Supporting Information. From Metal-Organic Framework to Nanoporous Carbon: Toward a Very High Surface Area and Hydrogen Uptake

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1 Supporting Information From Metal-Organic Framework to Nanoporous Carbon: Toward a Very High Surface Area and Hydrogen Uptake Hai-Long Jiang, Bo Liu, Ya-Qian Lan, Kentaro Kuratani, Tomoki Akita, Hiroshi Shioyama, Fengqi Zong, and Qiang Xu*, National Institute of Advanced Industrial Science and Technology (AIST), Ikeda, Osaka , Japan Analytical and Testing Center, Changzhou University, Changzhou, Jiangsu, China q.xu@aist.go.jp S1

2 S1. Materials and Instrumentation. All chemicals were from commercial and used without further purification: ZIF-8 (Zn(MeIM) 2 (DMF) (H 2 O) 3, MeIM = 2-methylimidazole, Sigma-Aldrich), furfuryl alcohol (Sigma-Aldrich, 99.%) and methanol (CH 3 OH, Kishida Chemical Co., Ltd., 99.8%). Powder X-ray diffraction (PXRD) was carried out with an X-ray diffractometer of Rigaku, Rint 2. IR spectra were recorded on a BIO-RAD FTS-6e spectrometer at.5 cm -1 resolution by using a liquid-nitrogen-cooled HgCdTe (MCT) detector for the range of 4-4 cm -1. The nitrogen sorption isotherms were measured by using automatic volumetric adsorption equipments (Mircomeritics, ASAP21 or/and BELSORP mini II, BEL Japan, Inc.). The hydrogen sorption isotherms were obtained by using an automatic volumetric adsorption equipment (BELSORP mini II, BEL Japan, Inc.). The large surface area of the carbon material involves the use of small amounts of product (1-2 mg) for each sorption experiment. The structure and morphology of resultant carbon materials were observed by using a scanning electron microscope (SEM, Hitachi, S-5) equipped with an energy dispersive X-ray detector (EDX) at 2 kv and a transmission electron microscope (TEM, JEOL, JEM-3F) at an acceleration voltage of 3 kv. The electrochemical experiments were performed under ambient conditions. Before the measurements, the capacitor cell was evacuateded for 3 min to allow the active material fully soaked in the electrolyte. Cyclic voltammograms at different sweep rates for the capacitor were carried out on an ALS CHI68B electrochemical analyzer. The specific capacitance is calculated according to the following equation (1): C = 2 Q / ( V m) (1) Where Q is the charge integrated from the whole voltage range, V is the whole voltage difference, and m is the mass of carbon on an electrode. Galvanostatic charge/discharge examinations at various current densities were performed on an ALS CHI68B electrochemical analyzer and a voltage range of -.5 to.5 V was set. Specific capacitance of each electrode was calculated according to the following equation: C = 2 I t / ( V m) (2) S2

3 where I is the discharge current, t is the discharge time from to -.4 V, V is the voltage difference within the discharge time t, and m is the mass of carbon on an electrode. The factor of two in these equations comes from the fact that the total capacitance measured from the test cells is the sum of two equivalent single electrode capacitors in series. S2. Capacitor Construction. All electrochemical measurements were carried out in a two-electrode cell (capacitor) with 1. M sulfuric acid aqueous solution as electrolyte (each electrode containing 2. mg nanoporous carbon without adding any binder and conductive agents), in which a glassy paper separator was sandwiched between two electrodes and Pt plates were used as electronic collectors. Two identical electrodes were adopted as cathode and anode for the cell configuration. S3. Pretreated method for ZIF-8. Prior to carbon precursor loading, the commercial ZIF-8 was pretreated as follows: ZIF-8 was immersed in methanol under ambient conditions for over 48 h, evacuated at room temperature for over 1 h, then at 3 ºC for 2 h to obtain optimally evacuated sample. S4. Preparation and characterizations of C6 sample. For comparative study, C6 sample was also prepared under the same preparation procedure/conditions except for the calcination temperature (6 ºC). Powder XRD showed the mixture of ZnO and carbon was left as the final product and the ZnO species can be effectively removed by washing with HCl solution (Figure S3). The surface area of C6 sample is as low as 97 m 2 /g after removing ZnO species (Figure S5). Accordingly, as shown in Figure S6, its pore densities and electrochemical capacitor capacity are also very low compared to C8 and C1 samples. S5. Discussion on introducing FA into ZIF-8. S3

