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Polyhedral ternary oxide FeCo2O4: A new electrode material for supercapacitors
Journal of Alloys and Compounds 735 (2018) 1339e1343
Contents lists available at ScienceDirect
Journal of Alloys and Compounds journal homepage: http://www.elsevier.com/locate/jalcom
Letter
Polyhedral ternary oxide FeCo2O4: A new electrode material for supercapacitors a b s t r a c t Keywords: Polyhedral morphology FeCo2O4 Supercapacitors
In this study, Fe-Co-ZIF(iron and cobalt in the ZIF-67) with an earlier shape of ZIF-67 was synthesized successfully. After thermal treatment, the Fe-Co-ZIF precursor was turned into FeCo2O4 with polyhedral morphology. A comparative analysis was made with pure ZIF-67 oxide, finding its great improvement in the electrochemical performance. The FeCo2O4 showed a specific capacity of 510 F g1 (52.42 mAh g1) at 1 A g1 in 1.0 M KOH electrolyte, while it was only 273 F g1 (28.1 mAh g1) for pure ZIF-67 oxide Co3O4. The FeCo2O4 cycle life increased from 52.1% to 75.5%. These data suggested that this ternary oxide FeCo2O4 with polyhedral morphology could be used for supercapacitors. © 2017 Elsevier B.V. All rights reserved.
1. Introduction With the prosperity of energy industry, many countries have paid more attention to the development of power sources [1]. Recently, the studies on supercapacitors have been concerned extensively in the world. As a new energy source, supercapacitors have such advantages as high power densities, long cycling stability and low costs advantages. The electrode material plays a leading role in influencing the performance of supercapacitors [2]. The metal-organic frameworks (MOFs) have exerted a great influence on the development of supercapacitors since the MOFs were found in late 1990s [3e5]. Great attention was paid to ZIF-67 recently because of its polyhedral morphology. Moreover, ZIF-67 has a large surface area and adjustable pore sizes, and can be turned into Co3O4 after oxidation. As its morphology is not changed, so it can be used as an electrode material. In addition to oxidation, there are also carbonization, insertion host [6,7] and bimetallic carbides [8] to improve the electrochemical performance of supercapacitors. Among electrode materials, the electroactive material with multiple oxidation states/structures that enable rich redox reactions to be available for pseudocapacitance generation is desirable for supercapacitors. The transition metal oxides are such materials that have drawn intensive attention in researches. However, as an alternative candidate among metal oxides, the ternary nickel cobaltite (NiCo2O4) possesses much better electronic conductivity (at least two orders of magnitude higher) and higher electrochemical activity than NiO and Co3O4 binary oxides [9]. As we all know, iron oxide and cobalt oxide both have high electrochemical performance. Thus iron cobaltite (FeCo2O4) is expected to be an excellent electrode material. However, few reports were involved in FeCo2O4 as an electrode material for supercapacitors. In this study, the ternary oxide FeCo2O4 with a special morphology was synthesized successfully. First, Fe-Co-ZIF precursor was made, and then the final product (FeCo2O4) was https://doi.org/10.1016/j.jallcom.2017.11.251 0925-8388/© 2017 Elsevier B.V. All rights reserved.
synthesized after the one-step calcination process, where the polyhedral morphology of ZIF-67 was unchanged. A high quality electrode material of supercapacitors was obtained by making use of the polyhedral morphology and the advantages of ternary oxide.
