High-Performance Porous Molybdenum Oxynitride Based Fiber

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High-performance porous molybdenum oxynitride based fiber supercapacitors Dan Ruan, Rui Lin, Kui Jiang, Xiang Yu, Yaofeng Zhu, Yaqin Fu, Zilong Wang, He Yan, and Wenjie Mai ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.7b07522 • Publication Date (Web): 16 Aug 2017 Downloaded from http://pubs.acs.org on August 17, 2017

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ACS Applied Materials & Interfaces

High-performance porous molybdenum oxynitride based fiber supercapacitors Dan Ruan1,‡, Rui Lin2,‡, Kui Jiang3, Xiang Yu4, Yaofeng Zhu5, Yaqin Fu5, Zilong Wang1,*, He Yan3,* and Wenjie Mai1,* 1

Siyuan laboratory, Guangzhou Key Laboratory of Vacuum Coating Technologies and New

Energy Materials, Department of Physics, Jinan University, Guangzhou, Guangdong 510632, China. 2

Department of Chemistry, Jinan University, Guangzhou, Guangdong 510632, China

3

Department of Chemistry, The Hong Kong University of Science and Technology, Clear Water

Bay, Hong Kong. 4

Analytical and Testing Center, Jinan University, Guangzhou, Guangdong 510632, China

5

Key Laboratory of Advanced Textile Materials and Manufacturing Technology, Ministry of

Education, Zhejiang Sci-Tech University, Hangzhou 310018, P.R. China Keywords: fiber supercapacitor; molybdenum oxynitride; 3D porous structure; highperformance; self-powered system

Abstract

ACS Paragon Plus Environment

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Scalable manufacturing of flexible, fiber-shaped energy storage devices has enabled great technological advances in wearable and portable technology. Replacing inefficient oxides with inexpensive and high-performance oxynitrides with more favourable 3D structures is critical if the practical applications of these technologies are to be realised. Here we developed a facile and controllable approach for the synthesis of 3D porous micropillars of molybdenum oxynitride, which exhibit high conductivity, robust stability and excellent energy storage properties. Our fiber electrode, containing a 3D hierarchical molybdenum oxynitride (MON)-based anode, yields remarkable linear and areal specific capacitances of 64.8 mF cm-1 and 736.6 mF cm-2, respectively, at a scan rate of 10 mV s-1. Moreover, a wearable asymmetric supercapacitor based on TiN/MON//TiN/MnO2 demonstrates good cycling stability with a linear capacitance of 12.7 mF cm-1 at a scan rate of 10 mV s-1. These remarkable electrochemical properties are mainly attributed to the synergistic effect between the chemical composition of oxynitride and the robust 3D porous structure composed of interconnected nanocrystalline morphology. The presented strategy for the controllable design and synthesis of novel-oxide-derived functional materials offers prospects in developing portable and wearable electronic devices. We also demonstrate that these fiber supercapacitors can be combined with an organic solar cell to construct a selfpowered system for broader applications.

1. Introduction Recently, modern smart electronics, such as smart watches/phones and e-skins, have enabled a range of functionalities to be conveniently integrated into on-body equipment.1-2 However, powering these devices remains challenging. In various forms of energy storage systems, wearable asymmetric supercapacitors (ASCs) have attracted substantial attention because of their fast chargeability, ultralong cycle life and suitable power density.3 In particular, considering the


