PHENOLIC COMPOUNDS FROMSYNTHESIS AND CHARACTERIZATIONS OF POLYMER ELECTROLYTE MEMBRANES FROM POLYSTYRENE MATERIAL FOR FUEL CELL APPLICATIONS

• Main Author: Tandi Gonggo, Siang
• Format: Dissertations
• Language: Indonesia
• Subjects: Kimia
• Online Access: https://digilib.itb.ac.id/gdl/view/34614
• Institution: Institut Teknologi Bandung

The energy source is an important necessity in human life. The need of energy increases with increasing population and the quality of human life. The main energy source for human life at present is fossil fuel. The existence of energy crisis that is happening at present is due to the depletion of fossil fuel reserves. Therefore, it is crucial to perform the research to find the alternative fuels as the substitution of fossil fuels. Recently, one focus of research depeloved to substitute the energy source of fossil fuels is the use of fuel cell with an hydrogen fuel (Proton Exchange Membrane Fuel Cell, PEMFC) and with a methanol fuel (Direct Methanol Fuel Cell, DMFC). The principal part of fuel cell is a polymer electrolyte membrane. The polymer electrolyte membrane widely used in PEMFC and DMFC is Nafion®, due to its good chemical stability, high proton conductivity, and thermal stability. In the other hand, Nafion® has disadvantages such as: The raw material of polymer used is still quite expensive and difficult to control humidity. Their methanol permeability is still quite high, which decreases the efficiency in the direct methanol fuel cell, and a recycling problem when it is not used anymore. One of the polymers with low cost and used widely is polystyrene (PS). Polystyrene can be modified by sulfonation and blending with other polymers, thus it is potentially used as proton exchange membrane. The aims of this study are to synthesize polyelectrolytes material for PEMFC and DMFC applications from sulfonated polystyrene (SPS) with the addition of lignosulfonate (LS) and silica. The parameters that will be examined in this study were reaction conditions of sulfonation and the composition of each component on the structure and properties of resulted polymer electrolyte membranes and its application for fuel cells. The first stage of this research was initiated with sulfonation of polystyrene. Sulfonated polystyrene (PS) was prepared by homogeneously sulfonation with acetyl sulfate as a sulfonating reagent. Some parameters such as temperature and duration of sulfonation, and compositions of the sulfonating reagent were used for optimising sulfonated polystyrene. The second stage was preparation of polymer electrolyte membrane by blending between the optimum sulfonated polystyrene (SPS) obtained in the first stage with lignosulfonate (LS). The blending of SPS and LS was carried out by casting polymer solution at various compositions of LS to obtain the optimum SPS-LS membrane. The third stage was the synthesis of polymer electrolyte membrane by blending between the optimum SPS-LS membrane obtained in the second stage with silica (SiO2) at various compositions, thus it is produced a polyelectrolyte membrane of SPS-LS-SiO2 with good mechanical and thermal properties, high proton conductivity, low methanol permeability, and also low cost. To obtain the information about the structure and its relation with characteristics of polymer electrolyte membranes, the membranes were characterized by analysis of functional groups, thermal stability, mechanical properties, surface morphology, water uptake, ion exchange capacity, proton conductivity, and methanol permeability. Based on the research results obtained, it can be indicated that the polystyrene has been successfully modified to become electrolyte membrane material for fuel cell by sulfonation and blending with LS and SiO2. The sulfonation of PS has been well carried out, which was qualitatively shown by analysis of functional groups and intrinsic viscosity. The optimum conditions for sulfonating polystyrene to produce the optimum sulfonated polystyrene (SPS) that can be applied as an electrolyte membrane fuel cell is obtained when the mole ratio of PS to the sulfonate reagent for 1 / 736 or written SPS (2:4) in DCM solvent at a temperature of 40?C for 80 minutes. The influence of adding LS on PSS membranes can be shown by analysis of functional groups (FTIR). The ion exchange capacity (IEC), water uptake, methanol permeability, thermal stability and pore formation of membranes increase with the increase of LS ratio in the membranes. The proton conductivity and mechanical strength of membranes increase and reach a maximum at LS content of 7.5 % (w/w). Based on the physicochemical properties of SPS-LS membranes, the SPS-LS membrane with LS content of 7.5% (w/w) (SPS-LS7.5) is the optimal membrane and potentially to be used as the electrolyte membrane in PEMFC and DMFC. Similarly, the effect of adding silicate (SiO2) on the SPS-LS7.5 membrane can be shown from the analysis of functional groups (FTIR) and energy dispersive X-ray spectroscopy (EDS). The ion exchange capacity (IEC), water uptake, proton conductivity and mechanical strength of the membranes increase when the ratio of SiO2 content in membranes is increased. However, the methanol permeability and pore surface of membranes decrease with increasing SiO2 content. Based on the physicochemical properties, the membranes of SPS-LS-SiO2-1 (1 % silica) and SPS-LS- SiO2-2 (2 % silica) are very potentially used as the electrolyte membrane, particularly in PEMFC or DMFC.