Facile synthesis of Co3O4-CeO2 composite oxide nanotubes and their multifunctional applications for lithium ion batteries and CO oxidation

Journal of Colloid and Interface Science 494 (2017) 274–281

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Regular Article

Facile synthesis of Co3O4-CeO2 composite oxide nanotubes and their multifunctional applications for lithium ion batteries and CO oxidation Chenpei Yuan, Heng-guo Wang ⇑, Jiaqi Liu, Qiong Wu, Qian Duan ⇑, Yanhui Li School of Materials Science and Engineering, Changchun University of Science and Technology, Changchun 130022, China

g r a p h i c a l a b s t r a c t

a r t i c l e

i n f o

Article history: Received 8 December 2016 Revised 19 January 2017 Accepted 20 January 2017 Available online 2 February 2017 Keywords: Electrospinning Metal oxides Lithium ion batteries CO oxidation

a b s t r a c t In this study, Co3O4-CeO2 composite oxide nanotubes (CCONs) have been fabricated by using a simple electrospinning technique followed subsequent annealing and their multifunctional applications for lithium ion batteries and CO oxidation have also been investigated for the first time. When utilized as attractive anodes for lithium-ion batteries (LIBs), the CCONs exhibit good rate capability (497.3 mA h g
1 at 2 A g
1), high initial capacity (826.2 mA h g
1 at 0.05 A g
1) and improved cycling stability (1286.3 mA h g
1 after 180 cycles at 0.1 A g
1 and 300.5 mA h g
1 with 63.5% retention after 1500 cycles at 1 A g
1). Furthermore, a preliminary CO catalytic oxidation study has demonstrated that the CCONs samples exhibit high catalytic activity. Thus, these properties endorse CCONs as attractive candidates for both LIBs and CO oxidation and this strategy might open new avenues for the design of a series of transition metal oxides with multicomponent for multifunctional applications. Ó 2017 Elsevier Inc. All rights reserved.

1. Introduction Transition metal oxides are now renowned for their fascinating electronic properties and potential applications, for example, as electrode materials for lithium-ion batteries (LIBs) [1–4] and

⇑ Corresponding authors. E-mail address: [email protected] (H.-g. Wang). http://dx.doi.org/10.1016/j.jcis.2017.01.074 0021-9797/Ó 2017 Elsevier Inc. All rights reserved.

catalysts for CO oxidation [5,6]. Thus, continual researches have been devoted to either optimizing their morphologies/structures or constructing composite transition metal oxides. In the former strategy, various kinds of morphologies/structures of transition metal oxides have been prepared. Interestingly, both theoretical and experimental studies have demonstrated that the unique morphologies/structures could effectively modify its electronic and chemical properties [7–10]. Among these morphologies/

