Polybenzimidazole 及其奈米複合材 料薄膜在直接甲醇燃料電池的應用

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1 遠東科技大學材料科學與工程系專題演講 Polybenzimidazole 及其奈米複合材 料薄膜在直接甲醇燃料電池的應用 許聯崇教授 國立成功大學材料科學及工程學系中華民國 97 年 3 月 19 日

2 utline Fuel Cells and Proton Exchange Membranes Synthesis of Polybenzimidazoles (PBIs) Research work regarding PBI, PBI/clay and PBI/silica nanocomposite membranes at our Lab

3 Introduction of Fuel Cells and Proton Exchange Membranes

4 What is a Fuel Cell? Anode: H 2 2H + + 2e - Cathode: ½ 2 + 2H + + 2e - H 2 verall reaction: H 2 + ½ 2 H 2 + electrical energy +heat

5 燃料電池之優點 (Ⅰ) 內燃機..經由熱能轉換, 效率低 燃料電池..化學能直接轉變成電能, 效率高

6 燃料電池之優點 (Ⅱ) 低噪音 低污染 多用途 多種進料選擇 免充電

7 Types of Fuel cells

8 PEMFC

9 PEMFC Membrane Electrode Assembly (MEA)

10 PEMFC MEA

11 Motorcycle powered with a fuel cell

12 Chrysler F-Cell

13 Ballard Power Systems

14 Mobile Hydrogen Station

15 Direct Methanol Fuel Cell ( DMFC) 目前以氫氣與氧氣為反應進料的質子交換膜燃料電池組, 因為其堆疊串聯方式與氫氣鋼瓶體積的限制, 尚無法達到真正輕薄短小的要求 因此近年來開始研究使用甲醇為進料的直接甲醇燃料電池 (DMFC), 並設計微小型燃料電池組的串聯方式與製作方法以及燃料卡匣, 使其能達到輕薄短小的目的

16 DMFC Anode:CH 3 H + H 2 C 2 + H + + 6e - Cathode:3/2 2 + H + + 6e - 3H 2 verall reaction: CH 3 H + 3/2 2 C 2 + 2H 2 + electrical energy + heat

17 TSHIBA DMFC

18 HITACHI DMFC Mobile Phone

19 TSHIBA MP3 Player

20 DMFC used in PDA

21 otebook Computer

22 The Desired Properties of PEMFC Membranes High proton conductivity Low electronic conductivity Low permeability of fuel or oxygen Low electro-osmotic drag coefficient Good mechanical properties Thermal, oxidative and hydrolytic stability Low cost

23 Category of Polymers Used in PEMFC Membranes Perfluorinated polymers: afion Partially fluorinated polymers: PVDF-g- PSSA on-fluorinated hydrocarbon polymers: PVA/PWA on-fluorinated aromatic polymers: PSSA, S-PEEK, S-polyimide, S-PP,S-PPS, S-PPP etc. Acid-base blend polymers: PBI/H 3 P 4

24 Commercial Proton Exchange Membrane -afion CF 2 CF 2 CF 2 CF n x CF 2 CF CF 2 CF 2 S m 3 CF 3 - H +

25 Problems of afion for PEMFC and DMFC afion relies on water for proton conductivity, so it cannot operate at high temperatures (> 80 ). afion has a lot of methanol crossover when used in DMFC. That causes loss of fuel and reduces cathode voltage. afion is very expensive (US$ 700 /m 2 ).

26 ecessary Properties of ew Proton Exchange Membranes for DMFC High thermal stability at high temperature. (>100 ) High proton conductivity under an anhydrous condition at high temperatures. Low methanol crossover. Polybenzimidazole (PBI) can meet these requirements!

27 Synthesis of Polybenzimidazole (PBI)

28 Synthesis of Polybenzimidazole (PBI) (1) AA+BB type PBI H 2 H 2 H 2 H 2 HC X CH H in PPA 170 ~ o 200 C H X n

29 Synthesis of Polybenzimidazole (PBI) (2) AB type PBI H HC H 2 PPA H o C n

30 Commercial PBI H H n poly[2,2 -(m-phenylene)-5,5 -bibenzimidazole] PMPBI It is a base polymer (pka=5.5) and can be easily doped with an acid to form a single phase polymer

31 Advantages of PBI membranes for PEMFC and DMFC High thermal stability and good mechanical properties at high temperatures High proton conductivity under an anhydrous condition through hopping mechanism. Low electro-osmotic drag coefficient (near zero). They can be operated at higher temperatures (up to 200 ) than afion (< 80 ). High C tolerance (up to several percent) Low methanol crossover.

