Interface Engineering for Efficient Raindrop Solar Cell

High-Entropy Ceramics Enhanced Droplet Electricity Generator for Energy Harvesting and Bacterial Detection

The droplet electricity generator (DEG) is a solid-liquid triboelectric nanogenerator with transistor-inspired bulk effect, which is regarded as an effective strategy for raindrop energy harvesting. However, further enhancement of DEG output voltage is necessary to enable its widespread applications. Here, high-entropy ceramics are integrated into the design of DEG intermediate layer for the first time, achieving a high output voltage of 525 V. High-entropy ceramics have colossal dielectric constant, which can help to reduce the triboelectric charge decay for DEG. Furthermore, the effect of factors on DEG output performance when employing high-entropy ceramics as the intermediate layer is extensively analyzed, and the underlying mechanisms and mathematical models are explored. Finally, the enhanced output voltage of DEG not only facilitates faster energy harvesting but also develops a novel method for rapid bacterial detection. This work successfully integrates high-entropy ceramics into DEG design, significantly enhances the output voltage, and offers a novel direction for DEG development.

Droplet Energy Harvesting System Based on Total-Current Nanogenerator

The droplet-based nanogenerator (DNG) is a highly promising technology for harvesting high-entropy water energy in the era of the Internet of Things. Yet, despite the exciting progress made in recent years, challenges have emerged unexpectedly for the AC-type DNG-based energy system as it transitions from laboratory demonstrations to real-world applications. In this work, we propose a high-performance DNG system based on the total-current nanogenerator concept to address these challenges. This system utilizes the water-charge-shuttle architecture for easy scale-up, employs the field effect to boost charge density of the triboelectric layer, adopts an on-solar-panel design to improve compatibility with solar energy, and is equipped with a novel DC-DC buck converter as power management circuit. These features allow the proposed system to overcome the existing bottlenecks of DNG and empower the system with superior performances compared with previous ones. Notably, with the core architecture measuring only 15 cm × 12.5 cm × 0.3 cm in physical dimensions, this system reaches a record-high open-circuit voltage of 4200 V, capable of illuminating 1440 LEDs, and can charge a 4.7 mF capacitor to 4.5 V in less than 24 min. In addition, the practical potential of the proposed DNG system is further demonstrated through a self-powered, smart greenhouse application scenario. These demonstrations include the continuous operation of a thermohygrometer, the operation of a Bluetooth plant monitor, and the all-weather energy harvesting capability. This work will provide valuable inspiration and guidance for the systematic design of next-generation DNG to unlock the sustainable potential of distributed water energy for real-world applications.

The regulation and its application of the charge decay rate in triboelectric nanogenerator

The decay rate of charge in the friction layer is one of the key factors affecting the output performance of triboelectric nanogenerators (TENG). Reducing the decay rate of the triboelectric charge can increase the charge-carrying capacity of the friction layer and improve the output current and voltage of the TENG. This makes a friction generator more suitable for discontinuous driving environments. In contrast, increasing the decay rate of the charge in the friction layer can greatly improve the recovery time of the device, although it reduces the output performance of the generator. This is conducive to the application of friction generator in the field of sensors. In this study, polystyrene (PS) and carbon nanotubes (CNTs) were added to polyvinylidene fluoride (PVDF) nanofibers to adjust the charge decay time in the friction layer, thereby regulating the output performance of the friction generator and sensor. When the amount of added PS in the PVDF nanofiber reached 20%, the charge density on the friction surface increased by 1.9 times, and the charge decay time decreased by 64 times; when 0.1 wt% CNTs were added in the PVDF nanofiber, the charge decay time increased by more than 10 times. The former is more conducive to improving the power generation performance of the TENG, and the latter significantly improves the stability and repeatability of TENG-based sensors.

Polynary energy harvesting and multi-parameter sensing in the heatwave environment of industrial factory buildings by an integrated triboelectric-thermoelectric hybrid generator

Taking advantage of a hybrid generator to simultaneously collect polynary energy from a single energy source provides a feasible solution for the energy dilemma in the new era. Herein, we integrate a triboelectric nanogenerator and a thermoelectric generator for polynary energy harvesting and self-powered sensing of heatwaves in large-scale industrial factory buildings, which contains both thermal energy and wind energy. The new design of the fan-shaped rotation triboelectric nanogenerator (FR-TENG) makes it more compact and easily integrated. After structure modeling, the energy conversion efficiency of the FR-TENG can reach a maximum of 37.2%, which can successfully power a Bluetooth hygrothermograph transmitting environmental information wirelessly every 30 s at a wind speed of 4.67 m s-1. An all-inorganic flexible thermoelectric generator (iThEG) is developed based on copper and constantan with an output power density of 0.73 W m-3, and maintains its original mechanical properties after 10 000 bending tests. Moreover, a self-powered hot wind sensing system based on Labview is established which can display wind-speed and wind-temperature in real time. The working concept presented here is also applicable to other single energy sources containing multiple energy forms, such as falling raindrops and sunlight, which can lift energy utilization and conversion efficiency and alleviate the energy crisis.

