Facile synthesis of nickel-cobalt selenide nanoparticles as battery-type electrode for all-solid-state asymmetric supercapacitors

Accepted Manuscript Facile Synthesis of Nickel-cobalt Selenide Nanoparticles as battery-type electrode for All-solid-state Asymmetric Supercapacitors Yahui Wang, Ruonan Liu, Shuxian Sun, Xiaoliang Wu PII: DOI: Reference:

S0021-9797(19)30471-0 https://doi.org/10.1016/j.jcis.2019.04.049 YJCIS 24878

To appear in:

Journal of Colloid and Interface Science

Received Date: Revised Date: Accepted Date:

12 February 2019 13 April 2019 15 April 2019

Please cite this article as: Y. Wang, R. Liu, S. Sun, X. Wu, Facile Synthesis of Nickel-cobalt Selenide Nanoparticles as battery-type electrode for All-solid-state Asymmetric Supercapacitors, Journal of Colloid and Interface Science (2019), doi: https://doi.org/10.1016/j.jcis.2019.04.049

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Facile Synthesis of Nickel-cobalt Selenide Nanoparticles as battery-type electrode for All-solid-state Asymmetric Supercapacitors Yahui Wang, Ruonan Liu, Shuxian Sun Xiaoliang Wu* Department of Chemistry and Chemical Engineering, College of Science, Northeast Forestry University, 26 Hexing Road, Harbin 150040, P. R. China *

Address correspondence to [email protected]

ABSTRACT Transition metal selenides attract extensive attentions in the aspect of electrochemical energy storage due to the good conductivity and significant electrochemical activity. Herein, we develop a facile mothed to synthesize nickel cobalt selenides nanoparticles by solvothermal approach. Benefiting from the synergistic effect between Co and Ni, the optimized Ni0.6Co0.4Se2 electrode shows a specific capacity of 602.6 C g-1 at 1 A g-1 and superior rate characteristic (468.5 C g–1 at 20 A g-1). More interestingly, an all-solid-state asymmetric supercapacitor was constructed utilizing the BNPC material as the negative electrode and the Ni0.6Co0.4Se2 samples as the positive electrode shows a high energy density of 42.1 Wh kg−1 and superior cycling stability (91.0 % capacity maintenance after 5000 cycles) in KOH/PVA gel electrolyte. These exciting characteristics provide a new idea for the construction of transition metal selenide electrode materials for high performance supercapacitors. Keywords: NiSe2, CoSe2, Energy density, All-solid-state, Asymmetric supercapacitor

1

1. Introduction With the progress of the economy, the energy dilemma and environmental contamination are becoming more and more serious, which are the problems we have to face now. Developing highly effective energy storage device is an important way to relieve these problems [1, 2]. As an efficient energy storage device, supercapacitors have attracted numerous attentions in recent years because of the distinctive characteristics of ultrahigh power density, outstanding electrochemical stability, environmental friendly and safety [3-6]. Supercapacitors can be split into electrical double layer capacitors (EDLCs) and pseudocapacitors according to the energy storage mechanism. In contrast with the EDLCs, pseudocapacitors have higher specific capacities due to they generate redox reactions with electrolyte ion on surface of the electrode materials. Transition metal oxides/hydroxides have been extensively researched as electrode materials for pseudocapacitors, such as MnO2 [7, 8], CoOx [9], NiO [10], Ni(OH)2 [11], NiCo2O4 [12], etc. Unfortunately, one of the major practical problems that still exist is the intrinsic low conductivity of these materials, which result in their poor rate performance and electrochemical stabilization [13]. Accordingly, it is highly urgent need to research new type electrode materials with excellent electrochemical characteristics, such as superior specific capacity, excellent rate characteristic and good electrochemical stabilization. Recently, transition metal selenides have been regarded as the promising electrode materials for supercapacitors because of the good conductivity and significant electrochemical activity [14-17]. The elemental Se possesses good electrical conductivity, which enable the transition metal selenides show excellent conductivity and outstanding capability as electrode material for supercapacitors. For instance, Ogale et al. using Kirkendall effect to develop Co0.85Se hollow nanowires and the prepared electrode exhibits a specific capacity of 929.5 at 1 mA cm−2 [18]. Sun et al. developed NiSe nanowire film on nickel foam and the obtained 2

