POLYSULFONE/SULFONATED-POLYSULFONE/TiO2 COMPOSITE MEMBRANES FOR FUEL CELL APPLICATION
THESIS As pre-requisite to achieve Master Degree from Institut Teknologi Bandung
By EDI PRAMONO 20506032 CHEMISTRY DEPARTMENT
INSTITUT TEKNOLOGI BANDUNG 2007
ABSTRACT At present most of the world’s energy supply come from fossil sources. Environmental impacts of fossil fuel usage are now considered to be not environmental friendly. Production of CO2 from human activities has been causing the earth temperature to rise and indirectly affected the climate. recently, the development of alternative clean energy and energy conversion are the major project to solve that problem. The development of alternative clean energy and energy conversion based on liquid electrolyte as ion conductor has been known to cause corrosion problems. Therefore, there is a demand for solid proton conductor based on solid polymer. In this research, sulfonated polysulfone (SPSf) cation exchange membranes, which were prepared by sulfonation of polysulfone (PSf) using chlorosulfonic acid in chloroform, were evaluated as Polymer Electrolyte Membrane (PEM). This work consists of three main stages, namely sulfonation of polysulfone, membrane preparation and its characterization. The effects of inorganic filler, TiO2 nanoparticles on the properties of PSf/SPSf/TiO2 composite membrane were also investigated. The sulfonation was done by varying the concentration of chlorosulfonic acid from 5 to 15% v/v in chloroform and nitrogen atmosphere. Membranes preparation were done using phase inversion method by casting the dope (casting solution) onto clean glass. The dope was made by dissolving the polymer (PSf and SPSf) in DMAc (dimethylacetamide). SPSf powder and the resulting membranes were characterized using 1H NMR and FTIR spectroscopies, acid base titration, thermal and mechanical analysis as well as morphologies surface and cross section by SEM (Scanning Electron Microscope) and electrochemical analysis. It was found that the sulfonation induces a decrease in the glass transition temperature (Tg) of polymer which indicate the occurrence of polymer main chain degradation. Sulfonation of PSf with 5% of chlorosulfonic acid achieved high yield (94.53%), but higher concentrations (10 and 15%) may cause chemical degradations which make the polymer soluble in water. High degree of sulfonation caused the polymer to be hydrophilic and the polymer chain shortening caused by the degradation make the polymer-water interaction easier, thus the polymer is soluble in water. Therefore, sulfonation product from 10 and 15% of chlorosulfonic acid can’t be uses as PEM materials. The presence TiO2 increased the mechanical stability and also the membranes ion conductivity. The increase of inter chain interaction and the interaction between polymer and TiO2 particles resulted in an increased membrane mechanical stability. The presence of TiO2 in membrane structure also facilitated ion movement from anode to cathode which causes an increasing of membrane ion conductivity. Higher concentration SPSf (10%) in the membrane composition results in brittle membranes. Hydrophilic-hydrophobic inters polymer chain results crack-like area in the membrane surfaces, which caused in decrease of membrane elasticity.
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Impedance data showed the presence of TiO2 results in a decrease of membranes resistance or increase of membrane conductivity. Addition of inorganic filler can improve ion transport through the membrane and increase the membrane conductivity. Higher concentration of SPSf (10%) resulted in decreasing membranes resistance in compared to PSf membrane. Composite membrane with composition PSf/SPSf/TiO2 10/10/5 produces membrane which has highest ion conductivity. Electrochemical performance, thermo-mechanical stability and low cost fabrication the resulting membranes are attractive as PEM material. However, modification still needed to improve the membrane performance.