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structures, one dimensional (1D) hollow nanostructures have been demonstrated to be attractive [11–14], since this kind of structure not only brings advantages of synergistic effects of accommodating the severe volume change and facilitating Li+ion fast transfer, but also enables reactant molecules to diffuse into the active sites easily. Nevertheless, conventional synthetic strategy for the fabrication of transition metal oxides nanotubes needs to involve the multi-step growth of designed shell materials on various removable or sacrificial templates, which suffers from more or less severe drawbacks, such as the requirement of time consuming, costly and tedious process. In the latter strategy, due to the synergistic effect, the hybrids composed by selected transition metal oxides exhibit high lithium storage capacity and excellent catalytic activity in CO oxidation. In other words, the properties of the composite metal oxides cannot be regarded as a simple superposition of the single oxides. Our previous work had identified that composite transition metal oxides can show improved lithium-ion battery performance owing to the synergistic effect of the binary composition [15,16]. Zhang’s group has also demonstrated that the composite transition metal oxides can show remarkably enhanced catalytic performance for CO oxidation compared to the single component [17,18]. Obviously, integrating suitable transition metal oxides can not only further improve the performance of simple application, but also enable them to apply many fields. Therefore, the construction of composite transition metal oxides with unique morphologies/ structures could take full advantages of two strategies stated above, and thus there is a great surge in optimizing their performance for practical application. Among various transition metal oxides, Co3O4, a typical spinelstructure transition metal oxide, has received intense attention because of its high theoretical capacity of 890 mA h g
1 and excellent catalytic CO oxidation capability, and is regarded as one of the promising anode materials [19–22] or alternative to noble metal catalysts [23,24]. In addition, CeO2, a typical multifunctional rare earth oxide, has also garnered intense interest recently due to its high oxygen storage capacity and easy conversion between Ce (III) and Ce(IV) oxidation states [25–27]. More importantly, it can also exhibit excellent synergistic effects with other active components [28–31]. Therefore, it is desirable to develop Co3O4-CeO2 composite, especially with 1D hollow nanostructures, that can provide a great opportunity for boosting structural stability or catalytic activity. In this regards, electrospinning, a cost effective and flexible platform for 1D nanostructures, is a general and promising way due to its simplicity, high yield and high degree of reproducibility [32–34]. More importantly, combining the electrospinning and subsequent annealing could easily obtain composite nanotubes composed by various transition metal oxides. However, to the best of our knowledge, there are no reports on the electrospun Co3O4-CeO2 composite nanotubes, to say nothing of exploring its multifunctional applications for lithium ion batteries and CO oxidation. Herein, we used the facile and general electrospinning technique followed by controlled annealing in air to fabricate Co3O4-CeO2 composite oxide nanotubes (CCONs) and explored their applications as anode materials for LIBs and catalysts for CO oxidation. The effect of the annealing temperature on the lithium-ion battery performance and catalytic activity toward CO oxidation was investigated. Benefitting from the 1D hollow nanostructure and the synergistic effect of Co3O4 and CeO2, the as-obtained Co3O4-CeO2 composite oxide nanotubes exhibit improved lithium-ion battery performance and high catalytic activity toward CO oxidation. Our findings are expected to be very useful for the design and synthesis of novel metal oxides composite as advanced multifunctional materials for more potential applications.

275

2. Experimental 2.1. Synthesis of Co3O4-CeO2 composite oxide nanotubes In a typical synthesis, 0.68 g poly(vinyl pyrrolidone) (PVP, Mw = 1,300,000) was mixed in 3.32 g N,N-dimethylformamide (DMF) solution with intense mechanical stirring for 12 h to obtain the pristine PVP/DMF solution with a solid content of 17 wt%. Then, 0.257 g cobalt (III) acetylacetonate and 0.217 g Ce(NO3)26H2O were added into the above mixture solution with intense mechanical stirring for 12 h. The mixture was transferred into 5 mL plastic syringe equipped with a 21-gauge blunt tip needle and electrospun at a DC voltage of 15 kV. The electrospun nanofibers were collected on aluminum foil that was placed 18 cm between the nozzle and collector. Finally, the as-collected films were annealed in a tube furnace at 500, 600 and 700 °C for 3 h in air at a rate of 1 °C min
1. The obtained samples were labelled as CCONs-500, CCONs-600 and CCONs-700, respectively. For reference purpose, pure CeO2 and Co3O4 were also prepared. 2.2. Electrochemical measurements Electrochemical experiments were evaluated using two electrode coin-type cells (CR2025). The working electrode was prepared by casting a slurry of 70 wt% active material (CCONs-500, CCONs-600 and CCONs-700), 20 wt% conductive material (acetylene black), and 10 wt% binder (polyvinylidene fluoride, PVDF) dispersed in N-methyl-2-pyrrolidinone (NMP) on a copper foil. After the slurry was dried at 80 °C in a vacuum for 8 h, the electrode was cut into disks before transferring into an argon-filled glove box. Coin cells (CR2025) were laboratory-assembled by using Celgard 2400 membrane as the separator, lithium foil as both counter and reference electrode, and 1 M LiPF6 in ethylene carbonate (EC)/ dimethyl carbonate (DMC)/diethyl carbonate (DEC) (1:1:1 by volume) as the electrolyte. Galvanostatic charge-discharge experiments were carried out on a Land Battery Measurement System (Land, China). Cyclic voltammetry (CV) tests were performed on a VMP3 Electrochemical Workstation (Bio-logic Inc.). 2.3. Catalytic measurements The CO catalytic oxidation was carried out in a stainless-steel reaction tube loaded 20 mg of catalyst. A gas mixture composed of 1% CO and 20% O2 in N2 at a fixed space velocity of 50 mL/min flowed through the reactor. And the gas chromatography was used to monitor online the composition of the gas. The conversion ratio of CO was determined on the basis of the CO consumption and CO2 formation. 3. Results and discussion The Co3O4-CeO2 composite oxide nanotubes were prepared by a facile and extensive method employing the electrospinning and subsequent annealing. Schematic illustration of the synthesis process was shown in Fig. 1. First, the typical electrospinning technique was used to prepare the composite precursor nanofibers. A subsequent annealing process was introduced to convert the composite precursor nanofibers into the Co3O4-CeO2 composite oxide nanotubes. The morphology of the samples is investigated by SEM. Fig. 2a and b shows that the precursor nanofibers are continuous and randomly distributed forming an interconnected network. It could be observed that they are characteristic 1D structure with a relatively smooth surface and without hollow structures and the average diameter of them is ca. 460 nm. After annealing, the

