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A facile method for synthesis of Co2Mn(PO4)2 nanorods as high-performance electrodes for supercapacitors
Accepted Manuscript A facile method for synthesis of Co2Mn(PO4)2 nanorods as high-performance electrodes for supercapacitors Hui Mao, Yongteng Qian, Zhunian Jin, Yan Zhang PII: DOI: Reference:
S0167-577X(18)30927-3 https://doi.org/10.1016/j.matlet.2018.06.021 MLBLUE 24461
To appear in:
Materials Letters
Received Date: Revised Date: Accepted Date:
2 April 2018 29 May 2018 8 June 2018
Please cite this article as: H. Mao, Y. Qian, Z. Jin, Y. Zhang, A facile method for synthesis of Co2Mn(PO4)2 nanorods as high-performance electrodes for supercapacitors, Materials Letters (2018), doi: https://doi.org/10.1016/j.matlet. 2018.06.021
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
A facile method for synthesis of Co2Mn(PO4)2 nanorods as high-performance electrodes for supercapacitors Hui Maoa,*, Yongteng Qianb,*, Zhunian Jina, and Yan Zhangc
a
Pharmaceutical and Material Engineering School, Jinhua Polytechnic, Jinhua, 321000, Zhejiang Province, P. R. China. b Department of Physics and Institute of Basic Sciences, Sungkyunkwan University, 2066, Seobu-ro, Jangan-gu, Suwon, 16419 Gyeonggi-do, Republic of Korea. c Department of Chemistry, Zhejiang Normal University, Jinhua 321004, Zhejiang Province, P. R. China. ＊
Author to whom the correspondence should be made: [email protected]; [email protected].
ABSTRACT: Herein, we described a mild method to synthesize Co2 Mn(PO4)2 nanorods. The scanning electron microscopy results indicated that the Co2Mn(PO4)2 nanorods have average widths and lengths of 50 nm and 600 nm, respectively. The electrochemical performance of Co2 Mn(PO4)2 was examined in a three-electrode system, which revealed a specific capacitance of 525 F g-1 at a current density of 1.0 A g-1. Importantly, the capacity retention of the prepared Co2 Mn(PO4)2 electrode is 95.3% after 5,000 cycles in 3M KOH aqueous electrolyte at the current density of 1.0 A g-1. These extraordinary electrochemical performance of the Co2 Mn(PO4)2 nanorods made it an excellent candidate for application in energy storage devices.
Keywords: Co2Mn(PO4)2, Electrochemical, Supercapacitors, Energy storage and conversion, Crystal structure. 1. Introduction Supercapacitors are considered one of the most promising energy storage devices due to light weight and superior characteristics such as long cycling life, high power density and low fabrication cost [1]. Up to now, there are numerous reports using transition metal oxides [2], transition metal chalcogenide [3] and transition metal phosphates [4] as an electrode material for supercapacitors. Among them, transition metal phosphates (TMPs) are considered to be an 1
excellent electrode material for supercapacitors because of their outstanding properties. Hence, tremendous efforts have been made to enhance the activity of electrode materials for supercapacitors based on TMPs [5]. For example, Nithya et al. successfully synthesized BiPO4 microcrystals as supercapacitive materials with good activity via hydrothermal approach, which revealed a specific capacitance of 202 F g-1 with current density of 5 mA cm-2 [6]. Pang et al. prepared supercapacitor electrode based on CoHPO4 nanosheets, which achieved a superior specific capacitance of 413 F g-1 at a current density of 1.5 A g-1 [7]. Although there have been some reports about the electrode material based on TMPs, to achieve supercapacitor with high-performance and good cycle stability is still a great challenge. On the other hand, many methods have been developed to synthesize TMPs, including sol-gel method [8], hydrothermal method [9], and exfoliated method [10]. However, the aforesaid methods have some drawbacks, such as low yield, complicated procedure, high temperature and high energy-consuming, etc. Thus, the