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ABSTRAK Dampak pemakaian bahan bakar fosil dirasa telah membahayakan bagi kehidupan manusia. Gas CO2 yang dihasilkan oleh aktivitas manusia telah mengakibatkan peningkatan temperatur bumi dan secara tidak langsung telah mempengaruhi terjadinya perubahan iklim. Berkurangnya persedian minyak bumi juga menjadi masalah besar yang perlu diatas. Saat ini pengembangan bahan bakar alternatif dan konversi energi terus digalakan untuk mengatasi masalah tersebut. Pengembangan bahan bakar alternatif yang didasarkan pada elektrolit cair sebagai konduktor ion seringkali menimbulkan masalah misalnya korosi. Oleh karena itu saat ini dibutuhkan suatu konduktor ion berbasis elektolit padat. Pada penelitian membran penukar kation berbasis polisufon tersulfonsi (SPSf) dibuat dan dikarakterisasi sebagai membran elektrolit polimer (Polymer Electrolyte Membrane, PEM). Penelitian ini terbagi atas tiga tahapan utama yaitu sulfonasi polisulfon (PSf), pembuatan membran, serta karakterisasi terhadap polimer dan membran yang dihasilkan. Pada penelitian ini juga dianalisa pengaruh penambahan TiO2 pada membran komposit polisulfon/SPSf/TiO2. Proses sulfonasi dilakukan dengan memvariasikan konsentrasi asam klorosulfonat sebagai agen pensulfonasi dari 5 sampai 15% v/v dalam pelarut kloroform dan atmosfer nitrogen. Pembuatan membran dilakukan dengan metode inverse fasa melalui proses casting larutan cetak pada permukaan kaca. Larutan cetak dibuat dengan melarutkan polimer (PSf dan SPSf) dalam DMAc (dimetilasetamida) dengan komposisi tertentu. Polimer maupun membran yang dihasilkan dikarakterisasi dengan spektroskopi 1H NMR dan FTIR, kapasitas penukar ion, stabilitas termal dan mekanik, serta analisa morfologi dan impendansi membran. Hasil mununjukkan proses sulfonasi mengakibatkan terjadinya degradasi pada rantai utama polimer yang ditunjukkan dengan penurunan temperature transisi glas (Tg) polimer. Pada konsentrasi asam klorosulfonat 5% v/v dihasilkan prosentase rendemen yang cukup tinggi (94,53%), namun demikian sulfonasi dengan konsentrasi asam klorosulfonat cukup tinggi (10 dan 15%) menghasilkan produk yang larut dalam air. Kadar sulfonasi yang terlalu tinggi mengakibatkan polimer menjadi hidrofil dan pemendekan rantai polimer yang diakibatkan oleh degradasi mempermudah interaksi antara polimer dengan air sehingga polimer dapat larut dalam air. Dengan demikian produk sulfonasi dengan konsentrasi asam klorosulfonat 10 dan 15% v/v tidak dapat digunakan sebagai material PEM. Penambahan partikel TiO2 pada komposisi membran mampu meningkatkan stabilitas mekanik membran serta konduktifitas ion membran. Peningkatan interaksi antar rantai polimer pada stuktur membran serta dengan adanya interaksi antara polimer dengan partikel TiO2 mengakibatkan peningkatan stabilitas mekanik membran. Keberadaan TiO2 dalam struktur membran juga mampu memfasilitasi proses pergerakan ion dari anoda ke katoda dan hal inilah yang mengakibatkan peningkatan konduktivitas ion membran. Penurunan elastisitas membran terjadi pada komposisi membran dengan kadar SPSf yang cukup tinggi (10%). Interaksi hidrofil dan hidrofob antar rantai polimer meghasilkan daerah retakan pada membran yang ditunjukkan oleh data SEM,
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daerah retakan tersebut mengakibatkan membran mengalami penurunan pada elastisitasnya. Pengukuran impedansi membran menunjukkan terjadinya penurunan hambatan membran atau meningkatnya konduktivitas membran dengan meningkatnya kadar SPSf dan TiO2 pada membran. Hambatan listrik terendah diperoleh pada komposisi membran dengan kadar SPSf 10% b/b dan TiO2 5% b/b. Secara umum membran yang dihasilkan pada penelitian ini cukup menjajikan sebagai PEM, hal ini didukung oleh performa elektrokimia yang cukup baik, stabilitas termal dan mekanik yang tinggi, serta harga yang cukup murah dalam proses pembuatannya, namun demikian perbaikan masih perlu dilakukan untuk menghasilkan kinerja membran yang lebih baik.