4 Although the highly porous character and robust and oxygen-free framework of ZIF-8 make itself suitable as both precursor and template for porous carbon synthesis, only limited FA can be loaded into the framework due to the small pores in ZIF-8, as indicated by elemental analysis results for ZIF-8: C 42.5%, N 24.19%, H 4.35%; for PFA/ZIF-8, C 42.44%, N 23.88%, H 4.37%. Polymerized FA, designated as PFA, was prepared after polymerization process (after 8 ºC and 15 ºC heat treatment). The increase of C content and decrease of N content in the elemental analysis results and characteristic IR peaks of FA involved in FA/ZIF-8 and PFA/ZIF-8 samples (Figure S4) reveal the successful inclusion of PFA, while the slight C/N content change and weak IR signals may be owing to the limited inclusion amounts of FA in the small pore space in ZIF-8. S6. Regarding the precursor role of ZIF-8. ZIF-8 was pretreated/desolvated and then subjected to the same heat treatment procedure as that for C1 sample. Two independently prepared samples show slight differences in their high surface areas up to 3148 m 2 /g (Figure S1a), both of which are lower than that of C1 sample. The results show that ZIF-8 as a precursor mostly contributes and the addition of the other FA precursor can reasonably improve the pore texture of the resultant carbon material. S7. Regarding the template role of ZIF-8 and the accessibility of FA molecule to the pores of ZIF-8. Although the free window size of ZIF-8 is comparable to that of furfuryl alcohol (FA), the accessibility of FA molecule to ZIF-8 cavity can be simply demonstrated from recent reports, where benzyl alcohol and benzaldehyde, even the larger benzylidene malononitrile can access the pores of ZIF-8. 1,2 All these molecules are not smaller than FA. On the other hand, control experiment was performed by replacing ZIF-8 with the starting materials for its synthesis (Zn(NO 3 ) 4 4H 2 O and 2-methylimidazole with weight ratio of 7:2) whereas other experimental parameters were kept the same for preparation of C1. No carbon material can be obtained as product. Therefore, S4

5 the FA molecule is able to access the ZIF-8 cavity and the template/precursor role of ZIF-8 is approved. S8. Discussion on determination of BET surface area for resultant carbon materials. The BET surface area and pore volume were measured by using an automatic volumetric adsorption equipment (Mircomeritics, ASAP21) and using the data in the relative pressure range of For the BET analysis, one of the most important things is to select an appropriate linear region on the BET plot. Snurr and coworkers have shown that BET analysis based on the standard BET pressure range (.5 < P/P <.3) for MOFs and zeolites with ultra-micropores (< 7 Ǻ) usually underestimates the surface areas. 3 Therefore, we have also re-chose the linear region and obtained BET surface area based on consistency criteria. 3,4 In order to obtain the adsorption data in the lower pressures, another adsorption equipment (BELSORP, BEL Japan, Inc.) was used for N 2 sorption measurement. The N 2 sorption curves obtained with different equipments almost match each other (Figures S8a, S9a and S1a). As displayed in Figures S8-1, the resultant linear regions and BET surface areas based on the consistency criteria are almost similar to those from ASAP21 automatic calculations, which is probably due to the fact that all the carbon materials involve not only micropores but also considerable meso- even macro-pores (Table S1). References (1) Esken, D.; Turner, S.; Lebedev, O. I.; Van Tendeloo, G.; Fischer, R. A. Chem. Mater. 21, 22, (2) Tran, U. P. N.; Le, K. K. A.; Phan, N. T. S. ACS Catal. 211, 1, 12. (3) Bae, Y.-S.; Yazaydın, A. Ö.; Snurr, R. Q. Langmuir, 21, 26, (4) Rouquerol, J.; Llewellyn, P.; Rouquerol, F. Stud. Surf. Sci. Catal. 27, 16, 49. S5

6 Table S1. Pore volume and pore size distribution analyses [a] for the obtained carbon materials. carbon obtained from ZIF-8 and FA carbon obtained from ZIF-8 only [h] C8 C1 total pore volume (cm 3 /g) micropore volume (cm 3 /g) [b] mesopore volume (cm 3 /g) [c] macropore volume (cm 3 /g) [d] BET surface area (m 2 /g) micropore area (m 2 /g) [e] mesopore area (m 2 /g) [f] macropore area (m 2 /g) [g] [a] the data obtained by ASAP21 adsorption equipment. [b] t-plot micropore volume. [c] calculated from total pore volume subtracting to micropore and macropore volumes. [d] calculated from adsorption curve by BJH method. [e] t-plot micropore area. [f] calculated from BET surface area subtracting to micropore and macropore areas. [g] calculated from adsorption curve by BJH method. [h] calcination temperature: 1 ºC. S6