development of a simple and large-scale yield method to fabricate TMPs has become the most significant step for related fields. More importantly, to date, there was no report about the synthesis of Co2Mn(PO4)2 nanorods, as well as their applications for supercapacitors. In this work, Co2 Mn(PO4)2 nanorods were successfully fabricated through a facile route. The SEM results indicated the Co2 Mn(PO4 )2 nanorods have widths and lengths of 50 nm and 600 nm, respectively. Particularly, such Co2 Mn(PO4)2 electrode revealed a specific capacitance of 525 F g-1 at a current density of 1.0 A g-1, with a capacity retention of 95.3% after 5,000 cycles in 3M KOH aqueous electrolyte. 2. Experimental The Co2Mn(PO4)2 nanorods were synthesized by a facile method. The experimental details, 2
electrode fabrication process and sample characterizations are as shown in Supporting Information. 3. Results and discussion As shown in Fig. 1a, the characteristic diffraction peaks at 13.15°, 26.86°, 30.15°, 33.09°, 54.66°, 58.25°, 63.62°, and 70.05° agree well with the (020), (13-1), (201), (041), (35-2), (620), (640), and (-391) diffraction planes of Co2 Mn(PO4)2 (JCPDS No. 51-563). X-ray photoelectron spectroscopy (XPS) was further employed to evaluate the chemical composition of the as-obtained sample. Five elements (P, Co, Mn, O and C) were identified from the survey scan spectrum of the Co2 Mn(PO4)2 (Fig. 1b). Fig. 1c presents the XPS spectra of O 1s, and three fitted peaks located at 530.9, 532.1, and 534.0 eV are attributed to the P-O, oxygen of OH group, and adsorbed water in Co2Mn(PO4)2 [11]. The XPS spectrum of P 2p (Fig. 1d) has three fitted peaks at 133.4 eV, 134.0 eV and 135.2 eV, which could correspond to the P 2p3/2 in Co2 Mn(PO4)2 [12]. The two peaks (Fig. 1e) located at the binding energy of 782.0 eV and 798.2 eV along with two satellites peaks are assigned to Co 2p3/2 and Co 2p1/2, respectively, indicating the presence of a Co2+ oxidation state [13]. For XPS spectra of Mn 2p (Fig. 1f), two distinct peaks located are at 641.4 and 653.3 eV (with two satellites peaks 645.5 and 655.6 eV), which are attributed to the Mn2+ 2p3/2 and Mn2+ 2p1/2 in Co2 Mn(PO4)2. Thus, the XPS and XRD results confirmed that the Co3(PO4)2 was successfully synthesized. The low magnification SEM micrographs (Fig. 2a,b) show that the Co2 Mn(PO4)2 nanorods were uniformly distributed. The high magnification SEM images are shown in Fig. 2c and d, indicating that the Co2 Mn(PO4)2 nanorods have lengths and widths in the range 500-700 nm and 40-60 nm, respectively. Generally, the nanorods have a larger surface area to volume ratio, which not only 3
increases the specific surface area of the sample but also facilitates electron transport in the process of charge-discharge [14, 15]. To confirm the specific surface area of the Co2Mn(PO4)2, Brunauer-Emmett-Teller (BET) measurement was performed, which is shown in Fig. S1. The calculated specific surface area of the Co2 Mn(PO4)2 nanorods was 58.2 m2/g and the pore size was ranging from 20 to 60 nm (inset of Fig. S1). The electrode material with larger specific surface area would be beneficial for supplying more surface active sites, favoring rapid transport of electrons, and further resulting in enhancement of electrochemical performance for supercapacitors [16]. Fig. 2e shows the typical TEM image of Co2Mn(PO4)2, which demonstrates that the sample has nanorods structure. The high-resolution TEM (HRTEM) result (Fig. 2f) exhibits that the lattice fringes have the spacing of 0.42 nm, which is assigned to the (020) planes of Co2 Mn(PO4)2. The electrochemical performances of the Co2 Mn(PO4)2 nanorods were investigated in a three-electrode system. The CV curves of the Co2 Mn(PO4)2 electrodes at different scan rates ranging from 5 to 100 mV s-1, are presented in Fig. 3a. We can clearly see that the CV curves have a pair of redox reaction