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Polysulfone/Sulfonated-Polysulfone/TiO2 Composite Membranes for Fuel Cell Application
By Edi Pramono 20506032
Chemistry Department Institut Teknologi Bandung
Has been approved as pre-requisite to achieve Master Degree from Institut Teknologi Bandung
Date ………………….
Supervisor,
Supervisor,
Supervisor,
Dr. Ing. Cynthia L. Radiman
Dr. Katja U. Loos
Dr. Veinardi Suendo
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GUIDELINES OF USING THESIS Unpublished master theses that are registered and available in library of Institut Teknologi Bandung, opened for public with copyright in the author following rules of HAKI of Institut Teknologi Bandung. References are allowed to write, but quotation or summary is only allowed with the permission of author, by following scientific ethic to put the source of it. Copying or publishing part or entire thesis must have permission from Director of Graduated Program, Institut Teknologi Bandung.
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Dan kamu lihat gunung-gunung itu, kamu sangka ia tetap di tempatnya, padahal ia berjalan sebagai berjalannya awan. (Begitulah) Perbuatan Allah yang membuat dengan kukuh tiap-tiap sesuatu; sesungguhnya Allah Maha Mengetahui apa yang kamu kerjakan. (QS Al-Qashash : 88) Allah meninggikan langit tanpa tiang (sebagaimana) yang kamu lihat, kemudian Dia bersemayam di atas (menguasai) Arsy, dan menundukan matahari dan bulan. Masing-masing beredar hingga waktu yang ditentukan. Allah mengatur urusan (makhluk-Nya), menjelaskan tanda-tanda (kebesaran-Nya), supaya kamu meyakini pertemuan (mu) dengan Tuhan-mu. (QS Ar-Rad : 2)
Tesis ini ku persembahkan untuk Bapa, Mama, mas Jon, Ebit, mbah dan iank yang selalu penulis sayangi, serta teman-teman seperjuangan.
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ACKNOWLEDGEMENT In the Name of Allah, Most Gracious, Most Merciful. All praise and thanks are due to Allah, and peace and blessings be upon His Messenger. Only with Allah blessing that this thesis “Polysulfone/sulfonated-polysulfone/TiO2 composite membranes for fuel cell application” can be finished. In the period of finishing this thesis, I have received lots of help from people around me. Therefore, I would like to give my thanks to : •
My family, for always supporting me
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Dr. Ing. Cynthia L. Radiman, as my supervisor
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Dr. Katja Loos, for accepting me in her Laboratory and be my supervisor
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Dr. Veinardi S., as my supervisor
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Fida M. W., Ph.D for helping us to arrange the scholarship
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DIKTI, for providing the scholarship for us
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All the staff in Chemistry Department- ITB
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Dian Kencana Ayudhia, for always supporting me
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Kurawas n Emban, for struggling together in Groningen
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And all who are not mentioned here
Best Regards,
Edi Pramono
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Table of Content ABSTRACT............................................................................................................ ii ABSTRAK ............................................................................................................. iv GUIDELINES OF USING THESIS ..................................................................... vii ACKNOWLEDGEMENT ................................................................................... viii ACKNOWLEDGEMENT ..................................................................................... ix Table of Content...................................................................................................... x List of Figures ....................................................................................................... xii List of Tables ....................................................................................................... xiii List of Appendix .................................................................................................. xiv Chapter I Introduction ............................................................................................. 1 I.1 Background.................................................................................................... 1 I.2 Objective of Research.................................................................................... 2 Chapter II Literature Study ..................................................................................... 3 II.1 Fuel Cells...................................................................................................... 3 II.2 Classification of Fuel Cells .......................................................................... 4 II.3 Polymer Electrolyte Membranes .................................................................. 8 II.4 Polysulfone as Membrane Materials .......................................................... 10 II.4.1 Sulfonation of Polysulfone .................................................................. 11 II.4.2 Measurement of degree of sulfonation ................................................ 11 II.5 Composite Membranes............................................................................... 12 Chapter III Experimental ...................................................................................... 