PANI coaxial heterostructure nanobelts by in situ polymerization for high performance supercapacitors

Nano Energy (2014) 7, 72–79

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RAPID COMMUNICATION

MoO3/PANI coaxial heterostructure nanobelts by in situ polymerization for high performance supercapacitors Feiran Jianga, Wenyao Lia,b, Rujia Zoua,n, Qian Liua, Kaibing Xua, Lei Ana, Junqing Hua,n a

State Key Laboratory for Modification of Chemical Fibers and Polymer Materials, College of Materials Science and Engineering, Donghua University, Shanghai 201620, China b School of Material Engineering, Shanghai University of Engineering Science, Shanghai 201620, China Received 28 January 2014; received in revised form 4 March 2014; accepted 16 April 2014 Available online 24 April 2014

KEYWORDS

Abstract

α-MoO3; PANI; Nanobelts; Coaxial heterostructure; Supercapacitor

A large-scale of MoO3/PANI coaxial heterostructure nanobelts have been fabricated for highperformance supercapacitors via a simple and green approach without any surfactant. Herein, the assembly of PANI conductive layer on the surface of the well-crystallized α-MoO3 nanobelts was carried out using ammonium persulfate (APS) as oxidant by in-situ polymerization at room temperature. As-prepared MoO3/PANI coaxial heterostructure nanobelts have been successfully employed as supercapacitor electrodes. It was found that the as-synthesized MoO3/PANI coaxial heterostructure nanobelts exhibited excellent supercapacitor performance with high specific capacitances of 714 F g 1 at a scan rate of 1 mV s 1 and 632 F g 1 at a current density of 1 A g 1 in 1 M H2SO4 electrolyte, whereas the original α-MoO3 nanobelts just showed initial specific capacitances of 275 F g 1 and 267 F g 1 at 1 mV s 1 and 1 A g 1, respectively, which attributed to the synergic effect between the PANI coating and the original α-MoO3 nanobelts. & 2014 Elsevier Ltd. All rights reserved.

Introduction

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Corresponding authors. E-mail addresses: [email protected] (R. Zou), [email protected] (J. Hu). http://dx.doi.org/10.1016/j.nanoen.2014.04.007 2211-2855/& 2014 Elsevier Ltd. All rights reserved.

Because of the global warming and the energy crisis, developing electric vehicles and hybrid electric vehicles have already become an irresistible trend, which have driven the rapid research in the field of electrochemical energy storage (EES) systems [1,2]. Owing to their excellent

High performance supercapacitors properties such as high power density, fast charge–discharge rate and long cycle life [3–6], supercapacitors, one of the key EES systems, also called electrochemical capacitors (ECs) can complement or even replace batteries in the energy storage field, especially when high power delivery or uptake is needed [2], which has put forward an evergrowing demand for environmentally friendly and highperformance supercapacitors. Nowadays, the development of nanostructured electrode materials has received great interest because of the unique properties of nanostructures leading to the improved performances [7,8]. In particular, one dimensional (1D) coaxial nanostructures as interesting quasi-one-dimensional nanostructures have recently attracted considerable attention owing to their added functionalities [9] or synergic properties [10,11], arising from the combination of different materials. Various materials such as carbon/metal oxide [12], metal/metal oxide [13], and metal oxide/metal oxide [14], have been employed as coaxial nanostructures. Moreover, transition-metal oxides (TMOs, such as RuO2 [15], NiO [16,17], Co3O4 [18], MnO2 [19], and VOx [20], etc.) and conducting polymers [21,22] are both considered as ideal electrode materials for the pseudocapacitors which can provide higher specific capacitance. The combination of these two materials at 1D coaxial nanostructures may exhibit improved electrical, electrochemical, and mechanical properties for electrochemical energy storage due to the synergic effect [23]. Thus, the rational design and fabrication of TMOs and conducting polymers forming 1D coaxial nanostructures for achieving high-performance ECs has become one of the most important research focuses. Of various transition metal oxides, orthorhombic α-MoO3 with a typical two-dimensional layered structure is of most practical interest due to its unique structures that is precisely suitable for insertion/removal of small ions such as H + and K + [24] and multiple oxidation states that enable rich redox reactions for pseudocapacitors [25], which contributes to high specific capacitances. Unfortunately, its low electronic conductivity usually affects its high performances in supercapacitors and cannot reach its theoretical capacity [26]. To overcome this problem, an effective way to improve electrochemical performance of MoO3 is coating the original materials with a conductive layer [27]. Polyaniline (PANI) is considered to be one of the most promising conducting polymers because of its high pseudocapacitance, good environmental stability, low cost, facile synthesis and good conductive ability at the doping state, which is beneficial to the increase of the electrons and ions exchange rate [28–30]. Moreover, the theoretical specific capacitance of PANI is able to reach 2000 F g 1 [31]. Combining these two materials to form heterostructured nanomaterials has the potential to exhibit excellent properties for capacitive performance due to the dual charge storage redox processes contributed from both materials, but there have been few studies on the coaxial nanostructures with α-MoO3 and PANI. To verify our hypothesis, the novel MoO3/PANI coaxial heterostructure nanobelts were designed and synthesized on a large-scale by a simple and green approach without any surfactant. It was found that the as-synthesized MoO3/PANI coaxial heterostructure nanobelts exhibit excellent supercapacitor performance with a high specific capacitances of

