Large-Scale Production of Flexible, High-Voltage Hydroelectric Films

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Energy, Environmental, and Catalysis Applications

Large-Scale Production of Flexible, HighVoltage Hydroelectric Film Based on Solid Oxides Changxiang Shao, Bingxue Ji, Tong Xu, Jian Gao, Xue Gao, Yukun Xiao, Yang Zhao, Nan Chen, Lan Jiang, and Liangti Qu ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.9b09582 • Publication Date (Web): 04 Aug 2019 Downloaded from pubs.acs.org on August 7, 2019

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ACS Applied Materials & Interfaces

Large-Scale Production of Flexible, High-Voltage Hydroelectric Film Based on Solid Oxides Changxiang Shao,a Bingxue Ji,a Tong Xu,a Jian Gao,a Xue Gao,a Yukun Xiao,a Yang Zhao,a Nan Chen,a Lan Jiang,b and Liangti Qu*ac

aBeijing

Key Laboratory of Photoelectronic/Electrophotonic Conversion Materials

Key Laboratory of Cluster Science, Ministry of Education School of Chemistry and Chemical Engineering Beijing Institute of Technology Beijing 100081, P. R. China. E-mail: [email protected] bLaser

Micro-/Nano-Fabrication Laboratory

School of Mechanical Engineering Beijing Institute of Technology Beijing 100081, P. R. China cKey

Laboratory for Advanced Materials Processing Technology

Ministry of Education of China State Key Laboratory of Tribology Department of Mechanical Engineering

ACS Paragon Plus Environment

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Tsinghua University, Beijing 100084, PR China.

KEYWORDS: large-scale production, flexibility, high-voltage, hydroelectric film, solid oxides

ABSTRACT

Spontaneous electricity generation through water evaporation is becoming a hot research area. However, low power output, limited material availability and unscalable fabrication largely hinder its wide applications. Here, we report scalable painting and blade coating approaches for mass production of flexible hydroelectric film (HEF) based on solid oxides (e.g., Al2O3), which is of tolerance to mechanical deformation and is compatible with three-dimensional diverse configuration. The electricity power is generated continuously and can last for more than 10 days in the ambient condition. A single HEF unit is capable of supplying an output voltage of more than 2.5 V, and even up to 4.5 V at specific condition. The accumulative energy output can be tuned


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conveniently by means of series/parallel connection or size control to meet the practical needs of commercial electronics. A family of solid oxides has been verified to have the ability for water evaporation induced electricity generation, which offers a considerable room for development of high performance energy-supplying devices.

INTRODUCTION

Electricity generation via unconventional strategy is becoming a burgeoning area of interest because of the growing energy crisis and environmental deterioration. The converting energy from the ambient environment into electricity through an environmental-friendly way is regard as one of the most promising approaches to deal with the challenge.1-4 Thus considerable investigations aiming at developing solar cells57

piezoelectric/triboelectric nanogenerators,8-11 thermoelectric generators12-17 and moist-

electric generators18-22 have been carried out in the past few decade. Meanwhile, the natural water evaporation-enabled electricity generation is arousing widespread interest due to the highly spontaneous and continuous power generation process.23-34


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The active materials, mainly carbon-based nanoparticles, are used to produce electricity via water evaporation.25-28, 32, 33 The generated open circuit voltage of a device unit is still relatively low. Effort has been made to introduce the additional molecular and polymer modifications of carbon materials for enhanced energy output despite of the complicated preparation process.34 Generally, the available material systems are still limited to date. And most devices reported previously rely on the bulky and rigid substrates with monotonous structures and poor mechanical flexibility, thus heavily restricting their large-scale production and compatibility with portable, deformable devices in complex and mutable conditions.25-29,35,36

In this regard, we develop the simple painting and blade coating technologies for large-scale fabrication of flexible hydroelectric film (HEF) based on the solid oxides such as Al2O3 nanoparticles. The Al2O3 based HEF can achieve a high voltage output of more than 2.5 V without significant performance attenuation even after 10 days. The asprepared HEF is able to tolerate the large mechanical deformation for forming multidimensional configurations and exhibits stretchable character after predesigned laser


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pattern processing. The preparation method of HEF enables the easy device integration for the further enhancement of power output via series/parallel connection to power commercial electronics. Many solid oxides beyond Al2O3 has also been verified to have the ability for water evaporation induced electricity generation, which offer a family of materials with considerable room for development of high performance energygenerating devices.