7 (a) (b) Figure S1. View of ZIF-8 framework and its simplified topology and corresponding pore openings via (a) (1) and (b) (111) directions, respectively. The pore space in topology figures (right side) was highlighted with light yellow. S7

8 5 Intensity B R = B/A Intensity (a. u.) 1 A Theta (degrees) R(C8) = 1.7 R(C1) = Theta (degrees) Figure S2. Powder XRD patterns of the porous carbons (C8 and C1). The inset is a sketch map for the calculation of the R values. Intensity (a. u.) (b) (a) Theta (degrees) Figure S3. Powder XRD profiles of (a) pristine C6 and (b) C6 after ultrasonication and washing with HCl solution. The sharp peaks in (a) could be assigned to ZnO species. S8

9 6 FA/ZIF-8 ZIF-8 PFA/ZIF-8 FA * * * * Transparency 4 2 * * Wavelength (cm -1 ) Figure S4. IR spectra for FA, ZIF-8, FA/ZIF-8 and PFA/ZIF-8 samples. The asterisk showing the distinguishable FA characteristic peaks. S9

10 3 25 V ads /cm 3.g -1 (STP) as(bet) = 97 m 2 /g Figure S5. N 2 adsorption-desorption isotherms at 77 K for C6 sample after washing with HCl solution and drying. Specific Capacitance (F/g) (a) Cell Voltage (V) (c) 5 mv/s 1 mv/s 2 mv/s 5 mv/s Cell Voltage (V) (b) 5 ma/g 1 ma/g 25 ma/g 5 ma/g Time (sec) (d) Figure S6. (a, b) TEM images with different magnifications, (c) cyclic voltammograms at different scan rates and (d) galvanostatic charge/discharge curves at different current densities for C6 sample after washing with HCl solution and subsequent drying. S1

11 Figure S7. SEM images and related energy dispersive X-ray spectroscopy (EDS) elemental analyses for (a, b) C8 and (c, d) C1 carbon materials, indicating the C species mostly involved in the samples. The Cu signals originated from the TEM grid V ads /cm 3.g -1 (STP) (a) S11

12 5 4 V(P -P) P/P (b).6 P / [V(P -P)].4.2 R 2 = BET surface area = 2181 m 2 /g (c) Figure S8. (a) N 2 sorption curves for C8 measured by BELSORP mini (blue) ASAP21 (purple) machines at 77 K. The N 2 sorption data from BELSORP mini used for the following (b) and (c) analyses due to its available data points at lower pressure. (b) A plot of V(P -P) vs P/P for determining the first consistency criterion. (c) The selected linear plot (red line) and the resulting BET surface area obtained by fitting the solid black data points, which satisfies the second consistency criterion. Low pressure data and high pressure data with empty blue symbols indicate the points not used in the BET linear plot. S12

13 V ads /cm 3.g -1 (STP) (a) 8 6 V(P -P) (b) S13

14 .6.5 P / [V(P -P)] R 2 = BET surface area = 3453 m 2 /g (c) Figure S9. (a) N 2 sorption curves for C1 measured by BELSORP mini (blue) ASAP21 (purple) machines at 77 K. The N 2 sorption data from BELSORP mini used for the following (b) and (c) analyses due to its available data points at lower pressure. (b) A plot of V(P -P) vs P/P for determining the first consistency criterion. (c) The selected linear plot (red line) and the resulting BET surface area obtained by fitting the solid black data points, which satisfies the second consistency criterion. Low pressure data and high pressure data with empty blue symbols indicate the points not used in the BET linear plot V ads /cm 3.g -1 (STP) (a) S14

15 7 6 5 V(P -P) (b).5 P / [V(P -P)] R 2 = BET surface area = 367 m 2 /g (c) Figure S1. (a) N 2 sorption curves for porous carbon from ZIF-8 precursor only measured by BELSORP mini (blue) ASAP21 (purple) machines at 77 K. The N 2 sorption data from BELSORP mini used for the following (b) and (c) analyses due to its available data points at lower pressure. (b) A plot of V(P -P) vs P/P for determining the first consistency criterion. (c) The selected linear plot (red line) and the resulting BET surface area obtained by fitting the solid black data points, which satisfies the second consistency criterion. Low pressure data and high pressure data with empty blue symbols indicate the points not used in the BET linear plot. S15