Anion Conductive Block Poly(arylene ether)s: Synthesis, Properties, and Application in Alkaline Fuel Cells

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1 Supporting Information Anion Conductive Block Poly(arylene ether)s: Synthesis, Properties, and Application in Alkaline Fuel Cells Manabu Tanaka, Keita Fukasawa, Eriko ishino, Susumu Yamaguchi, Koji Yamada, Hirohisa Tanaka, Byungchan Bae, Kenji Miyatake,*,, and Masahiro Watanabe*, Fuel Cell anomaterials Center and Clean Energy Research Center, University of Yamanashi, 4 Takeda, Kofu , Japan Daihatsu Motor Co. Ltd., Frontier Technology R&D Division, 3000 Ryuo, Gamo, Shiga , Japan miyatake@yamanashi.ac.jp (KM), m-watanabe@yamanashi.ac.jp (MW) S1

2 EXPERIMETAL SECTI Materials. 4,4 -Difluorodiphenyl sulfone (FPS) and 4,4 -dihydroxybenzophenone (DHBP) were purchased from TCI Inc. and crystallized from toluene. 9,9-Bis(4-hydroxyphenyl)fluorene (BHF) was purchased from TCI Inc. and used as received. Chloromethyl methyl ether (CMME), zinc chloride, trimethylamine aqueous solution (30 wt%), potassium carbonate, calcium carbonate, sodium hydroxide, potassium hydroxide, sodium bicarbonate, 1,1,2,2-tetrachloroethane (TCE), tetrahydrofurane (THF), toluene, methanol, chloroform, acetone, and,-dimethylformamide (DMF) were purchased from Kanto Chemical Co. and used as received.,-dimethyl acetamide (DMAc, organic synthesis grade, 99%) was purchased from TCI Inc. and dried over 3 A molecular sieves prior to use. Hydrazine hydrate aqueous solution (60 wt%) was supplied from tsuka Chemical Co., Ltd. Polymerization. Precursor multiblock poly(arylene ether)s (PEs) were prepared according to our previously reported method. 1,2 A typical polymerization procedure for PE-X16Y11, in which X represents the number of repeat units in the hydrophobic segment and Y represents the number of repeat units in the fluorene-containing (later hydrophilic) segment, was as follows. The hydrophobic oligomer was first synthesized. A 300 ml round-bottomed flask was charged with FPS ( g, mmol), DHBP ( g, mmol), and potassium carbonate ( g, mmol). The polymerization reaction was carried out in 160 ml of DMAc and 40 ml of toluene with a Dean-Stark trap under nitrogen flow. The reaction temperature was maintained at 150 C for 3 h before the Dean-Stark trap was removed. The reaction was continued at 170 C for another 3 h under nitrogen flow to obtain a light yellow, viscous mixture. A small amount of FPS ( g, mmol) was added to the mixture to ensure end-capping of the oligomer with fluorine-containing terminal groups. The mixture was stirred at 170 C for 1 h, and poured into a large excess of hot water while hot. The precipitated crude oligomer was washed with deionized S2

3 water and methanol several times. After being collected with a glass filter (G2) and drying at 80 C under vacuum, the hydrophobic oligomer was obtained. The degree of polymerization of the hydrophobic oligomer was determined to be X = 8 from the integral ratio in the 1 H MR spectrum. The fluorene-containing oligomer was synthesized similarly to the hydrophobic oligomer. A 300 ml round-bottomed flask was charged with FPS (5.000 g, mmol), BHF ( g, mmol), and potassium carbonate ( g, mmol). The polymerization reaction was carried out in 80 ml of DMAc and 20 ml of toluene with a Dean-Stark trap under nitrogen flow. The reaction temperature was maintained at 140 C for 2 h before the Dean-Stark trap was removed. The reaction was continued at 165 C for another 2 h under nitrogen flow, and then a small amount of BHF ( g, mmol) was added to ensure end-capping. After stirring the mixture at 165 C for 1 h, the oligomer was recovered and purified in a similar way to the above-mentioned hydrophobic oligomer. The degree of polymerization of the fluorene-containing oligomer was determined to be Y = 11 from the integral ratio in the 1 H MR spectrum. Block copolymerization was carried out as follows. The hydrophobic oligomer ( g, [-F] = mmol), the fluorene-containing oligomer ( g, [-H] = mmol), potassium carbonate ( g, mmol), calcium carbonate ( g, mmol), DMAc (100 ml), and toluene (25 ml) were mixed in a 300 ml round-bottomed flask. The mixture was stirred at 145 C for 3 h under nitrogen flow before the Dean-Stark trap was removed. The polymerization was continued at 160 C for 5 h. The mixture was diluted with ca. 100 ml of DMAc at 160 C and poured dropwise into a large excess of hot water while hot. The crude product obtained was washed with deionized water and methanol several times. After being collected with a glass filter (G2) and drying at 80 C under vacuum, the multiblock copolymer was obtained as a white powder. The copolymer was dissolved in 400 ml of chloroform, and then 600 ml of acetone was slowly added into the solution to precipitate the copolymer with a narrower molecular weight distribution. The S3

