Supporting Information Functionalized Bimetallic Hydroxides Derived from Metal- Organic Frameworks for High Performance Hybrid Supercapacitor with Exceptional Cycling Stability Chong Qu,, Bote Zhao, Yang Jiao, Dongchang Chen, Shuge Dai, Ben M. deglee, Yu Chen, Krista S. Walton, Ruqiang Zou*,, and Meilin Liu*, Department of Material Science and Engineering, College of Engineering, Peking University, Beijing 100871, China School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, GA 30332-0245, United States School of Chemical and Biomolecular Engineering, Georgia Institute of Technology, Atlanta, GA 30332, United States 1
Experimental section Synthesis of Ni-Co MOF-74: MOF-74 with different Ni: Co ion ratios were synthesized by a one-pot solvothermal reaction according to a reported procedure. [1] Typically, 0.049 g of Ni(NO3)2 6H2O and 0.026 g of Co(NO3)2 6H2O along with 0.025 g of 2,5-dihydroxy-1,4- benzenedicarboxylic (DOBDC) were dissolved in a mixed solvent with 3.5 ml of dimethylformamide (DMF), 3.5 ml of ethanol, and 3.5 ml of deionized water under stirring. The solution was transferred into a Teflon-lined autoclave, tightly capped, and placed in an oven at 120 C for 24 h. After cooling to room temperature, the parent liquor was decanted, the obtained material was washed thoroughly with methanol and DMF before immersed in anhydrous methanol for 3 days, during which the activation solvent was decanted and replaced once per day. The obtained material was then dried under vacuum at 80 C for 24 h to remove the solvent and obtain as-synthesized MOF-74. For comparison, Ni-Co MOF-74 with different Ni: Co molar ratios were also fabricated by the same process. Synthesis of MOF-74-derived Ni-Co double hydroxide (MDH): 5.0 mg of prepared Ni-Co MOF-74 were dispersed in a 2 M KOH solution (15 ml). The mixture was gently stirred for 2 h at room temperature and then transferred into a 30 ml Teflon-lined stainless autoclave. The autoclave was sealed and placed in an oven at 120 C for 2 h. The as-obtained material was filtered and washed repeatedly with ethanol and deionized water and then dried under vacuum at 80 C for 24 h. Synthesis of N-doped porous carbon (N-C) negative electrode material: A nitrogen-doped hierarchically porous carbon material (denoted as N-C) was prepared from chitosan by a facile molten salt (ZnCl2) method. [2] Briefly, chitosan and ZnCl2 were mixed at a weight ratio of 1:10, and then heat-treated at 110 C for 2 h and 600 C for 2 h under Ar. The as-calcined product was washed by 1 M HCl aqueous solution and de-ionized water for several times to obtain the N-C sample. Characterization: The crystallographic structures of the materials were obtained using an X Pert X-ray PANalytical diffractometer with an X celerator module and Cu Kα (λ = 1.5418 Å) radiation at room temperature, with a step size of 0.02 in 2θ. Surface characterization of elemental electronic states was measured by X-ray photoelectron spectroscopy (Thermo K-Alpha XPS, Thermo Fisher Scientific). The instrument was equipped with a monochromatic Al-Kα X- ray source (hv=1468.6 ev). The spectra were taken in 0.1 ev increments with a beam spot size of 400 µm, constant pass energy of 50 ev, and dwell time of 50 ms per increment. Spectra were averaged over at least 10 scans. The nitrogen isotherms of the materials were measured at 77K using a Quadrasorb system from Quantachrome Instruments. Applying the Brunauer Emmett Teller (BET) model to these isotherms, specific surface areas and pore sizes distribution were determined for each material. FTIR was used to determine different functional groups in electrode materials. The microstructure and morphology were examined by using a scanning electron microscope (LEO 1530 field emission SEM). Raman spectra were obtained using a Renishaw RM 1000 spectromicroscopy system equipped with a 20 objective optical microscope. A He-Ne laser with a 633 nm wave length was used for 2
excitation of the Raman signal in this study with a total power of 17 mw. The spectra were collected every 90 s to obtain in situ information about the formation process of MOF-74 derived Ni-Co functionalized hydroxide. Lenses with focal lengths >8 mm were used to allow a sufficient distance between the lens and the sample surface. Electrochemical measurement: The electrochemical measurements were carried out by using a Solartron SI 1286 electrochemical workstation in case of both three-electrode configuration and two-electrode device. For the working electrode of three-electrode system, a mixture slurry containing of 80 wt% active materials, 10 wt% Super P, and 10 wt% PTFE binder was prepared then rolled with the assistance of ethanol to form a uniform film with a typical areal mass of approximately 3.5 mg cm -2. The film electrode was then pressed between two nickel foam, and dried under vacuum at 80 C for 12 h. A platinum mesh electrode and an Ag/AgCl electrode prefilled with 4 M KCl aqueous solution saturated with AgCl were used as the counter