peaks. Moreover, as the scan rates increase, the current density gradually increases, which indicates the pseudocapacitive behavior with relatively good stability while the CV curves maintain their shapes even at the scan rate up to 100 mV s-1 [17]. Fig. 3b shows the GCD curves for Co2 Mn(PO4)2 electrode obtained in 3.0 M KOH aqueous electrolyte at different current densities (1 to 8 A g-1). The GCD curves show symmetric charge-discharge processes at various current densities, suggesting that the Co2Mn(PO4)2 electrode exhibits an ideal capacitive behavior and excellent reversible redox reactions [18]. The specific capacitance of the Co2 Mn(PO4)2 electrode at different current densities was calculated from GCD curves, which is 4
presented in Fig. 3c. The specific capacitance of the Co2Mn(PO4)2 electrode is 525, 490, 452, 391 and 305 F g-1 at the current densities of 1, 2, 4, 6, and 8 A g-1, respectively. Compared with previous reports of using metal phosphates as an electrode material, the results of our Co2 Mn(PO4)2 electrode are better than those reports as shown in Table S1 in Supporting Information, suggesting that our Co2 Mn(PO4)2 electrode maybe a potential candidate for high performance supercapacitor. The superior electrochemical performance is attributed to the following properties: (i) the nanorod structure can provide more electrons transfer pathway; (ii) larger specific surface area would be beneficial for supplying more active sites; (iii) the synergistic effect of Co and Mn ions can boost the specific capacitance and conductivity of Co2 Mn(PO4)2, resulting in enhanced electrochemical performance. Additionally, the electrochemical stability is another crucial factor for supercapacitor applications. Thus, the cycling stability of the Co2 Mn(PO4)2 electrodes were examined at the different current density (1, 4, and 8 A g-1) for 5000 cycles. As presented in Fig. 3d, 95.3%, 92.7%, and 90.8% of the initial specific capacitance for the Co2 Mn(PO4)2 electrodes were retained after 5000 cycles at the different current density of 1, 4, and 8 A g-1. To determine the electrical conductivity of the Co2 Mn(PO4)2 electrode, the EIS was employed at AC voltage amplitude of 5 mV over a frequency range of 0.01 Hz-100 k Hz. The Nyquist plots of Co2Mn(PO4)2 electrode are shown in Figure S2. The EIS results of Co2Mn(PO4)2 electrode present a small internal resistance (Ri ≈ 0.82 Ω), indicating good electrical conductivity. 4. Conclusions In conclusion, the Co2 Mn(PO4)2 nanorods have been successfully synthesized via a simple method without adding any surfactant. The electrochemical performance of Co2Mn(PO4)2 electrode was investigated in a three-electrode system, which revealed the specific capacitance of 525 F g-1 at a 5
current density of 1.0 A g-1, with a capacity retention of 95.3% after 5,000 cycles in 3M KOH aqueous electrolyte. These superior results suggest that the Co2Mn(PO4)2 nanorods are promising to be an excellent electrode material for high performance electrochemical supercapacitor. Acknowledgements This work was supported by the National Natural Science Foundation of China (21702188). References [1] J. Chang, M. Jin, F. Yao, T. Kim, V. Le, H. Yue, F. Gunes, B. Li, A. Ghosh, S. Xie, Y. Lee, Adv. Funct. Mater., 23 (2013) 5074-5083. [2] T. Liu, C. Jiang, W. You, J. Yu, J. Mater. Chem. A, (2017). [3] J. Du, K. Li, Y. Qian, W. He, V. Harnchana, M. Yang, H. Wang, Nano, 11 (2016) 1650133. [4] H. Li, H. Yu, J. Zhai, L. Sun, H. Yang, S. Xie, Mater. Lett., 152 (2015) 25-28. [5] J. Chang, S. Adhikari, T.H. Lee, B. Li, F. Yao, D.T. Pham, V.T. Le, Y.H. Lee, Adv. Energy Mater., 5 (2015) 1500003. [6] V. Nithya, R. Selvan, L. Vasylechko, J. Phys. Chem. Solids, 86 (2015) 11-18. [7] H. Pang, S. Wang, W. Shao, S. Zhao, B. Yan, X. Li, S. Li, J. Chen, W. Du. Nanoscale 5 (2013) 5752-5757. [8] T. Drezen, N. Kwon, P. Bowen, I. Teerlinck, M. Isono, I. Exnar, J. Power