13 III.1 Over-all experiment .................................................................................. 13 III.2 Materials.................................................................................................... 14 III.3 Sulfonation of polysulfone........................................................................ 14 III.4 Membrane preparation .............................................................................. 14 III.5 Characterization ........................................................................................ 14 III.5.1 Analysis by 1H NMR and Fourier Transformed Infra Red (IR) spectroscopies ............................................................................................... 14 III.5.2 Acid base titration .............................................................................. 15 III.5.3 Impedance measurements .................................................................. 15 III.5.4 Mechanical properties ........................................................................ 16 x
III.5.5 Swelling degree.................................................................................. 16 III.5.6 Thermal properties ............................................................................. 16 III.5.7 Morphology observation .................................................................... 17 Chapter IV Results and Discussion....................................................................... 18 IV.1 Sulfonation of Polysulfone ....................................................................... 18 IV.2 Cationic Exchange Capacity (CEC) measurement by 1H NMR and acid base titration ...................................................................................................... 20 IV.3 Thermal Properties of PSf and SPSf......................................................... 21 IV.4 Membranes Characterizations................................................................... 23 IV.4.1 Morphology of the membranes.......................................................... 23 IV.4.2 Mechanical stability ........................................................................... 25 IV.4.3 Swelling degree.................................................................................. 27 IV.4.4 Impedance analysis ............................................................................ 29 Chapter V Conclusion ........................................................................................... 30 References ............................................................................................................. 31
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List of Figures Figure II. 1 Schematic of an individual fuel cell..................................................... 3 Figure II. 2 Types of fuel cells ................................................................................ 7 Figure II. 3 Catalyst and membrane layers in the PEM fuel cells........................... 9 Figure II. 4 PSf structure....................................................................................... 10 Figure II. 5 Fouling on the membrane surfaces .................................................... 10 Figure II. 6 Sulfonated polysulfone ...................................................................... 11 Figure II. 7 Hs position in the polymer structure .................................................. 12 Figure III. 1 Flowchart of the experiment............................................................. 13 Figure IV. 1 Sulfonation of PSf with chlorosulfonic acid .................................... 18 Figure IV. 2 Chemical degradation mechanism of polysulfone ........................... 19 Figure IV. 3 FTIR spectra of PSf, SPSf, and SPSf-Na ......................................... 20 Figure IV. 4 1H NMR spectra of PSf and SPSf .................................................... 21 Figure IV. 5 TGA thermogram of PSF and SPSf ................................................. 22 Figure IV. 6 DSC thermogram of PSf and SPSf................................................... 23 Figure IV. 7 SEM images of PSf/TiO2 composite membranes............................. 24 Figure IV. 8 SEM images of PSf/SPSf blend membranes .................................... 25 Figure IV. 9 SEM images of PSf, SPSf, and TiO2 composite membranes ........... 26 Figure IV. 10 Mechanical properties of blend and composite membranes........... 27 Figure IV. 11 Impedance spectra of (A) PSf/TiO2, (B) PSf/SPSf (5%)/TiO2, (C) PSf/SPSf (10%)/TiO2 composite membranes ....................................................... 28
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List of Tables Table III. 1 Composition of membranes ............................................................... 15 Table IV. 1 Sulfonation product based on concentration of sulfonating agent..... 18 Table IV. 2 SPSf properties obtained by 1H NMR and titration method.............. 21 Table IV. 3 Swelling degree of blend and composite membranes........................ 28
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List of Appendix Appendix A Cationic Exchange Capacity (CEC) Measurement .......................... 35 Appendix A. 1 Acid base titration method........................................................ 35 Appendix A. 2 1H NMR method....................................................................... 35 Appendix B Swelling Degree Data ....................................................................... 37
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