane Fuel Cell (PEMFC) and Direct Methanol Fuel Cell (DMFC) are often use for portable applications. The most widely implemented electrolyte in PEMFC and DMFC is Nafion, which is manufactured by DuPont. nafion provides high chemical resistant, high mechanical strength, and high ionic conductivity. Unfortunately, Nafion costs very expensive and it has high methanol crossover. Consequently, the development of new solid polymer electrolytes to replace the function of Nafion grows rapidly. <br /> <br /> Chitosan is a natural polymer that has been studied for use as a promising inexpensive source for membrane material. It has several important characteristic such as inert, hydrophilic, and insoluble in water, alkali, and organic solvents. Chitosan can also act as a cationic polyelectrolyte because of its free amino groups. With respect to its ionic properties, the chitosan membrane is expected has capability to replace the function of Nafion as fuel cell electrolyte. This study presents the potential of chitosan membrane and its derivatives which are ion pair complexes as fuel cell electrolyte. Chitosan is produced from shrip shell and modified by submersion in various concentrations of sulfuric acid solution. The degree of deacetylation (DDA), viscosity-average molecular weigth (Mv), and Fourier Transform Infra Red (FTIR) absorption spectra of chitosan are investigated FTIR absorption spectra, water uptake, ion exchange capacity (IEC), mechanical properties, membrane potential, and Impedance Spectroscopy (IS) of chitosan membranes and its deriviatives are also investigated. <br /> <br /> The chitosan Mv is 1.03 x 10 6 g mol -1 for the sample with 76.78% of DDA. The chitosan FTIR absorption spectra shows the presence of OH, NH2, C=) amide, and CH3 groups. These groups also appear in chitosan membrane its derivative FTIR spectra. There is a specific peak that only observe at chitosan membrane derivative FTIR spectra which is 619,15 cm -1. This peak is recognize as the vibration mode of S-O bond, it indicates the presence of SO4 2- groups that form ion pair complex with NH3 + groups from protonated chitosan. The SO4 2- act as bridge between two chain of protonated chitosan. The water uptake increases with the sulfuric acid concentration. It may come from SO4 2- groups that make the membrane become more hydrophilic. Submersion of chitosan membranes also affects to its mechanical properties. In dry state, the value of tensile strength and elongation at break decrease with the presence of SO4 2- in membrane matrix. However in hydrated state, elongation at break increases. If the membrane become more hydrophilic, the tensile strength at hydrated state will decrease as well. <br /> <br /> The presence of SO4 2- groups also affects the value of IEC. Here, the IEC is describe the content of ionic groups and it is the first clue for the expected conductivity. The IEC of chitosan membranes increase with the sulfuric acid concentration, from 0.200 for CTSN to 0.732, 2.485, and 7.960 meq/g for CTSN-3, CTSN-5, and CTSN-7, respectively. Those membranes posses higher IEC than 0.91 meq/g of Nafion. The conductivity needs to be measured because the high IEC of the chitosan membranes may be due to various ionic groups that presence in membrane matrix. It is proved by the effective charge which is come from membrane potential analysis. CTSN and CTSN-5 effective charge is around 0.002 mol L -1 which is lower than 0.536 mol L -1 of Nafion. It is indicating most of the ionic groups in CTSN and CTSN-5 are tightly bound or immobile groups. <br /> <br /> In dry state, CTSN-5 has higher impedance than CTSN. It means that CTSN-5 has lower conductivity than CTSN. But in hydrated state, CTSN-5 has higher conductivity than CTSN. It is similar to the behavior of salt and base in water. Salt is dissociated more easily than base, so the ion which is charge carrier becomes more easily to move along the membrane. The threshold frequency of CTSN and CTSN-5 in hydrated state is very different, it shows that they have a different proton conducting mechanism. In general, chitosan membranes and its derivatives have lower conductivity than Nafion. Howeber, chitosan membranes and its derivatives show a good potential to be developed as fuel cell electrolyte. In addition, some modifications are required to improve both physical and chemical properties to compete Nafion.