Sources, 174 (2007) 949-953. [9] H. Kim, J. Park, I. Park, K. Jin, S. Jerng, S. Kim, K. Nam, K. Kang, Nat. Commun., 6 (2015) 8253. [10] C. Yang, L. Dong, Z. Chen, H. Lu, J. Phys. Chem. C, 118 (2014) 18884-18891. [11] X. Liang, B. Zheng, L. Chen, J. Zhang, Z. Zhuang, B. Chen, ACS Appl. Mater. Interfaces, 9 (2017) 23222-23229. [12] P. Arunachalam, M. Shaddad, A. Alamoudi, M. Ghanem, A. Al-Mayouf, Catalysts, 7 (2017) 119. [13] J. Li, G. Wei, Y. Zhu, Y. Xi, X. Pan, Y. Ji, I.V. Zatovsky, W. Han, J. Mater. Chem. A, 5 (2017) 14828-14837. [14] T. Zhou, Y. Zheng, H. Gao, S. Min, S. Li, H.K. Liu, Z. Guo, Adv. Sci. 2 (2015) 1500027. [15] Y. Qian, M. Yang, F. Zhang, J. Du, K. Li, X. Lin, X. Zhu, Y. Lu, W. Wang, D.J. Kang, Mater. Charact., 142 (2018) 43-49. [16] W. Yu, X. Jiang, S. Ding, B.Q. Li, J. Power Sources, 256 (2014) 440-448. [17] X. Lu, M. Yu, G. Wang, T. Zhai, S. Xie, Y. Ling, Y. Tong, Y. Li, Adv Mater, 25 (2013) 267-272. [18] H. Kim, M. Cho, M. Kim, K. Park, H. Gwon, Y. Lee, K. Roh, K. Kang, Adv. Energy Mater., 3 (2013) 1500-1506.
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Figure captions Figure 1. (a) XRD patterns of Co2 Mn(PO4)2 nanorods. XPS spectrum of Co2Mn(PO4 )2, (b) survey scan spectrum, (c) O 1s, (d) P 2p, (e) Co 2p, and (f) Mn 2p. Figure 2.(a, b) low-magnification and (c, d) high-magnification SEM images of Co2Mn(PO4)2 nanorods. (e) TEM image and (f) HRTEM image of Co2 Mn(PO4)2 nanorods. Figure 3. Electrochemical performance of Co2Mn(PO4)2 . (a) CV curves with different scan rates; (b) Charge-discharge curves with different current densities; (c)Specific capacitance calculated based on the discharge curve from (b); (d) Cycling stability performance.
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Graphical abstract
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Highlights: Co2Mn(PO4)2 nanorods were prepared by a facile method. The Co 2Mn(PO4)2 electrode exhibits enhanced capacity. The superior capacitance retention of 95.3% after 5,000 cycles.
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S0167-577X(18)30927-3 https://doi.org/10.1016/j.matlet.2018.06.021 MLBLUE 24461
To appear in:
Materials Letters
Received Date: Revised Date: Accepted Date:
2 April 2018 29 May 2018 8 June 2018
Please cite this article as: H. Mao, Y. Qian, Z. Jin, Y. Zhang, A facile method for synthesis of Co2Mn(PO4)2 nanorods as high-performance electrodes for supercapacitors, Materials Letters (2018), doi: https://doi.org/10.1016/j.matlet. 2018.06.021
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
A facile method for synthesis of Co2Mn(PO4)2 nanorods as high-performance electrodes for supercapacitors Hui Maoa,*, Yongteng Qianb,*, Zhunian Jina, and Yan Zhangc
a
Pharmaceutical and Material Engineering School, Jinhua Polytechnic, Jinhua, 321000, Zhejiang Province, P. R. China. b Department of Physics and Institute of Basic Sciences, Sungkyunkwan University, 2066, Seobu-ro, Jangan-gu, Suwon, 16419 Gyeonggi-do, Republic of Korea. c Department of Chemistry, Zhejiang Normal University, Jinhua 321004, Zhejiang Province, P. R. China. ＊
Author to whom the correspondence should be made: [email protected]; [email protected].
ABSTRACT: Herein, we described a mild method to synthesize Co2 Mn(PO4)2 nanorods. The scanning electron microscopy results indicated that the Co2Mn(PO4)2 nanorods have average widths and lengths of 50 nm and 600 nm, respectively. The electrochemical performance of Co2 Mn(PO4)2 was examined in a three-electrode system, which revealed a specific capacitance of 525 F g-1 at a current density of 1.0 A g-1. Importantly, the capacity retention of the prepared Co2 Mn(PO4)2 electrode is 95.3% after 5,000 cycles in 3M KOH aqueous electrolyte at the current density of 1.0 A g-1. These extraordinary electrochemical performance of the Co2 Mn(PO4)2 nanorods made it an excellent candidate for application in energy storage devices.
