A Three-Dimensional Copper Coordination Polymer Constructed by 3

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A 3D copper coordination polymer constructed by 3-methyl-1Hpyrazole-4-carboxylic acid with higher capacitance for supercapacitors Lili Yu, Xianmei Wang, Mei-Ling Cheng, Hongren Rong, Yidan Song, and Qi Liu Cryst. Growth Des., Just Accepted Manuscript • DOI: 10.1021/acs.cgd.7b01219 • Publication Date (Web): 17 Nov 2017 Downloaded from http://pubs.acs.org on November 19, 2017

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Crystal Growth & Design

A 3D copper coordination polymer constructed by 3-methyl-1H-pyrazole-4-carboxylic acid with higher capacitance for supercapacitors Lili Yu†, Xianmei Wang†, Meiling Cheng†, Hongren Rong†, Yidan Song†, Qi Liu

*†,‡

†

School of Petrochemical Engineering, Jiangsu Key Laboratory of Advanced Catalytic Materials and Technology, and Advanced Catalysis and Green Manufacturing Collaborative Innovation Center, Changzhou University, 1 Gehu Road, Changzhou, Jiangsu 213164, P. R. China. ‡

State Key Laboratory of Coordination Chemistry, Nanjing University, Nanjing, Jiangsu 210093, China

Abstract: 3D copper-based coordination polymer, ([Cu(H2mpca)(tfbdc)], Cu-CP; H2mpca

=

3-methyl-1H-pyrazole-4-carboxylic

acid;

H2tfbdc

=

2,3,5,6-tetrafluoroterephthalic acid) has been synthesized and characterized by IR spectrum, thermogravimetric analysis, elemental analysis and single-crystal X-ray diffraction. In Cu-CP, each Cu(II) ion is located in a triangular bipyramid geometry, and these Cu(II) ions

are linked by tfbdc2- ligands to produce a

3D network.

Variable-temperature magnetic susceptibility data display that weak antiferromagnetic interactions between the adjacent Cu (II) ions exist in Cu-CP. Cu-CP was evaluated as an electrode material for supercapacitors. It displayed a higher specific capacitance of 735 F g−1 in 1M KOH solution at a current density of 1 A g-1, and remained 375 F g−1 after 1500 cycles at 2 A g-1.

*

Corresponding author: Tel: +86 0519 83288656. E-mail: [email protected]

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A 3D copper coordination polymer constructed by 3-methyl-1H-pyrazole-4-carboxylic acid with higher capacitance for supercapacitors Lili Yu†, Xianmei Wang†, Meiling Cheng†, Hongren Rong†, Yidan Song†, Qi Liu*†,‡ †

School of Petrochemical Engineering, Jiangsu Key Laboratory of Advanced Catalytic Materials and Technology, and Advanced Catalysis and Green Manufacturing Collaborative Innovation Center, Changzhou University, 1 Gehu Road, Changzhou, Jiangsu 213164, P. R. China. E-mail: [email protected] ‡

State Key Laboratory of Coordination Chemistry, Nanjing University, Nanjing, Jiangsu 210093, China

Abstract: 3D copper-based coordination polymer, ([Cu(H2mpca)(tfbdc)], Cu-CP; H2mpca

=

3-methyl-1H-pyrazole-4-carboxylic

acid;

H2tfbdc

=

2,3,5,6-tetrafluoroterephthalic acid) has been synthesized and characterized by IR spectrum, thermogravimetric analysis, elemental analysis and single-crystal X-ray diffraction. In Cu-CP, each Cu(II) ion is located in a triangular bipyramid geometry, and these Cu(II) ions

are linked by tfbdc2- ligands to produce a

3D network.

Variable-temperature magnetic susceptibility data display that weak antiferromagnetic interactions between the adjacent Cu (II) ions exist in Cu-CP. Cu-CP was evaluated as an electrode material for supercapacitors. It displayed a higher specific capacitance of 735 F g−1 in 1M KOH solution at a current density of 1 A g-1, and remained 375 F g−1 after 1500 cycles at 2 A g-1.