2. Experiment section In the experiment, Fe-Co-ZIF was synthesized according to the method proposed by Adam F. Gross et al. [10]. 0.477 g Co(NO3)2$6H2O and 0.331 g Fe(NO3)3$9H2O (with a Co2þ/Fe3þ molear radio of 2:1) were dissolved in 50 ml DI water, and the solution was marked with A; 1.622g 2-methylimidazole and 3 ml triethylamine (TEA) were dissolved in another 50 ml DI water, and the solution was marked with B. Solution A was immediately poured into solution B after both solutions were stirred uniformly. The resulting solution was mixed homogeneously. After 24 hours, the deep purple solid product came into being by centrifugation, and it was socalled Fe-Co-ZIF precursor. The product was washed three times and dried at 80 C for 12 hours. The obtained Fe-Co-ZIF was calcined at 300 C, 350 C, 400 C, 450 C and 500 C successively. When the oxidation temperature was 350 C, the electrochemical performance of this material was better than that of other materials (Fig. S3). So the following research was mainly done at 350 C. The X-ray diffraction (XRD) pattern of the sample was recorded using an X-ray diffractometer (XRD, Rigaku TTR-III). Transmission electron microscopy (TEM) images of the sample were obtained using a JEM-1200EX microscope (TEM, JEOL). Morphologies of the electrode material were investigated by a scanning electron microscopy (SEM, S-4800). All electrochemical measurement was performed in an electrochemical workstation according to the threeelectrode system. 1.0 M KOH solution was used as electrolyte. The electroactive mass was about 0.5e0.75 mg cm-2.
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Letter / Journal of Alloys and Compounds 735 (2018) 1339e1343
3. Results and discussion The phase structure of the Fe-Co-ZIF precursor was analyzed by XRD (Fig. 1a) for a comparison with pure ZIF-67. The XRD peaks of Fe-Co-ZIF corresponded well with the pure ZIF-67 XRD patterns, indicating that ZIF-67 morphology was unchanged. The surface morphology of the Fe-Co-ZIF was characterized by SEM (Fig. 1b and c). Fig. 1b shows the overall morphology of Fe-Co-ZIF. Obviously, and it is polyhedral and similar to pure ZIF-67. Fig. 1c shows a higher magnification of the polyhedral morphology, where clear morphology of ZIF-67 can be seen. After the Fe-Co-ZIF precursor was heated up to 350 C, the resulting product was FeCo2O4. As is shown in the XRD pattern in Fig. 2a, the FeCo2O4 XRD presents the diffraction peaks of (111), (220), (311), (222), (400), (422), (511) and (440), which agreed well with the spinel FeCo2O4 reported previously [11]. The average crystallite sizes was around 250nm in size according to Scherrer formula. SEM image (Fig. 2b) of FeCo2O4 revealed that the polyhedral morphology of ZIF-67 was maintained perfectly after a onestep calcination process. Fig. 2b shows the polyhedron structure of FeCo2O4. In sharp contrast with the smooth surface of Fe-CoZIF, it is known that the surface of the FeCo2O4 polyhedron is made up of numerous primary particles and interstices. As supplementary, the high-resolution TEM (HRTEM) image (Fig. 3d) shows that these primary crystallites with clear lattice fringes are attached with each other in a different orientation. There are two resolved lattice fringes at around 1.13 nm and 0.47 nm respectively, and they are distributed in the (551) and (111) planes of the FeCo2O4 cubic phase. This result further confirms the formation of crystalline FeCo2O4, and has a consistency with the XRD pattern. The selected area electron diffraction patterns in Fig. 2c have also been indexed and the relevant items (hkl) are marked. Fig. 2def shows the SEM images and elemental mappings in order to further confirm that the iron and cobalt are evenly distributed. On the surface of the sample in Fig. 2d, it can be seen that FeCo2O4 presents a good polyhedral morphology of ZIF-67. Particularly worth mentioning is that iron perfectly replaced some cobalt, and cobalt content was significantly higher than the iron content. This is corresponding to the experimental design that the iron/cobalt molar ratio is 1:2. Fig. 3a shows the cyclic voltammetry (CV) curves at different scan rates