electrode shows a specific capacity of 1790 F g-1 at 5 A g-1 [19]. Particularly, the bimetallic nickel cobalt selenides composites exhibit ameliorative electrochemical activity than monometallic nickel or cobalt composites, which can be also confirmed in the bimetallic nickel or cobalt oxides, hydroxides, and sulfides [20-24]. Some research works have been focused on developing nickel cobalt selenides materials for supercapacitor. However, achieving high energy density at high power density is still a great challenge for transition metal selenides based supercapacitors. Herein, we report a facile, novel mothed for the construction of nickel cobalt selenide nanoparticles by a one-step solvothermal process. Benefiting from the synergistic effect between Ni and Co, the optimized Ni0.6Co0.4Se2 electrode displays high specific capacity and excellent rate performance. More interestingly, an all-solid-state asymmetric supercapacitor was constructed utilizing the BNPC material as the negative electrode and Ni0.6Co0.4Se2 as the positive electrode displays high energy density and good cycling stability in KOH/PVA gel electrolyte. 2. Results and discussion Typically, the NixCo1-xSe2 samples were prepared through a simple hydrothermal way based on the following equation: 4NaBH4 + 2Se + 7H2O = 2NaHSe + Na2B4O7 + 14H2 2NaHSe + xNi2+ + (1-x) Co2+ = NixCo1-xSe2 + 2Na+ + 2H+ The crystal structures of the NixCo1-xSe2 samples were characterized by X-ray diffraction (XRD) measurement. As exhibited in Fig. 1 a, the characteristic peaks of Ni selenide and Co selenide are in accord with NiSe2 (JCPDS No. 41-1495) and CoSe2 (JCPDS No. 09-0234), respectively. It is worth noting that with the increase of cobalt content, the characteristic peak shifts to larger angle, which is caused by the cobalt substituted nickel. The results confirm successful synthesis of nickel cobalt selenides. 3

The chemical states of the NixCo1-xSe2 samples were checked by X-ray photoelectron spectroscopy (XPS). Fig. 1b displays the survey spectrum of the Ni0.6Co0.4Se2 samples, and the marked peaks of Ni, Co, Se, C and O further confirms the coexistence of Ni and Co. The marked C and O characteristic peaks are originated from the ineluctable surface adsorption due to the exposure of air. The high resolution Co 2p spectra of Ni0.6Co0.4Se2 can be fitted into two spin−orbit and two shakeup satellites (denoted as “ Sat. ”), which can be attributed to Co2+ and Co3+ [25]. Moreover, the high resolution Ni 2p spectra of Ni0.6Co0.4Se2 can be fitted into be fitted into two shakeup satellites and two spin−orbit, which can be attributed to Ni2+ and Ni3+ [25]. The results further confirm successful synthesis of nickel cobalt selenides. The microstructures of the NixCo1-xSe2 samples were firstly conducted by scanning electron microscopy (SEM). As seen in Fig. 2a-f, all the NixCo1-xSe2 samples have similar structures, which consist of a large number of nanoparticles. The morphology and shape of nanoparticles are all irregular. These results indicate that different proportions of cobalt and nickel have negligible effect on their morphology. The elemental distributions of the Ni0.6Co0.4Se2 samples are conducted by energy dispersive spectroscopy (EDS) mapping tests (Fig. 2g-j). The EDS results confirm that the Ni, Co, and Se elements are homogeneously distributed in Ni0.6Co0.4Se2, demonstrating the coexistence of Ni and Co in the composites. The microstructure of the Ni0.6Co0.4Se2 materials was further conducted by transmission electron microscopy (TEM) measurments. As seen in Fig. 3a, the Ni0.6Co0.4Se2 samples are composed of massive irregular nanoparticles, which is in accord with the SEM results. The highresolution TEM image of Ni0.6Co0.4Se2 (Fig. 3b) further confirms the lattice fringe of 0.27 and 0.31 nm, which corresponding to the (101) and (100) crystalline planes of the Ni0.6Co0.4Se2 materials. The electrochemical characteristics of the NixCo1-xSe2 materials were firstly conducted by cyclic voltammetry (CV) measurements via a three-electrode system in 6 M KOH solution. 4