RESULTS AND DISCUSSION

Preparation and Characterization


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Figure 1. (a) Schematic illustration to the fabrication process of HEF. (b) Digital photograph of a 5 m roll of HEF. (c) Photos showing HEF with a large degree of distortion and bending. (d) SEM image of Al2O3 layer. (e) Cross-section SEM image of HEF.

The scalable fabrication of HEF is depicted in Figure 1a. Commercial carbon paste is first painted on a hydrophilic frosted polyethylene terephthalate (PET) film with contact


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angle of 40° (Figure S1a) to work as electrodes. After carbon paste is dried, Al2O3 nanoparticles suspension (0.5 g mL-1, in ethanol) (Figure S1b) is painted on the whole PET substrate. The HEF is obtained after ethanol is completely vaporized within few minutes. The binding between nanoparticles and the adhesion of the particles to the substrate are be attributed to the drying process,37 which is capillary-driven self-assembly, as shown in Figure S2. The suspension begin to shrink pronouncedly as solvent evaporates after painting the suspension on the substrate. During the suspension shrinkage regime, capillary force exists between the adjacent nanoparticles on the nanoparticles liquid-air interface. When the capillary force is larger than a critical force, the nanoparticles will collapse. The nanoparticles approach each other and finally form the solid porous structure that will form the backbone of the dry film. As film shrinkage is completed, the pores deplete and the gas-liquid interface recedes into the porous structure with further solvent evaporation until the film is dry. Besides, the van der Waals forces and hydrogen bonds are also contribute to the adhesion between nanoparticles as well as substrate and nanoparticles. In order to improve the production efficiency, blade coating method (Figure S1c and Supporting Movie S1) is utilized to manufacture a roll of


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HEF longer than 5 meters (Figure 1b). The fabrication process is simple enough and avoids strict condition requirement, allowing the low-cost large-scale production. The asmade HEF in both dry (Figure 1c) or wet (Figure S3 )state has highly mechanical flexibility and can withstand large degree of deformation such as distortion and bending as shown in Supporting Movie S2 and S3, which will largely expand its application scenarios in different fields.

The scanning electron microscopy (SEM) image shows that Al2O3 layer is composed by a mass of randomly distributed nanoparticles of roughly 200~300 nm in diameter (Figure 1d). These nanoparticles are packed tightly with a large number of nanoholes. These interconnected nanoholes could serve as narrow nanochannels for water flow. The crosses section SEM images of HEF (Figure 1e and Figure S4a) exhibit that Al2O3 layer with thickness of 20 µm adheres to the PET film closely. The Al2O3 used here has high purity (Figure S4b) and the identity of α-Al2O3 is confirmed by transmission electron microscopy (TEM) and X-ray diffraction (XRD) pattern (Figure S4c,d). The carbon paste


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is composed of nanoparticles (Figure S5a) only containing carbon and oxygen elements (Figure S5b-d), excluding the possible influence of impurities on power generation.


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Power Generation Evaluation of Flexible HEF

Figure 2. (a) Schematic diagrams of planar HEF in contact with water for test. (b) The corresponding voltage output of HEF with size of 18 cm × 4 cm. (c) A voltage output performance comparison of the reported moisture/deionized water-enabled power generation systems based on various materials as well as the commercial dry Leclanché


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cell. (d) Stability of the HEF with size of 4.5 cm × 4 cm for long time test in an open environment. (e) The power generation performance of HEF after 2000 bending cycles. Inset: photographs of the HEF with size of 10 cm × 4 cm under unbending/bending conditions.

The experimental set-up for measuring water triggered electricity generation of HEF is illustrated in Figure 2a. When HEF is partially immersing in deionized water, the signal of open circuit voltage gradually increases and eventually stabilizes at ~2.5 V (Figure 2b) with a short circuit current stabilizing at ~0.8 µA (Figure S6). Compared with other pulsed energy output or non-direct current energy output, this device has a great advantage in maintaining continuous direct current energy generation. More important, the voltage output performance is compared with other reported moisture/deionized water-induced power generation systems based on various materilas (e.g., layered double hydroxides, polymers, graphene derivatives and other carbon-based materials) and dry Leclanché cell as illustrated in Figure 2c and Table S1. It clearly show that the volatge output of the Al2O3-based HEF is higher than most of the previous reports and commercial dry


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Leclanché cell, which greatly facilitates the implementation of powering practical electronic devices.

