Three-Dimensional Graphene

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Functional Inorganic Materials and Devices

Polydimethylsiloxane/ZnO Nanoflakes/Three-Dimensional Graphene Heterostructures for High Performance Flexible Energy Harvesters with Simultaneous Piezoelectric and Triboelectric Generation Yongteng Qian, and Dae Joon Kang ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b05636 • Publication Date (Web): 30 Aug 2018 Downloaded from http://pubs.acs.org on August 30, 2018

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ACS Applied Materials & Interfaces

Polydimethylsiloxane/ZnO Nanoflakes/Three-Dimensional Graphene Heterostructures for High Performance Flexible Energy Harvesters with Simultaneous Piezoelectric and Triboelectric Generation Yongteng Qian and Dae Joon Kang*

Department of Physics and Institute of Basic Science, Sungkyunkwan University, 2066, Seobu-ro, Jangan-gu, Suwon-si, Gyeonggi-do 16419, Republic of Korea

ABSTRACT Herein,

we

report

the

successful

synthesis

of

polydimethylsiloxane/ZnO

nanoflakes/three-dimensional graphene (PDMS/ZnO NFs/3D Gr) heterostructures using Ni foams as the template substrate via a facile route, while adapting a rational material design for high-performance energy harvester application. The PDMS/ZnO NFs/3D Gr heterostructure-based hybrid energy harvester simultaneously exploits the piezoelectric effect and triboelectrification and shows peak-to-peak output voltages up to 122 V and peak-to-peak current densities up to 51 µA cm-2, resulting in an ultra-high power density of 6.22 mW cm–2. Furthermore, we have evaluated the performance of PDMS/ZnO NFs/3D Gr heterostructure-based hybrid energy harvester by demonstrating its capacity to instantaneously power up 68 commercially available light-emitting diodes without the need for an additional energy storage device. The excellent performance of these energy harvesters suggests that PDMS/ZnO NFs/3D Gr heterostructures present a viable strategy for the development of high-performance flexible, wearable energy harvesting devices.

Keywords: hybrid energy harvesters, polydimethylsiloxane, ZnO nanoflakes, 3D graphene, Ni foam, heterostructure *

Author to whom the correspondence should be addressed: [email protected] (+82-31-290-5906) 1

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Introduction The continuous increase in environmental pollution as well as diminishing fossil fuel resources have triggered a tremendous demand for high-efficiency energy harvesters, which have the capability to scavenge ubiquitous mechanical energy present in ambient environment, and thereby offer green, sustainable energy sources.1-6 A relatively simple and feasible strategy to exploit mechanical energy in its various forms, such as human activity, water waves, and wind energy, is to combine piezoelectrification and triboelectrification for fabricating energy harvesters, which in turn can mitigate the various environment-related problems described above.7-10 Following the first demonstration of piezoelectric energy harvesters (PEHs) based on nanorods of piezoelectric oxides11 and triboelectric energy harvesters (TEHs) using triboelectric polymers,12 much effort has been dedicated to develop high-efficiency PEHs and TEHs that are capable of exploiting the various forms of mechanical energy available in the ambient environment. However, the poor output voltages and current densities of such devices have hampered their widespread use in self-powered systems.13-18 Moreover, achieving higher output voltage and current density simultaneously in a single energy harvester has remained a great challenge. To surmount the aforementioned issues, numerous strategies have been explored, including hybridizing piezoelectric and triboelectric materials,19-22 introducing integrated rhombic gridding structures, addition of nanofillers,23-26 and engineering of triboelectric surfaces.27 For instance, Chen et al. demonstrated hybrid energy harvesters (HEHs) comprising cascaded piezoelectric and triboelectric units with enhanced piezoelectricity through a rational material selection strategy and by optimizing the device configuration.28 Zhang and co-workers also reported that the output performance can be greatly improved via the synergistic hybridization of triboelectric and piezoelectric effects.29 Although some recent work has demonstrated the seamless integration of TEHs with PEHs,30-33 there are still several outstanding problems to be resolved, such as complexity of structure design, poor durability over long-term exposure to repeated mechanical operation, and relatively expensive 2


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fabrication process that limits large-scale production. Hence, reliable HEHs with high output performance need to be developed through rational design of materials to take full advantage of both piezoelectric and triboelectric effects in a single unit. In this context, flake-shaped ZnO has gained tremendous interest as a high-performance piezoelectric material as compared to ZnO nanowires and nanoneedles, because of its unique advantageous morphology originating from a high surface charge density.34,35 Recently, much effort has been directed to enhance the mechanical durability, piezoelectricity, and flexibility of PEHs by incorporating ZnO on two-dimensional graphene (2D Gr).36-39 For example, Kumar et al. directly grew ZnO nanostructures on 2D Gr and obtained hybrid structures with high piezoelectric response and mechanical durability, originating from a synergistic effect between the ZnO nanostructure and the 2D Gr film.37 Choi et al. demonstrated that coupling ZnO nanostructures with a 2D Gr film is an effective way to improve device flexibility while retaining superior performance.38 However, 3D Gr is considered to be a more attractive candidate than 2D Gr for this application, in view of its larger surface area and the high power densities40 that can be realised owing to its highly interconnected 3D porous network. In addition, the 3D network nature of Gr can provide a greater number of accessible sites for seeds on the surface, which facilitates the growth of ZnO nanoflake crystals.41 In this work, we propose a cost-effective and flexible energy harvester that combines different mechanisms in one device. We have successfully prepared high-quality ZnO nanoflakes (NFs)/3D Gr heterostructures using Ni foams as template substrates. Piezoelectric