Fig 4a displays the CV profiles of the NixCo1-xSe2 samples at 20 mV s-1. All the NixCo1-xSe2 samples have a pair of redox peaks in CV curves, indicates the battery-type characteristics. As reported by literatures, after CV test, the high conductivity of the newly formed CoOOH/NiOOH can be detected and so the redox peaks are corresponding to the following equations [26, 27]: CoSe2 + H2O + 1/2 O2 → Co(OH)2 + 2Se

(1)

Co(OH)2 + OH- → CoOOH + H2O + e-

(2)

NiSe2 + H2O + 1/2 O2 → Ni(OH)2 + 2Se

(3)

Ni(OH)2 + OH- → NiOOH + H2O + e-

(4)

Furthermore, the coexistence of Ni and Co in nickel cobalt selenides possesses higher electrochemical activity than NiSe2 and CoSe2 due to their synergistic effect. Furthermore, the CV curve of Ni0.6Co0.4Se2 exhibits the largest integral area, demonstrating the highest specific capacity. Fig. S1 displays the CV profiles of Ni0.6Co0.4Se2 at various scan rates. The CV profiles occur to no obvious deformation with the scan rate increases, indicating excellent rate capability. Fig. 4b displays the galvanic charge/discharge (GCD) profiles of Ni0.6Co0.4Se2 at different current densities. The symmetry of GCD profiles confirms excellent Coulombic efficiency during charge/discharge process. The specific capacity of the NixCo1-xSe2 samples were calculated by the GCD profiles at various current densities. As seen in Fig. 4b, with the Ni and Co ratio gradually increased the specific capacity of the NixCo1-xSe2 samples increase first and then decrease. This means moderate amount Co ions are propitious to higher electrochemical performance and better rate characteristic due to synergistic effect. The Ni0.6Co0.4Se2 electrode delivers a specific capacity of 602.6 C g-1 at 1 A g-1, which is much higher than other NixCo1-xSe2 electrodes and other previously reported transition metal selenide in literature (Table 1). Notably, the Ni0.6Co0.4Se2 electrode shows a high specific capacity of 468.5 C g-1 (77.7% of capacity retention) even at 20 A g-1, demonstrating 5