In order to further optimize the performance of HEF, the possible influencing factors are explored. The spacing between the top and bottom electrodes is adjusted from 0.5 cm to 2.5 cm. As the electrode spacing increases to some extent, the energy outputs enhance probably due to the synergistic effect of faster water evaporation at higher capillary height and accumulation of potential differences (Figure S7a).25 The HEF length and thickness of Al2O3 layer have no significant effect on voltage, but mainly on current. The longer HEF or HEF with thicker Al2O3 layer will induce the larger current output owning to more nanochannels contributing to electricity generation (Figure S7b,c). In addition, HEFs with different electrode materials (e.g., carbon, Au, Ag and ITO) mainly woking as conductor for charge collection in Figure S8 have similar energy generating performance. Other commercial flexible substrates, such as polyimide (PI), polyvinyl chloride (PVC), polypropylene (PP) and polytetrafluoroethylene (PTFE), could also serve as the supporting plates. The corresponding HEFs maintain similar mechanical and


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power generation properties (Figure S9). The testing results not only show that electricity generation is independent of electrode materials and substrates, but also indicate that the fabrication method is universal with easily adapting to different electrode materials and flexible substrates.

For practical applications, it is of importance for power devices to possess stable and continuous electricity production under different circumstances. The integrity of HEF is not damaged easily even HEF immersed in water partially for a week (Figure S10) due to the strong capillary forces between adjacent nanoparticles and between particles and substrates. We tested the voltage and current outputs of HEF every day under the open environment. The output signals can maintain for consecutive 10 days at least (Figure 2d), although fluctuation within a certain range occurs caused by a constantly change of external environment (e.g. temperature, ralative humidity and wind velocity) under the open environment. The power output stability of HEF after mechanical deformation is measured via applying repeated bending. The HEF without visible damage shows no


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significant degradation even after 2000 cycles (Figure 2e and Figure S11), demonstrating the high flexibility and energy generating stability of HEF.

Figure 3. Schematic diagrams and the corresponding experimental images of (a) cylindrical HEF, (b) folded HEF, (c) coniform HEF as well as their energy outs. The size of HEF in (a) and (b) is 18 cm × 4 cm. The cone in (c) is formed from three quarters of a


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circle with a radius of 5.5 cm. (d) Schematic diagrams of HEF with laser pattern processing to obtain stretchable HEF. (e) The voltage and current outputs of the welldesigned stretchable HEF with size of 5 cm × 4 cm under different stretching conditions from initial state to tensile state. Inset: photographs of stretchable HEF without/with stretching.

The flexibility endows HEF with the versatility in different geometry designs including planer (Figure 2a) and three-dimensional configurations, such as cylindrical HEF (Figure 3a), folded HEF (Figure 3b) and coniform HEF (Figure 3c), expanding the application potential of more scenarios. The voltage and current signals of above samples can reach 2.5 V and 0.8 µA, respectively. In addition to the extensible three-dimensional configurations, the excellent versatile processibility of HEF demonstrating by scissor cutting (Figure S12a) and laser pattern processing techniques (Figure S12b) largely increases its diversity. The HEF can realize stretchable properties via reasonable design (Figure 3d and Figure S12c). The energy outputs of the well-designed HEF from initial


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state to tensile state are basically unchanged (Figure 3e), indicating the excellent stability of stretchable HEF.


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Figure 4. Photograph of six HEF units connected in (a) series and (b) parallel. Scale bar: 5 cm. (c) Voltage outputs of 1-6 HEF units in series connection. (d) Current outputs of 16 HEF units in parallel connection. (e) Photograph showing calculator powered by two HEFs connecting in parallel. (f) Photograph showing LED bulbs of different colors (white, yellow, blue and red) driven in turn by two HEFs connecting in series. The sizes of polygonal stellate and cylindric HEFs are 30 cm × 4 cm and 20 cm × 4 cm, respectively.

The regulation of power output is extremely meaningful for practical electric devices with different energy requirements. The series and parallel integration of HEFs is easily realized through reasonable electrode pattern design and folding control (Figure 4a,b). The voltage or current output increase almost linearly via series or parallel connection, and six series-connected unites produce voltage as high as 14.8 V while six parallelconnected unites improve current output up to 2.2 µA (Figure 4c,d and Figure S13,14). The output performance of HEF with size of 16 cm × 4 cm is investigated by connecting external loads with different resistances. As the external resistance increases from 1 Ω to 1 GΩ, the voltage increases to ≈2.5 V, whereas the current decreases from ≈0.76 µA


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to nearly zero (Figure S15a,b). The maximum output power can be obtained up to 0.513 µW at an optimum load resistance of ≈6 MΩ (Figure S15c). Two different configurational HEFs (e.g., polygonal stellate and cylindric HEFs) are produced to show practicality. The commercial electronic device such as calculator is driven by two HEFs connecting in parallel easily (Figure 4e and Supporting Movie S4). Besides, two HEFs in series connection light the white LED bulb (Supporting Movie S5). The blue, yellow and red ones could also be powered in turn (Figure 4f). These applications are implemented without any assistance of energy storage devices, thus simplifying the energy supply system.