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1. Introduction Over the past decade, interest in the rational design and assembly of coordination polymers (CPs)/metal–organic frameworks (MOFs) has increased significantly, owing to their fascinating structural features, and their emerging applications in many fields, including gas storage and separation, catalysis, magnetism, sensors, lithium-ion batteries and so on.1-7 Many routes used to synthesize coordination polymers have been reported. Among them, it is an effective route to construct CPs via the assembly of metal ions and mixed bridging ligands, especially for the bridging ligands containing O/N atom.8-11 Recent years, pyrazole-carboxylic acids, as good building blocks in the assembly of CPs, are receiving considerable attention, due to them not only providing rich coordination modes, but also acting as acceptors and/or donors in hydrogen bond interactions. Many CPs with functional properties based on 3,4-pyrazoledicarboxylic acid, 3,5-dimethyl-1H-pyrazole-4-carboxylic acid, 1H-pyrazole-4-carboxylic acid,

5-methyl-1H-pyrazole-3-carboxylic acid, and

1-carboxymethyl-3,5-dimethyl-1H-pyrazole-4-carboxylic acid etc have been synthesized by us and other research groups.12-23 However, to the best of our knowledge, only a few CPs derived from 3-methyl-1H-pyrazole-4-carboxylic acid (H2mpca) have been reported by us so far.24,25 Tetrafluoroterephthalic acid (H2tfbdc), as a versatile linker similar to 1,4-benzenedicarboxylic acid, has been used in synthesizing CPs with interesting structures and properties.26-37 For instance, 2D CPs Ln(tfbdc)1.5·DMF·H2O (Ln = Pr3+ (1), Nd3+ (2)) present



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antiferromagnetic property;36 [Mn(tfbdc)(4,4′-bpy)(H2O)2], a 2D CP, serves as an anode material for Li-ion batteries, displaying a reversible specific capacity of 390 mA h g−1.37 But, 3D CPs based on H2tfbdc and H2mpca ligands have not been reported so far. On the other hand, face to the problems of environmental pollution, the use of clean energy sources, such as wind and solar energy, is becoming more and more important. Owing to these energies are intermittent, energy storage devices are indispensable for the application of them. Supercapacitors, as an energy storage system, have higher power density, superior cyclability and short charging time relative to batteries, so they have been applied in computer memory backup systems and mobile consumer electronics.38-40 But, the energy density of them has not fully satisfied the need of many fields, such as hybrid electric vehicles (HEVs) and electric vehicles (EVs). Considerable research efforts are centered on the development of new electrode materials with high capacitance for improving the energy density.41-45 Recent years, coordination polymers (CPs)/MOFs directly acted as electrode materials for supercapacitors have begun to receive attention, due to them providing metal cations for pseudo-capacity and pores/space for the diffusion of electrolyte solution.46-58 For example,

two-dimensional

[Ni3(OH)2(C8H4O4)2(H2O)4]·2H2O51

(2D) and

layered

MOFs,

[Cu(hmt)(tfbdc)(H2O)],56

such

as

as

high

performance supercapacitor electrode materials, have been reported by Wei’s group and us; Very recently, M. Dincǎ et al reported a conductive 2D MOF (Ni3(2,3,6,7,10,11-hexaiminotriphenylene)2,

Ni3(HITP)2) as an electrode material


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for stable supercapacitors with high areal capacitance.58 Inspired by these results and as the continuation of our research in this field, we used H2tfbdc and H2mpca as mixed bridging ligands to react with copper(II) chloride, and synthesized a 3D copper based CP ([Cu(H2mpca)(tfbdc)], Cu-CP). This is the first copper based CP derived from H2mpca. Herein, we reported its synthesis, crystal structure, magnetic property and electrochemical properties for supercapacitors.