outstanding rate performance. Electrochemical impedance spectroscopy (EIS) measurements were conducted to check the electrode kinetics. Nyquist plots of the NixCo1-xSe2 electrodes were shown in Fig. 4d. All the Nyquist plots show a similar shape with a semicircle in the high-frequency range and a linear part in the low-frequency range. Compared with NiSe2, the NixCo1-x selenide and CoSe2 electrodes display a smaller semicircle, indicating that Co ions can tremendously decrease ions transfer resistance. In the low-frequency region, the slope of lines becomes much higher with the increase of Co ions ratios, confirming that Co ions in favor of faster charge transfer. To further research the electrochemical capability of the Ni0.6Co0.4Se2 electrode, an asymmetric supercapacitor was constructed using the Ni0.6Co0.4Se2 electrode as positive electrode and boron and nitrogen co-doped porous carbon foam (BNPC) as negative electrode in KOH/PVA gel electrolyte. The BNPC materials were synthetized according to our previously work [38]. Due to the unique pore structure with suitable specific surface and massive nitrogen and boron functional groups, the BNPC electrode exhibits an ultrahigh specific capacitance of 402 F g−1 at 0.5 A g−1 in 6 M KOH electrolyte. Fig. 5a displays the CV profiles of the as-assembled BNPC//Ni0.6 Co0.4Se2 asymmetric supercapacitor measured at various scan rates in KOH/PVA gel electrolyte and it exhibits both pseudocapacitive and double-layer behaviors. The CV profiles occur to no obvious deformation with the scan rate increases, confirming superior rate characteristic. Due to the wide voltage range and high specific capacity, the BNPC//Ni0.6Co0.4Se2 asymmetric supercapacitor displays an energy density of 42.1 Wh kg−1 (based on the overall mass of the active material of both electrodes), which is higher than other previously reported transition metal selenides based asymmetric supercapacitors, for instance, Ni0.33Co0.67Se2//activated carbon (29.1 Wh kg-1 at 800 W kg-1) [28], Ni0.85Se@MoSe2//graphene nanosheets (25.5 Wh kg-1 at 420 W kg-1) [34], [email protected]//active

carbon

(AC)

(17 6

Wh

kg-1

at

1526.8

W

kg-1)

[39],

Co0.85Se//nitrogen-doped porous carbon networks (N-PCNs) (21.1 Wh kg-1 at 400 W kg-1) [40], (Ni0.1Co0.9)9Se8@carbon fiber cloth//reduced graphene oxide@carbon fiber cloth (17.0 Wh kg-1 at 3.1 kW kg-1) [41], CoSe//activated carbon (18.6 Wh kg-1 at 750 W kg-1) [42], NiSe@MoSe2//nitrogen-doped carbon nanosheet (32.6 Wh kg-1 at 415 W kg-1) [43], Ni3Se2//activated carbon (32.8 Wh kg-1 at 677.03 W kg-1) [44]. Notably, even at an ultrahigh power density of 16.3 kW kg−1, it still remains a high energy density of 14.5 Wh kg−1. Moreover, the electrochemical performance of the BNPC//Ni0.6Co0.4Se2 asymmetric supercapacitor was measured at 100 mV s−1 for 5000 cycles. As shown in Figure 5f, the BNPC//Ni0.6Co0.4Se2 asymmetric supercapacitor shows superior electrochemical stabilization with 91.0% of the initial capacity retention. More interestingly, two BNPC//Ni0.6Co0.4Se2 asymmetric supercapacitor devices connected in series can light the red commercial light emitting diodes (LEDs) for 30 mins, indicating its practical application (inset of Fig. 5d). 3. Conclusion In summary, we report a facile, novel mothed to synthesize bimetallic nickel cobalt selenides nanoparticles by solvothermal approach. Benefiting from the synergistic effect between Ni and Co, the optimized Ni0.6Co0.4Se2 electrode dispalys high specific capacity and superior rate characteristic. More interestingly, the constructed all-solid-state asymmetric supercapacitor displays an energy density and good electrochemical stability. Conflicts of interest There are no conflicts to declare. Acknowledgment This work was supported by National Natural Science Foundation of China (51702043) and Heilongjiang Postdoctoral Foundation (LBH-Z18008).

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13

20

40

60

1000

C 1s

S e 3s S e 3p Ni 3s C o 3s S e 3d

O 1s

600

400

200

(d) C o 2p 3/2

C o 2p

s at.

Co

+3

C o 2p 1/2 Co

800

Co

+2

Co

In te rs ity (a .u .)

In te rs ity (a .u .)

800

0

B inding energy (eV)

(c)

810

Ni 2s

80

2  (degree)

Ni

NiS e 2

Co

C o 0.2 Ni 0.8 S e 2

(b)

Ni 2p

C o 0.4 Ni 0.6 S e 2

C o 2p

C o 0.8 Ni 0.2 S e 2

C o 0.6 Ni 0.4 S e 2

C o 2s

C oS e 2

In te rs ity (a .u .)

