Enhancing the Output of Liquid-Solid Triboelectric Nanogenerators through Surface Roughness Optimization

Research on the Superlubricity of Lotus Root Starch/Carbon Nanotube Composite Water-Based Lubricant

Lubricants are widely used in the mechanical, electronic, and medical fields; however, traditional mineral oil-based lubricants cause environmental pollution. Therefore, the search for renewable, nontoxic, and environmentally friendly lubricants has become a current research focus. In this study, a lotus root starch (LRS)/carbon nanotube (CNT) composite water-based lubricant was introduced into a lotus root starch water-based lubricant, and frictional experiments were conducted using a GCr15-SiC ball-on-disk tribopair. Additionally, by investigating the formation mechanism of the polarization electric field between friction pairs, the enhancing effect of the lotus root starch particles and CNTs in the composite lubricant on the polarization electric field was explored. Finally, the lubrication and friction reduction mechanisms of the lotus root starch/CNT composite water-based lubricant were elaborated in detail. The results showed that the LRS2.5%/0.075%CNT lubricant exhibited excellent superlubricity under medium- and high-speed conditions (1200 and 1800 rpm, respectively), with a friction coefficient as low as 0.004-0.005. Furthermore, the lubricant showed good robustness during the 120 min experiment and could enter the superlubricity stage within a short running-in period (180 s). A study of the polarization electric field at the interface revealed that the LRS2.5%/0.075%CNT composite lubricant promoted the formation of a polarization electric field on mutually repulsive friction surfaces, significantly enhancing the load-bearing capacity of the tribopair. The findings of this study provide an important reference for the development of green lubricants with significant environmental benefits and application value.

A high recognition accuracy tactile sensor based on boron nitride nanosheets/epoxy composites for material identification

Tactile sensors based on triboelectric nanogenerators (TENGs) showed great potential for self-driven sensing in material identification. The existing TENG devices used strongly electrophilic materials as friction layers. For test materials with electrophilicity, their output signals are weak and difficult to efficiently recognize. Here, a TENG-based sensor with boron nitride nanosheets/waterborne epoxy (BNNSs/WEP) composites as the friction layer was proposed for improving the accuracy of identifying negative charged materials. During the process of contact friction with negative charged objects, the as-fabricated TENG device displayed excellent output performance, with a maximum output voltage of 2.7 V and a charge density of 88.32 nC m-2. Combining deep machine learning and the friction electric effect, we developed a material recognition system for TENG sensors with integrated fatigue testing, data processing, and display modules. Following the training of the convolutional neural network (CNN) model with friction electrical signals generated by TENGs, the model demonstrated high accuracy in recognizing eight different materials, with a confusion matrix accuracy of 100%. Then, a sensor was developed for real-time device monitoring, with recognition accuracy of 100%, 100%, 55% and 49% for four kinds of materials. This work will further facilitate the development of a material perception system in the machine intelligence field.

Bimodal Droplet-Based Electricity Generation Through Semi Cassini Oval Dynamic Morphology Control

Droplet-based electricity generator (DEG) is the promising energy harvesting technology applicable in versatile scenarios. Despite numerous optimizations in DEG's materials and structures, few has paid attention to the droplet dynamics and morphology control. Here the droplet's spread-retraction dynamics and the resultant semi Cassini oval (SCO) morphology are reported, characterized by convex at both ends and concave in the middle. The lifted top electrode (LTE) is designed to respond to the dynamic SCO morphology in two steps: 1) LTE first contacts the leading edge of the spreading droplet, generating a negative voltage peak; 2) LTE second contacts the trailing edge of the retracting droplet, generating a positive voltage peak. In this way, bimodal electrical output is obtained, which exhibits 25% increase in peak-to-peak voltage and 33% increase in average power compared to the traditional DEG with only one voltage peak. These results prove that incorporating the droplet dynamics and morphology control into DEG design uplifts the energy harvesting limit from individual droplet. The proposed LTE-DEG inspires alternative route for DEG power enhancement by maximizing energy utilization of individual droplet from the perspective of droplet dynamic morphology design.