ZnO

NFs/3D

Gr

heterostructures

are

encapsulated

with

polydimethylsiloxane (PDMS), which functions as a negative triboelectric material. The as-prepared energy harvester produces an peak-to-peak output voltage of up to 122 V, which is ~2 and 6 times that of the corresponding ZnO NFs- and 3D Gr-based energy harvesters. A maximum peak-to-peak current density of 51 µA cm-2 is achieved under the application of a vertical force of 7 N. The excellent output power density (~6.22 mW cm-2) has the capability to instantaneously power up 68 3



light-emitting diodes, activated by simple palm tapping. Our results indicate that ZnO NFs/3D Gr heterostructures can be a feasible strategy to obtain high-performance energy harvesters suitable for wearable electronic devices.

Results and discussion Structural characterization The schematic illustration of the growth of ZnO NFs/3D Gr heterostructure on Ni foam is presented in Figure S1 in the Supporting Information. The crystallinity of the as-synthesized samples was examined by XRD. Figure 1a shows the XRD patterns of ZnO NFs, where distinct diffraction peaks at 2θ values of 31.76, 34.45, 36.32, 47.48, 56.52, 62.85, 66.40, 67.85, 69.05, 72.51 and 76.96º are precisely correspond to the (100), (002), (101), (102), (110), (103), (200), (112), (201), (004), and (202) crystal planes of ZnO (PDF No. 5-664). The diffraction peaks at the 2θ values of 26.22, 44.36 and 53.97° can be assigned to (002), (101) and (004) crystal planes of Gr (PDF No. 75-1621); no other diffraction peaks are detected, indicating the absence of impurity phases. The Raman spectra of the ZnO NFs, 3D Gr, and ZnO NFs/3D Gr heterostructure are shown in Figure S2 (Supporting Information). The Raman spectrum of 3D Gr has two distinctive peaks located at 1600 and 2730 cm-1 corresponding to G and 2D bands of Gr. No defect peak (D band) is observed, indicating that the grown Gr is of high quality.42 The surface morphologies of the as-prepared samples were further analysed by FE-SEM. Figure 1b shows the FE-SEM image of 3D Gr, where a highly-interconnected 3D structure resulting in increased surface areas of the samples is seen. The FE-SEM images of ZnO NFs/3D Gr heterostructure shown in Figures 1c (low-resolution) and 1d (high-resolution) indicate that ZnO NFs with a large area, and uniformly grown on the 3D Gr surface; this is due to the large number of sites available for ZnO NFs-growth. The FE-SEM images of Ni foam, 3D Gr/Ni foam, ZnO NFs/Ni foam, and ZnO NFs are shown in Figure S3 (Supporting Information). TEM was performed to investigate the microstructure of ZnO NFs in greater detail. Figure 1e shows a typical TEM image of ZnO NFs; it 4


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should be noted here that the thickness of a ZnO NF is less than 10 nm, which is critical to obtain maximum piezoelectric response. The high-resolution TEM (HRTEM) image shown in Figure 1f shows individual ZnO NFs, where clear lattice fringes are seen, confirming their highly crystalline nature. The spacing between neighbouring fringes is measured to be 0.51 nm, which agrees with the distance between the (0001) planes in hexagonal ZnO.41 Device structure and working mechanism of PDMS/ZnO NFs/3D Gr-based energy harvesters A schematic depicting ZnO NFs/3D Gr-based HEHs and a photograph of the device are presented in Figures 2a and b. The typical fabrication procedure for HEHs is described below. ZnO NFs are grown on the surface of a 3D Gr/Ni foam, and PDMS sols are prepared through a one-pot sol–gel procedure following previously published procedures.28 Hydroxyl-terminated PDMS (which is both an organic modifier and a triboelectric spacer) is mixed with tetraethyl orthosilicate in the weight ratio of 1:10 to be used as an inorganic precursor. The PDMS sols are then spin-coated on the ZnO NFs/3D Gr/Ni foam. Au/PET is used as the top electrode for electrical measurements. We have investigated the electrical characteristics of PDMS/ZnO NFs/3D Gr/Ni foam-based HEHs of 1.0 cm×1.0 cm area under periodic mechanical compression by a heavy object, at a frequency of 5 Hz under a vertical force of 7 N. When a vertical force is applied to PDMS/ZnO NFs/3D Gr/Ni foam- based harvesters, the devices show a maximum peak-to-peak open-circuit voltage of 122 V over a single pressing and releasing load cycle (Figure 2c) and a peak-to-peak short-circuit current density of 51 µA cm-2 (Figure 2d). The effective output power density (P), which is an important figure of merit for energy harvesters43,44 is obtained from the formula of P=U2/RA,44 where U is the output voltage, A is the effective size of the energy harvester (1.0 cm×1.0 cm) and R is the load resistance. We obtained a maximum output power density of ~6.22 mW cm−2 for PDMS/ZnO NFs/3D Gr/Ni foam-based HEHs using an oscilloscope (LeCroy WaveRunner 6100A) with an input resistance of 10 MΩ. In addition, the output performance of the TEHs and PEHs were also 5