Keywords: Co2Mn(PO4)2, Electrochemical, Supercapacitors, Energy storage and conversion, Crystal structure. 1. Introduction Supercapacitors are considered one of the most promising energy storage devices due to light weight and superior characteristics such as long cycling life, high power density and low fabrication cost [1]. Up to now, there are numerous reports using transition metal oxides [2], transition metal chalcogenide [3] and transition metal phosphates [4] as an electrode material for supercapacitors. Among them, transition metal phosphates (TMPs) are considered to be an 1
excellent electrode material for supercapacitors because of their outstanding properties. Hence, tremendous efforts have been made to enhance the activity of electrode materials for supercapacitors based on TMPs [5]. For example, Nithya et al. successfully synthesized BiPO4 microcrystals as supercapacitive materials with good activity via hydrothermal approach, which revealed a specific capacitance of 202 F g-1 with current density of 5 mA cm-2 [6]. Pang et al. prepared supercapacitor electrode based on CoHPO4 nanosheets, which achieved a superior specific capacitance of 413 F g-1 at a current density of 1.5 A g-1 [7]. Although there have been some reports about the electrode material based on TMPs, to achieve supercapacitor with high-performance and good cycle stability is still a great challenge. On the other hand, many methods have been developed to synthesize TMPs, including sol-gel method [8], hydrothermal method [9], and exfoliated method [10]. However, the aforesaid methods have some drawbacks, such as low yield, complicated procedure, high temperature and high energy-consuming, etc. Thus, the development of a simple and large-scale yield method to fabricate TMPs has become the most significant step for related fields. More importantly, to date, there was no report about the synthesis of Co2Mn(PO4)2 nanorods, as well as their applications for supercapacitors. In this work, Co2 Mn(PO4)2 nanorods were successfully fabricated through a facile route. The SEM results indicated the Co2 Mn(PO4 )2 nanorods have widths and lengths of 50 nm and 600 nm, respectively. Particularly, such Co2 Mn(PO4)2 electrode revealed a specific capacitance of 525 F g-1 at a current density of 1.0 A g-1, with a capacity retention of 95.3% after 5,000 cycles in 3M KOH aqueous electrolyte. 2. Experimental The Co2Mn(PO4)2 nanorods were synthesized by a facile method. The experimental details, 2
electrode fabrication process and sample characterizations are as shown in Supporting Information. 3. Results and discussion As shown in Fig. 1a, the characteristic diffraction peaks at 13.15°, 26.86°, 30.15°, 33.09°, 54.66°, 58.25°, 63.62°, and 70.05° agree well with the (020), (13-1), (201), (041), (35-2), (620), (640), and (-391) diffraction planes of Co2 Mn(PO4)2 (JCPDS No. 51-563). X-ray photoelectron spectroscopy (XPS) was further employed to evaluate the chemical composition of the as-obtained sample. Five elements (P, Co, Mn, O and C) were identified from the survey scan spectrum of the Co2 Mn(PO4)2 (Fig. 1b). Fig. 1c presents the XPS spectra of O 1s, and three fitted peaks located at 530.9, 532.1, and 534.0 eV are attributed to the P-O, oxygen of OH group, and adsorbed water in Co2Mn(PO4)2 [11]. The XPS spectrum of P 2p (Fig. 1d) has three fitted peaks at 133.4 eV, 134.0 eV and 135.2 eV, which could correspond to the P 2p3/2 in Co2 Mn(PO4)2 [12]. The two peaks (Fig. 1e) located at the binding energy of 782.0 eV and 798.2 eV along with two satellites peaks are assigned to Co 2p3/2 and Co 2p1/2, respectively, indicating the presence of a Co2+ oxidation state [13]. For XPS spectra of Mn 2p (Fig. 1f), two distinct peaks located are at 641.4 and 653.3 eV (with two satellites peaks 645.5 and 655.6 eV), which are attributed to the Mn2+ 2p3/2 and Mn2+ 2p1/2 in Co2 Mn(PO4)2. Thus, the XPS and XRD results confirmed that the Co3(PO4)2 was successfully synthesized. The low magnification SEM micrographs (Fig. 2a,b) show that the Co2 Mn(PO4)2 nanorods were uniformly distributed. The high magnification SEM images are shown in Fig. 2c and d, indicating that the Co2 Mn(PO4)2 nanorods have lengths and widths in the range 500-700 nm and 40-60 nm, respectively. Generally, the nanorods have a larger surface area to volume ratio, which not only 3
