Strategies to Improve the Output Performance of Triboelectric Nanogenerators

Triboelectric nanogenerators (TENGs) can collect and convert random mechanical energy into electric energy, with remarkable advantages including broadly available materials, straightforward preparation, and multiple applications. Over the years, researchers have made substantial advancements in the theoretical and practical aspects of TENG. Nevertheless, the pivotal challenge in realizing full applications of TENG lies in ensuring that the generated output meets the specific application requirements. Consequently, substantial research is dedicated to exploring methods and mechanisms for enhancing the output performance of TENG devices. This review aims to comprehensively examine the influencing factors and corresponding improvement strategies of the output performance based on the contact electrification mechanism and operational principles that underlie TENG technology. This review primarily delves into five key areas of improvement: materials selection, surface modification, component adjustments, structural optimization, and electrode enhancements. These aspects are crucial in tailoring TENG devices to meet the desired performance metrics for various applications.

Improving the Performance of Polydimethylsiloxane-Based Triboelectric Nanogenerators by Introducing CdS Particles into the Polydimethylsiloxane Layer

Energy harvesting and power generation technologies hold significant potential for meeting future energy demands and improving environmental sustainability. A triboelectric nanogenerator (TENG), which harnesses energy from the surrounding environment, has garnered significant attention as a promising and sustainable power source applicable in various fields. In this study, we present a technique to improve the triboelectric performance of a PDMS-based TENG by incorporating nanostructured cadmium sulfide (N-CdS). This study investigates the utilization of CdS nanomaterials in TENG production, where mechanical energy is converted into electrical energy. We conducted a comparative analysis of TENGs utilizing N-CdS/PDMS, commercial CdS/PDMS (C-CdS/PDMS), and pure PDMS substrates. The N-CdS/PDMS substrates demonstrated superior triboelectric performance compared to TENG devices based on pure PDMS and C-CdS/PDMS. The triboelectric open-circuit voltage (Voc) and short-circuit current (Isc) of the N-CdS/PDMS-based TENG device were approximately 236 V and 17.4 µA, respectively, when operated at a 2 Hz frequency. These values were approximately 3 times and 2.5 times higher, respectively, compared to the pure PDMS-based TENGs. They were further studied in detail to understand the effect of different parameters such as contact-separation frequency and contact force on the TENGs' operation. The stability of the TENG devices was studied, and their potential to be integrated into self-powered smart textiles as power sources was demonstrated.

Influence of Molecular Structure and Material Properties on the Output Performance of Liquid-Solid Triboelectric Nanogenerators

With the advantages of superior wear resistance, mechanical durability, and stability, the liquid-solid triboelectric nanogenerator (LS-TENG) has been attracting much attention in the field of energy harvesting and self-powered sensors. However, most of the studies on LS-TENG focused on device innovations, changes in solid materials, and the effect of solid properties on output performance, and there is a lack of studies on liquids, especially at the molecular level. A U-tube LS-TENG was assembled to conduct experiments, whereby the effects of molecular structures, including molecular composition, carbon chain length, functional groups and material properties on the output performance were investigated. The deuterium replacing hydrogen and the atomic compositions could not achieve the enhancement of the output performance. Whether the chemical functional groups improve the output performance of LS-TENG depends on the mating solid material. Hydroxyl and cyanogenic groups can improve the output performance for the FEP case, while amide and cyanogenic groups can improve the output performance for the PTFE case. The order of output performances for functional groups of four groups of liquids with both FEP and PTFE materials is also obtained. It was also found that the dielectric constant is not positively correlated with the output performance. The results of this study might provide a reference for the deeper study and application of LS-TENG.