Wood Lamella-Inspired Photothermal Stearic Acid-Eutectic Gallium-Indium-Based Phase Change Aerogel for Thermal Management and Infrared Stealth

Eutectic Gallium-Indium (EGaIn) liquid metal is an emerging phase change metal material, but its low phase transition enthalpy and low light absorption limit its application in photothermal phase change energy storage materials (PCMs) field. Here, based on the dipole layer mechanism, stearic acid (STA)-EGaIn-based PCMs which exhibit extraordinary solar-thermal performance and phase change enthalpy are fabricated by ball milling method. The wood lamella-inspired cellulose-derived aerogel and molybdenum disulfide (MoS2 ) are used to support the PCMs by the capillary force and decrease the interfacial thermal resistance. The resulted PCMs achieved excellent photothermal conversion performance and leakage proof. They  have excellent thermal conductivity of 0.31 W m-1 K-1 (this is increased by 138% as compared with pure STA), and high phase change enthalpy of187.50 J g-1 , which is higher than the most of the reported PCMs. Additionally, the thermal management system and infrared stealth materials based on the PCMs are developed. This work provides a new way to fabricate smart EGaIn-based PCMs for energy storage device thermal management and infrared stealth.

Standardized Volume Power Density Boost in Frequency-Up Converted Contact-Separation Mode Triboelectric Nanogenerators

The influence of a mechanical structure's volume increment on the volume power density (VPD) of triboelectric nanogenerators (TENGs) is often neglected when considering surface charge density and surface power density. This paper aims to address this gap by introducing a standardized VPD metric for a more comprehensive evaluation of TENG performance. The study specifically focuses on 2 frequency-up mechanisms, namely, the integration of planetary gears (PG-TENG) and the implementation of a double-cantilever structure (DC-TENG), to investigate their impact on VPD. The study reveals that the PG-TENG achieves the highest volume average power density, measuring at 0.92 W/m3. This value surpasses the DC-TENG by 1.26 times and the counterpart TENG by a magnitude of 69.9 times. Additionally, the PG-TENG demonstrates superior average power output. These findings introduce a new approach for enhancing TENGs by incorporating frequency-up mechanisms, and highlight the importance of VPD as a key performance metric for evaluating TENGs.

Triboelectric Nanogenerator for Droplet Energy Harvesting Based on Hydrophobic Composites

Triboelectric nanogenerators (TENG) have shown great potential in harvesting energy from water. For the TENG that harvests water energy, surface hydrophobicity is crucial for its performance. In this paper, we prepare a hydrophobic composite film of Polyvinylidene Fluoride/Polydimethylsiloxane/Polytetrafluoroethylene (PVDF/PDMS/PTFE) and an electrode of Polyaniline/Carbon nanotubes/Silver nanowires (PANI/CNTs/AgNWs) by electrospinning technology and a doping method, respectively, which are served as the friction layer and top electrode of TENG. The contact angle of the hydrophobic film and electrode both reach over 120°, which makes the separation process between water and the interface complete and promotes the output of TENG. The open-circuit voltage (Voc) and short-circuit current (Isc) can reach 150 V and 60 μA approximately. In addition, the composite electrode can be applied in the preparation of complex electrode shapes. Furthermore, the different reactions of TENG to different liquids indicate that it may contribute to liquid-type sensing systems. This work presents an efficient approach to fabricating hydrophobic films and electrodes, laying a foundation for the development of TENG for harvesting water energy.

A Liquid Triboelectric Series

The triboelectric series is a generally accepted method for describing the triboelectric effect. It provides a way to control the double face of the ubiquitous triboelectric effect: causes of unpredictable accidents and the resultant surface charge as energy sources. However, previous studies have been biased in solids despite being observed in liquids (liquid-solid contact electrification). Therefore, a liquid triboelectric series is necessary to be established to manipulate the liquid triboelectric effect according to the appropriate goal. In this study, a liquid triboelectric series is first established to describe the triboelectric properties of each liquid when contact electrification occurs with a solid surface. The liquid triboelectric series covers electrolytes, organic solvents, oxidants, and higher sugar alcohols. Common chemical groups can be derived from the liquid triboelectric series that hydroxyl groups enhance, and benzene groups suppress the liquid triboelectric effect. The results are demonstrated by the amplified efficiency of an energy harvester and particle contamination after surface washing. This study will play a pivotal role in understanding the liquid-solid contact electrification phenomenon and providing new perspectives on the applications of the liquid triboelectric effect.