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Mechanism Analysis

Figure 5. (a) Schematic of the ion-selective transport through nanochannels with positively charged surface. The arrows indicate the direction of flow. (b) The zeta potential of Al2O3, the inset is graphic illustration of the electrode polarity of Al2O3 based HEF. (c) The voltage and current outputs of HEF with size of 4 cm × 4 cm under different


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environment of temperature, wind-velocity and relative humidity. I: 252 ºC, 0.0150.005 m s-1, 102%. II: 352 ºC, 0.0150.005 m s-1, 102%. III: 252 ºC, 0.150.02 m s-1, 102%. IV: 252 ºC, 0.0150.005 m s-1, 932%. (d) The voltage and current outputs of HEFs with size of 5 cm × 4 cm based on various solid oxide (Al2O3, Fe2O3, Mn3O4, ZnO, CuO, SnO2, TiO2, Fe3O4 and SiO2) nanoparticles and the corresponding zeta potentials of these solid oxides.

A series of experiments are carried out to explore the power generation mechanism of HEF. The PET film with only two electrodes partially submerged by water (Figure S16a,b) and the HEF without water immersion (Figure S16c,d) can not produce power, indicating that Al2O3 and water are indispensable parts for electricity generation. Moreover, when HEF completely submerged by water, no appreciable electrical signals are detected (Figure S16e,f), which demonstrates that water flows along the internal nanochannels is vitally important for electricity generation. When the direction of the electrodes is parallel to the water flow direction, it is unable to collect the induced electricity effectively (Figure S16g,h). Based on previous testing results, the mechanism


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is speculated to be electrokinetic phenomenon. It has been reported that electrically neutral liquids have a distribution of electrical charges near the surface because of the charged solid surface. This region is known as the electrical double layer (EDL). Due to the presence of an EDL at the solid–liquid interface, when the fluid flows through a narrow passage with charged property under external pressure gradient, the streaming current and potential are induced according to previous studies.38-44 In our test system, the construction of narrow channel using tightly packed Al2O3 nanoparticles is achieved by the solvent evaporation induced self-assembly process. The charged nanochannels will cause water to diffuse upwards by capillary action (Figure 5a). Stronger capillary forces of Al2O3 layer will promote the water diffusion rate before reaching the dynamic equilibrium, thus speeding up the power generation process. For example, the HEF with 30 s air plasma treatment owning the enhanced hydrophilicity can reach the stable signal value more quickly than HEF without air plasma treatment under the same conditions (Figure S17). Noted that continuous water flow can not be maintained by capillarity alone. It is a synergistic result of capillary-induced water upward diffusion and incessant water evaporation, which is highly similar to water transport in plants.


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As shown in Figure S14, when the top and bottom electrodes are reversed, opposite signals of voltage are measured. This result indicates that the potential of bottom electrode is invariably higher than that of the top electrode for Al2O3 based HEF. Al2O3 nanoparticles in pH-neutral solution with the zeta potential of +40.3 mV have positively charged surface (Figure 5b):45-48

Al ― OH + H + ↔Al ― OH2 +

The polarity of the power generator is determined by the charge polarity of the solid surface when the flow direction is fixed. In this system, water evaporation determines the direction of water flow from the bottom up. When the channel surface is positively charged, the channel will repel cations and allow anions to pass through, corresponding to the high potential of the bottom electrode. Thus, it can be deduced that the bottom and top electrodes of Al2O3 based HEF correspond to the positive and negative poles of generator, which is consistent with the test results in Figure S18.