in a fixed potential range of 0.3e0.8 V vs SCE in 1.0 M KOH electrolyte. According to Gao et al. [12], the morphology of CV curves for FeCo2O4 had a clear pair of redox peaks related to the redox reactions FeCo2O4 þ H2O þ OHˉ 4 FeOOH þ 2CoOOH þ eˉ, CoOOH þ OHˉ4CoO2 þ H2O þ eˉand FeOOH þ H2O 4 Fe(OH)3 4 (FeO4)2ˉþ 3eˉ. With the increase of sweep rate, the absolute value of the anodic and cathodic peaks increased clearly, revealing a relatively low resistance of the electrode and the fast redox reactions on the interface between the electrode and electrolyte. The galvanostatic charge-discharge (GCD) test of FeCo2O4 between 0.3 and 0.67 V at different current densities was done, as shown in Fig. 3b. It shows that the FeCo2O4 has a higher specific capacitance (510 F g1) at a current density of 1 A g1. Obviously, there are a couple of redox platforms, where the pseudocapacitance characteristics from faradic redox reaction can be verified. When the current density increases to 10 A g1, the sample maintains 67% of capacitance retention. This electrode material has desirable rate performance that is ideal for supercapacitors. The stability of the working electrodes was also studied at an applied current density of 10 A g1 for 3000 cycles. The respective graphs are shown in Fig. 3c. It can be seen that the composite electrode architecture possesses the good cyclic stability and exhibits higher retention even after 3000 cycles. Such good cycling stability
Fig. 1. (a) XRD patterns for the pure ZIF-67 and Fe-Co-ZIF samples, (b, c) SEM images of Fe-Co-ZIF.
Letter / Journal of Alloys and Compounds 735 (2018) 1339e1343
Fig. 2. (a) XRD pattern, (b) typical SEM images, (c) HRTEM analysis, (d, e and f) SEM image and elemental mappings of FeCo2O4.
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Letter / Journal of Alloys and Compounds 735 (2018) 1339e1343
Fig. 3. (a) CV cures of FeCo2O4 electrode at different scanning rates, (b) Galvanostatic charge-discharge curves of the FeCo2O4 electrode at different current densities, insets in (a) and (b) are the CV curves, galvanostatic charge-discharge curves of FeCo2O4 and Co3O4, (c) Cycling performance of FeCo2O4 electrode, (d) Nyquist plots of FeCo2O4 electrode.
is mainly ascribed to the special morphology of FeCo2O4. The electrochemical impedance spectroscopy (EIS) measurements were conducted to further explore the electrochemical performance. Fig. 3d shows a small diameter of semicircle at high frequencies and a steep slope of straight line at low frequencies. Inset, the top left corner is the equivalent circuit. This also demonstrates that this electrode material presents sound electrochemical properties. ZIF-67 was heated to 350 C to get oxidation Co3O4, and its electrochemical performance was compared with FeCo2O4. Fig. 3a shows CV data for FeCo2O4 and Co3O4 at a scanning rate of 50 mV s1 and a potential range of 0.3e0.8 V. It is remarkable that the CV area of FeCo2O4 is evidently larger than that of Co3O4. This indicates FeCo2O4 has a larger specific capacity than Co3O4. The GCD comparison results of FeCo2O4 and Co3O4 are shown in Fig. 3b. With a current density of 1 A g1 and a potential window of 0.3e0.67 V, it can be seen that the discharge time of FeCo2O4 is obviously higher than that of Co3O4. This also indicates that the electrical performance of FeCo2O4 is better than that of Co3O4. Fig. 3c shows the cycling life of the material. After 3000 cycles, the capacitance retention is 75.5% and 52.1% respectively. This is also a progress for supercapacitors. 4. Conclusions In this study, the ternary oxide FeCo2O4 with polyhedral morphology of ZIF-67 was synthesized. The as-prepared FeCo2O4 electrode presented excellent electrochemical performance due to the special morphology. The FeCo2O4 sample showed a high specific capacitance value of 510 F g1 and excellent cycle profile
with a retention of 75.5% after 3000 charge-discharge cycles. All of this suggests that the FeCo2O4 material is a promising electrode material for high performing supercapacitors. Acknowledgments This work was supported by the Fundamental Research Funds for the Central Universities (2017XKQY004).