increases the specific surface area of the sample but also facilitates electron transport in the process of charge-discharge [14, 15]. To confirm the specific surface area of the Co2Mn(PO4)2, Brunauer-Emmett-Teller (BET) measurement was performed, which is shown in Fig. S1. The calculated specific surface area of the Co2 Mn(PO4)2 nanorods was 58.2 m2/g and the pore size was ranging from 20 to 60 nm (inset of Fig. S1). The electrode material with larger specific surface area would be beneficial for supplying more surface active sites, favoring rapid transport of electrons, and further resulting in enhancement of electrochemical performance for supercapacitors [16]. Fig. 2e shows the typical TEM image of Co2Mn(PO4)2, which demonstrates that the sample has nanorods structure. The high-resolution TEM (HRTEM) result (Fig. 2f) exhibits that the lattice fringes have the spacing of 0.42 nm, which is assigned to the (020) planes of Co2 Mn(PO4)2. The electrochemical performances of the Co2 Mn(PO4)2 nanorods were investigated in a three-electrode system. The CV curves of the Co2 Mn(PO4)2 electrodes at different scan rates ranging from 5 to 100 mV s-1, are presented in Fig. 3a. We can clearly see that the CV curves have a pair of redox reaction peaks. Moreover, as the scan rates increase, the current density gradually increases, which indicates the pseudocapacitive behavior with relatively good stability while the CV curves maintain their shapes even at the scan rate up to 100 mV s-1 [17]. Fig. 3b shows the GCD curves for Co2 Mn(PO4)2 electrode obtained in 3.0 M KOH aqueous electrolyte at different current densities (1 to 8 A g-1). The GCD curves show symmetric charge-discharge processes at various current densities, suggesting that the Co2Mn(PO4)2 electrode exhibits an ideal capacitive behavior and excellent reversible redox reactions [18]. The specific capacitance of the Co2 Mn(PO4)2 electrode at different current densities was calculated from GCD curves, which is 4
presented in Fig. 3c. The specific capacitance of the Co2Mn(PO4)2 electrode is 525, 490, 452, 391 and 305 F g-1 at the current densities of 1, 2, 4, 6, and 8 A g-1, respectively. Compared with previous reports of using metal phosphates as an electrode material, the results of our Co2 Mn(PO4)2 electrode are better than those reports as shown in Table S1 in Supporting Information, suggesting that our Co2 Mn(PO4)2 electrode maybe a potential candidate for high performance supercapacitor. The superior electrochemical performance is attributed to the following properties: (i) the nanorod structure can provide more electrons transfer pathway; (ii) larger specific surface area would be beneficial for supplying more active sites; (iii) the synergistic effect of Co and Mn ions can boost the specific capacitance and conductivity of Co2 Mn(PO4)2, resulting in enhanced electrochemical performance. Additionally, the electrochemical stability is another crucial factor for supercapacitor applications. Thus, the cycling stability of the Co2 Mn(PO4)2 electrodes were examined at the different current density (1, 4, and 8 A g-1) for 5000 cycles. As presented in Fig. 3d, 95.3%, 92.7%, and 90.8% of the initial specific capacitance for the Co2 Mn(PO4)2 electrodes were retained after 5000 cycles at the different current density of 1, 4, and 8 A g-1. To determine the electrical conductivity of the Co2 Mn(PO4)2 electrode, the EIS was employed at AC voltage amplitude of 5 mV over a frequency range of 0.01 Hz-100 k Hz. The Nyquist plots of Co2Mn(PO4)2 electrode are shown in Figure S2. The EIS results of Co2Mn(PO4)2 electrode present a small internal resistance (Ri ≈ 0.82 Ω), indicating good electrical conductivity. 