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need to fit the curved surface of the human body and be integrable into everyday textiles, wearable ASC devices with fiber shapes have attracted much attention for their promising mechanical advantages of low weight, minuscule volume and high flexibility.4-6 However, the electrodes of these wearable ASCs require further development to meet the critical requirement of sufficient energy density. For ASCs, higher energy densities are mainly achieved by increasing the operating voltage, which can be enabled by introducing suitable anode materials. Molybdenum trioxide (MoO3) is an excellent anode material because of its low cost, diversity of chemical valence states and high work function (6.9 eV).7 Specifically, a large difference between the work functions of the anode and cathode pair will lend ASCs a wide operating voltage, deemed the dominant factor for capacitive performance.8 However, the application of MoO3 is limited by its disappointing intrinsic conductivity (10-5 S/cm).9 Therefore, most reported MoO3 anodes suffer from performance degradation, sluggish faradic redox kinetics and poor rate capability.10 To circumvent this issue, various carbon materials have been utilised as supports to provide larger contact surface areas and enhanced electrical conductivity.11 However, the carbon supports tend to have low capacitance, which lowers the overall performance of wearable ASCs. Therefore, the development of a MoO3-based anode with both high conductivity and capacitance is a key challenge in the creation of a high-performance wearable ASC. Fortunately, great progress has been made in the discovery of metal nitrides that can dramatically boost conductivity while also providing more active sites for electrochemical reactions, thus representing promising systems in energy technology.12-13 Additionally, recent studies have revealed that certain oxides present within metal nitrides very effectively improve the electrochemical capacity and reaction kinetics, without deterioration of the rich structural morphology and material conductivity.14-16 For example, Tong et al. synthesised ‘holey’ tungsten


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oxynitride nanowires by nitridation of WO3 nanowires and applied them as an electrochemical electrode. They found that the synergistic effect between the two phases (oxide and nitride) greatly enhanced the energy storage performance, which suggests that metal oxynitrides with complex compositions may show improved electrochemical activity compared with single-phase oxides or nitrides.14 Drawing on these advances, we anticipate the development of a controllable preparation process to construct optimised molybdenum oxynitride (MON) and enable the assembly of wearable ASCs, thus promoting the development of energy storage electronics. Herein, we designed a novel in situ nitridation strategy to produce TiN nanotubes supported mesoporous 3D MON micropillars as anodes for wearable ASCs. This strategy can not only construct high-performance oxynitride but also produce a conductive TiN layer. Compared with carbon support, the TiN support shows superior capacitance performance which can bring better performance to the anode and cathode.17 In addition, 3D electrode architecture of MON micropillars maximized the number of active sites accessible to ions during charge/discharge process and simultaneously provided high energy density without compromising the intrinsic power density.18 Furthermore, in the nitridation process, low-valence-state molybdenum atoms were produced with nitrogen dopant. As the result, the 3D hierarchical TiN/MON anode electrode yielded a remarkable specific capacitance of 64.8 mF cm-1/736.6 mF cm-2 at a scan rate of 10 mV s-1. And when it applied in wearable ASC of TiN/MON//TiN/MnO2, this wearable device exhibited an excellent capacitance performance of 12.7 mF cm-1/75.1 mF cm-2. Notably, the as-prepared ASC device showed benign mechanical performance of highly flexible and tailorable properties, which would be seen as a promising application in wearable devices. After charged by a non-fullerene organic solar cell for 30 s,19 our wearable ASC could successfully power a light emitting diode (LED, green). Based on these facts it is believed that our wearable


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ASC, upon being integrated using simple preparation methods with 3D electrode active materials, will hold a great promise as an alternative electrode in the energy storage system. 2. Results and Discussion The fabrication process of the wearable supercapacitor as functional energy textile is shown in Scheme 1. Firstly, TiO2 nanotubes array was prepared on the surface of Ti wire via anodization method (details are shown in Supporting Information, Figure S1). Then the orderly 3D MoO3 micropillars were successfully synthesized on the surface of Ti@TiO2 wire through hydrothermal method (donated as Ti@TiO2/MoO3, Figure 1a-c). To produce high conductive TiN layer and introduce dopants such as low-valence-state Mo and N atoms, the as-prepared Ti@TiO2/MoO3 materials was thermally treated in NH3 atmosphere for 30, 60 and 90 minutes (denoted as MON-1, MON-2, MON-3). The morphology of the as-synthesized electrodes was characterized by field-emission scanning electron microscopy (SEM) and transmission electron microscopy (TEM). As observed from SEM images in Figure 1d-f and S2, the as-fabricated MON on TiN layer inherited the morphology of 3D MoO3 micropillars and formed rough surface with mesoporous structure. It is believed that this structure comes from the anion exchange and phase transformation process.16 And this unique structure would provide efficient channels allowing fast and easy access of electrolyte ions to the surface of electrode and increase surface area bringing more active sites for ion adsorption. The TEM images confirmed the morphology change from MoO3 (Figure 2a) to MON (Figure 2b) after thermal treatment in NH3 atmosphere. Transmission Electron Microscope (HRTEM) image of MoO3 (inset in Figure 2a) exhibits the lattice-resolved fringe with the spacing of 0.326 nm, corresponding to (021) plane of MoO3. And the selected area electron diffraction (SAED) image demonstrates the hexahedral