measured (at a frequency of 5 Hz under a vertical force of 7 N) as shown in Figure S4 in the Supporting Information. For TEHs and PEHs, the peak-to-peak output voltage were 11 V and 38 V, and the current density were 5.2 µA cm-2 and 16 µA cm-2, respectively. Note that the output performance of our HEHs (the peak-to-peak output voltage up to 122 V and current density up to 51 µA cm-2) is higher than the TEHs and PEHs, suggesting our hybrid energy harvester has a great potential as sustainable, green, cost-effective, and reliable power sources for portable electronic devices. To evaluate the output voltage and current density under periodic compression, various configurations of the harvesters (PDMS/ZnO NFs/3D Gr/Ni foam, PDMS/Ni foam, PDMS/ZnO NFs/Ni foam and PDMS/3D Gr/Ni foam) were investigated under the same frequency (5 Hz), while the vertical force was varied (1, 3, 5, 7 and 9 N). Figures 3a and b show the output voltages and current densities observed under different vertical forces for PDMS/ZnO NFs/3D Gr/Ni foam-based HEHs. The peak-to-peak output voltages of 52, 77, 100, 122 and 70 V are observed when vertical forces of 1, 3, 5, 7, and 9 N, respectively, are applied; the corresponding current densities are 13, 25, 40, 51 and 24 µA cm-2, respectively. We find that the maximum output voltage and current density are obtained at the vertical force of 7 N. If the force is increased to 9 N, the output voltage and current density are decreased to 70 V and 24 µA cm-2, respectively, which may be attributed to damage caused by the excessive vertical force. The output voltage and the corresponding current density at different vertical forces for the other devices (namely, PDMS/3D Gr/Ni foam-, PDMS/ZnO NFs/Ni foam- and PDMS/Ni foam-based energy harvesters) are shown in Figure S5 (Supporting Information). It is well known that the thickness of PDMS layer has a key influence on the output performance. Thus, we further performed the cross-section of the fabricated devices through SEM to evaluate the thickness of PDMS layer. As presented in Figure S6 (Supporting Information), all SEM images exhibit the thickness of the PDMS layer is about 2 µm, indicating roughly the same thickness of PDMS layer in all devices. The histograms of the output voltage and the current density distributions for all the devices measured under the application of vertical 6


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forces of different magnitude are shown in Figures 3(c) and (d). For comparison, the output voltage, current density, power, and power density of all devices were calculated as presented in Table S1 in the Supporting Information. We find that the output voltage (with vertical force of 7 N) of the PDMS/ZnO NFs/3D Gr/Ni foam-based HEHs is 2, 6 and 8.5 times higher than those obtained for PDMS/ZnO NFs/Ni foam-, PDMS/3D Gr/Ni foam- and PDMS/Ni foam-based energy harvesters, respectively; the corresponding current densities are 3, 8 and 10 times higher. It is interesting to note that the excellent output voltage and current density of PDMS/ZnO NFs/3D Gr/Ni foam-based HEHs is due to its 3D porous nature that provides a highly-interconnected network, and thus enables a greater number of charge transfer pathways between ZnO NFs and 3D Gr.45-47 To better understand the correlation between the device area and device performance, we fabricated devices of various sizes (i.e., 1.0 cm×1.0 cm, 2.0 cm×2.0 cm and 3.0 cm×3.0 cm). Figures 4a and b reveal a linear relationship for both peak-to-peak output voltage and current density with respect to the device size. With an increase in the device size, both output voltage and current density increase. It is significant that the PDMS/ZnO NFs/3D Gr/Ni foam-based HEHs show a good response in terms of output voltage and current density for the different device sizes tested; this may be due to a better interface between ZnO NFs and 3D Gr. Furthermore, we evaluated the flexibility of PDMS/ZnO NFs/3D Gr/Ni foam-based HEHs. The photograph of our device with a bend angle, as shown in Figure S7 (Supporting Information). Following repeated bending for 100 times (while varying the bending curvatures (30o, 45o, 60o, and 90o)), the devices were subjected to a periodic mechanical compression using a heavy object at a frequency of 5 Hz under different vertical forces (1, 3, 5, 7 and 9 N). As shown in Figures 4c and d, the output voltage and current density show nearly no change before (Figures 3a and b) and after the bending cycles. This observation demonstrates the excellent flexibility of the as-prepared devices. Figure 5 shows a schematic that provides a plausible mechanism of operation of PDMS/ZnO NFs/3D Gr/Ni foam-based HEHs. Let us first consider the initial position 7