32 Hopping Mechanism of PBI Y. L. Ma et al, J. Electrochem. Soc. 151 (2004) A8

33 Conductivity of PMPBI Film doped with Acids B. Xing et al, J. ew Mater. Electrochem. Syst. 2 (1999) 95.

34 Research work of PBI, PBI/clay and PBI/silica nanocomposite membranes at our Lab

35 Problems of PMPBI for DMFC Although the PMPBI has very good mechanical properties, it has a very rigid molecular structure, which is not good for proton transfer. The PMPBI is difficult to dissolve in common organic solvents for the preparation of membranes by solution casting. After doping with acids, the PMPBI membrane becomes brittle.

36 bjectives of ur Research Synthesis of organosoluble, flexible and tough PBI membranes for DMFC application Preparation of PBI/clay and PBI/silica nanocomposite membranes to improve PBI s performance in DMFC application

37 Part 1 Synthesis and properties of a new fluorinecontaining polybenzimidazole for high temperature fuel cell applications Shih-Wei Chuang, Steve Lien-Chung Hsu*, Journal of Polymer Science, Polymer Chemistry Edition, 2006, 44(15) 4508

38 Synthesis of fluorine-containing PBI for DMFC An amorphous, organosoluble, flexible fluorine-containing PBI was synthesized through molecular modification that still retains enough thermal and mechanical properties. H 2 H 2 CF 3 H 2 H 2 + HC CH CF 3 inherent viscosity =2.5 dl/g (conc.=0.5g/dl at 30 o C) H PPA Polyphosphoric acid,200 CF 3 H Fluorinated PBI CF 3 n

39 1 H-MR of fluorine-containing PBI H CF 3 H CF 3 n

40 IR Spectra of PBI membranes doped with different amounts of phosphoric acid H 3100~3250 cm -1 CF 3 H CF cm -1 n Transmittance (%) PBI PBI-1.2H 3 P 4 PBI-1.7H 3 P 4 PBI-2.1H 3 P 4 PBI-3.0H 3 P ~3000 cm Protonation of PBI H Wavenumber (cm -1 ) 3 P 4 + [-C=-] H 2 P 4- + [-C=H-] +

41 Wide angular X-ray diffraction (XRD) pattern of fluorine-containing PBI Intensity amorphous θ (Degree)

42 Solubility of the PBI Polymer Solvent a MP DMAc DMS DMF MSA Methanol THF Chloroform Acetone PBI Polymer b a MP =-methyl-2-pyrrolidone; DMAc =dimethylacetamide; DMS =dimethylsulfone; DMF =dimethylformamide; MSA= methanesulfonic acid; THF =tetrahydrofuran. b + = soluble; - = insoluble

43 TGA thermograms of PBI membranes doped with different amount of phosphoric acid in air Weight (%) PBI PBI-1.2H 3 P 4 PBI-1.7H 3 P 4 PBI-2.1H 3 P 4 PBI-3.0H 3 P 4 The 5% weight loss is at Temperature ( o C) 2 H 3 P 4 H 4 P 2 7 H 2 180

44 Mechanical properties of PBI membranes Modulus (GPa) Stress (MPa) Elongation (%) PBI PBI-1.2H 3 P PBI-1.7H 3 P PBI-2.1H 3 P PBI-3.0H 3 P

45 Methanol permeability of PBI membranes Permeability a (10-9 cm 2 /sec) PBI PBI-1.2H 3 P 4 PBI-3.0H 3 P 4 afion a In 6 wt% methanol solution at room temperature

46 Proton conductivity of PBI membranes doped with different amount of phosphoric acid at different temperatures log ( σ / Scm -1 ) afion117 PBI-3.0H 3 P 4 PBI-2.1H 3 P 4 PBI-1.7H 3 P (S/cm -1 ) Temperature ( o C)

47 Conclusions of our research (1) An amorphous, organosoluble fluorine-containing polybenzimidazole (PBI) can be synthesized from 3,3 -diaminobenzidine and 2,2-bis(4- carboxyphenyl)-hexafluoropropane. The PBI can be easily dissolved in common organic solvents for the preparation of membranes by solution casting. The PBI membrane has good thermoxidative stability (5% weight loss temperature of the polymer is at 520 ) and good mechanical properties. The PBI membrane has low methanol permeability ( cm 2 /sec at 6 wt% methanol). After doping with phosphoric acid, the PBI membranes show higher proton conductivity than afion 117 membrane at high temperatures ( PBI- 3.0H 3 P 4 can reach 1.7x10-4 Scm -1 at 160 ).