73 714 F g 1 at a scan rate of 1 mV s 1 and 632 F g 1 at a current density of 1 A g 1, whereas the original MoO3 nanobelts just show initial specific capacitances of 275 F g 1 and 267 F g 1 at 1 mV s 1 and 1 A g 1, respectively, indicating the contribution of the pseudocapacitance effect of PANI coating on the original α-MoO3 nanobelt. Furthermore, the as-synthesized MoO3/PANI coaxial nanobelts electrode presents a good cycling stability with 76.7% of capacity retention after 3000 cycles, which is higher than the original MoO3 nanobelts (66.9%).

Experimental All reagents were of analytical grade and used without further purification.

Preparation of the α-MoO3 nanobelts The α-MoO3 nanobelts were prepared by a hydrothermal method [32]. In a typical synthesis, 40 mL of H2O2 (30%) was added dropwise into 4.78 g of molybdenum powders in the ice-water bath under magnetic stirring for 4 h to remove the redundant H2O2, forming a clear orange peroxomolybdic acid sol. The final orange solution was transferred into a Teflon autoclave (100 mL capacity) and kept at 180 1C for 12 h, then naturally cooled down to room temperature. The resultant precipitates were filtered and washed several times with distilled water and ethanol. Lastly, the α-MoO3 nanobelts were dried at room temperature under vacuum before use.

Preparation of the MoO3/PANI coaxial heterostructure nanobelts MoO3/PANI coaxial heterostructure nanobelts were prepared using an in-situ polymerization method. Prior to this, the above prepared MoO3 nanobelts (0.25 g) were redispersed in 10 mL deionized water. After ultrasonic treatment for 30 min, the milk white suspension was slowly added dropwise to a 10 mL HCl solution containing 0.3 mL aniline monomer under magnetic stirring. Subsequently, 1 M HCl (10 mL) containing 0.18 g ammonium persulfate (APS) was added dropwise into the above turbid solution, and the pH level was adjusted to 1–2 by HCl (1 M). Under the constant magnetically stirring, the solution became dark green gradually. The reaction was extending at room temperature for an additional 4 h, and then the dark-green precipitates were collected by centrifugation and washed with distilled water and ethanol several times.

Structure characterization The as-prepared products were characterized with a scanning electron microscope (SEM; S-4800) and a transmission electron microscope (TEM; JEM-2100F). X-ray diffraction (XRD) measurements were performed with a D/max-2550 PC X-ray diffractometer (XRD; Rigaku, Cu-Kα radiation), and Fourier transform infrared (FTIR) spectra were recorded using an IRPRESTIGE-21 spectrometer (Shimadzu). The mass

74 of the electrode materials was weighed on an XS analytical balance (Mettler Toledo; δ= 0.01 mg).