and the reference electrodes, respectively. The cyclic voltammograms (CV) were acquired in a potential range between 0 and 0.5 V at different scan rates, and the charge-discharge processes were performed between 0 and 0.45 V at different current densities in a 2 M KOH aqueous electrolyte. Based on the galvanostatic discharge curve, the specific capacity Q (C g -1 ) of the battery-type MDH was calculated as follows: [3] = S(1) where i m =I/m (A g -1 ) is the current density, m is the mass of the active material, t (s) is the discharge time. The cyclic stability was evaluated by galvanostatic charge-discharge (GCD) measurements at a current density of 20 A g -1. The electrochemical measurements of the two-electrode device containing MDH as positive electrode and N-C as negative electrode (-1.2-0 V) with separator of MPF30AC-100 (Nippon Kodoshi Corporation, Kochi, Japan) in a split test cell (MTI Corporation) configuration were carried out in a 2 M KOH electrolyte. The negative electrode film was prepared with the same method described above with 90 wt% N-C and 10 wt% PTFE binder. The mass ratio of positive electrode to negative electrode is determined according to charge balance theory ( = ). Based on the CV results from three-electrode system, = / S(2) where q represents the charge, m is the mass of the active material, and / is the integral area from CV. In order to achieve charge balance, =, thus, = : = : S(3) 3
The CV was acquired in a potential range between 0 and 1.7 V at different scan rates, and the charge-discharge processes were performed by cycling the potential from 0 to 1.7 V at different current densities. The cyclic stability was evaluated by galvanostatic charge-discharge measurements at a current density of 20 A g -1. The specific capacitance C (F g -1 ) was calculated from the galvanostatic charge-discharge measurements using the following equation, [4] C= 2 S(4) C represents the galvanostatic discharge specific capacitance. is the integral current area, where V is the potential with initial and final values of V i and V f, respectively. =I/m is the current density, where I is the current and m is the mass of active materials. Faradaic efficiency (Coulombic efficiency) was calculated as follows: = = = S(5) where η is the Faradaic efficiency, Q c /Q d are the charge/discharge specific capacities,, are the charge/discharge durations, i m =I/m (A g -1 ) is the current density. The energy density E (Wh/kg) and power density P (kw/kg) in Ragone plot were calculated with the following equations, = 1 2 3.6 =3.6 S(6) S(7) Where C is the specific gravimetric capacitance (F/g), V is the potential window (V), and t is the discharge time (S). 4
Figure S1. (a)-(d) SEM images of different Ni-Co ratio MOF-74 25Ni-MOF-74, 50Ni-MOF-74, 75NiMOF-74, and 85Ni-MOF-74, respectively, (e)-(h) SEM images of different Ni-Co ratio MOF-74 derived Ni-Co hydroxides 25Ni-MDH, 50Ni-MDH, 75Ni-MDH, and 85Ni-MDH, respectively. 5
Figure S2. (a) Schematic of secondary building unit and three-dimensional crystal structure of Ni-Co MOF-74, (b) XRD patterns of as-synthesized MOF-74 with different Ni-Co mole ratio and simulated MOF-74. 6
Figure S3. (a) N 2 absorption-desorption isotherm of 65Ni-MOF-74, (b) Pore size distribution (PSD) of 65Ni-MOF-74, (c) XPS survey scan of 65Ni-MDH, (d) O 1s high resolution spectrum of 65Ni-MDH. 7
Figure S4. (a), (b) High resolution XPS spectra of Ni 2p, and Co 2p in the 65Ni-MDH sample, respectively. 8
Figure S5. (a) CV curves of 65Ni-MDH and 65Ni-MOF-74 at 10 mv s -1, (b) CV curves of 65Ni-MOF-74 at different scan rates, (c) GCD curves of 65Ni-MDH and 65Ni-MOF-74 at 1 A g -1, (d)cycling performance of 65Ni-MDH and 65Ni-MOF-74. 9
Figure S6. (a) CV curves of 65Ni-MDH at various scan rates, (b) GCD profile of 65Ni-MDH at different current densities. 10
Figure S7. (a) GCD profile of 25Ni-MDH at different current densities, (b) GCD profile of 50Ni-MDH at different current densities, (c) GCD profile of 75Ni-MDH at different current densities, (d) GCD profile of 85Ni-MDH at different current densities. 11
Figure S8. (a) CV curves of N-C at various scan rates, (b) Specific capacitance of N-C at different scan rates, (c) CV curves comparison between 65Ni-MDH positive electrode active material and N-C negative electrode material at 10 mv s -1. 12
TableS1. Ni-Co oxides/hydroxides cycling performance comparison. Figure S9. (a) GCD profiles and (b) corresponding specific capacitance of the 65Ni-MDH//N-C device at different current densities. 13
Figure S10. (a) Faradic efficiencies of the 65Ni-MDH//N-C at different current densities, (b) GCD curves of 65Ni-MDH//N-C devices based on different m+ to m- ratios. Figure S11. Ragone plot of the 65Ni-MDH//N-C device compared to reported materials in the literatures (see references 45-50 in manuscript). 14
Figure S12. 1 st and 5,000 th cycle Raman spectra of 65Ni-MDH (highlighted area: the characteristic peaks for Ni-Co hydroxides). 15
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