where no external force is applied and no charges are induced on the top (Au/PET) and the bottom (PDMS/ZnO NFs/3D Gr/Ni foam) surfaces (Figure 5a). Upon application of a vertical force on the top electrode, the top and bottom surfaces will be brought into contact (Figure 5b). Due to the triboelectric effect, electrons can now be induced to migrate from the Au surface into the PDMS/ZnO NFs/3D Gr heterostructure, which results in positive triboelectric charges on the surface of the Au layer.48 At the same time, due to positive triboelectric charges on the surface of the Au layer, the polarity of the charge dipole will have to be oriented from the top to the bottom in the ZnO NFs/3D Gr heterostructure under the application of an external force.49 This positive piezoelectric potential established on the PDMS/ZnO NFs/3D Gr heterostructure could then attract more electrons from the Au layer (Figure 5c). When the external force is removed, the top and the bottom electrodes are separated from each other and the potential difference between the two electrodes enables the electrons to flow from the bottom electrode to the top electrode through the external circuit (Figure 5d).50 The energy harvester then returns to its initial state and the positive triboelectric charges on the Au surface are totally screened; however, the negative triboelectric charges remain on the surface of the PDMS/ZnO NFs/3D Gr heterostructure (Figure 5e). Thus, the continuous application and removal of a vertical force on the top electrode of the HEHs results in current flow between the top and the bottom electrodes across the external load by the charges, thereby generating an alternating current signal. The high output performance may be due to the following reasons: (i) 3D Gr can not only provide a continuous pathway for load transfer but also harvest the energy from all direction; (ii) ZnO NFs/3D Gr heterostructure grown on Ni foam can improve device stability; (iii) the synergistic effect of ZnO NFs and 3D Gr, leading to improved output performance; (iv) the better interface between ZnO NFs and 3D Gr enhances both conductivity and stability of our device, resulting in a high output performance. To further investigate the practical application of the as-prepared devices (PDMS/ZnO NFs/3D Gr/Ni foam HEHs), we attempted to power up multiple light-emitting devices 8


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(LEDs). For this purpose, we connected a commercial bridge rectifier (GBJ1006-BP) to the HEH to convert the alternating current into direct current output. The HEHs are then connected to an array of commercially available green-emission LEDs (LSG/R/Y50343), each with a forward voltage of 2.5 V, in series (Figure 6 (a)). Under the periodic vertical force applied in the form of tapping by a human palm, the as-prepared HEHs instantaneously and simultaneously light up 68 LEDs, as shown in Figure 6 (b) as well as in Movie S1. Moreover, we also tested other energy harvester configurations based on PDMS/Ni foam, PDMS/3D Gr/Ni foam and PDMS/ZnO NFs/Ni foam for comparison, where 10, 22 and 39 LEDs, respectively, were instantaneously and simultaneously lit up (shown in Figure S8 in the Supporting Information). Our results clearly demonstrate the superior performance of the rationally-designed unique heterostructure (ZnO NFs/3D Gr), thus demonstrating the considerable application potential of this structure in flexible and wearable systems.

Conclusion We have successfully synthesised a unique ZnO NFs/3D Gr heterostructure for application as HEHs using Ni foam as a template substrate for the 3D growth of graphene. XRD and SEM indicated that the ZnO NFs/3D Gr heterostructures had high crystallinity and a 3D porous structure. These heterostructure-based HEHs successfully delivered a peak-to-peak output voltage of up to 122 V, which is ~6 and 2 times higher than that observed for 3D Gr and ZnO NFs, respectively. Moreover, the self-powered ZnO NFs/3D Gr heterostructure-based HEHs result in a very high power density (~6.22 mW cm–2) during repetitive tapping by hand, owing to synergistic effects between 3D Gr and ZnO, which serve to enhance both conductivity and stability. This superior output power density is capable of instantaneously powering 68 LEDs, activated simply by palm-tapping. These excellent results demonstrate that the PDMS/ZnO NFs/3D Gr heterostructure-based HEHs have great potential as sustainable, green, cost-effective, and reliable power sources for portable electronic devices, optoelectronic devices, and monitoring and sensor networks for the Internet of Things. 9



Experimental Synthesis of 3D Gr on Ni foam by low-pressure chemical vapour deposition For Gr growth, Ni foam was used as the 3D template and CH4 was the carbon precursor. Details of the controlled growth process to coat 3D Gr on Ni foam by LPCVD are as follows. Briefly, a piece of Ni foam (3 cm × 3 cm) was placed at the centre of a tube furnace and heated from room temperature to 1000 ℃ in 30 min under a flow of Ar (150 sccm) and H2 (50 sccm). The sample was held at this temperature for 60 min to remove native oxides present on the surface of the Ni foam. Next, the Ar gas flow was turned off, and 15 sccm of CH4 gas was introduced; the optimum growth time was found to be 30 min. After the completion of graphene growth, H2 and CH4 gases were turned off and the furnace was cooled naturally to room temperature to obtain as-grown 3D Gr on Ni foam. Synthesis of ZnO NFs/3D Gr heterostructures A schematic illustrating the growth of ZnO NFs/3D Gr on Ni foam is shown in Figure S1 in the supporting information. First, a ZnO seed layer is deposited on the 3D Gr. To do this, 0.05 M zinc acetate is added to 20 mL of analytical grade ethanol. The solution is then dropped on the surface of 3D Gr and annealed at 160 °C for 90 min to form a ZnO seed layer on the surface of the 3D Gr network. Next, 0.5 mL of an aqueous solution of 1 M zinc acetate and 0.5 mL of 8 M aqueous NaOH solution are mixed for 10 min under stirring using a magnetic stirrer. The mixture is diluted by adding 100 mL of deionised (DI) water, while the 3D Gr substrate was held upside down in a glass bottle filled with the mixed solution, followed by vigorous stirring for 3 min. The above solution is then again diluted in 400 mL of DI water for 90 min. Finally, the 3D Gr substrate is washed with DI water and ethanol and dried in a vacuum oven at 60 ℃ to obtain ZnO NFs/3D Gr heterostructure.

