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CuS composites for supercapacitor electrodes
Materials Letters 264 (2020) 127400
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/mlblue
Spherical NiCo2O4/CuS composites for supercapacitor electrodes Yunyan Tian b, Zhanhua Su a,b,⇑, Zhifeng Zhao a,⇑, Bowen Cong c, Meijia Wang b a
College of Chemistry, Guangdong University of Petrochemical Technology, Maoming 525000, China College of Chemistry and Chemical Engineering, Harbin Normal University, Harbin 150025, China c School of Chemistry and Chemical Engineering, Harbin Institute of Technology, Harbin 150001, China b
a r t i c l e
i n f o
Article history: Received 27 November 2019 Received in revised form 17 January 2020 Accepted 20 January 2020 Available online 22 January 2020 Keywords: NiCo2O4/CuS Composite materials Mesoporous Supercapacitor
a b s t r a c t In this work, spherical NiCo2O4/CuS composites was synthesized by hydrothermal method. As electrode material, it possesses high specific capacitance (2169 F g 1 at 0.5 A g 1), while maintaining excellent stability with about 123% capacitance retention after 7000 cycles at 1 A g 1. The asymmetric supercapacitor based NiCo2O4/CuS electrode exhibits a high energy density of 173.5 W h kg 1 at at a power density of 360 W kg 1 and can provide power supply for red LEDs indicator. This is mainly attributed to the synergistic effect of CuS and NiCo2O4, which promotes electron transport and electrolyte ion diffusion. Ó 2020 Elsevier B.V. All rights reserved.
1. Introduction Supercapacitors have attracted attention because of its high energy density and power density [1–2]. Currently, transition metal oxides are extensive used in the preparation of electrode materials. NiCo2O4 has achieved great success in supercapacitors due to its mesoporous structure and excellent electrical performance [3]. Such as Xin reported flower-like NiCo2O4 material, which specific energy is 1609 F g 1 at 1 A g 1 [4]. Zhang constructed nanowire NiCo2O4 capacitance retention is 57% of the initial value after 5000 cycles [5]. However, due to lower conductivity and poor cycle performance, which hinder its practical application. The carbon coating was adopted overcome these problem [6–7], but the carbon coating can’t improve intrinsic conductivity of NiCo2O4, surface coating is different from in-situ growth, and its mechanical stress is bad, so it is easy to fall off during charging and discharging. CuS was widely reported due to its stable electrochemical performance, cycle life and lower cost. For example, Wang reported CuS/RGO/Ni3S2 with high specific capacitance (1692.7 F g 1 at 6.5 A g 1) [8]. Durga stated CuS@PbS composites with good cycling stability (only 2.9% loss after 3000 cycles at 2.85 A g 1) [9]. Based on the above analysis, we think that recombination of NiCo2O4 and CuS maybe is feasible, because the synergistic effect of the two
⇑ Corresponding authors at: College of Chemistry, Guangdong University of Petrochemical Technology, Maoming 525000, China (Z. Su). E-mail addresses: [email protected] (Z. Su), [email protected] (Z. Zhao). https://doi.org/10.1016/j.matlet.2020.127400 0167-577X/Ó 2020 Elsevier B.V. All rights reserved.
phase expose more active sites to increase electrochemical kinetics. Fortunately, fluffy spherical NiCo2O4/CuS was successfully prepared by hydrothermal synthesis. The specific capacitance of NiCo2O4/CuS at a current density of 0.5 A g 1 is 2169 F g 1, and the cycle retention rate of 7000 cycles is 123%. Meanwhile, the asymmetric supercapacitor is assembled based on NiCo2O4/CuS and graphene electrodes, and the energy density is up to 173.5 W h kg 1 at a power density of 360 W kg 1.
2. Experimental The 56 mM Ni(NO3)26H2O, 116 mM Co(NO3)26H2O, 34 mM NH4F, 82 mM urea, 100 mM CuSO4, 400 mM Na2S2O3 and 0.01 g of surfactant CTAB were dissolved in 70 mL of water, stirred for 30 min. After homogenization, it was added to a 100 mL reactor and heated to 120 °C for 5 h. The mixture was cooled at room temperature, and separated by centrifugation with water and ethanol, respectively. The sample was heated at 60 °C for 12 h. After the drying was completed, the sample was placed in a tube furnace and annealed at 350 °C for 2 h. Preparation of NiCo2O4 and electrochemical measurements see Supporting Information. The samples were characterized by scanning electron microscopy (SEM, S4800), energy-dispersive X-ray spectroscopy (EDS) and a transmission electron microscope (TEM, Tecnai G2 F20). Xray diffraction (XRD) measurement was collected using a Siemens D5005 diffractometer with Cu-Ka (k = 1.5418 Å) radiation. The BET surface area and pore volume were calculated based on the adsorp-
2
Y. Tian et al. / Materials Letters 264 (2020) 127400
tion isotherm. All electrochemical tests were carried by the CHI660e electrochemical workstation.