4. Conclusions In conclusion, the Co2 Mn(PO4)2 nanorods have been successfully synthesized via a simple method without adding any surfactant. The electrochemical performance of Co2Mn(PO4)2 electrode was investigated in a three-electrode system, which revealed the specific capacitance of 525 F g-1 at a 5
current density of 1.0 A g-1, with a capacity retention of 95.3% after 5,000 cycles in 3M KOH aqueous electrolyte. These superior results suggest that the Co2Mn(PO4)2 nanorods are promising to be an excellent electrode material for high performance electrochemical supercapacitor. Acknowledgements This work was supported by the National Natural Science Foundation of China (21702188). References [1] J. Chang, M. Jin, F. Yao, T. Kim, V. Le, H. Yue, F. Gunes, B. Li, A. Ghosh, S. Xie, Y. Lee, Adv. Funct. Mater., 23 (2013) 5074-5083. [2] T. Liu, C. Jiang, W. You, J. Yu, J. Mater. Chem. A, (2017). [3] J. Du, K. Li, Y. Qian, W. He, V. Harnchana, M. Yang, H. Wang, Nano, 11 (2016) 1650133. [4] H. Li, H. Yu, J. Zhai, L. Sun, H. Yang, S. Xie, Mater. Lett., 152 (2015) 25-28. [5] J. Chang, S. Adhikari, T.H. Lee, B. Li, F. Yao, D.T. Pham, V.T. Le, Y.H. Lee, Adv. Energy Mater., 5 (2015) 1500003. [6] V. Nithya, R. Selvan, L. Vasylechko, J. Phys. Chem. Solids, 86 (2015) 11-18. [7] H. Pang, S. Wang, W. Shao, S. Zhao, B. Yan, X. Li, S. Li, J. Chen, W. Du. Nanoscale 5 (2013) 5752-5757. [8] T. Drezen, N. Kwon, P. Bowen, I. Teerlinck, M. Isono, I. Exnar, J. Power Sources, 174 (2007) 949-953. [9] H. Kim, J. Park, I. Park, K. Jin, S. Jerng, S. Kim, K. Nam, K. Kang, Nat. Commun., 6 (2015) 8253. [10] C. Yang, L. Dong, Z. Chen, H. Lu, J. Phys. Chem. C, 118 (2014) 18884-18891. [11] X. Liang, B. Zheng, L. Chen, J. Zhang, Z. Zhuang, B. Chen, ACS Appl. Mater. Interfaces, 9 (2017) 23222-23229. [12] P. Arunachalam, M. Shaddad, A. Alamoudi, M. Ghanem, A. Al-Mayouf, Catalysts, 7 (2017) 119. [13] J. Li, G. Wei, Y. Zhu, Y. Xi, X. Pan, Y. Ji, I.V. Zatovsky, W. Han, J. Mater. Chem. A, 5 (2017) 14828-14837. [14] T. Zhou, Y. Zheng, H. Gao, S. Min, S. Li, H.K. Liu, Z. Guo, Adv. Sci. 2 (2015) 1500027. [15] Y. Qian, M. Yang, F. Zhang, J. Du, K. Li, X. Lin, X. Zhu, Y. Lu, W. Wang, D.J. Kang, Mater. Charact., 142 (2018) 43-49. [16] W. Yu, X. Jiang, S. Ding, B.Q. Li, J. Power Sources, 256 (2014) 440-448. [17] X. Lu, M. Yu, G. Wang, T. Zhai, S. Xie, Y. Ling, Y. Tong, Y. Li, Adv Mater, 25 (2013) 267-272. [18] H. Kim, M. Cho, M. Kim, K. Park, H. Gwon, Y. Lee, K. Roh, K. Kang, Adv. Energy Mater., 3 (2013) 1500-1506.
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Figure captions Figure 1. (a) XRD patterns of Co2 Mn(PO4)2 nanorods. XPS spectrum of Co2Mn(PO4 )2, (b) survey scan spectrum, (c) O 1s, (d) P 2p, (e) Co 2p, and (f) Mn 2p. Figure 2.(a, b) low-magnification and (c, d) high-magnification SEM images of Co2Mn(PO4)2 nanorods. (e) TEM image and (f) HRTEM image of Co2 Mn(PO4)2 nanorods. Figure 3. Electrochemical performance of Co2Mn(PO4)2 . (a) CV curves with different scan rates; (b) Charge-discharge curves with different current densities; (c)Specific capacitance calculated based on the discharge curve from (b); (d) Cycling stability performance.
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Graphical abstract
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Highlights: Co2Mn(PO4)2 nanorods were prepared by a facile method. The Co 2Mn(PO4)2 electrode exhibits enhanced capacity. The superior capacitance retention of 95.3% after 5,000 cycles.
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