2. Experimental 2.1 Materials All reagents and solvents were purchased from Shanghai Chemical Reagent Corporation and used as received. 3-Methyl-1H-pyrazole-4-carboxylic acid (H2mpca) was prepared according to the literature.24 2.2 Synthesis 2.2.1 Synthesis of [Cu(H2mpca)(tfbdc)] A water solution (4 mL) of CuCl2·2H2O (0.034g, 0.2 mmol) was slowly added to a methanol-ethanol (6 mL, v:v =1:1) solution of H2mpca (0.0126g, 0.10 mmol), H2tfbdc (0.0238g, 0.1 mmol) and NaOH (0.008g, 0.2 mmol), and mixed, then, a blue solution was obtained. Blue crystals of [Cu(H2mpca)(tfbdc)] were collected after the solvent evaporation for some days. Yield 38% (based on Cu). Anal. Cal. for C13H6CuF4N2O6 (Mr = 425.74): C, 36.67; H, 1.42; N, 6.58. Found: C, 36.74; H, 1.39; N, 6.55. IR (KBr, cm–1): 3216 (s), 3135 (m), 3100



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(m), 1698 (vs), 1608 (vs), 1536(s), 1452 (s), 1350 (vs), 1219 (m), 1176 (s), 1127 (s), 995 (m), 778(m), 737 (s), 671 (m), 545 (w). 2.3 Physical measurements Elemental analysis of C, H, and N was performed on a Perkin-Elmer 2400 Series II element analyzer. Using KBr pellets and in the range of 400–4000 cm-1, IR spectrum measurement was carried out on a spectrometer (Nicolet 460). Under N2 atmosphere, from room temperature to 800˚C and utilizing a heating rate of 10˚C·min-1, thermogravimetric (TG) measurement was performed on a Dupont thermal analyzer. Powder X-ray diffraction (XRD) patterns were recorded on an X-ray diffractometer with Cu−Kα radiation (λ = 1.5406 Å, Rigaku, D/max 2500 PC). The morphology and microstructure of the Cu−CP sample after grinding were investigated by field emission scanning electron microscopy (FESEM; Zeiss, Supra 55 system). A SQUID magnetometer was used to measure magnetic property of Cu-CP. 2.4 X-ray crystallography Single-crystal X-ray diffraction measurement for Cu-CP was performed using a Bruker Smart Apex CCD area detector diffractometer. Using Mo-Kα radiation ( λ = 0.71073 Å ) in the range of 1.94° ≤ θ ≤ 24.05°, intensity reflections were recorded. Employing the SHELXTL-97 program,59 and direct methods, the structure was solved. Anisotropic thermal factors were assigned to all the non-hydrogen atoms. H atoms linked to C were placed at the geometric positions

and

refined

with

an

isotropic

displacement


parameter.

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Crystallographic data for Cu-CP are summarized in table 1. CCDC-1510366 contains the supplementary crystallographic data for this paper. Table 1 Crystallographic data for Cu-CP Empirical formula

C13H6CuF4N2O6

Formula weight

425.74

T(K)

296(2)

Crystal system, space group

orthorhombic, Pb c n

a(Å)

14.5721(18)

b(Å)

15.1175(19)

c(Å)

13.6055(17)

α(deg)

90

β(deg)

90

γ(deg)

90

3

V(Å )

2997.2(6)

Z Dcalcd. (g·cm-3) µ (mm-1)

8 1.887 1.541

F(000)

1688

θ (deg)

1.94 to 24.05

Index ranges

-16/16,-17/12,-15/10

no. of total reflns unique reflns. Data/restraints /params

13903 2368(Rint=0.0709) 2368/2/236

GOF (F 2)

1.078

R1, wR2 [I>2σ(I)]

0.0453, 0.1215

R1, wR2 (all data)