3. Results and discussion Fig. S1 shows the SEM images of the NiCo2O4 at different magnifications. The morphology of NiCo2O4/CuS is fluffy spherical (Fig. S2). The corresponding EDS spectrum confirms the presence of elements such as Ni, Co, O, Cu and S in the prepared sample (Fig. S3a), the ratio of these elements is close to the target value. Fig. S3b shows the XRD results for NiCo2O4/CuS, NiCo2O4 and CuS. The diffraction peaks of (1 1 1), (3 1 1), (4 0 0), (5 1 1) and (4 4 0) can be classified as NiCo2O4 phase (JCPDS No.20–0781), and the diffraction peaks of (1 0 2), (1 0 3), (1 1 0), (1 0 8) and (1 1 6) can be classified as CuS (JCPDS No. 06–0464). All peaks were recorded and no additional peaks were detected, indicating high purity of the sample. The TEM image of the NiCo2O4/CuS is consistent with the above test SEM morphology (Fig. 1a). In addition, the corresponding elemental pattern results of sample are shown in Fig. 1b, and Ni, Co, O, Cu and S are uniformly distributed in the material, which proves the uniform formation of the NiCo2O4/CuS composites. The HRTEM image of sample shows that the measured lattice fringes are 0.47 and 0.30 nm (Fig. 1c), respectively, corresponding to the (1 1 1) crystal plane of NiCo2O4 and the (1 0 2) crystal plane of CuS. The
SAED mode shows well-defined diffraction rings indicating polycrystalline properties of sample (Fig. 1d). The nitrogen adsorption and desorption isotherms of NiCo2O4 and NiCo2O4/CuS are shown in Fig. S4. The BET values for NiCo2O4 and NiCo2O4/CuS were calculated to be 50.3 m2 g 1 and 106.2 m2 g 1, respectively. The distribution of sample was calculated by the desorption isotherm using the Barrete-JoynereHalenda (BJH) method. The maximum pore volumes of NiCo2O4 and NiCo2O4/CuS were found to be 0.323 cm3 g 1 and 1.92 cm3 g 1, respectively. Due to the larger specific surface area and pore volumes, NiCo2O4/CuS can provide efficient electrolyte ion channels and active sites for rapid ion transfer/diffusion, and is predicted to exhibit better electrochemical performance, so electrochemical testing was developed to prove this hypothesis. Capacitance characteristics are clarified from the results of cyclic voltammetry (CV) and constant current charge and discharge (GCD) tests. As shown in Fig. 2a, NiCo2O4/CuS electrodes exhibit larger area of the CV curve than NiCo2O4 at scan rate of 20 mV s 1, indicating that NiCo2O4/CuS electrode had better specific capacitance. Fig. 2b shows the charge/discharge curves of NiCo2O4 and NiCo2O4/CuS electrodes with a current density of 1 A g 1. According to the equation (S1), the specific capacitances of NiCo2O4 and NiCo2O4/CuS are calculated to be 794 F g 1 and 1740 F g 1, respectively. It can be seen that NiCo2O4/CuS composites has higher specific capacitance. This is mainly due to the unique morphology, the larger specific surface area and grain boundary of composites,
Fig. 1. (a) TEM images, (b) TEM elemental mapping, (c) HRTEM images and (d) SAED image of the NiCo2O4/CuS.