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Characterisation The crystal structures were elucidated from XRD patterns recorded using a Rigaku Ultima III X-ray diffractometer (XRD) equipped with a Cu-Kα radiation source (λ=1.5418 Å). Raman spectra were obtained using a micro Raman set up (Renishaw, InVia Basic) using laser with excitation wavelength 532 nm. The morphology and crystal structure of the samples were characterised by field emission scanning electron microscopy (FE-SEM, HITACHI-SU8010) and transmission electron microscopy (TEM, FEI, Tecnai G2 F20, 200 kV), respectively. Electrical measurement of devices The output voltage and current were performed through the LeCroy WaveRunner 6100A oscilloscope and SR570 (Stanford Research Systems) low-noise current preamplifier, respectively. The applied force was generated using a home-made digital force gauge. For the output performance measurement of the HEHs, the top part of the device (i.e., Au layer/PET) was secured on the digital force gauge and the bottom part of the device (PDMS/ZnO NFs/3D Gr/Ni foam) was fixed vertically just below the top layer, establishing a circuit. For the output performance measurement of the TEHs, the circuit is established by connecting the top Au layer and the bottom PDMS/Ni foam (Figure S4a). For the output performance measurement of the PEHs, the circuit is established by connecting the top Au layer and the bottom Ni foam (Figure S4b).

Supporting Information. Raman spectra; SEM images; Output voltage and output current density; Powering of LEDs with electricity generated from the energy harvesters. Author Information Corresponding Author E-mail: [email protected] 11



ORCID Yongteng Qian: 0000-0002-4738-1598 Dae Joon Kang: 0000-0002-4030-4071 Note The authors declare they have no competing financial interest. Acknowledgements This work was supported by the Fundamental Technology Research Program through the National Research Foundation of Korea, with grants funded by the Korean government (2014M3A7B4052201 and 2017R1D1A1B03034847). Y. Qian wishes to thank the financial support through China Scholarship Council (CSC, 201808260016).

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References (1) Liu, C.; Li, F.; Ma, L. P.; Cheng, H. M., Advanced Materials for Energy Storage. Adv. Mater. 2010, 22, E28-62. (2) Hochbaum, A. I.; Chen, R.; Delgado, R. D.; Liang, W.; Garnett, E. C.; Najarian, M.; Majumdar, A.; Yang, P., Enhanced Thermoelectric Performance of Rough Silicon Nanowires. Nature 2008, 451, 163-167. (3) Lu, Y.; Li, B.; Zheng, S.; Xu, Y.; Xue, H.; Pang, H., Syntheses and Energy Storage Applications of MxSy (M=Cu, Ag, Au) and Their Composites: Rechargeable Batteries and Supercapacitors. Adv. Funct. Mater. 2017, 27, 1703949. (4) Cao, X.; Jie, Y.; Wang, N.; Wang, Z. L., Triboelectric Nanogenerators Driven Self-Powered Electrochemical Processes for Energy and Environmental Science. Adv. Energy Mater. 2016, 6, 1600665. (5) Fan, F. R.; Tang, W.; Wang, Z. L., Flexible Nanogenerators for Energy Harvesting and Self-Powered Electronics. Adv. Mater. 2016, 28, 4283-4305. (6) Shu, Y.; Li, B.; Chen, J.; Xu, Q.; Pang, H.; Hu, X., Facile Synthesis of Ultrathin Nickel-Cobalt Phosphate 2D Nanosheets with Enhanced Electrocatalytic Activity for Glucose Oxidation. ACS Appl. Mater. Interfaces 2018, 10, 2360-2367. (7) Song, Y.; Cheng, X.; Chen, H.; Huang, J.; Chen, X.; Han, M.; Su, Z.; Meng, B.; Song, Z.; Zhang, H., Integrated Self-Charging Power Unit with Flexible Supercapacitor and Triboelectric Nanogenerator. J. Mater. Chem. A 2016, 4, 14298-14306. (8) Li, X.; Wei, J.; Li, Q.; Zheng, S.; Xu, Y.; Du, P.; Chen, C.; Zhao, J.; Xue, H.; Xu, Q.; Pang, H., Nitrogen-Doped Cobalt Oxide Nanostructures Derived from Cobalt-Alanine Complexes for High-Performance Oxygen Evolution Reactions. Adv. Funct. Mater. 2018, 27, 1800886. (9) Jeong, C. K.; Baek, K. M.; Niu, S.; Nam, T. W.; Hur, Y. H.; Park, D. Y.; Hwang, G. T.; Byun, M.; Wang, Z. L.; Jung, Y. S.; Lee, K. J., Topographically-Designed Triboelectric Nanogenerator via Block Copolymer Self-Assembly. Nano Lett. 2014, 14, 7031-7038. (10) He, W.; Ngoc, H. V.; Qian, Y. T.; Hwang, J. S.; Yan, Y. P.; Choi, H.; Kang, D. J., Synthesis of Ultra-Thin Tellurium Nanoflakes on Textiles for High-Performance Flexible and Wearable Nanogenerators. Appl. Surf. Sci. 2017, 392, 1055-1061. (11) Wang, Z. L.; Song, J.; Piezoelectric Nanogenerators Based on Zinc Oxide Nanowire Arrays. Science, 2006, 312, 242-246. (12) Fan, F. R.; Tian, Z. Q.; Wang, Z. L., Flexible Triboelectric Generator. Nano Energy 2012, 1, 328-334. (13) Lee, K. Y.; Gupta, M. K.; Kim, S. W., Transparent Flexible Stretchable Piezoelectric and Triboelectric Nanogenerators for Powering Portable Electronics. Nano Energy 2015, 14, 139-160. (14) Xu, L.; Jiang, T.; Lin, P.; Shao, J. J.; He, C.; Zhong, W.; Chen, X. Y.; Wang, Z. L., Coupled 13