0.0771, 0.1547

Largest diff. peak and hole/e·Å -3

0.404 and -0.416

2.5 Electrochemical Measurements A

three-electrode

electrochemical

cell

was

used

to

investigate

electrochemical properties of Cu-CP. A Ni foam coated with Cu-CP, a platinum foil and a saturated calomel electrode (SCE) were used as the working electrode,



the counter and reference electrode, respectively. The fabrication procedure of the working electrode was as follow: a homogeneous slurry was obtained by mixture of Cu-CP, acetylene black, and poly(tetrafluoroethylene) in a mass ratio of 75:15:10 in ethanol. The slurry was coated on a nickel foam substrate (1 cm × 1 cm) and dried at 60°C for 8 h under vacuum. Then, the as-fabricated electrode was pressed at 10 MPa and further dried for 6 h at 100 °C. Poly(tetrafluoroethylene) and acetylene black were used as the binder and conductive agent, respectively. The mass loading of the active material was in the range of 2.2−4.9 mg cm–2. The measurements of cyclic voltammogram (CV) and galvanostatic charge–discharge were carried out in a 1 M KOH aqueous electrolyte at room temperature using a CHI 660D electrochemical workstation. The measurements of electrochemical impedance spectroscopy (EIS) were carried out at open circuit potential with an ac perturbation of 5 mV in a frequency range from 0.01 Hz to 100 kHz.

3 Results and discussion 3.1 Synthesis and Infrared Spectrum Cu-CP was synthesized by adding H2mpca, H2tfbdc, NaOH and CuCl2·2H2O in a molar ratio of 1:1:2:2 in EtOH-MeOH solution. The complex is insoluble in alcohol, acetone, acetonitrile and DMF. IR spectrum of Cu-CP is shown in Figure S2. A broad and strong peak at 3216 cm−1 should be ascribed to νs(OH) stretching vibration. The strong peaks at 1698 cm−1 can be assigned to


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νas(-COOH) from H2mpca ligand, while the strong peak at 1608 and 1350 cm−1 are attributed to νas(OCO) and νs(OCO) stretching vibrations of the tfbdc2anions.60 The strong peak of stretching vibrations from the C=N bond locates at 1536 cm−1. The peak of δ(OCO) bending vibrations appears at 737 cm-1. 3.2 Crystal structure description of [Cu(H2mpca)(tfbdc)] Crystal of complex [Cu(H2mpca)(tfbdc)] belongs to the orthorhombic space group Pb c n and the asymmetric unit contains one Cu(II) ion, one tfbdc2- anion, and one H2mpca molecule. As shown in Figure 1a, each Cu(II) ion is five-coordinated with slightly distorted triangular bipyramid geometry. The Cu(II)1 ion is coordinated by four oxygen atoms from four tfbdc2- anion and one nitrogen atom from H2mpca molecule. Three oxygen atoms (O3B, O5A, O6C) form the base plane of the triangular pyramidal structure, one oxygen atom and one nitrogen atom (O4, N1) occupy the apical positions. As displayed in Table S1, Cu1-N bond length is 1.954 Å, closing to the value observed in other pyrazolecarboxylate and pyrazolate based Cu(II) complexes.21, 61-63 The Cu1-O bond distances are in the range of 1.924-2.275Å. The bond angles of O4-Cu1-N1, O4-Cu1-O5A and O4-Cu1-O3B are 170.25(19), 90.01(19) and 91.73(17)° respectively. Notably, each carboxylate group of tfbdc2- anion links to two adjacent Cu(II) ions, resulting in the formation of a {Cu2(COO)2} binuclear loop. These {Cu2(COO)2} binuclear loops are linked each other to further form a 1D chain ( Figure 1). The distances of Cu1---Cu 1D and Cu1---Cu 1B are 3.9209(10) and 3.282(1) Å respectively, indicating there are



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two kinds of {Cu2(COO)2} binuclear loop existing in [Cu(H2mpca)(tfbdc)]. These 1D chains are further bridged to form a 3D framework by the coordination mode of tfbdc2- anion, as shown Figure 1b. The tfbdc2- ligand is in a