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Fig. 1. Schematic illustration of the formation of Co3O4-CeO2 composite oxide nanotubes.

Fig. 2. Low and high-resolution SEM images of the precursor nanofibers (a, b) and CCONs-500 (c, d). TEM (e) and HRTEM (f) images of CCONs-500.

as-prepared sample inherits the continuous 1D nanostructure from the precursor fibers (Fig. 2c). But the surface becomes rough and the diameter shrinks sharply to ca. 180 nm (Fig. 2d). As a result,

the nanotubes made up of the agglomerated nanoparticles are obtained. In order to further confirm the morphology of the samples, TEM analysis is also performed. Fig. 2e clearly demonstrates

C. Yuan et al. / Journal of Colloid and Interface Science 494 (2017) 274–281

the formation of nanotubes and porous surface, which is derived from pyrolysis of organic components such as PVP, acetylacetonate groups and the crystallization of the metal oxides precursor after annealing. The HRTEM image (Fig. 2f) displays two set of lattice fringe spacings of 0.25 and 0.31 nm, corresponding to the (3 1 1) plane of the cubic Co3O4 and the (1 1 1) plane of the fluoritephase CeO2, respectively, which clearly shows the simultaneous presence of Co3O4 and CeO2. In addition, the effect of calcination temperature on the morphology of the samples is also investigated (Fig. S1). The as-prepared samples calcined at 600 and 700 °C remain the hollow structures, which are also made up of the agglomerated nanoparticles, but their diameters shrink to 160 and 145 nm, respectively. It is obvious that further increasing the annealing temperature has little impact on the formation of Co3O4-CeO2 composite oxide nanotubes. The thermal decomposition characteristics of the composite precursor nanofibers are investigated by TGA and the corresponding TGA-DSC curves are given in Fig. 3a. The first weight loss from room temperature to 180 °C results from the removal of adsorbed water. The subsequent weight loss at 200–280 °C is possibly due to the release of NO2 and CO2 gaseous molecules from the oxidation of the organic components such as PVP and acetylacetonate groups, corresponding to a strong exothermic peak near 272 °C in the DSC curve. Further weight loss at 270–350 °C may be attributed to the decomposition of Ce(NO3)2 to CeO2. No more weight loss takes place with further increase of the temperature, suggesting the complete transformation of the composite precursor nanofibers into Co3O4-CeO2 composite oxide nanotubes. FTIR spectroscopy is used to examine the chemical structure of the samples. As shown in Fig. 3b, the precursor nanofibers show the characteristic peaks of PVP at 1656 cm
1 for C@O, 1426 cm
1 for