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monocrystalline structure of the MoO3 (inset in Figure 2a). A closer examination of a MON hexahedral micropillar reveals the highly porous texture throughout the whole pillar (inset in Figure 2b). Apparently, compared with pure-phase MoO3 shown in Figure 2a an obvious enrichment of nanocrystal and mesoporous appears on MON surface after nitridation. Additionally, the HRTEM image (Figure 2c) of the MON proves the existence of crystalline MoO2 and Mo2N. The observed lattice spacings of 0.243 nm and 0.19 nm correspond to the (211) plane of MoO2 and (202) plane of Mo2N, respectively. From the HRTEM images we can find the interconnected nanocrystalline structure which can reduce interfacial resistance and accelerate the rate of electrons and ions transport formed after nitridation.20 Besides, the scanning transmission electron microscopy (STEM) - EDS elemental mapping images (Figure 2d) of MON samples show that the Mo, N, and O elements are distributed throughout the whole micropillar, suggesting the successful transformation from MoO3 to MON micropillar. The X-ray diffraction (XRD) pattern (Figure 3a and S8c) confirms the structure change from oxide to oxynitride. It demonstrates that hexagonal MoO3 (JCPDS# 05-0508) slowly converted into molybdenum oxynitride containing MoO2 (JCPDS# 65-5787) and Mo2N (JCPDS# 251366). And the XRD results reveal the fully conversion from oxide to nitride when the thermal treatment time is up to 90 min (Figure S8c). Moreover, the formation of oxynitride can be verified by the X-ray photoelectron spectroscopy (XPS) result. The detailed analysis was conducted around the peaks at 230 eV and 395 eV standing for the Mo 3d and N 1s-Mo 3p3/2 peaks. Peak deconvolution of the Mo 3d XPS spectrum divulges the contribution from MoO3 (d5/2 at 235.4 eV), MoO2 (d5/2 at 230.0 eV), and Mo2N (d5/2 at 229.3 eV).21-22 The presence of Moδ+ (0 < δ+ < 4) in Mo2N is corresponding to a lower Mo phase with the N coordination, which means that the valence state of molybdenum ion from MoO3 is gradually reduced upon thermal


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treatment in NH3 (Figure 3b).21 Additionally, the N 1s-Mo 3p3/2 spectrum (Figure 3c) also reveals the strongest peak of N (1s at 396.7 eV) and the other peaks of MoO3 (3P3/2 at 398.5 eV), MoO2 (3P3/2 at 395.9 eV) and Mo2N (3P3/2 at 394.5 eV).23-24 The XPS results of other elements are shown in Figure S7. All above results confirm the formation of molybdenum oxynitride. The effect of nitridation strategy in capacitance behavior was studied as follow. Figure 4a shows the cyclic voltammogram (CV) curves of molybdenum oxide and molybdenum oxynitride electrodes (Ti@TiO2/MoO3 and Ti@TiN/MON) at a scan rate of 100 mV s-1 between the potential of -0.3 and -1 V with a saturated calomel electrode (SCE) as reference electrode. All the oxynitride samples show higher capacitance performance compared with the oxide one. Specially, the sample of Ti@TiN/MON-2 shows the highest capacitance of 64.8 mF cm-1/736.6 mF cm-2 (Figure 4b), which is much higher than Ti@TiN/MON-3 (consider to be Ti@TiN/Mo2N, 55.8 mF cm-1/634.3 mF cm-2). The improvement in capacitance performance may come from the higher conductivity of molybdenum oxynitride brought by nitridation strategy. Then the electrochemical impedance spectroscopy (EIS) was applied to evaluate the conductivity of different samples. In figure 4c, the Nyquist plots reveal that the equivalent series resistance (Rs) of the electrodes decreased after nitridation. The charge transfer resistances (Rct) value of Ti@TiN/MON-2 is 0.8 Ω which is much smaller than that of Ti@TiO2/MoO3 (9.4 Ω). This result proves the introduced metal nitride can effectively promote the conductivity and simultaneously facilitate electron transfer, resulting in superior capacitance performance.7 Moreover, as shown in Figure 4e, the Ti@TiN/MON-2 electrode also exhibits a satisfactory rate capability, which maintains 71 % capacitance when the scan rate increases from 10 to 100 mV s1