Y. Tian et al. / Materials Letters 264 (2020) 127400
3
Fig. 2. (a) CV curves and (b) GCD curves of NiCo2O4 and NiCo2O4/CuS, (c) CV curves and (d) GCD curves of NiCo2O4/CuS.
which provide more electrolyte channels and active sites, increasing charge storage and accumulation. In addition, the synergistic effect between NiCo2O4 and CuS improves their electrochemical activity and accelerates the transfer of electrons and electrolytes [10,11]. Further, CV curves of NiCo2O4/CuS electrodes at different scanning rates (2–100 mV s 1) are shown in Fig. 2c. Each CV curve has an obvious redox peak, which represents a Faraday redox reaction, and the position of the redox peak changes slightly as the scanning rate increases, indicating that NiCo2O4/CuS electrode has excellent redox reversibility and electrical conductivity. The GCD curves of the NiCo2O4/CuS electrode at different current densities have a significant voltage plateau (Fig. 2d). The specific capacitances of NiCo2O4/CuS electrodes are 2169, 1740, 1588, 1566 and 1267 F g 1 at current densities of 0.5, 1, 2, 4 and 8 A g 1, respectively, and results are presented in Fig. 3a. Compared with other reported electrodes, NiCo2O4/CuS electrodes have considerable specific capacitance, showing great energy storage potential [12]. The cycling stability was measured at 1 A g 1, the capacitor retention rate increased to 123% after 7000 cycles (Fig. 3b), and the specific capacitance increased from the original 1222 F g 1 to 1503 F g 1, the increase in specific capacitance may be due to
the progressive activation of the material by the electrolyte ions penetrating deeply into the electrode, which makes the insertion and de-intercalation of the electrochemical material more complete [13,14]. In addition, it is worth noting that the morphology of NiCo2O4/CuS composites after cycling can still maintain good uniformity (Fig. S5), which further demonstrates excellent stability after long cycling. Electrochemcial impedance spectroscopy (EIS) was shown in Fig. 3c, the NiCo2O4/CuS electrode has the larger linear slope in the low frequency region. The slope of the impedance spectrum in the low frequency range indicates the diffusion resistance caused by the diffusion/transmission of OH– ions in the electrode during the redox reaction [15–16]. And the smaller semicircular diameter in the high frequency region, which means it has excellent capacitance performance and small charge transfer resistance. In addition, after 7000 cycles of charge and discharge, the impedance slope of the composites increased significantly. This is also a testament to the increase in specific capacitance of composites after cycling stability testing. The Ragone plot of asymmetric supercapacitors composed of NiCo2O4/CuS composites and graphene reveals a high energy density of 173.5 W h kg 1 at a power density of 360 W kg 1 (Fig. 3d). As expected, LEDs could be lightened with connected in series
4
Y. Tian et al. / Materials Letters 264 (2020) 127400
Fig. 3. (a) Specific capacitance of the device at various current densities, (b) Cycle stability, (c) Nyquist plots and (d) Ragone plots of NiCo2O4/CuS electrode.
(Fig. S6), which suggested the potential application of supercapacitor based on the NiCo2O4/CuS electrodes.
4. Conclusion
Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
In summary, spherical NiCo2O4/CuS composites were prepared by hydrothermal synthesis. NiCo2O4/CuS composites exhibited high specific capacitance of 2169 F g 1 at 0.5 A g 1 and capacity retention rate of 123% after 7000 cycles at 1 A g 1. Furthermore, the asymmetric supercapacitor was prepared by assembling NiCo2O4/CuS and graphene, the device processed high energy density of 173.5 W h kg 1 at 360 W kg 1 and can be used as power supply for red LED lights, demonstrating a potential application of supercapacitor.
Acknowledgements
CRediT authorship contribution statement
References
Yunyan Tian: Conceptualization, Validation, Formal analysis, Writing - original draft. Zhanhua Su: . : Resources, Funding acquisition, Writing - review & editing, Supervision. Zhifeng Zhao: Data curation, Validation, Funding acquisition, Writing - review & editing. Bowen Cong: Investigation, Validation, Formal analysis. Meijia Wang: Validation, Formal analysis.
This work was supported by the Project of Introducing Talent of Guangdong University of Petrochemical Technology (2019rc052 and 2019rc054). Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi.org/10.1016/j.matlet.2020.127400.
[1] Q. Maqbool, C. Singh, P. Jash, A. Paul, A. Srivastava, Chem. Eur. J. 23 (2017) 4216–4226. [2] S.G. Chen, Y.H. Li, B.X. Wu, Z.X. Wu, F.J. Li, J.H. Wu, P. Liu, H.B. Li, Electrochim. Acta 275 (2018) 40–49. [3] Z. Wu, Y. Zhu, X. Ji, J. Mater. Chem. A2 (2014) 14759–14772. [4] H. Xin, Z.J. Xu, Y.F. Liu, W. Li, Z.H. Hu, J. Alloys Compd. 711 (2017) 670–676. [5] D.P. Zhao, M.Z. Dai, Y.L. Tong, CrystEngComm 21 (2019) 5789–5796. [6] A. Alshahrie, M.O. Ansari, Electron. Mater. Lett. 2 (2019) 238–246.
