FULL PAPER Blue Energy www.afm-journal.de Triboelectric Nanogenerator Networks Integrated with Power Management Module for Water Wave Energy Harvesting Xi Liang, Tao Jiang, Guoxu Liu, Tianxiao Xiao, Liang Xu, Wei Li, Fengben Xi, Chi Zhang,* and Zhong Lin Wang* by the consumption of fossil fuels have Ocean waves are one of the most promising renewable energy sources for attracted worldwide attention.[1,2] It is large-scope applications. Recently, triboelectric nanogenerator (TENG) network highly urgent to search for other renew- has been demonstrated to effectively harvest water wave energy possibly able and clean energy sources. Water toward large-scale blue energy. However, the absence of effective power wave energy, which has abundant reserves and little dependence on environmental management severely restricts the practicability of TENGs. In this work, a conditions, is a promising renewable energy hexagonal TENG network consisting of spherical TENG units based on spring- source with great potential for large-scale assisted multilayered structure, integrated with a power management module applications.[3–5] However, such energy has (PMM), is constructed for harvesting water wave energy. The output perfor- rarely been exploited due to lack of eco- mance of the TENG network is found to be determined by water wave frequen- nomical energy scavenging technologies in spite of the great efforts devoted.[6–8] cies and amplitudes, as well as the wave type. Moreover, with the implemented So far, most demonstrated converters for PMM, the TENG network could output a steady and continuous direct current water wave energy rely on the electromag- (DC) voltage on the load resistance, and the stored energy is dramatically netic generators, which are heavy, bulky, improved by up to 96 times for charging a capacitor. The TENG network inte- costly, easily corroded, and inefficient at grated with the PMM is also applied to effectively power a digital thermometer ocean wave frequency.[9,10] Hence, a light- and a wireless transmitter. The thermometer can constantly measure the water weight, small-sized, cost-effective, and all- in-one approach for harvesting the water temperature with the water wave motions, and the transmitter can send signals wave energy is greatly desirable. that enable an alarm to go off once every 10 s. This study extends the application Triboelectric nanogenerator (TENG) has of the power management module in the water wave energy harvesting. provided an effective route for converting ambient mechanical energy into electricity, with unique merits of high power density, 1. Introduction high efficiency, low weight, and low fabrication cost.[11–17] Through the coupling of triboelectrification and electrostatic induction, With the development of human society, energy is always a the TENGs can harvest energy from a variety of sources, such as key topic because of its indispensable role for people’s life. In human walking,[18] mechanical vibration,[19] rotation,[20] wind,[21] recent years, climate deterioration and energy crisis caused and water waves.[22–30] The TENGs exhibit obvious advantages over electromagnetic generators at low frequency, due to their X. Liang, Prof. T. Jiang, G. Liu, T. Xiao, Prof. L. Xu, Prof. W. Li, F. Xi, fundamental differences in the physical mechanisms,[31,32] dem- Prof. C. Zhang, Prof. Z. L. Wang onstrating the possible killer application of TENG in harvesting CAS Center for Excellence in Nanoscience [33] Beijing Key Laboratory of Micro-Nano Energy and Sensor low-frequency energy from motions such as ocean waves. In Beijing Institute of Nanoenergy and Nanosystems 2014, Wang proposed an idea of using TENG networks to harvest Chinese Academy of Sciences large-scale water wave energy,[34] which are made of millions of Beijing 100083, China spherical ball based TENG units connected as fishing net.[5] So E-mail: [email protected]; [email protected] far, a TENG network based on fully enclosed box-like device with X. Liang, Prof. T. Jiang, G. Liu, T. Xiao, Prof. L. Xu, F. Xi, Prof. C. Zhang, self-restorable arch-shaped TENGs and a coupled TENG network Prof. Z. L. Wang School of Nanoscience and Technology composed of rolling spherical TENGs have been constructed University of Chinese Academy of Sciences in our previous works.[22,35] Recently, the performance of single Beijing 100049, China spherical TENG unit in the network has been dramatically opti- Prof. Z. L. Wang mized by introducing the spring-assisted multilayered structure, School of Materials Science and Engineering and a small network has also been fabricated to harness the water Georgia Institute of Technology [36] Atlanta, GA 30332-0245, USA wave energy. Nevertheless, the TENG networks have difficul- ties in directly powering electronics or charging storages for the DOI: 10.1002/adfm.201807241 large impedance and unbalanced load matching.[37–39] Therefore, Adv. Funct. Mater. 