277

CAH, and 1287 cm
1 for CAN, indicating the formation of PVP [35]. There is no other peak of acetylacetonate groups, which is due to the overlay of high content PVP. After the thermal treatment, both CAH and C@O disappear, no peaks relating to carbonyls could be observed, indicating that these groups decompose during pyrolysis. Instead, the distinct peaks at 672 and 563 cm
1 appear, which are the characteristic peaks of metal oxides [36]. In addition, Co3O4-CeO2 composite oxide nanotubes obtained at different pyrolysis temperatures show similar FTIR spectra, suggesting these groups could be decomposed completely at 500 °C. The formation of Co3O4 and CeO2 phase is further confirmed by Raman spectra (Fig. S2), where the two major peaks centered around 475 and 685 may result from the Co3O4 and CeO2 phase [28,36]. In order to thoroughly investigate the phase composition of the samples, XRD test is conducted and the corresponding spectra are shown in Fig. 3c. The XRD patterns reveal that all the diffraction peaks could be indexed to face-centered cubic fluorite structured CeO2 (JCPDS 34-0394), and face-centered cubic phase of Co3O4 (JCPDS 43-1003), respectively. No obvious impurity peaks are found, confirming the formation of the phase purity of Co3O4 and CeO2. Similarly, no notable difference compared with the samples obtained at different pyrolysis temperatures, indicating the same crystalline structure. Nitrogen adsorption-desorption measurements were performed to investigate the Brunauer–Emmett–Teller (BET) specific surface area and the porous characteristics of the CCONs-500. As shown in Fig. 3d, the isotherm can be classified as a type IV curve with a distinct H3 hysteresis loop at the relative pressure of 0.8– 1.0, which indicates the existence of the typical mesoporous characteristics in the CCONs-500s. The BET specific surface area and total pore volume was measured to be 149.6 m2 g
1 and 0.311 cm3 g
1, respectively. In addition, the pore size distribution

Fig. 3. (a) TGA-DSC curves of the precursor nanofibers. (b) FT-IR spectra of the precursor nanofibers and CCONs-500, CCONs-600 and CCONs-700. (c) XRD patterns of CCONs500, CCONs-600 and CCONs-700. (d) Nitrogen adsorption–desorption isotherms of CCONs-500 and corresponding pore-size distribution (inset).

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mainly from 1 to 8 nm is all in the range of mesopores. The higher specific surface area and mesoporous structure will be also helpful to accommodate the volumetric change during the discharge/ charge process, ensuring a relatively high capacity and excellent cycling stability. In order to study the surface composition and the valence states of the as-prepared sample, XPS is performed and the corresponding XPS spectra are shown in Fig. 4. The XPS survey spectrum (Fig. 4a) shows the characteristic peaks of Co2p, Ce3d and O1s, respectively, indicating the presence of cobalt, cerium, and oxygen elements in the composites. In the high-resolution Co2p spectrum (Fig. 4b), the main peaks of Co3+2p3/2 and Co3+2p1/2 are observed at binding energies of 780.5 and  795.6 eV, respectively, whose energy difference is approximately 15 eV [37]. And the main peaks of Co2+2p3/2 and Co2+2p1/2 are observed at 782.1 and 797.3 eV, respectively. It is obvious that the Co atom in the as-prepared sample has two valence states (tetrahedral Co2+ and octahedral Co3+ contributing to 2p spectral profile) [38], indicating the formation of Co3O4. In the high-resolution Ce3d spectrum (Fig. 4c), two types of peaks marked as V (V, V0 , V00 , and V000 ) and U (U, U0 , U00 , and U0 00 ) could be corresponded to the Ce3d5/2 and Ce3d3/2 spin-orbit peaks of CeO2, respectively. Six obvious peaks marked as V, V00 , V000 , U, U00 , and U000 are assigned to Ce (IV) final states (Ce4+ ions), while two weak peaks marked as V0 and U0 indicate the presence of Ce3+ ions [8,28,30]. In addition, in the high-resolution O1s spectrum (Fig. 4d), the main peak in the range of 529–530 eV arises from the lattice oxygen, while the peak centered at 531.5 eV arises from defective or adsorptive oxygen species in CeO2. Herein, the absorbed O
x ions can react with the gas and the oxygen vacancies