Streaming potential and current are affected by the flow velocity which is tuned by evaporation rate in this system. The evaporation rate of the water is regulated by changing


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the environmental temperature, wind velocity and the relative humidity to verify its effect on the power output (Figure 5c and Figure S19). The HEF with size of 4 cm × 4 cm can produce 2.5 V and 0.18 µA under the ambient condition. When the temperature increase to 35 ºC through a solar simulator irradiation, the voltage and current has a big improvement to 4.08 V and 0.28 µA. When a breeze with wind velocity of 0.15 m s-1 is applied, there is an even greater increase with voltage and current outputs as high as 4.59 V and 0.31 µA. As expected, the voltage and current become very small when environmental relative humidity increases to 93%. This conclusion is further proved by measuring the continuous power generation of HEF and changement of external environment in an open environment simultaneously. The results in Figure S20 show that the power generation performance is strongly influenced by environmental condition. In addition, the dependence of the voltage on the ionic concentration is investigated by using NaCl solutions with different concentrations and other types of water in Figure S21. The potential output decreases as the NaCl concentration increases from 10−7 mol L–1 to 1 mol L–1 nearly monotonically. And the performance based on tap water, lake water, seawater and ionic liquid in water also significantly decreased than that based on


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deionized water. The results are mainly attributed to the shorter Debye length in high concentration of ions. The Debye length is determined by ionic strength. When the size of channel is fixed, EDL overlapping is more likely to achieve in low concentration solution. The narrow channels become ion selective and expel co-ions when EDL overlap, thus benifiting for enhancing energy conversion efficiency.

Generally, solid oxides are electrically charged in aqueous suspension caused by amphoteric dissociation of surface OH groups or adsorption of hydroxo complexes derived from the hydrolysis products of material dissolved from the solid.49-51 Based on the above analysis, we boldly speculate that the solid oxides besides Al2O3 should also have the ability to generate electricity via water evaporation. To prove the conjecture, HEFs based on various solid oxides like Fe2O3 (Figure S22), Mn3O4 (Figure S23), ZnO (Figure S24), CuO (Figure S25), SnO2 (Figure S26), TiO2 (Figure S27), Fe3O4 (Figure S28) and SiO2 (Figure S29) are fabricated. Exhilaratingly, all of HEFs with size of 5 cm × 4 cm show varying electricity production with potential range from 2.5 V to -1.6 V and current range from 0.24 µA to -0.38 µA (Figure 5d). It clearly show that the polarity of generator is related to the surface charge of solid oxides in neutral aqueous suspension


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as discussed above. The positive or negative charged surface of these solid oxides in deionized water is confirmed by zeta potential measurement. The results show that the Al2O3, Fe2O3, Mn3O4, ZnO and CuO have positive charged surface while SnO2, TiO2, Fe3O4 and SiO2 have negative charged surface. Therefore, the polarity of HEFs based on Al2O3, Fe2O3, Mn3O4, ZnO and CuO are different form HEFs based on SnO2, TiO2, Fe3O4 and SiO2. The electrical energy output of different solid oxide is roughly positively correlated with their zeta potential which is an important and reliable indicator of surface charge. A critical factor in this phenomenon is the surface charge, and the efficiency increased with an increase of the surface charge density generally. A less completely linear correlation between power output and zata potential may be related to the different nanochannels resulted by different sizes, morphologies and hydrophilic properties of these solid oxide, the different evaporation rates coused by their different light absorption efficiency and photothermal conversion efficiency, and so on. Thus, future research could involve surface chemistry regulation, microstructure/size mediation, the rational nanochannel construction as well as the the light absorption/photothermal conversion efficiency adjustment to improve the performance. For example, compared with microchannel,


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nanochannel is more easily to cause the DEL to overlap and expel co-ions, thus increasing efficiency. In this system, the construction of nanochannel is related to the particle size and morphology. The size and the morphology of solid oxide in this experiment are different, which will induce formed channels with different size and then affect the performance. Undoubtedly, these exciting results will greatly enrich the variety of electricity-producing materials and provide valuable references for the exploration and development of more material systems.

CONCLUSION

In summary, a novel HEF based on Al2O3 nanoparticles is designed and fabricated through simple and scalable painting and blade coating technologies. The HEF with excellent mechanical flexibility can be curled and folded into three-dimensional configurations and displays stretchable characteristic after proper laser pattern treatment. The power generation performance of HEF can maintain at least 10 days and mechanical deformation of bending and stretching has little effect on energy output. A high potential of 2.5 V and even up to 4.5 V can be produced by single Al2O3 based HEF unit, and the


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energy output is further enhanced to power many electronic components by means of size enlargement or series/parallel connection. In addition, the feasibility of other solid oxides to generate electricity via water evaporation has been confirmed, thus the electricity-producing materials system is extended from Al2O3 to a family of solid oxides, which offers vast development space for the construction of new high-efficiency energy conversion devices.