Electrochemical characterization Electrochemical measurements were performed on an Autolab electrochemical workstation (PGSTAT302N) using a three electrode electrochemical cell and 1 M H2SO4 as the electrolyte at room temperature. The working electrodes were prepared by mixing the as-prepared products, acetylene black, and polytetrafluoroethylene with mass ratio of 80:15:5. A platinum foil and saturated calomel electrode (SCE) were used as counter and reference electrodes, respectively. All potentials were referred to the reference electrode. The cyclic voltammetry (CV) measurements of the samples were performed in the potential range of 0.4 to 0.6 V (vs. SCE) at different scan rates. The galvanostatic charge–discharge curves of samples were measured in the potential range of 0 to 0.6 V (vs. SCE) at different current densities.

Results and discussion The MoO3/PANI coaxial heterostructure nanobelts are prepared in a large-scale by a simple hydrothermal method and followed by in-situ polymerization. The schematic illustration of the typical synthetic process of the MoO3/PANI coaxial heterostructure nanobelts using in situ polymerization method is shown in Scheme 1. First of all, aniline monomers are well dispersed in HCl aqueous solution. In the presence of HCl, aniline monomers are protonated onto positively charged anilinium ions [33]. During the polymer coating process, the anilinium ions are adsorbed on the MoO3 nanobelts surface due to the large specific surface area of the nanobelts and electrostatic interaction [24,27], and then the polymerization of the aniline monomer proceeds by the introduction of ammonium persulfate (APS) used as an oxidant. Additionally, the polymerization process prefers to take place on the surfaces of the MoO3 nanobelts, resulting the uniform coating of the PANI on MoO3 nanobelts. The morphology of the as-synthesized α-MoO3 nanobelts and MoO3/PANI coaxial heterostructure nanobelts are

Scheme 1 Schematic illustration of the formation of the MoO3/PANI coaxial heterostructure nanobelts.

F. Jiang et al. examined by SEM images (Figure 1). Figure 1(a, b) shows the low and high magnification SEM images of the original αMoO3 nanobelts synthesized by hydrothermal method. It clearly shows that the as-prepared α-MoO3 nanobelts have a uniform morphological distribution with smooth surface. The length is about 2–4 μm, and the width is about  120 nm. Figure 1c and Figure S1 shows the general morphology of the MoO3/PANI coaxial nanobelts. It can be seen that after coating polyaniline monomers on the surface of MoO3 nanobelts, the morphology of the as-prepared product is similar to the original α-MoO3 nanobelts, only the width is wider than that of the corresponding α-MoO3 nanobelts and the surface becomes rougher, which indicates that there are polymers coated on the surface of original αMoO3 nanobelts. Figure 1d shows a single MoO3/PANI coaxial heterostructure nanobelt, a PANI layer coating on the surface of the α-MoO3 nanobelt can be clearly seen. Energy-dispersive X-ray spectroscopy (EDX) elemental mappings (Figure S2, in supporting information) of a representative MoO3/PANI coaxial nanobelt confirms that the Mo and O elements are evenly distributed within the nanobelt, while N element is less than both of them. As seen from a typical TEM image of the as-synthesized MoO3/PANI coaxial heterostructure nanobelts (Figure 2a), the product also present a nanobelt morphology and have uniform wraps. More detailed microstructure about the MoO3/PANI coaxial nanobelts can be demonstrated by a typical high-magnification TEM image (Figure 2b), where the nanobelt with a width about 300 nm is coated with a thin and brighter contrast layer, which indicates the nanobelt with a coaxial heterostructure is formed. The selected area electron diffraction (SAED) pattern (inset in Figure 4b) recorded perpendicular to the growth axis can be indexed to the [010] zone of a-MoO3, implying its preferential growth along c-axis [34]. Figure 2c shows a TEM image with higher magnification, the amorphous PANI coating is marked off by white lines and it shows the thickness of the PANI coating to be about 20–30 nm. The inner MoO3 nanobelt shows a single-crystal structure as shown in Figure 2d. The lattice spacing can be measured to be 0.21 nm, which corresponds to the interplanar spacing of α-MoO3 (141). The inset in Figure 4d shows a fast Fourier transformation (FFT) pattern of this image, which can be indexed to the caxis of the α-MoO3. This result agrees well with the above SAED pattern. The X-ray diffraction (XRD) patterns of the original MoO3 nanobelts and MoO3/PANI coaxial nanobelts are shown in Figure 3a. Our experimental results indicate that the XRD peaks from the both materials are in good agreement with the standard peaks of the orthorhombic MoO3 phase (JCPDS card 05-0508). Furthermore, the intensities of the (020), (040) and (060) diffraction peaks of the original MoO3 nanobelts are stronger than those of the other peaks, which reveal that there is a layered crystal structure or a highly anisotropic growth for the prepared nanobelts [35,36]. Also, the PANI coating on the MoO3 nanobelts did not have a negative effect on their crystallinity. Successfully coating a PANI layer on the surface of the αMoO3 nanobelts is also confirmed by the FTIR spectroscopy. For a comparison, the FTIR spectra for both the α-MoO3 nanobelts and MoO3/PANI coaxial nanobelts spectra are recorded and showed in Figure 3b. The original α-MoO3