can promote the dissociation of O2 into O
x ions, thus facilitating the CO oxidation [30]. The lithium storage properties of the samples are evaluated and presented in Fig. 5. From the cyclic voltammetry (CV) curves of the CCONs-500 in the potential range of 0.01–3.0 V (vs. Li/Li+) at a scan rate of 0.1 mV s
1, it is obvious that the curve of the first cycle is substantially different from those of the subsequent cycles, especially the reduction peak. And after the 1st cycle the CV curves almost overlap, implying a good cycling stability. Detailedly, in the first cycle, the strong reduction peak at about 0.95 V should be attributed to the initial electrochemical reduction of Co3O4 to metallic cobalt and the formation of amorphous Li2O, accompanying with a partially irreversible solid electrolyte interphase (SEI) layer [21,22], and the weak shoulder peak at about 1.23 V can be attributed to the reduction of the Co3O4 to CoO (or LixCo3O4) [39]. In the subsequent cycles, the intensity of the reduction peak decreases apparently and the peak shifts to a higher potential at about 1.18 V, which might result from the pulverization of the Co3O4 [40,41]. And the broad oxidation peak at about 2.06 V can be ascribed to the oxidation of metallic Co to cobalt oxide and the decomposition of Li2O [22,40]. In addition, the weak reduction peak at about 0.52 V can be ascribed to the initial lithium insertion into the crystal structure and the reductive transformation of CeO2 to Ce2O3 and Li2O. At the same time, the weak and wide oxidation peak at about 1.3 V could be assigned the oxidation of metallic Ce2O3 to CeO2 [42]. It is obvious that the reduction and oxidation peaks of CeO2 are very weak, such features indicate that the CeO2 is low active and its contribution is negligible in the Co3O4-CeO2 composite. For comparison, the CV curves of the only Co3O4 or

Fig. 4. XPS spectra of the CCONs-500: survey spectrum (a) and high-resolution Co2p (b), Ce3d (c) and O1s (d).

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279

Fig. 5. (a) CV curves of the CCONs-500 at a scan rate of 0.1 mV s
1 in the range of 3–0.01 V. (b) Charge/discharge curves of the CCONs-500 at 0.05 A g
1. (c) Cycling performance of the CCONs-500, CCONs-600 and CCONs-700 at 0.1 A g
1. (d) Rate performance of the CCONs-500, CCONs-600 and CCONs-700 at different current densities.

CeO2 nanomaterials are also tested. The two pairs of well-shaped redox peaks for Co3O4 (Fig. S3a) and CeO2 nanomaterials (Fig. S3b) are in good agreement with those observed for CCONs500. Furthermore, the as-prepared samples calcined at 600 and 700 °C also show similar CV curves (Fig. S4). Fig. 5b shows the galvanostatic charge/discharge profiles of the CCONs-500 electrode of the 1st, 2nd, 5th, 10th, and 20th cycles at a current density of 0.05 A g
1 in the potential range from 0.01 to 3.0 V (vs. Li/Li+). Consistent with the above CV analysis, the similar current peaks can be identified. The initial discharge and charge capacities are 826.2 and 567.6 mA h g
1, respectively, corresponding to the initial coulombic efficiency of 68.7%. The initial capacity loss may result from the incomplete conversion reaction and irreversible lithium loss due to the formation of the solid electrolyte interface (SEI) layer [21,22,40]. Interestingly, from the second cycle onwards, the CCONs-500 electrode shows gradually increasing reversible capacities, for example, 580.2 mA h g
1 for the 2nd cycle, 615.8 mA h g
1 for the 5th cycle, 6665.6 mA h g
1 for the 10th cycle and 752.9 mA h g
1 for the 20th cycle. Such phenomenon is more visual and obvious for the long cycling profile. The cycling performance together with the coulomibic efficiency of the CCONs-500 electrode at a current density of 0.1 A g
1 is shown in Fig. 5c. Similarly, the initial coulomibic efficiency of 69.6% is lower, but the subsequent one rises rapidly, reaching up to 92.4% at the 2nd cycle, and remains above 98% after 5th cycles, indicating an excellent reversible Li+-ion intercalation/ extraction performance. At the end of the 180 charge/discharge cycles, a reversible and increased capacity as high as 1286.3 mA h g
1 can be still retained. In fact, the gradually increasing reversible capacities during cycling are a common phenomenon for transition metal oxide electrodes, which may be attributed to the gradual activation process and electrochemical grinding effect [43–45]. The initial capacity fade may be attributed to the pulverization of original aggregated composite