Appendix A. Supplementary Data Supplementary data related to this article can be found at https://doi.org/10.1016/j.jallcom.2017.11.251. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11]
M. Huang, X.L. Zhao, F. Li, J. Power Sources 277 (2015) 36e43. W. Martin, R.J. Brodd, Chem. Rev. 35 (2004) 4245e4269. R.R. Salunkhe, Y.V. Kaneti, Y. Yamauchi, ACS Nano 11 (2017) 5293e5308. R.R. Salunkhe, Y.V. Kaneti, J. Kim, Acc. Chem. Res. 49 (2016) 2796e2806. Y.V. Kaneti, J. Tang, R.R. Salunkhe, Adv. Mater. 29 (2017) 1604898e1604938. A. Chaturvedi, P. Hu, V. Aravindan, J. Mater. Chem. A5 (2017) 9177e9181. W. Hu, D. Xu, X.N. Sun, Z.H. Xiao, ACS Sustain. Chem. Eng. 5 (2017) 8630e8640. K. Krishnamoorthy, P. Pazhamalai, S.J. Sahoo, Mater. Chem. A5 (2017) 5726e5736. G. Zhang, X.W. Lou, Adv. Mater. 25 (2013) 976e979. Adam F. Gross, Elena Sherman, John J. Vajo, Dalton Trans. 41 (2012) 5458e5460. S.G. Mohamed, C.J. Chen, C.K. Chen, ACS Appl. Mater. Interfaces 6 (2014)
Letter / Journal of Alloys and Compounds 735 (2018) 1339e1343 22701e22708. [12] H. Gao, J. Xiang, Y. Cao, Nanotechnology 28 (2017) 235401e235424.
Xin Liu, Fuxiang Wei*, Yanwei Sui, Jiqiu Qi, Yezeng He, Qingkun Meng School of Materials Science & Engineering, China University of Mining and Technology, Xuzhou, Jiangsu 221008, PR China
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* Corresponding author. E-mail address: [email protected] (F. Wei).
17 August 2017 Available online 23 November 2017
Contents lists available at ScienceDirect
Journal of Alloys and Compounds journal homepage: http://www.elsevier.com/locate/jalcom
Letter
Polyhedral ternary oxide FeCo2O4: A new electrode material for supercapacitors a b s t r a c t Keywords: Polyhedral morphology FeCo2O4 Supercapacitors
In this study, Fe-Co-ZIF(iron and cobalt in the ZIF-67) with an earlier shape of ZIF-67 was synthesized successfully. After thermal treatment, the Fe-Co-ZIF precursor was turned into FeCo2O4 with polyhedral morphology. A comparative analysis was made with pure ZIF-67 oxide, finding its great improvement in the electrochemical performance. The FeCo2O4 showed a specific capacity of 510 F g1 (52.42 mAh g1) at 1 A g1 in 1.0 M KOH electrolyte, while it was only 273 F g1 (28.1 mAh g1) for pure ZIF-67 oxide Co3O4. The FeCo2O4 cycle life increased from 52.1% to 75.5%. These data suggested that this ternary oxide FeCo2O4 with polyhedral morphology could be used for supercapacitors. © 2017 Elsevier B.V. All rights reserved.