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Figure 1 (a, b) Low- and high-magnification SEM images of the as-synthesized original α-MoO3 nanobelts. (c, d) Low- and highmagnification SEM images of the as-synthesized MoO3/PANI coaxial heterostructure nanobelts.

Figure 2 (a, b) TEM images of the as-synthesized MoO3/PANI coaxial heterostructure nanobelts and corresponding SAED pattern (inset of (b)). (c) TEM image of an individual MoO3/PANI coaxial heterostructure nanobelt shows the thickness of PANI coating. (d) HRTEM image of the as-synthesized MoO3/PANI coaxial heterostructure nanobelts, the inset in (d) showing its corresponding FFT pattern.

nanobelts exhibit three main vibrational modes in the range of 400–1000 cm 1, in which the terminal oxygen symmetry stretching mode of MoQO and the bridge oxygen asymmetry and symmetry stretching modes of Mo–O–Mo are at 995, 888, and 601 cm 1, respectively [37]. The O–H absorption bands appeared at 3438 and 1633 cm 1 which could be assigned due to the presence of water molecules. By contrast, in the

spectrum of MoO3/PANI coaxial nanobelts, the aforesaid peaks at 995, 888 and 601 cm 1 shift to 991, 864 and 596 cm 1, respectively, reflecting a mutual interaction between the PANI and original α-MoO3. Furthermore, the characteristic peaks of PANI also appear in the spectrum of the MoO3/PANI coaxial nanobelts. For example, The CQN and CQC stretchings of the quinonoid and benzenoid units

76

Figure 3 (a) XRD and (b) FTIR pattern of the original α-MoO3 nanobelts and the MoO3/PANI coaxial heterostructure nanobelts.

are at 1581 and 1485 cm 1, respectively. The bands at 1302 and 1245 cm 1 are assigned to the C–N stretching of the benzenoid unit while the band at 1143 cm 1 is due to the quinonoid unit of doped [38]. FTIR spectrum of the MoO3/ PANI coaxial nanobelts exhibits characteristic bands of PANI as well as of α-MoO3, which confirms the presence of both components in the coaxial heterostructures. Figure S3 shows the Raman spectra of the MoO3/PANI coaxial nanobelts and original MoO3 nanobelts. It can be found that besides the Raman peaks of the MoO3 nanobelts(682, 816 and 975 cm 1), the peak of C–H bond vibration in benzenoid units (1170 cm 1), and those of C–N and CQC vibration in quinonoid units, C–C stretching (1341, 1582 and 1616 cm 1) could be clearly observed [39]. The CQN stretching vibration of the quinonoid units and the C–N stretching mode of the polaronic units were situated in 1507 and 1254 cm 1, respectively [40]. Thus, the Raman analyses further show that the final product consists of PANI and MoO3. Moreover, the thermal stability of the MoO3/PANI coaxial nanobelts has been further characterized by TG measurement, as shown in Figure S4, which is also confirmed the component of MoO3/ PANI coaxial nanobelts.

