Facile Fabrication of Micro-Nano Structured Triboelectric Nanogenerator with High Electric Output

Zhang et al. Nanoscale Research Letters (2015) 10:298 DOI 10.1186/s11671-015-1001-5 NANO EXPRESS Open Access Facile Fabrication of Micro-Nano Structured Triboelectric Nanogenerator with High Electric Output Feifei Zhang, Baozhang Li, Jianming Zheng and Chunye Xu* Abstract In this article, a new method is used to fabricate a high-performance triboelectric nanogenerator (TENG), which is convenient and cost-effective. A polyformaldehyde (POM) film with novel structures is prepared through electrospinning and is combined with a polytetrafluoroethylene (PTFE) film to assemble micro-nano structured TENG. The short-circuit current (Is) and open-circuit voltage (Vo) of the TENG are up to 0.4343 mA and 236.8 V, respectively, and no significant change is observed by applying different frequencies of external impact forces from 1 to 10 Hz. Finally, we successfully drive an electrochromic device (ECD) directly using TENG within just 2 min for the first time. Keywords: Triboelectric nanogenerator; Electrospinning; Polyformaldehyde; Polytetrafluoroethylene; Electrochromic device PACS: 84.60.-h; 81.40.-z; 73.61.Ph Background Energy’s critical importance in social development and people’s lives is now universally recognized. A lot of technologies, such as photoelectric [1], pyroelectric [2], magnetoelectric [3], and piezoelectric [4], have been invented to collect energy in the environment, for example, in the form of light, heat, and motion. In recent years, triboelectricity is applied to a new type of generator named triboelectric nanogenerator (TENG) to harvest mechanical energy [5–9]. The TENG is efficient, flexible, and easy to fabricate, so it has aroused intense scholarly interest since its advent. Typically, TENG is multilayered, consisting of friction layers and electrode layers (Fig. 1). It mainly utilizes the static charges generated during tribological process to induce electricity between the electrodes. Compared to the untreated friction surface, the micro and nano friction surface improved the output of TENG as it increased the area of friction layers and resulted in the generation of more electrostatic charges on the friction layers [10, 11]. Various * Correspondence: CAS Key Lab of Soft Matter Chemistry, Department of Polymer Science and Engineering, Hefei National Laboratory for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei 230026, People’s Republic of China methods have been tried to modify the friction surface such as ion beam etching [12], silicon template [10], anodic aluminum oxide template [13], and synthesis and assembly of nanoparticles and nanowires [11, 14]. However, these methods are either complicated or costly. Electrospinning is one of the novel fiber fabrication techniques because it is easy to produce continuous polymer fibers with diameters ranging from several nanometers to micrometers [15–17]. Using electrospinning to prepare nanowire-based TENG simplifies the preparation process and reduces the cost [18]. In this article, we propose a facile method to fabricate high-output TENG by preparing a micro-nano structured polyformaldehyde (POM) film through electrospinning as one friction layer and utilizing a polytetrafluoroethylene (PTFE) film as the other, which not only simplifies the fabrication process but also enhances the electric output of TENG. The open-circuit voltage (Vo) of our prototype TENG reaches 236.8 V, and the short-circuit current (Is) is up to 0.4343 mA. Such high output current makes it sufficient to drive a homemade electrochromic device (ECD) directly. For these obvious advantages, TENG has potential application in the area of electronics, health care, and other practical applications. © 2015 Zhang et al. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly credited. Zhang et al. Nanoscale Research Letters (2015) 10:298 Page 2 of 6 Fig. 1 Schematic diagram of the TENG fabrication process Methods Characterization and Measurement Preparation of POM Film The morphologies of the electrospun POM film and untreated PTFE film were investigated using a field emission scanning electron microscope (FE-SEM) (JSM6700F, JEOL, Japan). The electric output of TENG was measured using a digital multimeter (34410A, Agilent Technologies, Inc., USA). The external impact forces were provided by a vibration exciter (Baofei Vibration Instrument Plant, China). To prepare the solution for electrospinning, 0.8 g POM (Yunnan Yuntianhua Co., Ltd., China) was dissolved into 9.2 g hexafluoroisopropanol (Aladdin Industrial Inc., China) in a 10-mL glass sample bottle [19]. The process was conducted by a NEU nanofiber electrospinning unit (Kato Tech Co., Ltd., Japan). One copper plate collector covered by aluminum foil was located 15 cm away from the needle tip of the syringe and was grounded. A high direct current voltage of 18 kV was applied between the needle tip and the copper plate collector, and the volumetric flow rate of the polymer solution was 0.8 mL/h. All the experiments were done at room temperature with a relative humidity of 55 %. The electrospinning process was finished after 4 h. The electrospun POM film was dried in a vacuum oven at room temperature overnight to remove the residual solvent. Fabrication of TENG The typical fabrication process of TENG is depicted in Fig. 1. First, a thin layer of gold (100 nm) was deposited on two pieces of polyethylene terephthalate (PET) films (4 × 4 cm) (Dongguan Chang’an Chaoyuan Film Co., Ltd., China) by a sputter coater. Second, each PET film is adhered with a layer of double-sided adhesive tape on the gold side. Third, the PTFE film (4 × 4 cm) (Deqing Tonghe Plastics Research Institute, China) and electrospun POM film (4 × 4 cm) were respectively adhered onto the two arched PET films. Then, TENG was assembled by using adhesive tape to fix the two freshly prepared sheets along the straight sides with a width of 2 mm on each sheet. Results and Discussion Working Mechanism of TENG The working mechanism of TENG is illustrated in Fig. 2. In the initial state, each layer of TENG is electrically quasi-neutral. After applying external compressive force for the first time, the arched TENG is deformed. The top sheet contacts the bottom one, and friction takes place between the contact surfaces because of surface roughness in microscale. As a result, the friction surfaces carry opposite electrostatic charges which will not bleed off or be neutralized immediately since both the polymer films and air are insulative. When removing the external force, the TENG tends to recover to arched state and the friction surfaces move apart. Meanwhile, the electric potential between the two electrodes varies with the relative displacement of the oppositely charg (...truncated)