nanoparticles during the Li+ intercalation/extraction process and then the loss of electrical connectivity between the particles and current collector [45]. Then the composite nanoparticles become smaller and smaller, the dissolution and mechanical failure of these particles can be effectively prevented, which will facilitate the reversible reaction of the electrode [34,45]. Furthermore, the good cycling stability is mainly attributed to the unique features of the hollow nanostructure, which can efficiently enhance structural integrity with voids for buffering stresses caused by volume variation during the charge/discharge process. In order to clarify the capacity contribution of CeO2, the lithium storage properties of the only CeO2 nanomaterials are measured and its specific capacity is only 166.1 mA h g
1 (Fig. S5). Therefore, most of the reversible capacity comes from the Co3O4, which is in good agreement with those observed results from the CV curves. For comparison, the CCONs-600 and CCONs-700 electrodes are also investigated, both of them could show good cycling stability, but their capacity is much lower than that of CCONs-500 electrode, which indicate that higher annealing temperature may go against the lithium storage properties. This may ascribe to the lower kinetics of the large crystallites and serious agglomeration resulted from the higher annealed temperature [39]. Furthermore, a high current density of 1 A g
1 is applied and the initial charge capacity of the CCONs-500 electrodes can reach 473.1 mA h g
1 (Fig. S6). Even after 1500 cycles, the capacity of 300.5 mA h g
1 is retained, corresponding to the capacity retention of 63.5%, further confirming the long cycle stability. Similarly, the CCONs-500 electrode also shows higher capacity than that of the CCONs-600 and CCONs-700 electrodes. The rate capability of the CCONs-500 electrode is evaluated at different current densities between 0.05 and 2 A g
1. As shown in Fig. 5d, the CCONs-500 electrode exhibits decent capacity retention with discharge capacities of 723.7, 733.4, 679.2 and 579.7 mA h g
1 at current densities of 0.1, 0.2, 0.5 and 1 A g
1. Even

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Fig. 6. CO conversion curves of CCONs-500, pure CeO2 and pure Co3O4 (a) and the CCONs-500, CCONs-600 and CCONs-700 (b).

at a high current density of 2 A g
1, a large discharge capacity of 497.3 mA h g
1 still could be retained. Notably, when the current density is returned to the initial current density of 0.05 A g
1 after the back and forth high rate and 60 cycles of measurements, a discharge capacity of 952.2 mA h g
1 can be achieved, which is even higher than the initial reversible capacity. Interestingly, there is a gradual increase in the capacity (more than 1200 mA h g
1) in the following cycles up to 100 cycles. In stark contrast, the CCONs-500 electrode shows superior rate performance to the CCONs-600 and CCONs-700 electrodes. In addition, the electrochemical impedance spectroscopy (EIS) measurements are performed (Fig. S7). These three electrodes show similar Nyquist plots, which include a depressed semicircle (at high frequency) ascribed to the charge-transfer reaction at the electrolyte/electrode interface and a linear Warburg part (at low frequency) ascribed to the diffusion of the lithium ions in the bulk of the electrode. In order to demonstrate the multifunctional applications of Co3O4-CeO2 composite oxide nanotube, CO catalytic oxidation is carried out to evaluate its catalytic performance. Fig. 6 shows the typical CO conversion profile on the prepared composite catalysts as a function of temperature. For comparison, pure CeO2 and pure Co3O4 are characterized for the CO catalytic oxidation. As shown in Fig. 6a, it is obvious that the composite catalyst of CCONs-500 show superior catalytic performance compared with the pure CeO2 and pure Co3O4 catalysts, which can be attributed to the synergistic effect of the successful integration of the CeO2 and Co3O4 [8]. Furthermore, the catalytic performance of composite catalytic prepared at different temperatures is also investigated. As shown in Fig. 6b, CCONs-500 show the highest catalytic activity than those of CCONs-600 and CCONs-700. Therefore, the composite catalysts annealed at higher temperatures exhibit lower catalytic activity for CO oxidation, which can be ascribe to serious agglomeration resulted from the higher annealed temperature [46], which can be seen from Fig. S1. Hence, the composite catalyst of CCONs500 show the good catalytic performance, which can be attributed to the unique morphology of hollow 1D nanostructure and the strong synergistic interaction between CeO2 and Co3O4. On the one hand, the hollow interior space and penetrable shell not only provide the large specific surface area, but also promote the mass transfer of gas molecules to the active sites. On the other hand, the variable valence states of CeO2 and Co3O4 could provide high oxygen storage capacity and quick redox response and their interface contact also could enhance the catalytic activity [28–31].