2019, 1807241 1807241 (1 of 8) © 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.advancedsciencenews.com www.afm-journal.de effective power management is very necessary to break through structure of the spherical unit is the same as that reported in our this bottleneck and achieve more efficient utilization of water previous work.[36] For the spring-assisted structure; four flexible wave energy. springs adhered on bottom acrylic block support the mass block, In the present work, we designed and fabricated a hexagonal while four rigid springs attached on the top side of mass block TENG network by using spherical TENG units based on spring- utilize the resilience force to press the multilayered TENG. In the assisted multilayered structure for harvesting water wave energy, multilayered structure with increased space utilization, a 50 µm and managed the output energy through integrating with a power thick Kapton film shaped into a zigzag structure serves as the management module (PMM). First, the output performance of substrate of TENG basic units. The local structure of the multi- the TENG network was systematically measured in water as trig- layered TENG can be viewed from the enlarged figure at the right gered by real water waves under different water wave conditions. side of Figure 1a. Each basic TENG unit is based on the contact- The influences of the water wave frequency and amplitude were separation between the aluminum (Al) electrode and polarized investigated for three types of water waves, i.e., transverse sinu- fluorinated ethylene propylene (FEP) film bonded by another alu- soidal wave, transverse impulse wave, and longitudinal impulse minum electrode. The copper mass and basic unit number for wave. Then the TENG network was integrated with the PMM, each sphere are fixed as 100 g and 7 in this work. The fabrication and the output characteristics on the load resistance and capaci- details can be found in the Experimental Section. Figure 1b shows tance were respectively investigated. A steady and continuous the working principle of each TENG unit. Under the triggering direct current (DC) voltage on the load resistance was received, of water waves, the contact between Al and FEP film generates and the direct and managed charging speeds to a capacitor were opposite charges on the Al and FEP surface. Then their separa- compared. Finally, the TENG network integrated with the PMM tion produces an electric potential difference between electrodes was applied to power a digital thermometer and a wireless trans- driving the free electron flow at the external circuit. The periodic mitter, demonstrating the advantage and necessity of the TENG contact-separation will generate periodic alternating current. Our and PMM toward large-scale blue energy harvesting. TENGs with the spring-assisted and multilayered structure have a much higher output current than previous water wave-driven TENGs, because of the contact-separation working mode of the 2. Results and Discussion TENGs with the help of the springs and the integration of mul- tiple basic units. Then one spherical TENG can realize a higher A hexagonal TENG network was fabricated by using spherical power output (a maximum power of 7.96 mW).[36] TENG units, which have the spring-assisted multilayered Figure 1c presents the schematic diagram of the hexagonal structure as schematically illustrated in Figure 1a. The internal TENG network with seven TENG units linked by rigid strings Figure 1. a) Schematic diagram of a single spherical TENG unit with spring-assisted multilayered structure, and schematic representation for local enlarged structure of the multilayered TENG with seven basic units. b) Working principle of each TENG unit of the spherical TENG. c) Schematic diagram of the hexagonal TENG network with seven TENG units linked by rigid strings floating on the water surface. The right side shows the top view of the network. d) Photograph of as-fabricated TENG network device on the water surface. e) Photograph of dozens of LEDs with a “TENG” pattern which are lighted up by the TENG network under the water wave motions. f) Framework for the integrated self-powered system driven by the water wave motions. Adv. Funct. Mater. 2019, 1807241 1807241 (2 of 8) © 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.advancedsciencenews.com www.afm-journal.de floating on the water surface. In the network, one unit locates as functions of the water wave frequency under the transverse in the center of the hexagon, and six units locate at the apexes of sinusoidal waves. The current and voltage were expected to the hexagon. The top view at the right side shows the structure be measured under the short-circuit condition and open-circuit details of string connections. Figure 1d shows the photograph condition, respectively. However, due to the internal imped- of as-fabricated TENG network device on the water surface. The ance of current preamplifier and internal resistance of digital seven spherical units are linked by cable ties and connected oscilloscope, we could not obtain the real short-circuit current electrically in parallel.