µ4-bridging

fashion

µ2-η1:η1-syn-syn-bridging (O(2)-H(2)···O(6)i,

with mode.

two The

O(2)-H(2)···O(3)ii,

carboxylate

hydrogen

bonding

groups

in

interactions

N(2)-H(2A)···O(3)iii

and

N(2)-H(2A)···O(1)iv) further increase the stability of 3D structure (see Figure S1 and Table S2). It should be pointed out that Cu-CP includes uncoordinated carboxyl groups from H2mpca molecules, owing to H2mpca adopting unidentate coordination fashion (Figure 1a). These groups might serve as Lewis acid sites in catalytic reactions.64, 65

Figure 1.

(a) The coordination environment of Cu(II) ion in Cu-CP. (b) 3D grid (Hydrogen bonds are ignored).

3.3 Thermal Stability


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TG analysis curve for Cu-CP is displayed in Figure S3. As can be seen from it, there is not a weight loss before 238 °C, indicating Cu-CP has better thermal stability, then a greater mass loss of 81.80 % from 238°C to 332°C maybe belong to the loss of tfbdc2- anion and H2mpca ligands (calcd 85.07 %). About 19.20% CuO is left (calcd 18.68%). 3.4. Magnetic Property 1000

-1

0.36

χ MT / emu K mol

800

0.34

600

400

0.30

-1

0.32

-1

χM / emu mol

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


200

0.28

0 0

50

100

150

200

250

300

T/K

Figure 2

Plots of χMT (□) and χM −1 (○) as a function of temperature for Cu-CP. The

solid line represents the theoretical value based on the Curie-Weiss law. The χMT and χM−1 versus T curves for Cu-CP are displayed in Figure 2. The

χMT value at 300 K is 0.3376 emu K mol−1, close to the value of 0.375 emu K mol−1 for one isolated spin Cu(II) ion (g = 2). The χMT value almost keeps constant from room temperature to 65 K, and then smoothly decreases to 8 K and reaches at 0.3056 emu K mol−1 at 1.8 K. The feature suggests antiferromagnetic

interaction

is

operating

in

Cu-CP.

The

reciprocal

variable-temperature magnetic susceptibilities (1/χM) obeys the Curie-Weiss law χM = C/(T – θ) with Weiss constant θ = –0.0973 K and Curie constant C =



0.3379 emu·K·mol–1. The negative θ value also confirms the presence of intramolecular antiferromagnetic interactions between adjacent Cu(II) ions in Cu-CP. Based on the structure of Cu-CP, due to the longer length of the tfbdc2- anion ligands, the superexchange interactions between Cu(II) ions through the tfbdc2anion bridge can be ignored, the main magnetic interactions between Cu(II) ions should happen in one-dimensional chains formed by carboxylate groups bridged Cu(II) ions. Considering the Cu1---Cu 1D and Cu1---Cu 1B distances are different, the magnetic data of Cu-CP were fitted by a Heisenberg alternating antiferromagnetic copper(II) chain model given by equation 1(with

S = 1/2).66-68 A molecular field approximation was introduced to evaluate the interchain interactions (zJ′) (see Table S3).69

H = -2J∑[S2iS2i-1 + αS2iS2i+1]

(1)

The results of the best fit were J = -1.1 cm−1, g = 1.98 and zJ′ = -0.079 cm−1, α = 0.95, where R = Σ[(χM)obsd.- (χM)calcd.)2/Σ(χM)obsd.2]. The negative J value suggests that weak antiferromagnetic interactions between the adjacent Cu(II) ions are present in [Cu(H2mpca)(tfbdc)]. Usually, the bridging carboxylates can induce an antiferromagnetic coupling between Cu(II) ions,69 our result verify this inference once again. 3.5. Electrochemical performance Galvanostatic charge–discharge, cyclic voltammetry (CV) and electrochemical impedance spectrum (EIS) tests were used to investigate the electrochemical


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performances of the Cu-CP electrode for supercapacitors. The CV curves of the Cu-CP electrode at different scan rates in the voltage of 0-0.60 V in 1 M KOH electrolyte are presented in Figure 3a. It can be seen that the potential of the oxidation peak increases and that of the reduction peak decreases with the scan rate increasing. This result is related to the internal resistance of the electrode. Each CV curve has one couple of redox peaks, revealing the pseudocapacitance is produced by the surface redox reaction.