. Plus, the galvanostatic test shows similar result (Figure 4f): the decrease in capacitance is just

about 25% when the current density increases from 0.5 to 5 mA cm-1. The hydrophilicity of


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electrode materials is of great significance because it can provide an efficient access of the ions to the electrode/electrolyte interface when the electrode is used. The hydrophilicity of MoO3 and MON is measured and shown in Figure S5. Contact angles of the water droplets on MoO3 and MON samples gradually decrease along with the increasingly annealing duration. These results prove that the samples after thermal treatment in NH3 show superior wettability compared with pure MoO3. On the basis of the above results, the improved capacitance performance of 3D MON may stem from the two following aspects. First, the metal oxide and nitride in the nanocrystals may play an important role in the enhanced active-site accessibility, conductivity and charge transfer efficiency due to a synergistic combination.7,

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Second, the 3D MON

micropillars with the mesoporous structure can not only decrease the diffusion length of ions , but also increase the contact area with electrolyte and improve active material utilization.18 Based on the high-performance MON-2 materials, we designed a wearable fiber-shaped solidstate ASC device (marked as Ti@TiN/MON//Ti@TiN/MnO2-FSC), in which the Ti@TiN/MnO2 worked as the cathode. Here TiN/MnO2 is a mature cathode material with high performance for FSC (the synthesis and morphology are shown in Supporting Information).25 The wearable FSC device was fabricated by a novel facile design, which can avoid mixing-additive assembly and allow membrane-free preparation (the details are also shown in Supporting Information).17 The CV curves and corresponding capacitances shown in Figure 5a-b imply a suitable operating potential of 1.5 V for the Ti@TiN/MON//Ti@TiN/MnO2-FSC device. The nearly rectangular CV curves (Figure 5c) and triangular GCD curves (Figure 5d) reveal its ideal capacitive property. According to the CV results (Figure S10), the maximum linear and areal capacitances of Ti@TiN/MON//Ti@TiN/MnO2-FSC device are calculated to be 12.7 mF cm-1/75.1 mF cm-2 when the scan rate is 10 mV s-1. And our device still retains high linear and areal capacitance of


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5.9 mF cm-1/34.9 mF cm-2 even at a high current density of 2 mA cm-1. These results indicate that our device obtain promising application as a wearable power source. Herein, the power density and energy density are two important parameters to characterize the electrochemical performance of FSC device (Figure 5e). The maximum power density of our device reaches 8.84 mW cm-2 when it was operated at a short discharge time of 4.4 s. Simultaneously, our FSC device get the highest energy densities of 23.7 µWh cm-2. These two results are superior than many previous reports such as Ti@TiN/C-FSC (2.69 µWh cm-2 and 809 µW cm-2),17 PANI/stainless steel-FSC (0.95 µWh cm-2 and 100 µW cm-2),26 MnO2 coated CNT-FSC (1.14 µWh cm-2 and 210 µW cm-2)27 and CNT/ordered mesoporous carbon-FSC (1.77 µWh cm-2 and 43 µW cm-2).28 As the long cycling life at high scan rate is an important requirement for potential applications, the cycling-life test was carried out on the FSC device at a scan rate of 50 mV s-1 for 8000 cycles. Our FSC device shows good stability with 84.5 % of its initial capacitance was retained (Figure 5f). With a view to application of the Ti@TiN/MON//Ti@TiN/MnO2-FSC as a wearable electronic, the CV curves of our device with the bending angles of 0°, 120° and 180° are shown in Figure 6b. And there is no variation significantly observed from these CV curves. As is shown in the stress-strain curves (Figure S11, measured at the rate of 10 mm/min), the ultimate tensile strength of the Ti@TiO2/MoO3 electrode (the whole diameter of 280 um) is 350 MPa, while ultimate tensile strength of the Ti@TiN/MON electrode is 178.4 MPa. Here the total strength of the electrodes mainly depends on inter metal wire. These above results demonstrate that the annealing process reduces the flexibility of the electrode, which could be explained by metal intrinsic property. The FSC device shows the ultimate tensile strength of 103 MPa when the strain is 5.3 %. Here after the breakage of the two electrodes, the solid-state electrolyte is not completely destroyed in tests (Figure S11b). These results exhibit that the tensile strength of the