F. Jiang et al. The electrochemical tests are carried out in a threeelectrode configuration, in which platinum foils and saturated calomel electrode (SCE) were used as counter and reference electrodes in 1 M H2SO4 aqueous electrolyte. In our study, asprepared MoO3/PANI coaxial nanobelts and comparative original α-MoO3 nanobelts are both examined by cyclic voltammetry (CV) and galvanostatic charge–discharge (CD) measurements. Figure 4a shows the CV curves of the MoO3/PANI coaxial nanobelts and the original α-MoO3 nanobelts electrodes at a scan rate of 5 mV s 1 in a potential ranging from 0.4 to 0.6 V (vs. SCE). Obviously, the enclosed area of the MoO3/PANI coaxial nanobelts is much larger than that of the original α-MoO3 nanobelt, suggesting that the MoO3/PANI coaxial nanobelts have a larger specific capacitance. Furthermore, the cyclic voltammogram (CV) curves recorded for the MoO3/PANI coaxial nanobelts and comparative original α-MoO3 nanobelt in a potential window between 0.4 and 0.6 V at different scan rates are shown in Figure S5. The specific capacitance (Csp), as an important parameter, has been widely used to evaluate the performance of the electrochemical supercapacitors, and it can be calculated from the CV curves according to the following equation C=Q/mΔV, where Q (C) is the average charge during the charging and discharging processes, m (g) is the mass of the active materials in the electrodes, and ΔV (V) is the potential window[41]. Thus, the specific capacitances of two comparative materials can be calculated based on their corresponding CV curves with different scan rates (as shown in Figure S6). The specific capacitance of the MoO3/PANI coaxial nanobelts can reach 714 F g 1 at a scan rate of 1 mV s 1, while the original α-MoO3 nanobelts is just 275 F g 1 at the same scan rate. Moreover, the specific capacitance of the MoO3/PANI coaxial heterostructure nanobelts is also higher than some reported MoO3 and conducting polymers nanocomposites, such as, polypyrrole-coated α-MoO3 nanobelts (110 F g 1) [24], PANI/ MoO3 nanosheet (200 F g 1) [42], composite films of polyaniline and molybdenum oxide (363.6 F g 1) [43] and reduced-graphene oxide/molybdenum oxide/polyaniline ternary composites(553 F g 1) [38]. It is considered that the galvanostaic charge–discharge measurement is the most accurate technique especially for pseudocapacitors. The MoO3/PANI coaxial nanobelts and the original α-MoO3 nanobelts are further confirmed by CD tests performed at different current densities. Figure 4b displays the comparison of CD curves of the MoO3/PANI coaxial nanobelts and the original MoO3 nanobelts at the current density of 2 A g 1. As expected, the MoO3/PANI coaxial nanobelts demonstrate much longer discharging time than the original α-MoO3 nanobelts. It means that the former one exhibits higher specific capacitance values than the latter. The discharge specific capacitance is calculated from the discharge curves using the following equation: C= It/mΔV, where I (A) is the current used for the charge/discharge, t (s) is the discharge time, m (g) is the weight of the active electrode and ΔV (V) is the voltage interval of the discharge [41]. At a current density of 2 A g 1, the discharge specific capacitance of the MoO3/PANI coaxial nanobelts (613 F g 1) is larger than that of the original α-MoO3 nanobelts (242 F g 1). As we know, a high discharge rate or a high current density is of great importance for the practical devices that involve a fast charging/discharging process. So, the galvanic charge and discharge measurements were also carried out on the two comparative materials at a varying current

