Serious climate changes and energy-related environmental problems are currently critical issues in the world. In order to reduce carbon emissions and save our environment, renewable energy harvesting technologies will serve as a key solution in the near future. Among them, triboelectric nanogenerators (TENGs), which is one of the most promising mechanical energy harvesters by means of contact electrification phenomenon, are explosively developing due to abundant wasting mechanical energy sources and a number of superior advantages in a wide availability and selection of materials, relatively simple device configurations, and low-cost processing. Significant experimental and theoretical efforts have been achieved toward understanding fundamental behaviors and a wide range of demonstrations since its report in 2012. As a result, considerable technological advancement has been exhibited and it advances the timeline of achievement in the proposed roadmap. Now, the technology has reached the stage of prototype development with verification of performance beyond the lab scale environment toward its commercialization. In this review, distinguished authors in the world worked together to summarize the state of the art in theory, materials, devices, systems, circuits, and applications in TENG fields. The great research achievements of researchers in this field around the world over the past decade are expected to play a major role in coming to fruition of unexpectedly accelerated technological advances over the next decade.
The development of triboelectric nanogenerators (TENGs) technology has advanced in recent years. However, TENG performance is affected by the screened-out surface charge density owing to the abundant free electrons and physical adhesion at the electrode-tribomaterial interface. Furthermore, the demand for flexible and soft electrodes is higher than that for stiff electrodes for patchable nanogenerators. This study introduces a chemically cross-linked (XL) graphene-based electrode with a silicone elastomer using hydrolyzed 3-aminopropylenetriethoxysilanes. The conductive graphene-based multilayered electrode was successfully assembled on a modified silicone elastomer using a cheap and eco-friendly layer-by-layer assembly method. As a proof-of-concept, the droplet-driven TENG with the chemically XL electrode of silicone elastomer exhibited an output power of approximately 2-fold improvement owing to its higher surface charge density than without XL. This chemically XL electrode of silicone elastomer film demonstrated remarkable stability and resistance to repeated mechanical deformations like bending and stretching. Moreover, due to the chemical XL effects, it was used as a strain sensor to detect subtle motions and exhibited high sensitivity. Thus, this cheap, convenient, and sustainable design approach can provide a platform for future multifunctional wearable electronic devices.
Recently, triboelectric nanogenerators (TENGs) have been widely utilized to address the energy demand of portable electronic devices by harvesting electrical energy from human activities or immediate surroundings. To increase the surface charge and surface area of negative TENGs, previous studies suggested several approaches such as micro-patterned arrays, porous structures, multilayer alignment, ion injections, ground systems and mixing of high dielectric constant materials. However, the preparation processes of these nanocomposite TENGs have been found to be complex and expensive. In this work, we report a simple, efficient and inexpensive modification of poly(dimethylsiloxane) (PDMS) using graphene nanoplatelets (GNPs) fillers and a Na2CO3 template. This GNP-PDMS was chemically bonded using 3-aminopropylethoxysilane (APTES) as a linker with an electrode multilayer made by layer-by-layer deposition of polyvinyl alcohol (PVA) and poly(4-styrene-sulfonic acid) (PSS)-stabilized GNP (denoted as [PVA/GNP-PSS]n). A 33 wt.% Na2CO3 and 0.5 wt.% of GNP into a PDMS-based TENG gives an open-circuit voltage and short-circuit current density of up to ~270.2 V and ~0.44 µA/cm2, which are ~8.7 and ~3.5 times higher than those of the pristine PDMS, respectively. The higher output performance is due to (1) the improved surface charge density, 54.49 µC/m2, from oxygen functional moieties of GNP, (2) high surface roughness of the composite film, ~0.399 µm, which also increased the effective contact area, and (3) reduced charge leakage from chemical bonding of GNP-PDMS and [PVA/GNP-PSS]3 via APTES. The proposed TENG fabrication process could be useful for the development of other high-performance TENGs.