Triboelectric Nanogenerator Networks for Efficient Water Wave Energy Harvesting. ACS Nano 2018, 12, 1849-1858. (15) Hu, Y.; Lin, L.; Zhang, Y.; Wang, Z. L., Replacing A Battery by A Nanogenerator with 20 V Output. Adv. Mater. 2012, 24, 110-114. (16) Gupta, M. K.; Lee, J. H.; Lee, K. Y.; Kim,S. W., Two-Dimensional Vanadium-Doped ZnO Nanosheet-Based Flexible Direct Current Nanogenerator. ACS Nano 2013, 7, 8932-8939. (17) Li, X.; Xiao, X.; Li, Q.; Wei, J.; Xue, H.; Pang, H., Metal (M=Co, Ni) Phosphate Based Materials for High-Performance Supercapacitors. Inorg. Chem. Front. 2018, 5, 11-28. (18) Shin, S. H.; Kim, K. H.; Lee, M. H.; Jung, J. Y.; Seol, J. H.; Nah, J., Lithium-Doped Zinc Oxide Nanowires-Polymer Composite for High Performance Flexible Piezoelectric Nanogenerator. ACS Nano 2014, 8, 10844-10850. (19) Zhu, Y.; Yang, B.; Liu, J.; Wang, X.; Chen, X.; Yang, C., An Integrated Flexible Harvester Coupled Triboelectric and Piezoelectric Mechanisms using PDMS/MWCNT and PVDF. J. Microelectromech. S. 2015, 24, 513-515. (20) Wang, X.; Yang, B.; Liu, J.; Zhu, Y.; Yang, C.; He, Q., A Flexible Triboelectric-Piezoelectric Hybrid Nanogenerator Based on P(VDF-TrFE) Nanofibers and PDMS/MWCNT for Wearable Devices. Sci. Rep. 2016, 6, 36409. (21) Yang, X.; Daoud, W. A., Triboelectric and Piezoelectric Effects in a Combined Tribo-Piezoelectric Nanogenerator Based on an Interfacial ZnO Nanostructure. Adv. Funct. Mater. 2016, 26, 8194-8201. (22) Zhu, J.; Hou, X.; Niu, X.; Guo, X.; Zhang, J.; He, J.; Guo, T.; Chou, X.; Xue, C.; Zhang, W., The d-Arched Piezoelectric-Triboelectric Hybrid Nanogenerator as A Self-Powered Vibration Sensor. Sensor Actuat. A Phys. 2017, 263, 317-325. (23) Chen, B.; Tang, W.; Jiang, T.; Zhu, L.; Chen, X.; He, C.; Xu, L.; Guo, H.; Lin, P.; Li, D.; Shao, J.; Wang, Z. L., Three-Dimensional Ultraflexible Triboelectric Nanogenerator Made by 3D Printing. Nano Energy 2018, 45, 380-389. (24) Niu, S.; Wang, S.; Liu, Y.; Zhou, Y. S.; Lin, L.; Hu, Y.; Pradel, K. C.; Wang, Z. L., A Theoretical Study of Grating Structured Triboelectric Nanogenerators. Energy Environ. Sci. 2014, 7, 2339-2349. (25) Xie, Y.; Wang, S.; Niu, S.; Lin, L.; Jing, Q.; Yang, J.; Wu, Z.; Wang, Z. L., Grating-Structured Freestanding Triboelectric-Layer Nanogenerator for Harvesting Mechanical Energy at 85% Total Conversion Efficiency. Adv. Mater. 2014, 26, 6599-6607. (26) Yang, W.; Chen, J.; Zhu, G.; Yang, J.; Bai, P.; Su, Y.; Jing, Q.; Gao, X.; Wang, Z. L., Harvesting Energy from the Natural Vibration of Human Walking. ACS Nano 2013, 7, 11317-11324. (27) Wang, X.; Yang, B.; Liu, J.; He, Q.; Guo, H.; Yang, C.; Chen, X., Flexible Triboelectric and Piezoelectric Coupling Nanogenerator Based on Electrospinning P(VDF-TREE) Nanowires, in 2015 28th IEEE Int. Conf. Micro Electro Mechanical Systems (MEMS), IEEE, 2015, 14


