Remarkable Reinforcement Effect in Sulfonated. Aromatic Polymers as Fuel Cell Membrane

Transcription

1 Supporting Information Remarkable Reinforcement Effect in Sulfonated Aromatic Polymers as Fuel Cell Membrane Junpei Miyake, Masato Kusakabe, Akihiro Tsutsumida, and Kenji Miyatake*,, Clean Energy Research Center, and Fuel Cell Nanomaterials Center, University of Yamanashi, Takeda, Kofu, Yamanashi , Japan Material Solutions Research Institute, Kaneka Corporation, Torikai-nishi, Settu, Osaka , Japan Toray Research Center, Inc., Sonoyama, Otsu, Shiga , Japan Corresponding Author * S-1

2 EXPERIMENTAL METHODS Materials. The SPK ionomer was prepared according to the literature. 1 The nonwoven fabric (NF) was composed of glass fiber (70 wt%: average diameter = 0.5 µm, 30 wt%: average diameter = 6 µm), polyethylene terephthalate (PET) fiber (average diameter = 3 µm), and epoxy resin binder. The glass fiber/pet fiber mass ratio was adjusted to 60/40. The weight per unit area and the thickness of the NF were 3.4 g m -2 and 15 µm, respectively. Preparation of the NF-reinforced SPK membrane. A solution of SPK in DMSO (10 wt%) was spread onto a flat PET film (thickness = 188 µm) coated glass plate using a bar coater. After placing the NF (10 cm 10 cm) on the above, the SPK solution was spread again with the bar coater, and dried at 120 C for 12 h on a hot plate. Then, the resulting membrane was peeled from the substrate, treated with 6 M HCl, and washed with deionized water several times. Drying at 60 C for 30 min yielded the targeted NF-reinforced SPK membrane. Measurements. Apparent molecular weight was determined by gel permeation chromatography (GPC) measurement (system: HLC-8220GPC (Tosoh), column: TSKgel SuperAW4000 and 2500 (Tosoh), eluent: NMP containing 0.01 M LiBr) at 40 C. Molecular weight was calibrated with standard polystyrene samples (Tosoh). Ion exchange capacity (IEC) of membranes was obtained by acid-base titration. A piece of membrane (in H + form, ca mg) was equilibrated in saturated aqueous NaCl solution (30 ml) for 24 h at room temperature. The released HCl in the solution by the ion exchange reaction was titrated (AT-510, KEM kyoto) with standard 0.01 M aqueous NaOH solution at room temperature. For water uptake and dimensional change measurements, the membrane was cut into a rectangular shape (1.4 cm 3.0 cm). Drying at 105 C overnight in vacuo provided the dry sample, and immersing in deionized water at 80 C for 6 h provided the wet sample, respectively. From the change of the weight, and the lengths (four sides) and the thickness (three sites), the water uptake and the dimensional change ratio were determined. Proton conductivity of membranes was measured at 80 C with a S-2

3 solid electrolyte analyzer system (MSBAD-V-FC, Bel Japan) in a temperature and humidity controllable chamber. The proton conductivity was measured at given humidity using a fourprobe conductivity cell equipped with an AC impedance analyzer (Solartron 1255B and 1287, Solartron Inc.). Ion-conducting resistance (R (Ω)) was determined by the impedance plot obtained in the frequency range from 1 to 10 5 Hz at 300 mv. The proton conductivity (σ) was calculated from the equation: σ = l / (A R), where l (cm) and A (cm 2 ) are the distance (1.0 cm) between two reference electrodes and the cross-sectional area (1.0 cm thickness cm), respectively. Preparation of the catalyst paste. A catalyst paste was obtained from Pt/CB catalyst (TEC10E50E, Tanaka Kikinzoku Kogyo K. K.), Nafion dispersion ( mequiv g -1, D-521, Du Pont), deionized water, and ethanol by ball milling for 30 min. The mass ratio of Nafion to the carbon support (N/C) was adjusted to Fuel cell performance. The SPK (2.34 mequiv g -1, 24 µm) 2 and NF-reinforced SPK (1.92 mequiv g -1, 20 µm) membranes were used. The catalyst-coated membrane (CCM) was prepared by spraying the catalyst paste on both sides of a membrane. The CCM was dried at 60 C for 12 h and hot-pressed at 140 C and 10 kgf cm -2 for 3 min. The geometric electrode area and the Ptloading amount of the catalyst layer (CL) were 29.2 cm 2 (5.4 cm 5.4 cm) and 0.50 ± 0.05 mg cm -2, respectively. The CCM was sandwiched by gas diffusion layers (GDL, 240 µm, SGL 25BCH, SGL Carbon Group Co., Ltd.), and mounted into a JARI (Japan Automobile Research Institute) standard cell, which had serpentine flow channels on both the anode and the cathode sides. To evaluate the cell performance, polarization curves were measured at 80 C and 53% and 100% RH. Pure hydrogen and oxygen was supplied to the anode and the cathode, respectively. Wet-dry cycling test. The test was conducted according to the FCCJ (Fuel Cell Commercialization Conference of Japan) protocol. 3 The CCM was prepared by spraying the S-3

