Single-Electrode Triboelectric Nanogenerators Based on Ionic Conductive Hydrogel for Mechanical Energy Harvester and Smart Touch Sensor Applications

Recent advancements in wearable electronic technology demand advanced power sources to be flexible, deformable, durable, and sustainable. An ionic-solution-modified conductive hydrogel-based triboelectric nanogenerator (TENG) has advantages in wearable devices. However, fabricating a conductive hydrogel with better mechanical and electrical properties is still a challenge. Herein, a simple approach is developed to insert ion-rich pores inside the hydrogel, followed by ionic solution soaking. The suggested ionic conductive hydrogel is obtained by cross-linking the polyvinyl alcohol (PVA) hydrogel and carboxymethyl cellulose sodium salt (CMC), followed by soaking in the ionic solution. Furthermore, a flexible and shape-adaptable single-electrode TENG (S-TENG) is fabricated by combinations of ionic-solution-modified dual-cross-linked CMC/PVA hydrogel and silicone rubber. Additionally, the effects of the CMC concentration, type of ionic solution, and concentration of optimized ionic solutions on the hydrogel properties and S-TENG output performance are studied systematically. The well-dispersed CMC- and PVA-based hydrogel provides ion-rich pores with high ion migration, leading to enhanced conductivity. The fabricated S-TENG delivers maximum output performance in terms of voltage, current, and charge density of ∼584 V, 25 μA, and 120 μC/m², respectively. The rectified S-TENG-generated energy is used to charge capacitors and to power a portable electronic display. In addition to energy harvesting, the S-TENG is successfully demonstrated as a touch sensor that can automatically control the light and the speaker based on human motions. This investigation provides a deep insight into the influence of the hydrogel on the device performance and gives a guidance for designing and fabrication of highly flexible and stretchable TENGs.

Multistage SrBaTiO3 /PDMS Composite Film-Based Hybrid Nanogenerator for Efficient Floor Energy Harvesting Applications

Triboelectric nanogenerators are an emerging energy-scavenging technology that can harvest kinetic energy from various mechanical moments into electricity. The energy generated while humans walk is the most commonly available biomechanical energy. Herein, a multistage consecutively-connected hybrid nanogenerator (HNG) is fabricated and combined with a flooring system (MCHCFS) to efficiently harvest mechanical energy while humans walk. Initially, the electrical output performance of the HNG is optimized by fabricating a prototype device using various strontium-doped barium titanate (Ba_{1- x} Sr_x TiO₃ , BST) microparticles loaded polydimethylsiloxane (PDMS) composite films. The BST/PDMS composite film acts as a negative triboelectric layer that operates against aluminum. Single HNG operated in contact-separation mode could generate an electrical output of ≈280 V, ≈8.5 µA, and ≈90 µC m^-2 . The stability and robustness of the fabricated HNG are confirmed and eight similar HNGs are assembled in a 3D-printed MCHCFS. The MCHCFS is specifically designed to distribute applied force on the single HNG to four nearby HNGs. The MCHCFS can be implemented in real-life floors with an enlarged surface area to harvest energy generated while humans walk into direct current electrical output. The MCHCFS is demonstrated as a touch sensor that can be utilized in sustainable path lighting to save enormous electricity waste.

Eco-friendly pectin polymer film-based triboelectric nanogenerator for energy scavenging

Inspired by the desire to solve the energy-related issues in remote sensing applications, internet of things, wireless autonomous devices, and self-powered portable electronic devices, triboelectric nanogenerators (TENGs) have been highly promoted. However, for use in the specified applications, especially in wearable and biomedical devices, environmental-friendly materials are required. Herein, an eco-friendly pectin polymer is used as a positive triboelectric material to fabricate a TENG with excellent output performance. Working in conjunction with a polyimide, the polyimide and microarchitected pectin (MA@pectin) polymer film-based TENG (PP-TENG) generated open circuit voltage (V_OC), short circuit current (I_SC), and charge density (Q_SC) of ∼300 V, 14 μA, and 70 μC cm^-2, respectively, exhibiting remarkable enhancement compared to the TENG based on polyimide/pristine pectin polymer (V_OC, I_SC, and Q_SC of 170 V, 7.6 μA, and 47 μC cm^-2, respectively) under similar operating conditions. The output performance of the PP-TENG is particularly reliant on the pectin concentration, indicating an optimum concentration of 9 wt%. The improved performance of the PP-TENG was systematically analyzed and explained in terms of pectin concentration, dielectric constant, and surface roughness. Furthermore, the PP-TENG can power portable electronic devices and light-emitting diodes to prove the capability of the TENG in practical applications. The fabricated PP-TENG is anticipated to be a sustainable energy harvester via a low-cost and facile approach.

High-Efficiency Poly(Vinylidene Fluoride-Co-Hexafluoropropylene) Loaded 3D Marigold Flower-Like Bismuth Tungstate Triboelectric Films for Mechanical Energy Harvesting and Sensing Applications

Triboelectric nanogenerators (TENGs) are one of the most trending energy harvesting devices because of their efficient and simple mechanism in harvesting mechanical energy from the environment into electricity. Herein, ferroelectric and dielectric bismuth tungstate (Bi₂ WO₆ (BWO)) with a marigold flower-like structure is prepared via a hydrothermal method, which is embedded in poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), forming a PVDF-HFP/BWO composite polymer film (CPF) to fabricate TENGs. Generally, the ferroelectric materials exhibit a large piezoelectric coefficient, high electrostatic dipole moment, and high dielectric constant. The prepared PVDF-HFP/BWO CPF reveals a high polar crystalline β-phase which leads to enhanced piezoelectric and ferroelectric properties of the CPF, thus resulting in the increased electrical performance of the fabricated TENG. The electrical output performance of the proposed TENG is systematically investigated by varying the amount of BWO material embedded in the PVDF-HFP polymer. The fabricated PVDF-HFP/2.5 wt% BWO CPF-based TENG device exhibits the highest electrical output performance. Additionally, the robust test of the TENG device is conducted to investigate the electrical performance for long-term durability and mechanical stability. Finally, the proposed TENG is operated as a self-powered sensor, harvesting mechanical energy from daily life human activities, and powering various low-power portable electronics.

LiTaO3-Based Flexible Piezoelectric Nanogenerators for Mechanical Energy Harvesting

Mechanical energy is one of the freely available green energy sources that could be harvested to meet the small-scale energy demand. Piezoelectric nanogenerators can be used to harvest the biomechanical energy that is available in everyday human life and power various portable electronics. Herein, a ferroelectric material, i.e., lithium tantalate (LiTaO₃), was synthesized and used to fabricate a flexible piezoelectric nanogenerator (FPNG). Generally, ferroelectric materials display a strong electrostatic dipole moment and high piezoelectric coefficient, thus resulting in enhanced electrical performance. First, LiTaO₃ nanoparticles were synthesized and loaded into poly(vinylidene difluoride) (PVDF) to form a piezoelectric film and then, the piezoelectric composite film was sandwiched between two aluminum electrodes to fabricate an FPNG. The effect of the electrical performance of FPNG as a function of the concentration of LiTaO₃ loaded into PVDF was systematically investigated and optimized. The 2.5 wt % FPNG exhibited open-circuit voltage, short-circuit current, and power density values of ∼18 V, ∼1.2 μA, and ∼25 mW/m², respectively. Furthermore, the FPNG revealed good electrical stability and mechanical durability. Finally, the FPNG was employed as a weight sensor to harvest various biomechanical energies and operate low-power- electronics.