0.00 2mv/s 5mv/s 10mv/s 20mv/s

Potential/V(vs. SCE)

Current/A

b

0.6

a

0.05

0.5 -1

1Ag -1 2Ag -1 3Ag -1 4Ag -1 6Ag -1 8Ag -1 10Ag -1 20Ag

0.4 0.3 0.2 0.1

-0.05

0.0 0.2

0.3

0.4

0.5

0

0.6

200

800

400

600

800

1000

1200

Time/s

Potential/V(vs. SCE) 600

C

Specific Capacitance/F·g-1

Specific Capacitance/F·g-1

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


700 600 500 400 300 200

d 550

Current density: 2A·g-1

500 450 400 350 300 250

0

5

10

15

Current density/A·g-1

20

0

500

1000

1500

Cycle number

Figure 3. (a) Cyclic voltammetry plots at different scan rates. (b) The charge-discharge profiles of the Cu-CP electrode in 1M KOH electrolyte at different current densities. (c) Specific capacitances of the Cu-CP electrode at different current



densities. (d) Cycling performance of the Cu-CP electrode in the potential window of 0–0.60 V at 2 A g−1. Following two reversible processes might be used to explain this redox reaction mechanism. Similar processes have appeared in other CPs electrodes, such as [Ni3(OH)2(C8H4O4)2 (H2O)4]·2H2O and Ni3(btc)2·12H2O.52, 53 Cu(II) s + OH-↔Cu(II)(OH)ad +e--------(1) Cu(II)(OH)ad ↔Cu(III)(OH)ad +e--------(2) Figure 3b displays the galvanostatic charge-discharge profiles of the Cu-CP electrodes at different current densities within the potential range of 0 to 0.6 V in 1M KOH solution. As can be seen, these discharged curves obviously deviate from a straight line and all have a slope, indicating the redox reaction of Cu-CP is main source of the electrode pseudocapacitive behavior. The following equation can be used to estimate the specific capacitance of the Cu-CP electrode (C, F g−1):

C = It/(m∆V) Where m is the mass of the Cu-CP electroactive material (g), ∆V, I and t are the potential window (V), the constant current (A), and the discharge time (s), respectively. As shown in Figure 3c, when the current density is 1, 2, 6, 10 and 20 A g−1, the specific capacitance is 735, 526, 364, 313 and 226 F g−1, respectively, meaning a better rate capability. The decreasing of specific capacitance along with the current density increasing should be attributed to the decreasing of the effective interaction between electrolyte ions and electrode.57 Compared with Cu-based CP


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(Cu-LCP) reported by us recently (1274 F g−1 at a current density of 1 A g−1), the specific capacitance of Cu-CP is lower, but still higher than that of the CuO/Cu(OH)2 hierarchical arrays (278 F g−1)70 and Cu(OH)2 nanowires (114 F g−1). 71 The cause that the specific capacitance of Cu-LCP is higher than that of Cu-CP may be ascribed to Cu-LCP having layered structure, which provides enough interspaces for the diffusion of the ions. To investigate the cycle stability performance of the Cu-CP electrode, a charge–discharge cycling test at a current density of 2 A g−1 was carried out. As can be seen from Figure 3d, the specific capacitance remains 375 Fg−1 after 1500 continuous cycles. This result reveals that the Cu-CP electrode has better cycle stability. To investigate the stability of the Cu-CP electrode in 1 M KOH solution, the XRD patterns of the Cu-CP, the bare Cu-CP electrode including Cu−CP, acetylene black and polytetrafluoroethylene (PTFE) and the Cu-CP electrode after 100 cycles were measured. As displayed in Figure S4, the Cu−CP electrode after 100 cycles and the

