Three-dimensional graphene foam based triboelectric nanogenerators
Highlights
- Graphene foam presents unique mechanical-to-electrical energy conversion features.
- Triboelectric nanogenerators based on graphene foam exhibit record output powers.
- Distance dependent model allows the calculation of triboelectric charge density.
- Triboelectric nanogenerators play a key role in self-powered pressure sensing mats.
- Self-powered pressure mats are utilised to monitor anonymously room occupancy.
Abstract
In this work we investigate the potential of three-dimensional graphene (3DG) foam as an active layer in triboelectric nanogenerators (TENGs) and as an energy harvesting power source for autonomous sensors. A series of comprehensive measurements have been carried out to test the output characteristics of 3DG-TENG under cyclic mechanical stimulus, capable of operating TENG in contact-separation mode at different frequencies, gap distances between electrodes, and applied pressures. The triboelectric response of 3DG-TENG (with an effective surface of 16 cm2) showed maximum open-circuit voltage (Voc) and short-circuit current (Isc) of 400 V and 105.7 μA respectively when stimulated at 3 Hz (contact-separation frequency) and 70 mm (optimum gap distance). Under the same conditions, a maximum output power (Pout) of around 10.37 W/m2 is produced using an external load resistance of 40 MΩ; this is an order of magnitude lower resistance than that needed with other graphene based TENG variants. 3DG-TENG exhibited great stability in the output characteristics with 15,000 cyclic mechanical stimuli and a retention percentage in Pout above 95%. This is a significant improvement with respect to other carbon based TENG`s, which show enhanced deterioration of TENG performance due to material transfer between electrodes and plastic deformation of triboelectric materials. Simulations of TENG Voc using distance dependent model determined high triboelectric charge densities in the range of mC/m2. Here, we also demonstrate the potential of 3DG-TENG as an energy supply for energy storage devices, and as an active layer in an autonomous pressure sensing platform for anonymous room occupancy monitoring in smart buildings.
Introduction
The great advances achieved in 5G communication, and the successful miniaturisation of sensors and electronics have boosted the rapid development of the so-called Internet of Things (IoT) [1]. IoT devices and the new concepts of Internet of Everything (IoE) and Internet of Nano Things (IoNT) devices are planned to be utilised in a large range of sectors, including point-of-care health monitoring, mobile devices, navigation, automobiles, smart buildings, and manufacturing industry (Fig. 1) [2]. In 2020, the number of IoT devices interlinked worldwide reached around 10 billion, with a forecast for 2030 to have more than 100 billion IoT devices [3]. The high cost of electricity and incremental energy demand from IoT devices require new green energy sources, high efficiency energy harvesting & storing systems and low-power consumption (or batteryless self-powered/ autonomous) sensors [4], [5]. This strategy will prevent the constant replacement of batteries in trillions of devices [6], and will reduce the utilisation of wires, making the IoT technology of the near future to be wireless and energy autonomous.