EXPERIMENTAL SECTION

The fabrication of solid oxides based flexible hydroelectric film (HEF): First, Al2O3 nanoparticles (alpha phase, Adamas, China) is dispersed in ethanol by vigorous stirring, the concentration of Al2O3 nanoparticles suspension is 0.5 g mL-1. Then carbon paste (CH-8, Jelcon Corp., Japan) is painted on frosted polyethylene terephthalate (PET) film with width of 1 cm to serve as electrode. The distance between the two electrodes is 2 cm unless specifically mentioned. After carbon paste is dried, Al2O3 suspension is painted the while PET substrate. The thickness of Al2O3 layer is 20 µm unless specifically


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mentioned .To improve the production efficiency and uniformity of the HEF, scraping method performed by automatic film applicator (AFA-II, Shenyang Kejing Auto-Instrument Co., Ltd) is introduced. When the ethanol is evaporated completely within few minutes, the HEF is completely fabricated. Other solid oxides (Fe2O3, Mn3O4, ZnO, CuO, SnO2, TiO2, Fe3O4 and SiO2) (InnoChem, China) with size ranging from 100 nm to 2 µm are purchased from Beijing InnoChem Science & Technology Co., Ltd. Similarly, HEFs based on above solid oxides are prepared in the same manner. The HEFs based on Ag and Au electrodes with 150 nm thickness are made by using high purity gold and silver deposited onto PET film via magnetron sputtering. The HEF based on ITO electrodes is fabricated by using commercial ITO-PET film. To increase the hydrophilic property of Al2O3, The HEF is treated air plasma for 30 s by plasma treatment system. The stretchable HEF is obtained by a computer-programmed laser processing system (LW-UVY-5S-Y, Leijieming Laser corp., China).

Characterization: Scanning electron microscope (SEM) of the FHEG and X-ray energy disperse spectra (EDS) of the Al2O3 and carbon paste used in this experiment were


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carried out on JSM-7001F. X-ray diffraction (XRD) patterns were tested on a Netherlands 1710 diffractometer with a Cu Kα irradiation source (λ=1.54 Å). The transmission electron microscopy (TEM) images were obtained from JEM-2100 microscope (JEOL, Japan). The zeta potentials of solid oxides were measured by potentiometer (Zetasizer Nano ZS90, Malvern Instruments Limited, UK).

Power generation measurement: Silver wires were attached on carbon electrodes to work as an extending for easier connection. The deionized water is used for power generation. The output electric signals including open-circuit voltage and short-circuit current were recorded by a sourcemeter (Keithley 2612A). Unless otherwise specified, all the voltage and current signals measured refer to the open circuit voltage and short circuit current. The relative humidity and temperature were monitored by a humidity & temperature meter AR847+ in real time. The wind velocity generated by an electric fan was measured by an anemometer (Testo405). The voltage and current outputs on the electrical resistance of the external circuit is test by connect a HEF (16 cm × 4 cm) with a resistance box. The power output is calculate by the following equation:


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Pext =UI Where the U is the voltage tested on the resistance box. I is current in the circuit. ASSOCIATED CONTENT

Supporting Information. The Supporting Information is available free of charge on the ACS Publications website at DOI:.

Additional information (PDF)

Movie S1: The scraping method performed by automatic film applicator is used to fabricate HEF. (AVI)

Movie S2: The flexible HEF can withstand large degree of deformation. (AVI)

Movie S3: The wet HEF can withstand large degree of deformation. (AVI)

Movie S4: A calculator is powered by two HEFs connecting in parallel. (AVI)

Movie S5: The white LED bulb is light by two HEFs connecting in series. (AVI)

AUTHOR INFORMATION


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Corresponding Authors

*E-mail (L. Qu): [email protected]

ORCID

Liangti Qu: 0000-0002-0161-3816

Notes

The authors declare no competing financial interest.

ACKNOWLEDGMENT

We thank the financial support from the National Key R&D Program of China (2017YFB1104300, 2016YFA0200200), NSFC (Grant No. 51673026, 51433005, 21604003, 21671020), NSFC-MAECI (51861135202) and Graduate Technological Innovation Project of Beijing Institute of Technology. We appreciate the characterization work supported by Analysis & Testing Center, Beijing Institute of Technology.


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Large-Scale Production of Flexible, High-Voltage Hydroelectric Films

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