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fiber is robust enough for using in wearable electronics. These results indicate that our device has superior flexibility and suitable for flexible and wearable device, which exhibits wide difference deformation and strength. According to practical applications, a single FSC device was cut to test the tailorable ability (Figure 6a), form which the parted device showed 49.8 % and 50.1 % capacitance retentions compared to the original CV result. And then we reconnected the two damaged parts of FSCs in series or parallel to explore their mechanical and capacitive stability. From the result, it is only 5.1% loss that the capacitance of the paralleled devices showed compared with the untouched FSC device, revealing that the FSC device we fabricated can be resumed via a simple connection. In the future development of self-powered smart system of simultaneous solar energy harvesting and storage (Figure 6c),

non-fullerene organic solar cells designed by Yan in

HKUST19 were used as the photovoltaic cell energy harvesting module because of its portability and mobility for offering enough energy to the FSC device. Then, in consideration of the stitchability of the FSC device, Figure 6d shows that our devices could be well woven by introducing commercial cotton yarns, which demonstrates that our FSC devices are well utilized and combined in wearable electronics. As a result, the performance of integrated system of simultaneous solar energy harvesting (by non-fullerene organic solar cells) and storage (by Ti@TiN/MON//Ti@TiN/MnO2-FSC) is also demonstrated (Figure 6e-f), where the FSC devices (in series) woven in the textile could power a light emitting diode (LED, green) in the meantime after the energy conversion from polymer solar cells (in series). In general, with excellent flexibility, tailorability and stitchability, this Ti@TiN/MON//Ti@TiN/MnO2-FSC device presents great application potential in wearable energy storage system. 3. Conclusion


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In summary, we designed a scalable synthesis of 3D Ti@TiN/MON anode electrode, through one-step nitridation of the precursor oxides from anodization and seed-assisted hydrothermal methods, produce the low-value-statues Mo and meanwhile modify the smooth surface of micropillars, which works as high-performance negative materials. After assembling the whole fiber-shaped device, the solid-state wearable FSC exhibits the high capacitance of 12.7 mF cm-1 /75.1 mF cm-2 at a scan rate of 10 mV s-1. The exceptional electrochemical activity might be mainly attributed to the chemical composition and optimized structure of the mesoporous, crystalline formed as well as their robust overall 3D structure. Additionally, the as-fabricated FSC devices achieve maximum power density of 8.84 mW cm-2 and highest energy density of 23.7 µWh cm-2. On the other hand, FSC device that exhibits excellent flexibility and tailorable property as desired at the device level is significant for wearable electronics and paves the way for developing highly on-body device, which is appropriated to apply to the integration of selfpowered system and shows satisfactory application in the near future.

FIGURES Figure 1. Morphology characterization of the electrodes. (a-c) SEM images of Ti@TiO2/MoO3 and (d-f) Ti@TiN/MON electrodes at different magnifications.