48 Part 2 Synthesis and properties of fluorine-containing polybenzimidazole/montmorillonite nanocomposite membranes for direct methanol fuel cell applications Shih-Wei Chuang, Steve Lien-Chung Hsu*, Chiao-Ling Hsu, Journal of Power Sources, 168 (2007) 172

49 rganic/inorganic Hybrid Membranes For Fuel Cell Application Increase of mechanical properties Improvement of conductivity Improvement of thermal stability Increase of water adsorption Decrease of fuel crossover

50 Preparation of Fluorine-Containing PBI/Clay anocomposites for DMFC A modified montmorillonite (m-mmt) was incorporated into the organo-soluble, fluorinecontaining PBI. The PBI has good compatibility with the m-mmt. The high aspect ratio of MMT is expected to decrease the methanol permeation through polymer membranes due to a winding diffusion pathway for methanol.

51 Modification of Clay The modified montmorillonite (m-mmt) was formed by a cation exchange reaction between montmorillonite and an ammonium salt of dodecylamine. RH 2 + HCl RH 3 + Cl - R= CH 3 (CH 2 ) 11 - a + MT + RH 3+ Cl - RH 3+ MT + acl

52 XRD patterns of MMT and m-mmt 4.89(d=1.8nm) Intensity 6.95(d=1.27nm) m-mmt MMT θ

53 WAXD patterns of PBI/m-MMT nanocomposite membranes PBI/7 wt% m-mmt Intensity PBI/5 wt% m-mmt PBI/3 wt% m-mmt PBI θ (Degree)

54 TEM micrographs of PBI/m-MMT nanocomposites 3 wt% m-mmt 5 wt% m-mmt 7 wt% m-mmt

55 Mechanical properties of the PBI/m- MMT nanocomposite membranes Modulus (GPa) Stress (MPa) Elongation (%) PBI PBI/3 wt% m-mmt PBI/5 wt% m-mmt PBI/7 wt% m-mmt

56 Mechanical properties of PBI/m-MMT nanocomposite membranes and phosphoric acid doped PBI/m-MMT nanocomposite membranes Modulus (GPa) Stress (MPa) Elongation (%) PBI PBI/3 wt% m-mmt PBI/5 wt% m-mmt 41% increase 1.19 ± ± ± ± ± ± ± ± ± 0.6 PBI/7 wt% m-mmt 1.55 ± ± ± 1.2 PBI -3.0H 3 P ± ± ± 1.4 PBI/3 wt% m-mmt -3.0H 3 P ± ± ± 0.2 PBI/5 wt% m-mmt -3.0H 3 P ± ± ± 1.8 PBI/7 wt% m-mmt -3.0H 3 P ± ± ± 2.2 The tensile modulus of PBI-3.0H 3 P 4 had a 74 % decrease relative to the pure PBI films. The tensile modulus of PBI/5 wt % m-mmt-3.0h 3 P 4 only decreased by 42 % with respect to the PBI/5 wt % m-mmt without doped acid.

57 Methanol permeability of the PBI/m-MMT nanocomposite membranes in 6 wt% methanol aqueous solution at room temperature Methanol permeability (10-9cm2/sec) % decrease m-mmt content (wt %)

58 Proton conductivity (σ) of PBI/m-MMT nanocomposite membranes doped with different amounts of phosphoric acid at 160 o C under anhydrous condition log ( σ / Scm -1 ) PBI PBI/3 wt% m-mmt PBI/5 wt% m-mmt PBI/7 wt% m-mmt 21~27% decrease mole H 3 P 4 / per unit of PBI

59 Conclusions of our research (2) The amorphous, fluorine-containing PBI has good compatibility with m-mmt. WAXD and TEM analyses showed that the nano-scaled silicate layers were well dispersed in the PBI matrix up to 5 wt% loading. The addition of m-mmt can significantly enhance the mechanical properties of the acid-doped PBI membranes. The methanol permeability of the PBI/5 wt % m-mmt nanocomposite membrane was decreased by approximately 81 % with respect to the pure PBI membrane. The conductivity of the acid-doped PBI/m-MMT nanocomposite membrane was decreased by 21~27 % relative to the acid-doped pure PBI.