4 copolymer was dissolved in DMAc, reprecipitated from hot water, and washed with deionized water and methanol several times. The pure multiblock copoly(arylene ether), PE-X16Y11, was collected with a glass filter (G2) and dried at 80 C in a vacuum oven. Chloromethylation of Multiblock Copoly(arylene ether)s. A typical procedure for the chloromethylation reaction was as follows. A 50 ml pressure glass bottle was charged with PE-X16Y11 ( g, [fluorene unit] = mmol) and TCE (20 ml), and placed in a combinatorial reaction system (L-CS Pres., MRITEX Inc.). After stirring the mixture at 35 C for 30 min to ensure dissolution of the copolymer, zinc chloride ( g, mmol) in 1.0 ml THF solution and CMME ( g, mmol) were added into the mixture. The reaction was carried out at 35 C for 120 h to obtain a yellow mixture. The mixture was diluted with ca. 20 ml of TCE and poured dropwise into a large excess of methanol. The crude product was washed with deionized water and methanol several times. After being collected with a glass filter (G2) and drying at 80 C under vacuum, the chloromethylated copolymer, CMPE-X16Y11, was obtained as a white powder. Membrane Preparation and Quaternization. The chloromethylated copolymer, CMPE-X16Y11 (1.000 g) was dissolved in 25 ml of TCE and the solution was filtered with a 0.45 µm PTFE membrane filter. The filtrate was cast onto a flat glass plate and dried on a hot plate at 60 C overnight under ambient conditions to give a 50 ± 5 µm thick, transparent, tough membrane. The membrane was immersed in a 30 wt% trimethylamine aqueous solution at room temperature for 2 days for the quaternization reaction. The resulting quaternized copolymer membrane was washed with water several times and immersed in a 1 M sodium hydroxide aqueous solution at room temperature for 2 days to convert the counter anions from chloride to hydroxide ions. The quaternized copoly(arylene ether) (QPE-X16Y11) membrane obtained was washed with deionized water several times and stored in a closed vessel filled with deionized water. S4

5 Measurements. 1 H MR spectra, molecular weight (gel permeation chromatography (GPC)), water uptake, and ion conductivity were measured as previously reported. 3,4 For scanning transmission electron microscopic (STEM) observations, the membrane samples were stained (ion-exchanged) with tungstate ions by immersing in 1.0 M sodium tungstate aqueous solution, rinsing with deionized water, and drying in a vacuum oven for 12 h. The stained samples were embedded in epoxy resin and sectioned to yield 90 nm thick samples using a Leica microtome Ultracut UCT and placed on copper grids. Images were taken on a Hitachi HD-2300C STEM using an accelerating voltage of 200 kv. Stress versus strain curves were obtained for samples cut into a dumbbell shape (DI S3, 35 mm 6 mm (total) and 12 mm 2 mm (test area)). Measurement was conducted at 60% RH and 80 C at a stretching speed of 10 mm/min. Thermal and hydrothermal stability tests of the QPE membranes were performed at a typical fuel cell operating temperature (80 C). Small pieces of QPE-X16Y11 (IEC = 1.65 or 1.75 meq/g) membranes were placed in vials filled with hot water or air, respectively. The vials were sealed and maintained at 80 C for 500 h. Changes in chemical structure after these tests were investigated by 1 H MR spectra. Fabrication of Membrane/Electrode Assembly (MEA) and Fuel Cell peration. A 100 mg portion of i powder (Inco, type 210H, µm) was mixed with 0.96 ml of isopropanol, 0.24 ml of THF and 0.2 ml of 2 wt% anionic ionomer in THF solution (Tokuyama, A3). The mixture was sonicated for 5 min and mixed by a ball mill with Zr 2 beads (ikkato Corporation, diameter = 2.0 mm) for 15 min. The slurry obtained was sprayed onto a QPE-X16Y11 membrane (IEC = 1.93 meq/g, thickness (under ambient conditions) = 57 µm) to form the anode. For the cathode, the catalyst slurry was prepared from Co-polypyrrole (PPy)-C (Hokko Chemical Industry Co., Ltd.) powder and sprayed onto the other side of the membrane in a similar way to that described above. The loaded amounts of the catalysts were ca. 2.5 mg/cm 2 of i for the anode and ca. 0.2 mg/cm 2 of S5