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Figure 2. TEM images of the (a) MoO3 micropillar and (b) porous MON micropillar, (c) HRTEM image shows the lattice spacing, and (d) elemental mapping images of MON, respectively. Figure 3. (a) XRD pattern of MoO3 and MON-2, High-resolution XPS spectra of (b) Mo 3d and (c) N 1s-Mo 3p3/2. Figure 4. (a) The CV curves at a scan rate of 100 mV s-1, (b) linear capacitance and (c) Nyquist plots of the Ti@TiO2 and Ti@TiO2/MoO3 electrodes under different nitridation time. (d) The CV curves, (e) the calculated linear/areal capacitance and (f) galvanostatic charge-discharge curves of Ti@TiN/MON-2 electrode. Figure 5. (a) CV curves of the optimized FSC recorded over different potential windows. (b) Linear and areal capacitances with an increase in the potential window. (c) CV curves and (d) GCD curves of the FSC device. (e) Ragone plot of the FSC device (red) compared with other FSC devices (black dots). (f) Long cycle time of the FSC device. Figure 6. (a) CV curves of the original ASC, the two separated parts, and the serial and parallel connection of the two separated parts. (b) CV curves of the device in different bending angles. (c) Model of the self-powered smart system. (d) Magnified images of the solar cell and fabric weaved by FSC. (e) and (f) show the integrated system of simultaneous solar energy harvesting and storage. SCHEMES Scheme 1. Schematic illustrating the synthesis procedure of Ti@TiN/MON electrode and assembly of the wearable ASC with cotton yarn.


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ASSOCIATED CONTENT Supporting Information. Experimental section, Characterization, Calculation methods, XPS spectra, SEM image, TEM image, XRD pattern, N2 adsorption and desorption isotherms, Hydrophilicity image, CV and GCD curves AUTHOR INFORMATION Corresponding Author *

E-mail: [email protected]

*


*


Author Contributions ‡These authors contributed equally. Notes Any additional relevant notes should be placed here. Acknowledgments We thank Mr. Junpeng Xie and Ms. Ying Zhong for experiment assistance and helpful discussions. We acknowledge the financial supports from the National Natural Science Foundation of China (Grant No. 21376104), the Natural Science Foundation of Guangdong


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Province, China (Grant Nos. 2014A030306010, Science and Technology Planning Project of Guangdong Province, China (Grant No. 2016B020244002). References: 1. Kou, L.; Huang, T.; Zheng, B.; Han, Y.; Zhao, X.; Gopalsamy, K.; Sun, H.; Gao, C., Coaxial Wet-spun Yarn Supercapacitors for High-energy Density and Safe Wearable Electronics. Nat. Commun. 2014, 5, 3754. 2. Chen, J.; Huang, Y.; Zhang, N.; Zou, H.; Liu, R.; Tao, C.; Fan, X.; Wang, Z. L., Microcable Structured Textile for Simultaneously Harvesting Solar and Mechanical Energy. Nat. Energy 2016, 1 (10), 16138. 3. Simon, P.; Gogotsi, Y., Materials for Electrochemical Capacitors. Nat. Mater. 2008, 7 (11), 845-854. 4. Sun, H.; Zhang, Y.; Zhang, J.; Sun, X.; Peng, H., Energy Harvesting and Storage in 1D Devices. Nat. Rev. Mater. 2017, 2, 17023. 5. Lin, R.; Zhu, Z.; Yu, X.; Zhong, Y.; Wang, Z.; Tan, S.; Zhao, C.; Mai, W., Facile Synthesis of TiO2/Mn3O4 Hierarchical Structures for Fiber-shaped Flexible Asymmetric Supercapacitors with Ultrahigh Stability and Tailorable Performance. J. Mater. Chem. A 2017, 5 (2), 814-821. 6. Chai, Z.; Zhang, N.; Sun, P.; Huang, Y.; Zhao, C.; Fan, H. J.; Fan, X.; Mai, W., Tailorable and Wearable Textile Devices for Solar Energy Harvesting and Simultaneous Storage. ACS nano 2016, 10, 9201-9207. 7. Yu, M.; Cheng, X.; Zeng, Y.; Wang, Z.; Tong, Y.; Lu, X.; Yang, S., Dual-Doped Molybdenum Trioxide Nanowires: A Bifunctional Anode for Fiber-Shaped Asymmetric Supercapacitors and Microbial Fuel Cells. Angew. Chem. Int. Ed. 2016, 55, 6762-6766. 8. Chang, J.; Jin, M.; Yao, F.; Kim, T. H.; Le, V. T.; Yue, H.; Gunes, F.; Li, B.; Ghosh, A.; Xie, S.; Lee, Y. H., Asymmetric Supercapacitors Based on Graphene/MnO2 Nanospheres and Graphene/MoO3 Nanosheets with High Energy Density. Adv. Funct. Mater. 2013, 23 (40), 50745083. 9. Yao, B.; Huang, L.; Zhang, J.; Gao, X.; Wu, J.; Cheng, Y.; Xiao, X.; Wang, B.; Li, Y.; Zhou, J., Flexible Transparent Molybdenum Trioxide Nanopaper for Energy Storage. Adv. Mater. 2016, 28 (30), 6353-6358. 10. Lu, X.-F.; Huang, Z.-X.; Tong, Y.-X.; Li, G.-R., Asymmetric Supercapacitors with High Energy Density based on Helical Hierarchical Porous NaxMnO2and MoO2. Chem. Sci. 2016, 7 (1), 510-517. 11. Cao, X.; Zheng, B.; Shi, W.; Yang, J.; Fan, Z.; Luo, Z.; Rui, X.; Chen, B.; Yan, Q.; Zhang, H., Reduced Graphene Oxide-wrapped MoO3 Composites Prepared by Using Metal-organic Mrameworks as Precursor for All-solid-state Flexible Supercapacitors. Adv. Mater. 2015, 27 (32), 4695-4701. 12. Xu, J.; Jia, G.; Mai, W.; Fan, H. J., Energy Storage Performance Enhancement by Surface Engineering of Electrode Materials. Adv. Mater. Interfaces 2016, 3 (20), 1600430. 13. Xiao, X.; Yu, H.; Jin, H.; Wu, M.; Fang, Y.; Sun, J.; Hu, Z.; Li, T.; Wu, J.; Huang, L.; Gogotsi, Y.; Zhou, J., Salt-Templated Synthesis of 2D Metallic MoN and Other Nitrides. ACS nano 2017, 11 (2), 2180-2186.