160 140 120

-Z′′ (Ohm)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


100 80 60 40 20 0 0

20

40

60

80

100

120

140

160

Z′(Ohm)

Figure 4 Nyquist plot of the Cu-CP electrode and the equivalent circuit model bare electrode almost have same the XRD patterns, and contain main diffraction peaks from the Cu-CP. The fact shows that Cu-CP electrode is stability in 1 M KOH



solution. It can be clearly observed in the electrochemical impedance spectrum (EIS), the plot is composed of a semicircle and an inclined line (Figure 4). The inset of Figure 4 is the equivalent circuit for fitting the EIS data. Here Rs stands for the internal resistance containing the solution resistance, the intrinsic resistance of active material (Cu-CP), and the contact resistance at the current collector/the active material interface,57, 72 while CPE, Rct, W, and Cps represent the interfacial capacitance, the charge transfer resistance, Warburg impedance, and pseudocapacitance, respectively. The values of Rs and Rct are 2.86 and 94.88 Ω, respectively. The Rct value of Cu-CP is larger than that of CuO/reduced graphene oxide nanocomposite reported (2.47 Ω).73 The steeper line in the low frequency range suggests electrolyte ions have faster diffusion ability.57

Figure 5 FESEM images of the Cu−CP sample after grinding: (a) low magnification, (b) high magnification. The microstructure and morphology of the Cu-CP material after grinding for 2 h were investigated by FESEM. The FESEM image (Figure 5) shows that the Cu-CP sample is composed of many nanoparticles with the size of ca.75-220 nm. The better


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performances of the Cu-CP electrode should be ascribed to following factors: one is the smaller size of Cu-CP nanoparticles can provide more active sites of electrochemical reactions and decrease diffusion distance of the ions; another Cu(II) ion from Cu-CP can take part in the electron transfer process.

Conclusions In summary, an antiferromagnetically coupled 3D Cu-based coordination polymer (Cu-CP) has been successfully synthesized via a simple solution synthetic method.

Cu-CP was investigated as an electrode material of

supercapacitors for the first time, showing higher specific capacitance and better cyclability. Its maximum specific capacitance of 735 F g−1 was obtained in 1M KOH solution at 1 A g−1, and the capacitance of 375 F g−1 was still remained after 1500 cycles at 2 A g−1. The research result will encourage us to search for more coordination polymers with high capacitance and good cyclability. Associated Content Supporting Information The Supporting Information is available free of charge on the ACS Publications website. IR spectrum, TGA curve, Table of selected bond lengths and angles, Table of Hydrogen bond distances and angles. This material is available free of charge via the Internet at http://pubs.acs.org.



Author Information Corresponding Authors *E-mail: [email protected] Notes The authors declare no competing financial interest.

Acknowledgements L. Yu and X. Wang contributed equally to this work. This work was supported by the Natural Science Foundation of China (No. 20671045, 20971060 and 21101018), the Natural Science Research Key Project of Jiangsu Colleges and Universities (No. 16KJA430005), and the Natural Science Foundation of State Key Laboratory of Coordination Chemistry.

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For Table of Contents Use Only

A 3D copper coordination polymer constructed by 3-methyl-1H-pyrazole-4-carboxylic acid with higher capacitance for supercapacitors Lili Yu, Xianmei Wang, Meiling Cheng, Hongren Rong, Yidan Song, Qi Liu

Synopsis A copper-based 3D coordination polymer ([Cu(H2mpca)(tfbdc)], Cu-CP) was synthesized, showing a higher capacitance in supercapacitors and antiferromagnetic interactions between the adjacent Cu(II) ions.


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A Three-Dimensional Copper Coordination Polymer Constructed by 3

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