1. Introduction With the prosperity of energy industry, many countries have paid more attention to the development of power sources [1]. Recently, the studies on supercapacitors have been concerned extensively in the world. As a new energy source, supercapacitors have such advantages as high power densities, long cycling stability and low costs advantages. The electrode material plays a leading role in influencing the performance of supercapacitors [2]. The metal-organic frameworks (MOFs) have exerted a great influence on the development of supercapacitors since the MOFs were found in late 1990s [3e5]. Great attention was paid to ZIF-67 recently because of its polyhedral morphology. Moreover, ZIF-67 has a large surface area and adjustable pore sizes, and can be turned into Co3O4 after oxidation. As its morphology is not changed, so it can be used as an electrode material. In addition to oxidation, there are also carbonization, insertion host [6,7] and bimetallic carbides [8] to improve the electrochemical performance of supercapacitors. Among electrode materials, the electroactive material with multiple oxidation states/structures that enable rich redox reactions to be available for pseudocapacitance generation is desirable for supercapacitors. The transition metal oxides are such materials that have drawn intensive attention in researches. However, as an alternative candidate among metal oxides, the ternary nickel cobaltite (NiCo2O4) possesses much better electronic conductivity (at least two orders of magnitude higher) and higher electrochemical activity than NiO and Co3O4 binary oxides [9]. As we all know, iron oxide and cobalt oxide both have high electrochemical performance. Thus iron cobaltite (FeCo2O4) is expected to be an excellent electrode material. However, few reports were involved in FeCo2O4 as an electrode material for supercapacitors. In this study, the ternary oxide FeCo2O4 with a special morphology was synthesized successfully. First, Fe-Co-ZIF precursor was made, and then the final product (FeCo2O4) was https://doi.org/10.1016/j.jallcom.2017.11.251 0925-8388/© 2017 Elsevier B.V. All rights reserved.
synthesized after the one-step calcination process, where the polyhedral morphology of ZIF-67 was unchanged. A high quality electrode material of supercapacitors was obtained by making use of the polyhedral morphology and the advantages of ternary oxide.
2. Experiment section In the experiment, Fe-Co-ZIF was synthesized according to the method proposed by Adam F. Gross et al. [10]. 0.477 g Co(NO3)2$6H2O and 0.331 g Fe(NO3)3$9H2O (with a Co2þ/Fe3þ molear radio of 2:1) were dissolved in 50 ml DI water, and the solution was marked with A; 1.622g 2-methylimidazole and 3 ml triethylamine (TEA) were dissolved in another 50 ml DI water, and the solution was marked with B. Solution A was immediately poured into solution B after both solutions were stirred uniformly. The resulting solution was mixed homogeneously. After 24 hours, the deep purple solid product came into being by centrifugation, and it was socalled Fe-Co-ZIF precursor. The product was washed three times and dried at 80 C for 12 hours. The obtained Fe-Co-ZIF was calcined at 300 C, 350 C, 400 C, 450 C and 500 C successively. When the oxidation temperature was 350 C, the electrochemical performance of this material was better than that of other materials (Fig. S3). So the following research was mainly done at 350 C. The X-ray diffraction (XRD) pattern of the sample was recorded using an X-ray diffractometer (XRD, Rigaku TTR-III). Transmission electron microscopy (TEM) images of the sample were obtained using a JEM-1200EX microscope (TEM, JEOL). Morphologies of the electrode material were investigated by a scanning electron microscopy (SEM, S-4800). All electrochemical measurement was performed in an electrochemical workstation according to the threeelectrode system. 1.0 M KOH solution was used as electrolyte. The electroactive mass was about 0.5e0.75 mg cm-2.