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14. Yu, M.; Han, Y.; Cheng, X.; Hu, L.; Zeng, Y.; Chen, M.; Cheng, F.; Lu, X.; Tong, Y., Holey Tungsten Oxynitride Nanowires: Novel Anodes Efficiently Integrate Microbial Chemical Energy Conversion and Electrochemical Energy Storage. Adv. Mater. 2015, 27 (19), 3085-3091. 15. Wang, S.; Zhang, L.; Sun, C.; Shao, Y.; Wu, Y.; Lv, J.; Hao, X., Gallium Nitride Crystals: Novel Supercapacitor Electrode Materials. Adv. Mater. 2016, 28 (19), 3768-3776. 16. Chen, T. T.; Liu, H. P.; Wei, Y. J.; Chang, I. C.; Yang, M. H.; Lin, Y. S.; Chan, K. L.; Chiu, H. T.; Lee, C. Y., Porous Titanium Oxynitride Sheets as Electrochemical Electrodes for Energy Storage. Nanoscale 2014, 6 (10), 5106-5109. 17. Sun, P.; Lin, R.; Wang, Z.; Qiu, M.; Chai, Z.; Zhang, B.; Meng, H.; Tan, S.; Zhao, C.; Mai, W., Rational Design of Carbon Shell Endows TiN@C Nanotube Based Fiber Supercapacitors with Significantly Enhanced Mechanical Stability and Electrochemical Performance. Nano Energy 2017, 31, 432-440. 18. Lukatskaya, M. R.; Dunn, B.; Gogotsi, Y., Multidimensional Materials and Device Architectures for Future Hybrid Energy Storage. Nat. Commun. 2016, 7, 12647. 19. Liu, J.; Chen, S.; Qian, D.; Gautam, B.; Yang, G.; Zhao, J.; Bergqvist, J.; Zhang, F.; Ma, W.; Ade, H.; Inganäs, O.; Gundogdu, K.; Gao, F.; Yan, H., Fast Charge Separation in a Nonfullerene Organic Solar Cell with a Small Driving Force. Nature Energy 2016, 1 (7), 16089. 20. Leng, K.; Chen, Z.; Zhao, X.; Tang, W.; Tian, B.; Nai, C. T.; Zhou, W.; Loh, K. P., Phase Restructuring in Transition Metal Dichalcogenides for Highly Stable Energy Storage. ACS nano 2016, 10, 9208-9215. 21. Shi, C.; Zhu, A. M.; Yang, X. F.; Au, C. T., On the Catalytic Nature of VN, Mo2N, and W2N Nitrides for NO Reduction with Hydrogen. Appl. Catal., A 2004, 276 (1-2), 223-230. 22. Choi, J. G.; Thompson, L. T., XPS Study of As-prepared and Reduced Molybdenum Oxides. Appl. Surf. Sci. 1996, 93 (2), 143-149. 23. Wang, Y.; Lin, R. Y., Amorphous Molybdenum Nitride Thin Films Pepared by Ractive Sutter Dposition. Mater. Sci. Eng., B 2004, 112 (1), 42-49. 24. Kim, G.-T.; Park, T.-K.; Chung, H.; Kim, Y.-T.; Kwon, M.-H.; Choi, J.-G., Growth and Characterization of Chloronitroaniline Crystals for Optical Parametric Oscillators. Appl. Surf. Sci. 1999, 152 (1-2), 35-43. 25. Wang, W.; Liu, W.; Zeng, Y.; Han, Y.; Yu, M.; Lu, X.; Tong, Y., A Novel Exfoliation Strategy to Significantly Boost the Energy Storage Capability of Commercial Carbon Cloth. Adv. Mater. 2015, 27 (23), 3572-3578. 26. Meng, Q.; Wang, K.; Guo, W.; Fang, J.; Wei, Z.; She, X., Thread-like Supercapacitors Based on One-step Spun Nanocomposite Yarns. Small 2014, 10 (15), 3187-93. 27. Xu, P.; Wei, B.; Cao, Z.; Zheng, J.; Gong, K.; Li, F.; Yu, J.; Li, Q.; Lu, W.; Byun, J. H.; Kim, B. S.; Yan, Y.; Chou, T. W., Stretchable Wire-Shaped Asymmetric Supercapacitors Based on Pristine and MnO2 Coated Carbon Nanotube Fibers. ACS nano 2015, 9 (6), 6088-6096. 28. Ren, J.; Bai, W.; Guan, G.; Zhang, Y.; Peng, H., Flexible and Weaveable Capacitor Wire Based on a Carbon Nanocomposite Fiber. Adv. Mater. 2013, 25 (41), 5965-6970.