Page 14 of 23

Page 15 of 23 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Estoril, Portugal, 2015, 110-113. (28) Chen, S.; Tao, X.; Zeng, W.; Yang, B.; Shang, S., Quantifying Energy Harvested from Contact-Mode Hybrid Nanogenerators with Cascaded Piezoelectric and Triboelectric Units. Adv. Energy Mater. 2017, 7, 1601569. (29) Chen, X.; Han, M.; Chen, H.; Cheng, X.; Song, Y.; Su, Z.; Jiang, Y.; Zhang, H., A Wave-Shaped Hybrid Piezoelectric and Triboelectric Nanogenerator Based on P(VDF-TrFE) Nanofibers. Nanoscale 2017, 9, 1263-1270. (30) Xue, C.; Li, J.; Zhang, Q.; Zhang, Z.; Hai, Z.; Gao, L.; Feng, R.; Tang, J.; Liu, J.; Zhang, W.; Sun, D., A Novel Arch-Shape Nanogenerator Based on Piezoelectric and Triboelectric Mechanism for Mechanical Energy Harvesting. Nanomaterials 2014, 5, 36-46. (31) Jung, W. S.; Kang, M. G.; Moon, H. G.; Baek, S. H.; Yoon, S. J.; Wang, Z. L.; Kim, S. W.; Kang, C. Y., High Output Piezo/Triboelectric Hybrid Generator. Sci. Rep. 2015, 5, 9309. (32) Han, M.; Chen, X.; Yu, B.; Zhang, H., Coupling of Piezoelectric and Triboelectric Effects: from Theoretical Analysis to Experimental Verification. Adv. Electron. Mater. 2015, 1, 1500187. (33) Suo, G.; Yu, Y.; Zhang, Z.; Wang, S.; Zhao, P.; Li, J.; Wang, X., Piezoelectric and Triboelectric Dual Effects in Mechanical-Energy Harvesting using BaTiO3/Polydimethylsiloxane Composite Film. ACS Appl. Mater. Interfaces 2016, 8, 34335-34341. (34) Van, N. H.; Kang, D. J., Flexible, Transparent and Exceptionally High Power Output Nanogenerators Based on Ultrathin ZnO Nanoflakes. Nanoscale 2016, 8, 5059-5066. (35) Kong, X. Y.; Wang, Z. L., Polar-Surface Dominated ZnO Nanobelts and the Electrostatic Energy Induced Nanohelixes, Nanosprings, and Nanospirals. Appl. Phys. Lett. 2004, 84, 975-977. (36) Nam, G. H.; Baek, S. H.; Cho, C. H.; Park, I. K., A Flexible and Transparent Graphene/ZnO Nanorod Hybrid Structure Fabricated by Exfoliating A Graphite Substrate. Nanoscale 2014, 6, 11653-11658. (37) Kumar, B.; Lee, K. Y.; Park, H. K.; Chae, S. J.; Lee, Y. H.; Kim, S. W., Controlled Growth of Semiconducting Nanowire, Nanowall, and Hybrid Nanostructures on Graphene for Piezoelectric Nanogenerators. ACS Nano 2011, 5, 4197-4204. (38) Choi, D.; Choi, M. Y.; Choi, W. M.; Shin, H. J.; Park, H. K.; Seo, J. S.; Park, J.; Yoon, S. M.; Chae, S. J.; Lee, Y. H.; Kim, S. W.; Choi, J. Y.; Lee, S. Y.; Kim, J. M., Fully Rollable Transparent Nanogenerators Based on Graphene Electrodes. Adv. Mater. 2010, 22, 2187-2192. (39) Shin, D. M.; Tsege, E. L.; Kang, S. H.; Seung, W.; Kim, S. W.; Kim, H. K.; Hong, S. W.; Hwang, Y.-H., Freestanding ZnO Nanorod/Graphene/ZnO Nanorod Epitaxial Double Heterostructure for Improved Piezoelectric Nanogenerators. Nano Energy 2015, 12, 268-277. (40) Geng, P.; Zheng, S.; Tang, H.; Zhu, R.; Zhang, L.; Cao, S.; Xue, H.; Pang, H., Transition 15