Innovative Design of Bismuth-Telluride-Based Thermoelectric Transistors

Conventional thermoelectric generators, predominantly based on the π-type structure, are severely limited in their applications due to the relatively low conversion efficiency. In response to the challenge, in this work, a Bi2Te3-based thermoelectric transistor driven by laser illumination is demonstrated. Under laser illumination, a temperature difference of 46.7 °C is produced between the two ends of the transistor structure. Further, the hole concentrations in each region redistribute and the built-in voltages decrease due to the temperature difference, leading to the formation of the transistor circuit. Additionally, the operation condition of the thermoelectric transistor is presented. The calculation results demonstrate that the maximum output power of such a designed thermoelectric transistor is 0.7093 μW.

Multi-criteria assessment and triple-objective optimization of a bio-anode microfluidic microbial fuel cell

Microfluidic microbial fuel cell has lower costs and greater potential than typical microbial fuel cell due to the elimination of proton exchange membrane. However, the development has mostly relied on experiments, and there has been little research on numerical simulations. Based on experimental validation, a reliable and universal model for microfluidic microbial fuel cell without quantifying the biomass concentration is proposed. Subsequently, the primary work is to study the output performance and energy efficiency of the microfluidic microbial fuel cell under different operating conditions and to comprehensively optimize the cell performance by employing the multi-objective particle swarm algorithm. Compared the optimal case with the base case, the increase ratios of maximum current density, power density, fuel utilization and exergy efficiency are 40.96%, 20.87%, 61.58% and 32.19%, respectively. On the basis of improving energy efficiency, the maximum power density and current density can reach 1.193 W/m² and 3.51 A/m².

Constructing A/B-Side Heterogeneous Asynchronous Structure with Ag2Se Layers and Bushy-like PPy toward High-Performance Flexible Photo-Thermoelectric Generators

The enthusiasm for environmental energy harvesting has triggered a boom in research on photo-thermoelectric generators (PTEGs), and the relevant applications are mainly focused on self-energy supply sensors owing to the limitations of their output performances. For this purpose, high-output hierarchical heterogeneous PTEGs were constructed by assembling separately optimized thermoelectric (TE) and photothermal (PT) layers. The pressure and temperature conditions of Ag2Se films during the pressing process were first explored, and the sample with the optimal performance and least defects was selected as the TE layer. At the same time, different morphologies of polypyrrole (PPy) PT layers were electrochemically synthesized. It is found that the three-dimensional structure of Bushy-PPy could effectively improve the light absorption and thus enhance the PT conversion performance. The final assembled PTEG can produce an output voltage of -9.03 mV and an output power of 3.53 μW under the irradiation of a near-infrared light source of 300 mW cm-2 without a cooling source, and it can also achieve considerable output power under visible light irradiation of different intensities. Combining its high retentions of electrical conductivity (99%) and output performance (97%) after 1000 bending-tension cycles, it is proven to be a promising next-generation wearable flexible energy harvesting device.

Boosting Output Performance of Triboelectric Nanogenerator via Mutual Coupling Effects Enabled Photon-Carriers and Plasmon

Boosting the output performance of triboelectric nanogenerators via some unique methods is always a meaningful way to speed up their commercialization. However, the available approach to boost performance is mainly restricted to one physics effect based and the basic research of boosting performance via mutual coupling effects is little research. Herein, a new strategy is creatively proposed based on charge traps from mutual coupling effects, generated from g-C3 N4 /MXene-Au composites, to further promote the output performance of triboelectric nanogenerator. It is found that photon-generated carriers coupling surface plasmon effect enables composites filled into tribo-material with visible light is an excellent value in boosting performance. The charge traps from mutual coupling effects for boosting performance are analyzed theoretically and verified by experiments. The output power of boosting-triboelectric nanogenerator (TENG) achieves a sixfold enhancement (20 mW) of normal TENG with polydimethylsiloxane (PDMS) in ambient conditions. This work provides a profound understanding of the working mechanism of mutual coupling effects boosting the performance of TENG and an effective way for promoting TENG output.