Triboelectric Nanogenerator-Based Near-Field Electrospinning System for Optimizing PVDF Fibers with High Piezoelectric Performance

Electrospinning is an effective method to prepare polyvinylidene fluoride (PVDF) piezoelectric fibers with a high-percentage β phase. However, as an energy conversion material for micro- and nanoscale diameters, PVDF fibers have not been widely used due to their disordered arrangement prepared by traditional electrospinning. Here, we designed a near-field electro-spinning (NFES) system driven by a triboelectric nanogenerator (TENG) to prepare PVDF fibers. The effects of five important parameters (PVDF concentration, needle inner diameter, TENG pulse DC voltage (TPD-voltage), flow rate, and drum speed) on the β phase fraction of PVDF fiber were optimized one by one. The results showed that the electrospun PVDF fibers had uniform diameter and controllable parallel arrangement. The β phase content of the optimized PVDF fiber reached 91.87 ± 0.61%. For the bending test of a single PVDF fiber piezoelectric device, when the strain is 0.098%, the electric energy of the single PVDF fiber device of NFES reaches 7.74 pJ and the energy conversion efficiency reaches 13.5%, which is comparable to the fibers prepared by the commercial power-driven NFES system. In 0.5 Hz, the best matching load resistance of a PVDF single fiber device is 10.6 MΩ, the voltage is 6.1 mV, and the maximum power is 3.52 pW. Considering that TENG can harvest micromechanical energy in the low frequency environment, the application scenario of the NFES system can be extended to the wild or remote mountainous areas without traditional high-voltage power supply. Therefore, the electrospun PVDF fibers in this system will have potential applications in high-precision 3D fabrication, self-powered sensors, and flexible wearable electronic products.

Bioinspired Micro/Nanostructured Polyethylene/Poly(Ethylene Oxide)/Graphene Films with Robust Superhydrophobicity and Excellent Antireflectivity for Solar-Thermal Power Generation, Thermal Management, and Afterheat Utilization

The rational utilization and circulation of multiple energy sources is an effective way to address the crises of energy shortages and environmental pollution. Herein, microextrusion compression molding, an industrialized polymer molding technology that combines melt blending and compression molding, is proposed for the mass production of a bioinspired micro/nanostructured polyethylene/poly(ethylene oxide)/graphene (MN-PPG) film. The MN-PPG film exhibits robust shape stability, high storage energy density, and excellent thermal management capability owing to the cocontinuous network formed by poly(ethylene oxide) and the polyethylene matrix. The MN-PPG film has sufficient photothermal property due to the uniformly dispersed graphene nanosheets and the bioinspired surface micro/nanostructures. Interestingly, the MN-PPG film surface exhibits durable superhydrophobicity, acid/alkali resistance, and active deicing performance. Further, a multifunctional energy harvesting and circulation system was established by integrating the MN-PPG film, an LED chip, and a thermoelectric module. The hybrid system produced an open-circuit voltage of 315.4 mV and power output of 2.5 W m^-2 under 3 sun irradiation. Furthermore, the afterheat generated by the LED chips at night can be converted into electricity through thermoelectric conversion. The proposed method enables the large-scale fabrication of multifunctional phase change composites for energy harvesting in harsh environments.

Nanofiber-Enhanced "Lucky-Bag" Triboelectric Nanogenerator for Efficient Wave Energy Harvesting by Soft-Contact Structure

Developing clean and renewable ocean wave energy is a top priority and an effective way to achieve carbon neutrality. Triboelectric nanogenerators (TENGs) have emerged as promising green and clean energy-harvesting devices. To harvest low-frequency wave energy efficiently, much effort has been made on the modification of the contact surface, which leads to a higher fabrication cost. In this work, we designed a novel "Lucky-Bag" core (LBC) for spherical TENGs with a low-cost and easy fabricating process. The nanofiber/silicone hybrid porous outer layer of the LBC can switch freely from plane to surface and improve the output performance of both the plane and spherical TENGs. Several factors, such as the input frequency, direction, and resistive load, together with the thickness were systematically investigated; the unique porous soft-contact structure increased the triboelectric contact area, and the working mechanism was studied by using the COMSOL software. The experimental results showed that the peak-to-peak open-circuit voltage (Voc) and short-circuit current (Isc) could reach 580 V and 23.5 μA at 1.5 Hz, even under 2D linear motion. Besides, the maximum output power of the spherical TENGs reached 9.10 mW, which can fully power electronic devices such as capacitors and LEDs under water wave triggering. These findings provide useful guidance for optimizing the performance of spherical TENGs for practical applications in harvesting water wave energy.