Y. Tian et al. / Materials Letters 264 (2020) 127400 [7] Z.J. Wei, Y.X. Hou, C. Jiang, H.Y. Liu, X.R. Chen, Electron. Mater. Lett. 15 (2019) 582–594. [8] K. Wang, C.J. Zhao, Z.M. Zhang, S.D. Min, X.Z. Qian, RSC Adv. 6 (2016) 16963– 16971. [9] I.K. Durga, S.S. Rao, J.W. Ahn, T.Y. Park, B.J. Soo, C.I. Ho, K. Prabakar, H.J. Kim, Energies 11 (2018) 1624. [10] X.S. Feng, Y. Huang, C. Li, X.F. Chen, S.H. Zhou, X.G. Gao, C. Chen, Chem. Eng. J. 368 (2019) 51–60. [11] F. Yang, K. Zhang, W.Y. Li, K.B. Xu, J Colloid Interf. Sci. 556 (2019) 386–391.
5
[12] Q. Liu, X.D. Hong, X. Zhang, W. Wang, W.X. Guo, X.Y. Liu, M.D. Ye, Chem. Eng. J. 356 (2019) 985–993. [13] X.Y. Zhou, Y.F. Ren, Y. Lu, Z.J. Cheng, W.J. Wang, Q. Wang, W. Huang, X.C. Dong, Adv. Mater. Interfaces 6 (2019) 1901138. [14] D.S. Patil, S.A. Pawar, J.C. Shin, H.J. Kim, J. Power Sources 435 (2019) 226812. [15] C. Li, X.Y. Gao, S.D. Li, Y. Zhao, K. Gao, Mater. Lett. 244 (2019) 74–77. [16] Y. Zhang, M. Ma, J. Yang, H. Su, W. Huang, X. Dong, Nanoscale 6 (2014) 4303– 4308.
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/mlblue
Spherical NiCo2O4/CuS composites for supercapacitor electrodes Yunyan Tian b, Zhanhua Su a,b,⇑, Zhifeng Zhao a,⇑, Bowen Cong c, Meijia Wang b a
College of Chemistry, Guangdong University of Petrochemical Technology, Maoming 525000, China College of Chemistry and Chemical Engineering, Harbin Normal University, Harbin 150025, China c School of Chemistry and Chemical Engineering, Harbin Institute of Technology, Harbin 150001, China b
a r t i c l e
i n f o
Article history: Received 27 November 2019 Received in revised form 17 January 2020 Accepted 20 January 2020 Available online 22 January 2020 Keywords: NiCo2O4/CuS Composite materials Mesoporous Supercapacitor
a b s t r a c t In this work, spherical NiCo2O4/CuS composites was synthesized by hydrothermal method. As electrode material, it possesses high specific capacitance (2169 F g 1 at 0.5 A g 1), while maintaining excellent stability with about 123% capacitance retention after 7000 cycles at 1 A g 1. The asymmetric supercapacitor based NiCo2O4/CuS electrode exhibits a high energy density of 173.5 W h kg 1 at at a power density of 360 W kg 1 and can provide power supply for red LEDs indicator. This is mainly attributed to the synergistic effect of CuS and NiCo2O4, which promotes electron transport and electrolyte ion diffusion. Ó 2020 Elsevier B.V. All rights reserved.