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Letter / Journal of Alloys and Compounds 735 (2018) 1339e1343
3. Results and discussion The phase structure of the Fe-Co-ZIF precursor was analyzed by XRD (Fig. 1a) for a comparison with pure ZIF-67. The XRD peaks of Fe-Co-ZIF corresponded well with the pure ZIF-67 XRD patterns, indicating that ZIF-67 morphology was unchanged. The surface morphology of the Fe-Co-ZIF was characterized by SEM (Fig. 1b and c). Fig. 1b shows the overall morphology of Fe-Co-ZIF. Obviously, and it is polyhedral and similar to pure ZIF-67. Fig. 1c shows a higher magnification of the polyhedral morphology, where clear morphology of ZIF-67 can be seen. After the Fe-Co-ZIF precursor was heated up to 350 C, the resulting product was FeCo2O4. As is shown in the XRD pattern in Fig. 2a, the FeCo2O4 XRD presents the diffraction peaks of (111), (220), (311), (222), (400), (422), (511) and (440), which agreed well with the spinel FeCo2O4 reported previously [11]. The average crystallite sizes was around 250nm in size according to Scherrer formula. SEM image (Fig. 2b) of FeCo2O4 revealed that the polyhedral morphology of ZIF-67 was maintained perfectly after a onestep calcination process. Fig. 2b shows the polyhedron structure of FeCo2O4. In sharp contrast with the smooth surface of Fe-CoZIF, it is known that the surface of the FeCo2O4 polyhedron is made up of numerous primary particles and interstices. As supplementary, the high-resolution TEM (HRTEM) image (Fig. 3d) shows that these primary crystallites with clear lattice fringes are attached with each other in a different orientation. There are two resolved lattice fringes at around 1.13 nm and 0.47 nm respectively, and they are distributed in the (551) and (111) planes of the FeCo2O4 cubic phase. This result further confirms the formation of crystalline FeCo2O4, and has a consistency with the XRD pattern. The selected area electron diffraction patterns in Fig. 2c have also been indexed and the relevant items (hkl) are marked. Fig. 2def shows the SEM images and elemental mappings in order to further confirm that the iron and cobalt are evenly distributed. On the surface of the sample in Fig. 2d, it can be seen that FeCo2O4 presents a good polyhedral morphology of ZIF-67. Particularly worth mentioning is that iron perfectly replaced some cobalt, and cobalt content was significantly higher than the iron content. This is corresponding to the experimental design that the iron/cobalt molar ratio is 1:2. Fig. 3a shows the cyclic voltammetry (CV) curves at different scan rates in a fixed potential range of 0.3e0.8 V vs SCE in 1.0 M KOH electrolyte. According to Gao et al. [12], the morphology of CV curves for FeCo2O4 had a clear pair of redox peaks related to the redox reactions FeCo2O4 þ H2O þ OHˉ 4 FeOOH þ 2CoOOH þ eˉ, CoOOH þ OHˉ4CoO2 þ H2O þ eˉand FeOOH þ H2O 4 Fe(OH)3 4 (FeO4)2ˉþ 3eˉ. With the increase of sweep rate, the absolute value of the anodic and cathodic peaks increased clearly, revealing a relatively low resistance of the electrode and the fast redox reactions on the interface between the electrode and electrolyte. The galvanostatic charge-discharge (GCD) test of FeCo2O4 between 0.3 and 0.67 V at different current densities was done, as shown in Fig. 3b. It shows that the FeCo2O4 has a higher specific capacitance (510 F g1) at a current density of 1 A g1. Obviously, there are a couple of redox platforms, where the pseudocapacitance characteristics from faradic redox reaction can be verified. When the current density increases to 10 A g1, the sample maintains 67% of capacitance retention. This electrode material has desirable rate performance that is ideal for supercapacitors. The stability of the working electrodes was also studied at an applied current density of 10 A g1 for 3000 cycles. The respective graphs are shown in Fig. 3c. It can be seen that the composite electrode architecture possesses the good cyclic stability and exhibits higher retention even after 3000 cycles. Such good cycling stability
Fig. 1. (a) XRD patterns for the pure ZIF-67 and Fe-Co-ZIF samples, (b, c) SEM images of Fe-Co-ZIF.
Letter / Journal of Alloys and Compounds 735 (2018) 1339e1343
Fig. 2. (a) XRD pattern, (b) typical SEM images, (c) HRTEM analysis, (d, e and f) SEM image and elemental mappings of FeCo2O4.