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Scheme 1. Schematic illustrating the synthesis procedure of Ti@TiN/MON electrode and assembly of the wearable ASC with cotton yarn.


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Figure 1. Morphology characterization of the electrodes. (a-c) SEM images of Ti@TiO2/MoO3 and (d-f) Ti@TiN/MON electrodes at different magnifications.


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Figure 2. TEM images of the (a) MoO3 micropillar and (b) porous MON micropillar, (c) HRTEM image shows the lattice spacing, and (d) Elemental mapping images of MON, respectively.


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Figure 3. (a) XRD pattern of MoO3 and MON-2, High-resolution XPS spectra of (b) Mo 3d and (c) N 1s-Mo 3p3/2.


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Figure 4. (a) The CV curves at a scan rate of 100 mV s-1, (b) linear capacitance and (c) Nyquist plots of the Ti@TiO2 and Ti@TiO2/MoO3 electrodes under different nitridation time. (d) The CV curves, (e) the calculated linear/areal capacitance and (f) galvanostatic charge-discharge curves of Ti@TiN/MON-2 electrode.


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Figure 5. (a) CV curves of the optimized FSC recorded over different potential windows. (b) Linear and areal capacitances with an increase in the potential window. (c) CV curves and (d) GCD curves of the FSC device. (e) Ragone plot of the FSC device (red) compared with other FSC devices (black dots). (f) Long cycle time of the FSC device.


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Figure 6. (a) CV curves of the original ASC, the two separated parts, and the serial and parallel connection of the two separated parts. (b) CV curves of the device in different bending angles. (c) Model of the self-powered smart system. (d) Magnified images of the solar cell and fabric weaved by FSC. (e) and (f) show the integrated system of simultaneous solar energy harvesting and storage.


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High-Performance Porous Molybdenum Oxynitride Based Fiber

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