In te n s ity (a .u .)

(a)

+2

+3

s at.

790

890

780

Ni 2p

s a t.

Ni 2p 3/2

Ni 2p 1/2 Ni

Ni

+3

Ni

880

+2

870

+3

Ni

+2

s a t.

860

850

B inding energy (eV)

B inding energy (eV)

Fig. 1. (a) XRD patterns of Ni0.6Co0.4Se2. (b) XPS survey spectrum of Ni0.6Co0.4Se2. (c) Highresolution Co 2p of Ni0.6Co0.4Se2. (d) High-resolution Ni 2p of Ni0.6Co0.4Se2.

14

(b)

(a)

(c)

200 nm

200 nm

(f)

(e)

(d)

200 nm

(g)

200 nm

(h)

1 µm

200 nm

200 nm

(j)

(i)

1 µm

1 µm

1 µm

Fig. 2. SEM images of (a) CoSe2, (b) Ni0.2Co0.8Se2, (c) Ni0.4Co0.6Se2, (d) Ni0.6Co0.4Se2, (e) Ni0.8Co0.2Se2, (f) NiSe2. (g) SEM image of Ni0.6Co0.4Se2, and corresponding elemental mapping images of Ni (h), Co (i), Se (j).

15

(a)

(b) 0.27 nm

0.31 nm 5 nm

200 nm

Fig. 3. (a) TEM image of Ni0.6Co0.4Se2. (b) High- resolution TEM image of Ni0.6Co0.4Se2.

16

40

0

-40

-80

800

0.1

Ni 0.2 C o 0.8 S e 2

Ni 0.4 C o 0.6 S e 2

Ni 0.6 C o 0.4 S e 2

Ni 0.8 C o 0.2 S e 2

NiS e 2

0.2

0.3

0.4

P otential (V vs . Hg/HgO )

(c)

600

(b)

1Ag

0.4

0.3

-1

2Ag

-1

3Ag

-1

5Ag

-1

10 A g

-1

20 A g

-1

0.2

0.1

0.0 0.5

C oS e 2

Ni 0.2 C o 0.8 S e 2

Ni 0.4 C o 0.6 S e 2

Ni 0.6 C o 0.4 S e 2

Ni 0.8 C o 0.2 S e 2

NiS e 2

0

400

300

600

900

T ime (s )

1200

1500

10

(d) 8

-Z " (o h m )

-1

S pe c ific c a pa c ita n c e (C g )

0.0

C oS e 2

P o te n tia l (V v s . Hg/HgO )

0.5

(a)

-1

C u rre n t de n s ity (A g )

80

6 C oS e 2

4

Ni 0.2 C o 0.8 S e 2 Ni 0.4 C o 0.6 S e 2

200

Ni 0.6 C o 0.4 S e 2

2

Ni 0.8 C o 0.2 S e 2

0

NiS e 2

0 0

5

10

15

-1

C u rre n t d e n s ity (A g )

20

0

2

4

6

Z' (ohm)

8

10

Fig. 4. (a) CV curves of the CoSe2, Ni0.2Co0.8Se2, Ni0.4Co0.6Se2, Ni0.6Co0.4Se2, Ni0.8Co0.2Se2, NiSe2 electrodes at 20 mV s-1. (b) CV curves of the Ni0.6Co0.4Se2 electrode at different scan rates. (c) Specific capacitance of the CoSe2, Ni0.2Co0.8Se2, Ni0.4Co0.6Se2, Ni0.6Co0.4Se2, Ni0.8Co0.2Se2, NiSe2 electrodes at different current densities. (d) Nyquist plots of the CoSe2, Ni0.2Co0.8Se2, Ni0.4Co0.6Se2, Ni0.6Co0.4Se2, Ni0.8Co0.2Se2, NiSe2 electrodes.