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Figure 4 (a) A comparison of CV curves of the synthesized MoO3/PANI coaxial heterostructure nanobelts and the original α-MoO3 nanobelts at a scan rate of 5 mV s 1. (b) A comparison of the galvanostatic charge–discharge curves of the two comparative materials at a current density of 2 A g 1. (c) CD curves of the MoO3/PANI coaxial heterostructure nanobelts at different current densities. (d) Specific capacitances of two comparative materials at different current densities. (e) EIS spectra comparison of two comparative materials. (f) Cycling performance of the two comparative materials for 3000 cycles at a scan rate of 50 mV s 1.

density ranging from 1 to 10 A g 1, which were shown in Figure 4c and Figure S7. The resultant graph shows a straight line and symmetric charge and discharge curves. For comparison, based on the discharge curves of the two as-synthesized materials, the summary plots of the specific capacitance vs. the current density are shown in Figure 4d. It can be clearly seen that the discharge specific capacitance improves significantly after coating a layer of PANI. The calculated discharge specific capacitance of the MoO3/

PANI coaxial nanobelts at 1 A g 1 (632 F g 1) is higher than the original α-MoO3 nanobelts (267 F g 1) which indicates the contribution of the pseudocapacitance effect of PANI coating on the original α-MoO3 nanobelts. When the current density increases to 10 A g 1, the specific capacitance of the MoO3/ PANI coaxial nanobelts can still remain at 379 F g 1, which is higher than the original α-MoO3 nanobelt (202 F g 1) at the current density. Meanwhile, it can be seen that with the increase of the current density the specific capacitances of

78 these electrode materials decrease. This may be attributed to the arguments that a high current density prevents the accessibility of ions from entering into all the pores within the electrode materials, and thus the transport of ions is limited (due to their slow diffusion) and only the outer surface can be utilized for the charge storage [44]. In order to further identify the performance of the assynthesized MoO3/PANI coaxial heterostructure nanobelts used as electrode material, electrochemical impedance spectra (EIS) provide a beneficial tool to reveal the electronic conductivity during the redox process. As shown in Figure 4e, the value of ESR obtained from the original α-MoO3 nanobelts is 11.2 Ω, which is nearly ten times of the MoO3/PANI coaxial heterostructure nanobelts (1.17 Ω). These analyses reveal that the good electrical conductivity and ion diffusion behavior resulted in the high performance of as-synthesized MoO3/ PANI coaxial heterostructure nanobelts as electrode material for supercapacitor. Cycling performance is another key factor in determining the supercapacitors for many practical applications. In our study, a long-term cycle stability of the as-synthesized products as an electrode material was evaluated by repeating the CV test at a scan rate of 50 mV s 1 for 3000 cycles, as shown in Figure 4f. It can be seen that the specific capacitance retention of the MoO3/PANI coaxial nanobelts decreases sharply in the first 500 cycles and then increases gradually followed by slightly decreases (76.7% retention). There are various possible causes for the capacitance decreases of MoO3/PANI coaxial heterostructure nanobelts in the first 500 cycles: (1) mechanical expansion upon ion insertion; (2) delamination of electrode materials from substrates; (3) dissolution of Mo into the electrolyte [45]. In our situation, the decrease may be ascribed to the detach of the active material from the subtract during the redox reactions with harsh and frequent phase variations in the first 500 cycles [46]. For the original α-MoO3 nanobelts example, it shows a slight decrease in general (66.9% retention). In summary, a simple and green approach without any surfactant resulted in large-scaled synthesis of MoO3/PANI coaxial heterostructure nanobelts for high-performance supercapacitors. Such the architectures not only have individual merits of each component, but also show a strong synergistic effect between MoO3 and PANI constituents. The as-synthesized MoO3/PANI coaxial heterostructure nanobelts demonstrate excellent electrochemical performances in the supercapacitors with a high specific capacitances of 714 F g 1 at a scan rate of 1 mV s 1 and 632 F g 1 at a current density of 1 A g 1, whereas the original MoO3 nanobelts just show initial specific capacitances of 275 F g 1 and 267 F g 1 at 1 mV s 1 and 1 A g 1, respectively, indicating the contribution of the pseudocapacitance effect of PANI coating on the original MoO3 nanobelts. Furthermore, the as-synthesized MoO3/PANI coaxial nanobelts electrode presents a good cycling stability with 76.7% of capacity retention after 3000 cycles, which is higher than the original MoO3 nanobelts (66.9%).