Water-Triboelectrification-Complemented Moisture Electric Generator

Energy harvesting from ubiquitous natural water vapor based on moisture electric generator (MEG) technology holds great potential to power portable electronics, the Internet of Things, and wireless transmission. However, most devices still encounter challenges of low output, and a single MEG complemented with another form of energy harvesting for achieving high power has seldom been demonstrated. Herein, we report a flexible and efficient hybrid generator capable of harvesting moisture and tribo energies simultaneously, both from the source of water droplets. The moisture electric and triboelectric layers are based on a water-absorbent citric acid (CA)-mediated polyglutamic acid (PGA) hydrogel and porous electret expanded polytetrafluoroethylene (E-PTFE), respectively. Such a waterproof E-PTFE film not only enables efficient triboelectrification with water droplets' contact but also facilitates water vapor to be transferred into the hydrogel layer for moisture electricity generation. A single hybrid generator under water droplets' impact delivers a DC voltage of 0.55 V and a peak current density of 120 μA cm-2 from the MEG, together with a simultaneous AC output voltage of 300 V and a current of 400 μA from the complementary water-based triboelectric generator (TEG) side. Such a hybrid generator can work even under harsh wild environments with 5 °C cold and saltwater impacts. Significantly, an optical alarm and wireless communication system for wild, complex, and emergency scenarios is demonstrated with power from the hybrid generators. This work expands the applications of water-based electricity generation technologies and provides insight into harvesting multiple potential energies in the natural environment with high output.

Exploring Wettability: A Key to Optimizing Liquid-Solid Triboelectric Nanogenerators

Nowadays, the liquid-solid triboelectric nanogenerator (L-S TENG) has gained much attention among researchers because of its ability to be a part of self-powering technology by harvesting ultra-low-frequency vibration in the environment. The L-S TENG works with the principle of contact electrification (CE) and electrostatic induction, in which CE takes place between the solid and liquid. The exact mechanism behind the CE at the L-S interface is still a debatable topic because many physical parameters of both solid and liquid triboelectric layers contribute to this process. In the L-S TENG device, water or solvents are commonly used as liquid triboelectric layers, for which their wettability over the solid triboelectric layer plays a significant role. Hence, this review is extensively focused on the influence of the wettability of solid surfaces on the CE and the corresponding impact on the output performance of L-S TENGs. The present review starts with introducing the L-S TENG, a mechanism that contributes to CE at the L-S interface, the significance of hydrophobic materials/surfaces in TENG devices, and their fabrication methods. Further, the impact of the contact angle over the electron/ion transfer over various surfaces has been extensively analyzed. Finally, the challenges and future prospects of the fabrication and utilization of superhydrophobic surfaces in the context of L-S TENGs have been included. This review serves as a foundation for future research aimed at optimizing the L-S TENG performance and inspiring new approaches in material design and multifunctional energy-harvesting systems.

Harnessing Natural Evaporation for Electricity Generation using MOF-Based Nanochannels

Functionalized nanochannels can convert environmental thermal energy into electrical energy by driving water evaporation. This process involves the interaction between the solid-liquid interface and the natural water evaporation. The evaporation-driven water potential effect is a novel green environmental energy capture technology that has a wide range of applications and does not depend on geographical location or environmental conditions, it can generate power as long as there is water, light, and heat. However, suitable materials and structures are needed to harness this natural process for power generation. MOF materials are an emerging field for water evaporation power generation, but there are still many challenges to overcome. This work uses MOF-801, which has high porosity, charged surface, and hydrophilicity, to enhance the output performance of evaporation-driven power generation. It can produce an open circuit voltage of ≈2.2 V and a short circuit current of ≈1.9 µA. This work has a simple structure, easy preparation, low-cost and readily available materials, and good stability. It can operate stably in natural environments with high practical value.

Microalgae Film-Derived Water Evaporation-Induced Electricity Generator with Negative Carbon Emission

Water evaporation-induced electricity generators (WEGs) are regarded as one of the most promising solutions for addressing the increasingly severe environmental pollution and energy crisis. Owing to the potential carbon emission in the preparation process of WEGs, whether WEG represents a clean electricity generation technology is open to question. Here, a brand-new strategy is proposed for manufacturing negative carbon emission WEG (CWEG). In this strategy, the microalgae film is used as the electricity generation interface of WEG, which achieves a stable open-circuit voltage (Voc) of 0.25 V and a short-circuit current (Isc) of 3.3 µA. Since microalgae can capture carbon dioxide during its growing process, CWEG holds great promise to generate electricity without carbon emissions in the full life cycle compared with other WEGs. To the best of the author's knowledge, this is the first work using microalgae films to fabricate WEG. Therefore, it is believed that this work not only provides a new direction for designing high-efficiency and eco-friendly WEG but also offers an innovative approach to the resource utilization of microalgae.