17

Table 1. Comparison of electrochemical properties of transition metal selenides electrode

C (F g-1)

C (F g-1)

Electrolyte

Ref

(Ni0.33Co0.67)Se2 CHSs

827.9 (1 A g-1)

677.4 (20 A g-1)

3 M KOH

28

(Ni,Co)Se2

972 (2 A g-1)

612 (20 A g-1)

3 M KOH

29

(Ni,Co)Se2/NiCo-LDH

1224 (2 A g-1)

869（20 A g-1)

3 M KOH

29

NiSe2

1044 (3 A g-1)

601 (30 A g-1)

4 M KOH

30

CoSe2

759.5 (1 mA cm−2)

595.7 (15 mA cm−2)

3 M KOH

31

Porous CoSe2

713.2 (1 mA cm−2)

535.8 (20 mA cm−2)

1 M KOH

32

NiSe/graphene

1280 (1 A g-1)

1026 (10 A g-1）

6 M KOH

33

Ni0.85Se@MoSe2

774 (1 A g-1)

489 (15 A g-1)

2 M KOH

34

Ni-Co-Se-4-2

1123 (584 C g-1, 1A g-1)

652 (338.7 C g-1, 50 A g-1)

6 M KOH

35

Ni0.67Co0.33Se

1029 (535 C g-1, 1 A g-1)

781 (406.2 C g-1, 20 A g-1)

6 M KOH

36

Ni0.5Co0.5Se2

1007 (524 C g−1 at 1 A g−1)

661 (344 C g-1, 50 A g-1)

6 M KOH

37

Ni0.6Co0.4Se2

1339 (602.6 C g-1, 1 A g-1)

1041 (468.5C g-1, 20 A g-1)

6 M KOH

This work

18

-1

8 4 0 -4 -8

0.4

0.8

1.2

1.6

20 10 0 -10 -20

0.0

2.0

P otential (V)

100

(c)

-1

(b)

20 mV s

-1

50 mV s

-1

100 mV s

-1

200 mV s

-1

-30 0.0

。

1.6 V 1.7 V 1.8 V

1.0 V 1.2 V 1.4 V

-12

E n e rgy de n s ity (W h k g )

C u rre n t de n s ity (A g )

(a)

C a pa c ita n c e re te n tio n (% )

-1

C u rre n t de n s ity (A g )

30 12

10 B NP C //Ni 0.6 C o 0.4 S e 2 R ef. R ef. R ef. R ef.

1 100

1000

28 39 41 43

R ef. R ef. R ef. R ef. -1

34 40 42 44

10000

140 120

0.8

1.2

1.6

P otential (V)

(d)

100

0 min

10 min

20 min

30 min

80 60 40 20 0 0

P o w e r d e n s ity (W k g )

0.4

1000

2000

3000

4000

5000

C yc le

Fig. 5. (a) CV curves of the BNPC//Ni0.6Co0.4Se2 asymmetrical supercapacitor in different operation voltages at 50 mV s-1. (b) CV curves of the BNPC//Ni0.6Co0.4Se2 asymmetrical supercapacitor at different scan rate. (c) Ragone plots of the BNPC//Ni0.6Co0.4Se2 symmetrical supercapacitor and other previously reported transition metal selenides based asymmetric supercapacitors. (d) Electrochemical stability of the BNPC//Ni0.6Co0.4Se2 asymmetrical supercapacitor.

19

Graphical Abstract -1

E n e rgy de n s ity (W h kg )

100

20 min

10

0 min 20 20 min 1 min 100

10 min 30 min 1000

B NP C //Ni 0.6 C o 0.4 S e 2 R ef. R ef. R ef. R ef.

28 39 41 43

R ef. R ef. R ef. R ef. -1

P ow er dens ity (W kg )

20

10000

34 40 42 44