Acknowledgments This work was financially supported by the National Natural Science Foundation of China (Grant nos. 21171035 and 51302 035), the Key Grant Project of Chinese Ministry of Education

F. Jiang et al. (Grant no. 313015), the PhD Programs Foundation of the Ministry of Education of the People's Republic of China (Grant nos. 20110075110008 and 20130075120001), the National 863 Program of China (Grant no. 2013AA031903), the Science and Technology Commission of Shanghai Municipality (Grant no. 13ZR1451200), the Program for Changjiang Scholars and Innovative Research Team in University (Grant No. IRT1221), the Hong Kong Scholars Program, the Project funded by China Postdoctoral Science Foundation, the Fundamental Research Funds for the Central Universities, the Shanghai Leading Academic Discipline Project (Grant no. B603), and the Program of Introducing Talents of Discipline to Universities (No. 111-2-04).

Appendix A.

Supporting information

Supplementary data associated with this article can be found in the online version at http://dx.doi.org/10.1016/ j.nanoen.2014.04.007.

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Dr. Wenyao Li received his B.S. degree in Inorganic Non-metallic Materials Engineering from Jingdezhen Ceramic Institute (2009) and PhD in Material Physics and Chemistry from Donghua University under the supervisor of Prof. Junqing Hu (2014). At present, he is working in Shanghai University of Engineering Sciences. His current research interests focus on the preparation and properties of manganese-based metallic oxides and their composites for supercapacitors.

79 Dr. Rujia Zou received his M.S. degree in plasma physics from Donghua University (2006) and his PhD in Material Science from Donghua University (2009). At present, he is working in Donghua University. He has authored and co-authored more than 40 refereed journal publications and held over 10 patents. His current research interests are focusing on the properties of 1D inorganic nanomaterials (including nanotubes, nanowires, and nanoribbons), including optical, (in-situ in TEM) electrical, mechanical property and their potential applications. Qian Liu received her BS degree in physics from Ludong University (2010). She is currently pursuing her PhD in the Department of Materials Science and Engineering at Donghua University under the supervision of Prof. Junqing Hu. Her current research interests are focusing on mechanical and electrical properties of 1D nanostructures, including in situ nanomanipulation and testing in TEM. Kaibing Xu received his B.S. degree at Anhui Polytechnic University in 2010 and now is a Ph.D. candidate in Nanofiber and Hybrid Materials from Donghua University under the direction of Prof. Junqing Hu. His current research is focused on design and synthesis of novel hybrid nanomaterials for energy storage and conversion.

Lie An received his B.S. degree in Materials Science and Engineering from Southwest university of science and technology (2011) and now is a PhD candidate in Material Physics and Chemistry from Donghua University. His current research interests focus on the preparation and properties of transition metal oxides and their composites for electrochemical supercapacitors.

Prof. Junqing Hu received his PhD from the University of Science & Technology of China, in 2000. From 2000 to 2008, he worked at the City University of Hong Kong, and then the National Institute for Materials Science, Tsukuba, Japan. At present, he is a Full Professor of Donghua University, China. He has authored and co-authored more than 150 refereed journal publications and held over 20 patents. His current research interests focus on synthesis, property measurements, and applications of 1D nanostructures.