60 Part 3 Synthesis of polybenzimidazole/silica nanocomposite membranes by sol-gel process for high temperature proton exchange membrane fuel cells Shih-Wei Chuang, Steve Lien-Chung Hsu*, Yen-Hsin Liu, Journal of Membrane Science, 305, 353 (2007)

61 Sol gel process C 2 H 5 H 5 C 2 Si C 2 H 5 C 2 H 5 H 2 Hydrolysis H H Si H H - H 2 Condensation Si Si Si Si Si Si Si Si Si Si Si Si Si Tetraethyl orthosilicate (TES) Methanol barrier

62 The problem of polymer/silica composites bonding agent Si Si Si Si Si Si Si Si Si Si Si Si Si polymer organic phase separation silica inorganic

63 Synthesis of PBI copolymers H 2 H 2 CF 3 HC CH H 2 H 2 + HC CH + CF 3 H PPA H CF 3 H H x CF 3 H y H PBI10H --- x=0.1n, y=0.9n PBI30H --- x=0.3n, y=0.7n

64 PBI/silica hybrid materials bonding agent

65 IR spectra of PBI copolymers H CF 3 H C 2 H 5 H x CF 3 H y C CH 2 3 Si C 2 H 5 (a) H C 2 H 5 (b) PBI10H PBI30H Transmittance (%) PBI10H with bonding agent C H Transmittance (%) PBI30H with bonding agent C H -(CH 2 )- -(CH 2 ) Wavenumber (cm -1 ) Wavenumber (cm -1 )

66 TEM micrographs of PBI10H/silica nanocomposite membranes PBI10H/10 wt% Silica PBI10H/15 wt% Silica

67 TEM micrographs of PBI30H/silica nanocomposite membranes PBI30H/10 wt% Silica PBI30H/15 wt% Silica

68 Mechanical properties of PBI10H/Silica nanocomposite membranes PBI10H/5%Si 2-3.0H 3 P 4 PBI10H/10%Si 2-3.0H 3 P 4 PBI10H/15%Si 2-3.0H 3 P 4 Modulus (GPa) 0.70 ± ± ± 0.02 Stress (MPa) PBI10H 17% 1.17 ± ± ± 2.5 PBI10H/5%Si 2 increase 1.29 ± ± ± 0.7 PBI10H/10%Si ± ± ± 0.6 PBI10H/15%Si ± ± ± 1.0 PBI10H-3.0H 3 P ± ± ± ± ± ± 3.4 Elongation (%) 26.2 ± ± ± 3.7

69 Mechanical properties of PBI30H/silica nanocomposite membranes PBI30H 1.62 ± ± ± % PBI30H/5wt%Si 2 increase 1.81 ± ± ± 0.7 PBI30H/10wt%Si ± ± ± 1.0 PBI30H/15wt%Si ± ± ± 2.1 PBI30H-3.0H 3 P ± ± ± 4.5 PBI30H/5wt%Si 2-3.0H 3 P 4 Modulus (GPa) 0.88 ± 0.04 Stress (MPa) 41.2 ± 1.4 Elongation (%) 20.1 ± 4.7 PBI30H/10wt%Si 2-3.0H 3 P ± ± ± 3.6 PBI30H/15wt%Si 2-3.0H 3 P ± ± ± 3.3

70 Mechanical properties of PBI30H/silica nanocomposite membranes Modulus (GPa) Stress (MPa) Elongation (%) PBI30H 1.62 ± ± ± 1.5 PBI30H/5 wt% Si 2 PBI30H/10 wt% Si 2 (without bonding agent) 11% increase 1.81 ± ± % increase ± ± ± ± 1.7 PBI30H/10 wt% Si ± ± ± 1.0 PBI30H/15 wt% Si ± ± ± 2.1

71 Methanol permeability of PBI copolymer/silica nanocomposite membranes in 6 wt% methanol aqueous solution at room temperature. Methanol permeability (10-8cm2/sec) % decrease PBI30H/Si2 PBI10H/Si Si 2 content (wt%) 58 % decrease

72 Proton conductivity (σ) of PBI30H/Silica nanocomposite membranes doped with different amounts of phosphoric acid at 160 under anhydrous condition. log ( σ / Scm -1 ) PBI30H PBI30H/5 wt% Si 2 PBI30H/10 wt% Si 2 PBI30H/15 wt% Si 2 22~28% decrease mole H 3 P 4 / per unit of PBI

73 Conclusions of our research (3) The PBI copolymer with a bonding agent had good compatibility with silica. TEM analyses showed that nano-scaled silica particles were dispersed in the PBI copolymer matrix and particle size decreased with the increase of hydroxy group in PBI chain. The tensile modulus of PBI30H/10 wt % silica nanocomposite membranes had a 37 % increase compared to the pure PBI30H films. The methanol permeability of the PBI30H/10 wt % silica nanocomposite films had a 58 % decrease relative to the pure PBI 30H membranes. The conductivity of acid-doped PBI30H/Silica nanocomposites membranes had a 22~28 % decrease relative to the acid-doped pure PBI30H membranes.

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