1. Introduction Supercapacitors have attracted attention because of its high energy density and power density [1–2]. Currently, transition metal oxides are extensive used in the preparation of electrode materials. NiCo2O4 has achieved great success in supercapacitors due to its mesoporous structure and excellent electrical performance [3]. Such as Xin reported flower-like NiCo2O4 material, which specific energy is 1609 F g 1 at 1 A g 1 [4]. Zhang constructed nanowire NiCo2O4 capacitance retention is 57% of the initial value after 5000 cycles [5]. However, due to lower conductivity and poor cycle performance, which hinder its practical application. The carbon coating was adopted overcome these problem [6–7], but the carbon coating can’t improve intrinsic conductivity of NiCo2O4, surface coating is different from in-situ growth, and its mechanical stress is bad, so it is easy to fall off during charging and discharging. CuS was widely reported due to its stable electrochemical performance, cycle life and lower cost. For example, Wang reported CuS/RGO/Ni3S2 with high specific capacitance (1692.7 F g 1 at 6.5 A g 1) [8]. Durga stated CuS@PbS composites with good cycling stability (only 2.9% loss after 3000 cycles at 2.85 A g 1) [9]. Based on the above analysis, we think that recombination of NiCo2O4 and CuS maybe is feasible, because the synergistic effect of the two
⇑ Corresponding authors at: College of Chemistry, Guangdong University of Petrochemical Technology, Maoming 525000, China (Z. Su). E-mail addresses: [email protected] (Z. Su), [email protected] (Z. Zhao). https://doi.org/10.1016/j.matlet.2020.127400 0167-577X/Ó 2020 Elsevier B.V. All rights reserved.
phase expose more active sites to increase electrochemical kinetics. Fortunately, fluffy spherical NiCo2O4/CuS was successfully prepared by hydrothermal synthesis. The specific capacitance of NiCo2O4/CuS at a current density of 0.5 A g 1 is 2169 F g 1, and the cycle retention rate of 7000 cycles is 123%. Meanwhile, the asymmetric supercapacitor is assembled based on NiCo2O4/CuS and graphene electrodes, and the energy density is up to 173.5 W h kg 1 at a power density of 360 W kg 1.
2. Experimental The 56 mM Ni(NO3)26H2O, 116 mM Co(NO3)26H2O, 34 mM NH4F, 82 mM urea, 100 mM CuSO4, 400 mM Na2S2O3 and 0.01 g of surfactant CTAB were dissolved in 70 mL of water, stirred for 30 min. After homogenization, it was added to a 100 mL reactor and heated to 120 °C for 5 h. The mixture was cooled at room temperature, and separated by centrifugation with water and ethanol, respectively. The sample was heated at 60 °C for 12 h. After the drying was completed, the sample was placed in a tube furnace and annealed at 350 °C for 2 h. Preparation of NiCo2O4 and electrochemical measurements see Supporting Information. The samples were characterized by scanning electron microscopy (SEM, S4800), energy-dispersive X-ray spectroscopy (EDS) and a transmission electron microscope (TEM, Tecnai G2 F20). Xray diffraction (XRD) measurement was collected using a Siemens D5005 diffractometer with Cu-Ka (k = 1.5418 Å) radiation. The BET surface area and pore volume were calculated based on the adsorp-
2
Y. Tian et al. / Materials Letters 264 (2020) 127400
tion isotherm. All electrochemical tests were carried by the CHI660e electrochemical workstation.
3. Results and discussion Fig. S1 shows the SEM images of the NiCo2O4 at different magnifications. The morphology of NiCo2O4/CuS is fluffy spherical (Fig. S2). The corresponding EDS spectrum confirms the presence of elements such as Ni, Co, O, Cu and S in the prepared sample (Fig. S3a), the ratio of these elements is close to the target value. Fig. S3b shows the XRD results for NiCo2O4/CuS, NiCo2O4 and CuS. The diffraction peaks of (1 1 1), (3 1 1), (4 0 0), (5 1 1) and (4 4 0) can be classified as NiCo2O4 phase (JCPDS No.20–0781), and the diffraction peaks of (1 0 2), (1 0 3), (1 1 0), (1 0 8) and (1 1 6) can be classified as CuS (JCPDS No. 06–0464). All peaks were recorded and no additional peaks were detected, indicating high purity of the sample. The TEM image of the NiCo2O4/CuS is consistent with the above test SEM morphology (Fig. 1a). In addition, the corresponding elemental pattern results of sample are shown in Fig. 1b, and Ni, Co, O, Cu and S are uniformly distributed in the material, which proves the uniform formation of the NiCo2O4/CuS composites. The HRTEM image of sample shows that the measured lattice fringes are 0.47 and 0.30 nm (Fig. 1c), respectively, corresponding to the (1 1 1) crystal plane of NiCo2O4 and the (1 0 2) crystal plane of CuS. The