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Letter / Journal of Alloys and Compounds 735 (2018) 1339e1343
Fig. 3. (a) CV cures of FeCo2O4 electrode at different scanning rates, (b) Galvanostatic charge-discharge curves of the FeCo2O4 electrode at different current densities, insets in (a) and (b) are the CV curves, galvanostatic charge-discharge curves of FeCo2O4 and Co3O4, (c) Cycling performance of FeCo2O4 electrode, (d) Nyquist plots of FeCo2O4 electrode.
is mainly ascribed to the special morphology of FeCo2O4. The electrochemical impedance spectroscopy (EIS) measurements were conducted to further explore the electrochemical performance. Fig. 3d shows a small diameter of semicircle at high frequencies and a steep slope of straight line at low frequencies. Inset, the top left corner is the equivalent circuit. This also demonstrates that this electrode material presents sound electrochemical properties. ZIF-67 was heated to 350 C to get oxidation Co3O4, and its electrochemical performance was compared with FeCo2O4. Fig. 3a shows CV data for FeCo2O4 and Co3O4 at a scanning rate of 50 mV s1 and a potential range of 0.3e0.8 V. It is remarkable that the CV area of FeCo2O4 is evidently larger than that of Co3O4. This indicates FeCo2O4 has a larger specific capacity than Co3O4. The GCD comparison results of FeCo2O4 and Co3O4 are shown in Fig. 3b. With a current density of 1 A g1 and a potential window of 0.3e0.67 V, it can be seen that the discharge time of FeCo2O4 is obviously higher than that of Co3O4. This also indicates that the electrical performance of FeCo2O4 is better than that of Co3O4. Fig. 3c shows the cycling life of the material. After 3000 cycles, the capacitance retention is 75.5% and 52.1% respectively. This is also a progress for supercapacitors. 4. Conclusions In this study, the ternary oxide FeCo2O4 with polyhedral morphology of ZIF-67 was synthesized. The as-prepared FeCo2O4 electrode presented excellent electrochemical performance due to the special morphology. The FeCo2O4 sample showed a high specific capacitance value of 510 F g1 and excellent cycle profile
with a retention of 75.5% after 3000 charge-discharge cycles. All of this suggests that the FeCo2O4 material is a promising electrode material for high performing supercapacitors. Acknowledgments This work was supported by the Fundamental Research Funds for the Central Universities (2017XKQY004).
Appendix A. Supplementary Data Supplementary data related to this article can be found at https://doi.org/10.1016/j.jallcom.2017.11.251. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11]
M. Huang, X.L. Zhao, F. Li, J. Power Sources 277 (2015) 36e43. W. Martin, R.J. Brodd, Chem. Rev. 35 (2004) 4245e4269. R.R. Salunkhe, Y.V. Kaneti, Y. Yamauchi, ACS Nano 11 (2017) 5293e5308. R.R. Salunkhe, Y.V. Kaneti, J. Kim, Acc. Chem. Res. 49 (2016) 2796e2806. Y.V. Kaneti, J. Tang, R.R. Salunkhe, Adv. Mater. 29 (2017) 1604898e1604938. A. Chaturvedi, P. Hu, V. Aravindan, J. Mater. Chem. A5 (2017) 9177e9181. W. Hu, D. Xu, X.N. Sun, Z.H. Xiao, ACS Sustain. Chem. Eng. 5 (2017) 8630e8640. K. Krishnamoorthy, P. Pazhamalai, S.J. Sahoo, Mater. Chem. A5 (2017) 5726e5736. G. Zhang, X.W. Lou, Adv. Mater. 25 (2013) 976e979. Adam F. Gross, Elena Sherman, John J. Vajo, Dalton Trans. 41 (2012) 5458e5460. S.G. Mohamed, C.J. Chen, C.K. Chen, ACS Appl. Mater. Interfaces 6 (2014)
Letter / Journal of Alloys and Compounds 735 (2018) 1339e1343 22701e22708. [12] H. Gao, J. Xiang, Y. Cao, Nanotechnology 28 (2017) 235401e235424.
Xin Liu, Fuxiang Wei*, Yanwei Sui, Jiqiu Qi, Yezeng He, Qingkun Meng School of Materials Science & Engineering, China University of Mining and Technology, Xuzhou, Jiangsu 221008, PR China
1343
* Corresponding author. E-mail address: [email protected] (F. Wei).
17 August 2017 Available online 23 November 2017