SYNTHESIS OF ELECTROLYTE MEMBRANES FROM SULFONATED POLY(ARILEN ETHER KETONES) WITH PARTIAL SUBSTITUTION OF CARBOXYLATE GROUP AND ITS COMPOSITES WITH ADDITION OF NANOSILICA

• Main Author: Aziz, Abdul
• Format: Dissertations
• Language: Indonesia
• Subjects: Kimia
• Online Access: https://digilib.itb.ac.id/gdl/view/67064
• Institution: Institut Teknologi Bandung

Conductive polymer membranes in the last two decades have attracted the interest of researchers because of their very important function in electrolyte fuel cells and batteries. Currently the membranes used in electrolyte fuel cells are commercial perfluorosulphonate ionomer (PFSI) such as Nafion® (DuPont) and Aquivion (Solvay Solexis). The chemical structure of PFSI consists of a hydrophobic polytetrafluoro-ethylene main chain and a hydrophilic perfluoroaliphatic ether side chain with a sulfonate end group. The main chain of the PFSI membrane is responsible for providing superior mechanical properties, thermal and chemical stability, while the sulfonic acid groups are responsible for the high proton conductivity. However, these membranes have drawbacks such as a drastic drop in proton conductivity at temperatures above 80 ? or low humidity, they are expensive and the waste is not environmentally friendly because it contains fluorine. As a consequence, a lot of research has been carried out to find new materials to replace PFSI membranes. Among these new materials, sulfonated aromatic polymers, especially sulfonated poly(arylene ether ketone) (SPAEK) have attracted the interest of researchers because of their good mechanical properties, chemical and thermal stability, high proton conductivity. However, the commercial use of SPAEK as an electrolyte membrane is still constrained by several problems, such as the occurrence of dimensional instability which causes low cell performance because fuel can penetrate the membrane. This dimensional instability is triggered by the polymer structure and hydrophilic groups such as carboxylate and sulfonate. One of the variants of SPAEK that has attracted the interest of researchers is SPAEK with a side chain containing a carboxylate group (SPAEK-C). This research focuses on efforts to overcome the dimensional instability of the SPAEKC membrane through a structural modification approach and the development of composite membranes. Structural modification was carried out by partial substitution of hydrophilic dihydroxyphenyl valeric acid (DPA) monomer with hydrophobic dihydroxyphenyl propane (BPA) monomer, while the development of composite membranes was carried out by mixing inorganic silica additives. This partial substitution is intended to control the composition of the hydrophilic group to suppress excessive water absorption and swelling ratio to maintain dimensional stability of the membrane in operation The most important monomer required in the synthesis process of SPAEK-C polymer by direct sulfonation technique is sulfonated monomer. Oleum has been used on a patented basis and is the research choice for sulfonating aromatic monomers to produce sulfonated monomers. However, at this time oleum is not produced commercially with discontinued status. This study attempts to overcome this problem by replacing the sulfonating agent with concentrated sulfuric acid (H2SO4 98%). Sulfonation was carried out on difluorobenzophenone (DFBP) to produce sulfonated difluorobenzophenone (SDFBP) with an average yield of 53%. The sulfonated monomer product was confirmed using FTIR and NMR spectroscopy methods. The infrared spectrum shows the presence of sulfonate groups at wave numbers of 1354 cm-1 and 1082 cm-1 , respectively, which are stretching vibrations of asymmetry and symmetry of the O=S=O bond and characteristic for the sulfonate groups of arylsulphonates, and the absorption band at wave number 598 cm-1 confirms the vibrations of C-S bond. The 1H-NMR spectra showed the appearance of three proton chemical shift peaks at 7.53 ppm (2H = CH), 8.12 ppm (2H = C-H) and 8.50 ppm (2H = C-H). Modification of SPAEK-C was carried out in the SPAEK copolymer synthesis process by varying the mole ratio of DPA/BPA and SDFBP/DFBP so that the SPAEK-x/y copolymer series was obtained with x mole ratio of DPA/BPA and y mole ratio of SDFBP/DFBP. The SPAEK copolymer synthesis product was confirmed using the FTIR spectroscopy method to ascertain the presence of functional groups in the polymer and the SEM-EDS method to perform qualitative and quantitative elemental composition analysis. The indication of the formation of the SPAEK copolymer is confirmed by the presence of aromatic ether bonds as a new functional group formed from the monomer condensation process. The FT-IR spectrum shows the presence of aromatic ether bonds at the absorption peaks of the duplet 1307 cm-1 and 1275 cm-1 . The presence of sulfonate groups was confirmed by absorption bands at 1365 cm-1 and 1082 cm-1 which are O=S=O vibrations symmetrically and asymmetrically and absorption bands at 598 cm-1 by C-S bond vibrations. The EDS spectrum confirmed the formation of the copolymer according to the synthesis target qualitatively and quantitatively based on the elemental composition and ensured that each repeating unit in the SPAEK-50/50 copolymer had 1 sulfonate group. The printing process of SPAEK membranes is carried out by the casting solution method. All copolymers of the synthesis product were printed as a membrane, but the only stable membranes were SPAEK-50/00, SPAEK-50/25, SPAEK-50/50, SPAEK-75/25 and SPAEK-75/50. The results of the membrane properties test show that the SPAEK-50/50 membrane has superior properties than other SPAEK membranes. The SPAEK-50/50 membrane has the strongest mechanical properties of 23.6 MPa, the most thermally stable with a residue of 54.93%, more resistant to Fenton's oxidizing agents with a stability of 1 hour 99.57% and a stability of 96 hours of 55.52 %, has the most ideal water absorption and swelling ratio of 30.6% and 17.7% respectively at 80 ?, the highest proton conductivity at 80 ? is 0.102 S/cm, close to Nafion 117 at 0.120 S/cm . This finding confirms that the partial substitution of the hydrophilic monomer of DPA with 50% mole of BPA with a composition of 50% sulphonate group resulted in a better SPAEK membrane. Development of SPAEK membrane into SPAEK/Silica composite membrane using TEOS as silica source. The addition of 2.5%, 5% and 10% silica by weight to the SPAEK-50/50 membrane matrix showed a significant increase in the properties of the SPAEK/Silica composite membrane with a silica content of 5% and 10%. Of the two membranes, the composite with a silica content of 10% by weight showed superior properties. The addition of 10% silica to the SPAEK membrane gave a 27% increase in membrane strength, a 79% increase in thermal stability with a decrease in the maximum degradation rate from 8.7 to 1.8%/min, an increase in chemical resistance to Fenton's oxidation from 99.57% to 99.65% in Fenton's test for 1 hour at temperature 80?, an increase in water absorption and dimensional stability and an increase in proton conductivity from 0.102 S/cm to 0.113 S/cm at temperature 80? and relative humidity 100%.