Metal Sulfides Based on Graphene for Electrochemical Energy Storage. Adv. Energy Mater. 2018, 8, 1703259. (41) Li, X.; Chen, Y.; Kumar, A.; Mahmoud, A.; Nychka, J. A.; Chung, H. J., Sponge-Templated Macroporous Graphene Network for Piezoelectric ZnO Nanogenerator. ACS Appl. Mater. Interfaces 2015, 7, 20753-20760. (42) Qian, Y.; Van Ngoc, H.; Kang, D. J., Growth of Graphene/h-BN Heterostructures on Recyclable Pt Foils by One-Batch Chemical Vapor Deposition. Sci. Rep. 2017, 7, 17083. (43) Lee, J. W.; Cho, H. J.; Chun, J.; Kim, K. N.; Kim, S.; Ahn, C. W.; Kim, I. W.; Kim, J. Y.; Kim, S. W.; Yang, C.; Baik, J. M., Robust Nanogenerators Based on Graft Copolymers via Control of Dielectrics for Remarkable Output Power Enhancement. Sci. Adv. 2017, 3, e1602902. (44) Wang, Z. L.; Chen, J.; Lin, L., Progress in Triboelectric Nanogenerators as A New Energy Technology and Self-Powered Sensors. Energy Environ. Sci. 2015, 8, 2250-2282. (45) Yang, P. K.; Lin, L.; Yi, F.; Li, X.; Pradel, K. C.; Zi, Y.; Wu, C. I.; He, J. H.; Zhang, Y.; Wang, Z. L., A Flexible, Stretchable and Shape-Adaptive Approach for Versatile Energy Conversion and Self-Powered Biomedical Monitoring. Adv. Mater. 2015, 27, 3817-3824. (46) Choi, B. G.; Yang, M. H.; Hong, W. H.; Choi, J. W. ; Huh, Y. S., 3D Macroporous Graphene Frameworks for Supercapacitors with High Energy and Power Densities. ACS Nano 2012, 6, 4020-4028. (47) Wang, H.; Yan, T.; Liu, P.; Chen, G.; Shi, L.; Zhang, J.; Zhong, Q.; Zhang, D., In Situ Creating Interconnected Pores Across 3D Graphene Architectures and Their Application as High Performance Electrodes for Flow-Through Deionization Capacitors. J. Mater. Chem. A 2016, 4, 4908-4919. (48) Zhu, G.; Lin, Z. H.; Jing, Q.; Bai, P.; Pan, C.; Yang, Y.; Zhou, Y.; Wang, Z. L., Toward Large-Scale Energy Harvesting by A Nanoparticle-Enhanced Triboelectric Nanogenerator. Nano Lett. 2013, 13, 847-853. (49) Shi, B.; Zheng, Q.; Jiang, W.; Yan, L.; Wang, X.; Liu, H.; Yao, Y.; Li, Z.; Wang, Z. L., A Packaged Self-Powered System with Universal Connectors Based on Hybridized Nanogenerators. Adv. Mater. 2016, 28, 846-852. (50) Park, K. I.; Lee, M.; Liu, Y.; Moon, S.; Hwang, G. T.; Zhu, G.; Kim, J. E.; Kim, S. O.; Kim, D. K.; Wang, Z. L.; Lee, K. J., Flexible Nanocomposite Generator Made of BaTiO(3) Nanoparticles and Graphitic Carbons. Adv. Mater. 2012, 24, 2999-3004.

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Figure 1. Structural analysis of ZnO NFs/3D Gr heterostructures. (a) XRD patterns of ZnO NFs/3D Gr heterostructure. (b) SEM image of 3D Gr. (c, d) Low- and high-resolution SEM images of ZnO NFs on 3D Gr. (e) TEM image of ZnO NFs. (f) HRTEM image of ZnO NFs.

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Figure 2. PDMS/ZnO/3D Gr/Ni foam based-HEH. (a) Schematic and (b) photographic image of the HEH. (c) Open-circuit voltage of PDMS/ZnO NFs/3D Gr/Ni foam-based HEHs. (d) Short-circuit current density of PDMS/ZnO NFs/3D Gr/Ni foam based HEHs.

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Figure 3. Electrical properties of HEHs. (a, b) The open-circuit voltage and short-circuit current density of PDMS/ZnO/3D graphene/Ni foam-based HEHs during repetitive compressive motions under the driving frequency of 5 Hz and various compressive forces. (c, d) Histogram of the open-circuit voltage and short-circuit current density of PDMS/Ni foam-, PDMS/3D Gr/Ni foam-, PDMS/ZnO/Ni foam- and PDMS/ZnO/3D Gr/Ni foam-based HEHs during repetitive compressive motions under the driving frequency of 5 Hz and various compressive forces.

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Figure 4. Size dependence of electrical properties for all the devices. (a) The open-circuit voltage and (b) short-circuit current density of devices with different areas. Electrical measurements after bending operation. (c, d) The open-circuit voltage and short-circuit current density of the PDMS/ZnO NFs/3D Gr/Ni foam HEH during repetitive compressive motions under the driving frequency of 5 Hz and various compressive forces.

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Figure 5. A schematic illustrating the operational mechanism of PDMS/ZnO NFs/3D Gr/Ni foam based HEHs. (a) The initial state of HEHs. (b-e) The charging process of tribo- and piezoelectric effects under the compressive force.

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Figure 6. Powering LEDs using electricity generated from a HEH. (a) A photograph showing 68 LEDs loaded into the circuit. (b) Instantaneous lighting of 68 LEDs under periodic compression activated by tapping with a finger.

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Table of Contents Graphic

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Three-Dimensional Graphene

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