4. Conclusions In summary, we have successfully designed and synthesized Co3O4-CeO2 composite oxide nanotubes (CCONs) by using a simple

electrospinning technique and subsequent annealing. This elaborate nanoarchitecture combined the hollow interior structure and multicomponent endows the CCONs with multifunctional feature. When utilized as attractive anodes for LIBs, the CCONs exhibit good rate capability, high reversible capacity and improved cycling stability. Apart from LIBs application, for the first time, the significance of Co3O4-CeO2 composite oxide nanotube in CO oxidation is revealed, which shows good catalytic performance due to the unique morphology of hollow 1D nanostructure and the strong synergistic interaction between CeO2 and Co3O4. The method presented here could be further developed as a generalized process that can be used to synthesize the composite 1D nanotube with multicomponent for multifunctional applications. Acknowledgements This work was financially supported by the National Natural Science Foundation of China (Grant No. 21404014), Jilin Science & Technology Department (The Development Plan Project of Science and Technology No. 20150520002JH), China Postdoctoral Science Foundation (2015M581376), and Special Foundation of China Postdoctoral Science (2012T50293). Appendix A. Supplementary material Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.jcis.2017.01.074. References [1] P. Poizot, S. Laruelle, S. Grugeon, L. Dupont, J.M. Tarascon, Nature 407 (2000) 496–499. [2] Y. Zhao, X.F. Li, B. Yan, D.B. Xiong, D.J. Li, S. Lawes, X.L. Sun, Adv. Energy Mater. 6 (2016) 1502175. [3] C. Drosos, D. Vernardou, Sol. Energy Mater. Sol. Cells 140 (2015) 1–8. [4] D. Vernardou, Adv. Mater. Lett. 4 (2013) 798–810. [5] X.W. Xie, Y. Li, Z.Q. Liu, M. Haruta, W.J. Shen, Nature 458 (2009) 746–749. [6] H.J. Freund, G. Meijer, M. Scheffler, R. Schlcgl, M. Wolf, Angew. Chem. Int. Ed. 50 (2011) 10064–10094. [7] J.Y. Luo, M. Meng, Y.Q. Zha, L.H. Guo, J. Phys. Chem. C 112 (2008) 8694–8701. [8] J. Zhen, X. Wang, D. Liu, S. Song, Z. Wang, Y. Wang, J. Li, F. Wang, H. Zhang, Chem. – Eur. J. 20 (2014) 4469–4473. [9] D.L. Wang, H. He, L.L. Han, R.Q. Lin, J. Wang, Z.X. Wu, H.F. Liu, H.L. Xin, Nano Energy 20 (2016) 121–220. [10] H.E. Wang, D.S. Chen, Y. Cai, R.L. Zhang, J.M. Xu, Z. Deng, X.F. Zheng, Y. Li, I. Bello, B.L. Su, J. Colloid Interf. Sci. 418 (2014) 74–80. [11] G.Q. Zhang, B.Y. Xia, C. Xiao, L. Yu, X. Wang, Y. Xie, X.W. Lou, Angew. Chem. Int. Ed. 52 (2013) 8643–8647. [12] H.Y. Zhu, Z.L. Wu, D. Su, M.V. Gabriel, H.F. Lu, P.F. Zhang, S.H. Chai, S. Dai, J. Am. Chem. Soc. 137 (2015) 10156–10159. [13] L.H. Zhang, S.Q. Zhu, H. Cao, L.R. Hou, C.Z. Yuan, Chem. Eur. J. 21 (2015) 10771– 10777. [14] C.S. Yan, G. Chen, X. Zhou, J.X. Sun, C.D. Lv, Adv. Funct. Mater. 26 (2016) 1428– 1436.

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