SAED mode shows well-defined diffraction rings indicating polycrystalline properties of sample (Fig. 1d). The nitrogen adsorption and desorption isotherms of NiCo2O4 and NiCo2O4/CuS are shown in Fig. S4. The BET values for NiCo2O4 and NiCo2O4/CuS were calculated to be 50.3 m2 g 1 and 106.2 m2 g 1, respectively. The distribution of sample was calculated by the desorption isotherm using the Barrete-JoynereHalenda (BJH) method. The maximum pore volumes of NiCo2O4 and NiCo2O4/CuS were found to be 0.323 cm3 g 1 and 1.92 cm3 g 1, respectively. Due to the larger specific surface area and pore volumes, NiCo2O4/CuS can provide efficient electrolyte ion channels and active sites for rapid ion transfer/diffusion, and is predicted to exhibit better electrochemical performance, so electrochemical testing was developed to prove this hypothesis. Capacitance characteristics are clarified from the results of cyclic voltammetry (CV) and constant current charge and discharge (GCD) tests. As shown in Fig. 2a, NiCo2O4/CuS electrodes exhibit larger area of the CV curve than NiCo2O4 at scan rate of 20 mV s 1, indicating that NiCo2O4/CuS electrode had better specific capacitance. Fig. 2b shows the charge/discharge curves of NiCo2O4 and NiCo2O4/CuS electrodes with a current density of 1 A g 1. According to the equation (S1), the specific capacitances of NiCo2O4 and NiCo2O4/CuS are calculated to be 794 F g 1 and 1740 F g 1, respectively. It can be seen that NiCo2O4/CuS composites has higher specific capacitance. This is mainly due to the unique morphology, the larger specific surface area and grain boundary of composites,
Fig. 1. (a) TEM images, (b) TEM elemental mapping, (c) HRTEM images and (d) SAED image of the NiCo2O4/CuS.
Y. Tian et al. / Materials Letters 264 (2020) 127400
3
Fig. 2. (a) CV curves and (b) GCD curves of NiCo2O4 and NiCo2O4/CuS, (c) CV curves and (d) GCD curves of NiCo2O4/CuS.
which provide more electrolyte channels and active sites, increasing charge storage and accumulation. In addition, the synergistic effect between NiCo2O4 and CuS improves their electrochemical activity and accelerates the transfer of electrons and electrolytes [10,11]. Further, CV curves of NiCo2O4/CuS electrodes at different scanning rates (2–100 mV s 1) are shown in Fig. 2c. Each CV curve has an obvious redox peak, which represents a Faraday redox reaction, and the position of the redox peak changes slightly as the scanning rate increases, indicating that NiCo2O4/CuS electrode has excellent redox reversibility and electrical conductivity. The GCD curves of the NiCo2O4/CuS electrode at different current densities have a significant voltage plateau (Fig. 2d). The specific capacitances of NiCo2O4/CuS electrodes are 2169, 1740, 1588, 1566 and 1267 F g 1 at current densities of 0.5, 1, 2, 4 and 8 A g 1, respectively, and results are presented in Fig. 3a. Compared with other reported electrodes, NiCo2O4/CuS electrodes have considerable specific capacitance, showing great energy storage potential [12]. The cycling stability was measured at 1 A g 1, the capacitor retention rate increased to 123% after 7000 cycles (Fig. 3b), and the specific capacitance increased from the original 1222 F g 1 to 1503 F g 1, the increase in specific capacitance may be due to
the progressive activation of the material by the electrolyte ions penetrating deeply into the electrode, which makes the insertion and de-intercalation of the electrochemical material more complete [13,14]. In addition, it is worth noting that the morphology of NiCo2O4/CuS composites after cycling can still maintain good uniformity (Fig. S5), which further demonstrates excellent stability after long cycling. Electrochemcial impedance spectroscopy (EIS) was shown in Fig. 3c, the NiCo2O4/CuS electrode has the larger linear slope in the low frequency region. The slope of the impedance spectrum in the low frequency range indicates the diffusion resistance caused by the diffusion/transmission of OH– ions in the electrode during the redox reaction [15–16]. And the smaller semicircular diameter in the high frequency region, which means it has excellent capacitance performance and small charge transfer resistance. In addition, after 7000 cycles of charge and discharge, the impedance slope of the composites increased significantly. This is also a testament to the increase in specific capacitance of composites after cycling stability testing. The Ragone plot of asymmetric supercapacitors composed of NiCo2O4/CuS composites and graphene reveals a high energy density of 173.5 W h kg 1 at a power density of 360 W kg 1 (Fig. 3d). As expected, LEDs could be lightened with connected in series
4
Y. Tian et al. / Materials Letters 264 (2020) 127400
Fig. 3. (a) Specific capacitance of the device at various current densities, (b) Cycle stability, (c) Nyquist plots and (d) Ragone plots of NiCo2O4/CuS electrode.