4 catalyst paste on both sides of a membrane. The CCM was dried at 60 C for 6 h and hot-pressed at 140 C and 10 kgf cm -2 for 3 min. The geometric electrode area and the Pt-loading amount of the catalyst layer (CL) were 25 cm 2 (5.0 cm 5.0 cm) and 0.2 mg cm -2, respectively. The CCM was sandwiched by gas diffusion layers (GDL, 235 µm, SGL 25BC, SGL Carbon Group Co., Ltd.) and PTFE gaskets (200 µm), and mounted into a JARI (Japan Automobile Research Institute) standard cell, which had serpentine flow channels on both the anode and the cathode sides. The cell was operated at 80 C flowing N 2 gas into both the anode and cathode sides at a flow rate of 800 ml min -1. The wet-dry cycling test was conducted by toggling flow of dry gas (0% RH) for 2 min and wet gas (150% RH) for 2 min. After a certain period of time, linear sweep voltammogram was measured by sweeping the voltage ( V) with flowing H 2 gas (200 ml min -1 ) into the anode side and N 2 gas (200 ml min -1 ) into the cathode side (80 C, ambient pressure). The crossover current density (oxidation current density of hydrogen crossed over from the anode) was defined as the intercept which was obtained by extrapolating the linear portion (ca V) of the plot to 0 V. The membrane durability of the test was defined as the point at which the crossover current density reached 10 times compared with the initial value. Scanning electron microscope (SEM). The cross-section of the membrane was prepared with the cross-section polisher (SM-09010, JEOL). After coating with Pt, the image was obtained using S-4800 (Hitachi) with an accelerating voltage of 2 kv. S-4

5 SUPPLEMENTARY FIGURES (a) (b) Cell voltage (IR free) (V) Cell voltage (IR free) (V) Current density (A cm -2 ) Figure S1. IR-corrected H 2 /O 2 polarization curves of the SPK (black) and NF-reinforced SPK (red) cells at 80 C under humidity conditions of (a) 100% and (b) 53% RH. S-5

6 Figure S2. Photographic images of (a, b) the CCM (SPK membrane, 2.58 mequiv g -1 ) after the humidity cycling test and (c) the SPK membrane before the humidity cycling test. S-6

7 Figure S3. Photographic image of the CCM (NF-reinforced SPK membrane, 1.69 mequiv g -1 ) after the humidity cycling test. S-7

8 REFERENCES (1) Miyahara, T.; Hayano, T.; Matsuno, S.; Watanabe, M.; Miyatake, K. Sulfonated Polybenzophenone/Poly(arylene ether) Block Copolymer Membranes for Fuel Cell Applications. ACS Appl. Mater. Interfaces 2012, 4, (2) Mochizuki, T.; Uchida, M.; Uchida, H.; Watanabe, M.; Miyatake, K. Double-Layer Ionomer Membrane for Improving Fuel Cell Performance. ACS Appl. Mater. Interfaces 2014, 6, (3) Fuel Cell Commercialization Conference of Japan Home Page. (accessed Dec 27, 2017). S-8