6 Co-PPy-C for the cathode, respectively. The catalyst-coated membrane was pressed at 9 MPa for 30 s at 80 C to ensure tight contact between the catalyst layers and the membrane. The MEA thus prepared, with a geometric electrode area of 4.41 cm 2, was mounted in a single cell and treated with 1.0 M potassium hydroxide aqueous solution at a flow rate of 2 ml/min for 2 h at 80 C for the ion-exchange of the membrane to the hydroxide form. The fuel cell was operated at 80 C while supplying a mixture of 1.0 M potassium hydroxide and 5.0 wt% hydrazine aqueous solution to the anode at a flow rate of 2 ml/min and humidified oxygen or air (26 %RH) to the cathode at a flow rate of 500 ml/min. The operating pressure was set at 20 kpa for both electrodes. Serpentine and comb-shaped flow fields were used for the anode and the cathode, respectively. (1) Bae, B.; Yoda, T.; Miyatake, K.; Uchida, H.; Watanabe, M. Angew. Chem. Int. Ed. 2010, 49, (2) Bae, B.; Miyatake, K.; Watanabe, M. Macromolecules 2010, 43, (3) Tanaka, M.; Koike, M.; Miyatake, K.; Watanabe, M. Macromolecules 2010, 43, (4) Tanaka, M.; Koike, M.; Miyatake, K.; Watanabe, M. Polym. Chem. 2011, 2, S6

7 Complete reference 3. (3) Borup, R.; Meyers, J.; Pivovar, B.; Kim, Y.-S.; Mukundan, R.; Garland,.; Myers, D.; Wilson, M.; Garzon, F.; Wood, D.; Zelenay, P.; More, K.; Stroh, K.; Zawodzinski, T.; Boncella, J.; McGrath, J. E.; Inaba, M.; Miyatake, K.; Hori, M.; ta, K.; gumi, Z.; Miyata, S.; ishikata, A.; Siroma, Z.; Uchimoto, Y.; Yasuda, K.; Kimijima, K.; Iwashita,. Chem. Rev. 2007, 107, S7

8 Figure S1. 1 H MR spectra of (a) hydrophobic oligomer (X16) and (b) fluorene-containing oligomer (Y11). Figure S2. TEM image of QPE-X22Y11 (IEC = 0.89 meq/g) stained with tungstate ions. Figure S3. Possible degradation mechanisms of AEMs. Figure S4. 1 H MR spectra of QPE-X16Y11 (IEC = 1.65 meq/g) (a) before and (b) after long-term stability tests in hot water at 80 C for 500 h. Figure S5. 1 H MR spectra of QPE-X16Y11 (IEC = 1.75 meq/g) (a) before and (b) after long-term stability tests in hot air at 80 C for 500 h. Figure S6. 1 H MR spectra of QPE-X8Y8 (IEC = 1.26 meq/g) (a) before and after long-term conductivity tests in (b) hot water at 80 C for 5000 h. Table S1. Molecular weight of hydrophobic and fluorene-containing oligomers. S8

9 (a) F a b c d b' a' S C S F 16 CDCl 3 a c b d b' a' (b) e f H g' S h' g H h i' j' j i 11 k' l' k l CDCl 3 f i k h e g l j h' g' Figure S1. 1 H MR spectra of (a) hydrophobic oligomer (X16) and (b) fluorene-containing oligomer (Y11). S9

10 Figure S2. TEM image of QPE-X22Y11 (IEC = 0.89 meq/g) stained with tungstate ions. S10

11 1) H H 2) H 3 C H Stevens Rearragement H 2 H 3) H 3 C H H 2 4) H 3 C H Sommelet-Hauser rearrangement H 2 Figure S3. Possible degradation mechanisms of AEMs. S11

12 a b c d e f S C 16 S g H h o m i k H p n l h l g h 11 k j n DMS acetone (a) a,c,h,h b,d,f k,k e,g,g j,i,i l,l m,n m,n H2 o,p (b) ppm Figure S4. 1 H MR spectra of QPE-X16Y11 (IEC = 1.65 meq/g) (a) before and (b) after long-term stability tests in hot water at 80 C for 500 h. S12

13 a b c d e f S C 16 S g H h o m i k H p n l h l g h 11 k j n DMS (a) a,c,h,h b,d,f k,k e,g,g j,i,i l,l m,n m,n H2 o,p acetone (b) ppm Figure S5. 1 H MR spectra of QPE-X16Y11 (IEC = 1.75 meq/g) (a) before and (b) after long-term stability tests in hot air at 80 C for 500 h. S13

14 a b c d e f S C 8 S g H h o m i k H p n l h l g h 8 k j n DMS o,p (a) a,c,h,h b,d,f k,k e,g,g j,i,i l,l m,n m,n H2 acetone (b) ppm Figure S6. 1 H MR spectra of QPE-X8Y8 (IEC = 1.26 meq/g) (a) before and after long-term conductivity tests in (b) hot water at 80 C for 5000 h. S14

15 Table S1. Molecular weight of hydrophobic and fluorene-containing oligomers. Expected btained btained ligomer oligomer length oligomer length a oligomer length b M n (kg/mol) M w (kg/mol) M w /M n X ,000 12, X ,700 29, X ,500 52, Y ,300 13, Y ,600 12, Y ,800 19, a Estimated from the 1 H MR spectra. b Estimated from the GPC data. S15