(Fig. S6), which suggested the potential application of supercapacitor based on the NiCo2O4/CuS electrodes.
4. Conclusion
Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
In summary, spherical NiCo2O4/CuS composites were prepared by hydrothermal synthesis. NiCo2O4/CuS composites exhibited high specific capacitance of 2169 F g 1 at 0.5 A g 1 and capacity retention rate of 123% after 7000 cycles at 1 A g 1. Furthermore, the asymmetric supercapacitor was prepared by assembling NiCo2O4/CuS and graphene, the device processed high energy density of 173.5 W h kg 1 at 360 W kg 1 and can be used as power supply for red LED lights, demonstrating a potential application of supercapacitor.
Acknowledgements
CRediT authorship contribution statement
References
Yunyan Tian: Conceptualization, Validation, Formal analysis, Writing - original draft. Zhanhua Su: . : Resources, Funding acquisition, Writing - review & editing, Supervision. Zhifeng Zhao: Data curation, Validation, Funding acquisition, Writing - review & editing. Bowen Cong: Investigation, Validation, Formal analysis. Meijia Wang: Validation, Formal analysis.
This work was supported by the Project of Introducing Talent of Guangdong University of Petrochemical Technology (2019rc052 and 2019rc054). Appendix A. Supplementary data Supplementary data to this article can be found online at https://doi.org/10.1016/j.matlet.2020.127400.
[1] Q. Maqbool, C. Singh, P. Jash, A. Paul, A. Srivastava, Chem. Eur. J. 23 (2017) 4216–4226. [2] S.G. Chen, Y.H. Li, B.X. Wu, Z.X. Wu, F.J. Li, J.H. Wu, P. Liu, H.B. Li, Electrochim. Acta 275 (2018) 40–49. [3] Z. Wu, Y. Zhu, X. Ji, J. Mater. Chem. A2 (2014) 14759–14772. [4] H. Xin, Z.J. Xu, Y.F. Liu, W. Li, Z.H. Hu, J. Alloys Compd. 711 (2017) 670–676. [5] D.P. Zhao, M.Z. Dai, Y.L. Tong, CrystEngComm 21 (2019) 5789–5796. [6] A. Alshahrie, M.O. Ansari, Electron. Mater. Lett. 2 (2019) 238–246.
Y. Tian et al. / Materials Letters 264 (2020) 127400 [7] Z.J. Wei, Y.X. Hou, C. Jiang, H.Y. Liu, X.R. Chen, Electron. Mater. Lett. 15 (2019) 582–594. [8] K. Wang, C.J. Zhao, Z.M. Zhang, S.D. Min, X.Z. Qian, RSC Adv. 6 (2016) 16963– 16971. [9] I.K. Durga, S.S. Rao, J.W. Ahn, T.Y. Park, B.J. Soo, C.I. Ho, K. Prabakar, H.J. Kim, Energies 11 (2018) 1624. [10] X.S. Feng, Y. Huang, C. Li, X.F. Chen, S.H. Zhou, X.G. Gao, C. Chen, Chem. Eng. J. 368 (2019) 51–60. [11] F. Yang, K. Zhang, W.Y. Li, K.B. Xu, J Colloid Interf. Sci. 556 (2019) 386–391.
5
[12] Q. Liu, X.D. Hong, X. Zhang, W. Wang, W.X. Guo, X.Y. Liu, M.D. Ye, Chem. Eng. J. 356 (2019) 985–993. [13] X.Y. Zhou, Y.F. Ren, Y. Lu, Z.J. Cheng, W.J. Wang, Q. Wang, W. Huang, X.C. Dong, Adv. Mater. Interfaces 6 (2019) 1901138. [14] D.S. Patil, S.A. Pawar, J.C. Shin, H.J. Kim, J. Power Sources 435 (2019) 226812. [15] C. Li, X.Y. Gao, S.D. Li, Y. Zhao, K. Gao, Mater. Lett. 244 (2019) 74–77. [16] Y. Zhang, M. Ma, J. Yang, H. Su, W. Huang, X. Dong, Nanoscale 6 (2014) 4303– 4308.