High-Performance Flexible Piezoelectric Nanogenerator Based on Specific 3D Nano BCZT@Ag Hetero-Structure Design for the Application of Self-Powered Wireless Sensor System

With the popularity of portable and miniaturized electronic devices in people's live, flexible piezoelectric nanogenerators (PENG) have become a research hotspot for harvesting energy from the living environment to power small-scale electronic equipment and systems because of its stability. For further enhancing output performance of PENG, chemical modification and structural design for piezoelectric fillers are effective ways. Thus, the 3D porous hetero-structure fillers of BCZT@Ag are prepared by freeze-drying method and subsequent chemical seeding reduction. The silicone rubber as matrix is filled into the micro-voids of fillers to prepare specialized composite. The charge transport mechanism and stress transfer efficiency in PENG can be effectively improved through specialized design which is proven by experimental results and multi-physics simulations. The improved PENG exhibit a significantly enhanced output of 38.6 V and 5.85 µA, which is 3.3 and 3.5 times higher than those of PENG without specific design. The prepared PENG can effectively harvest biomechanical energy through walk and joint bending of human body. Moreover, the PENG can be used as a trigger to remotely control wireless collision alarm system, which can acquire rapid response and shows great potential application in Internet of Things.

Low-Cost, Environmentally Friendly, and High-Performance Triboelectric Nanogenerator Based on a Common Waste Material

With the great progress in human activities and production technologies, the waste inevitably produced causes not only environmental pollution but also resource waste; meanwhile, the mobile and portable electronic devices urgently need a distributed and sustainable energy source to ensure their stable operation. Here, the waste pollutants (milk cartons) generated from daily life, commonly associated with environmental concerns, are instead identified as an available resource for preparing an emerging energy harvester (triboelectric nanogenerator, TENG), which can convert ubiquitous mechanical energy into electric power. Consequently, based on the waste material, the initial charge density of the TENG is as low as 0.035 mC m^-2, which can be tremendously improved to 1.00 mC m^-2 through combining a charge excitation circuit, achieving efficient energy harvesting. In addition, compared to the common dielectric film, the waste material can reduce the cost and simplify the process of the preparation of TENG. This work provides not only an innovative approach to simultaneously realize environmental protection and energy harvesting but also more material choice for the preparation of a low-cost and high-performance TENG.

All-Fiber-Structured Triboelectric Nanogenerator via One-Pot Electrospinning for Self-Powered Wearable Sensors

With the rapid development in wearable electronics, self-powered devices have recently attracted tremendous attention to overcome the restriction of conventional power sources. In this regard, a simple, scalable, and one-pot electrospinning fabrication technique was utilized to construct an all-fiber-structured triboelectric nanogenerator (TENG). Ethyl cellulose was co-electrospun with polyamide 6 to serve as the triboelectric positive material, and a kind of strongly electronegative conductive material of MXene sheet was innovatively incorporated into poly(vinylidene fluoride) nanofiber to act as a triboelectric negative material. The assembled all-fiber TENG exhibited excellent durability and stability, as well as excellent output performance, which reached a peak power density of 290 mW/m² at a load resistance of 100 MΩ. More importantly, the TENG was capable of harvesting energy to power various light-emitting diodes (LEDs) and monitoring human movements as a self-powered sensor, providing a promising application prospect in wearable electronics.

Is Inequality Among Universities Increasing? Gini Coefficients and the Elusive Rise of Elite Universities

One of the unintended consequences of the New Public Management (NPM) in universities is often feared to be a division between elite institutions focused on research and large institutions with teaching missions. However, institutional isomorphisms provide counter-incentives. For example, university rankings focus on certain output parameters such as publications, but not on others (e.g., patents). In this study, we apply Gini coefficients to university rankings in order to assess whether universities are becoming more unequal, at the level of both the world and individual nations. Our results do not support the thesis that universities are becoming more unequal. If anything, we predominantly find homogenisation, both at the level of the global comparisons and nationally. In a more restricted dataset (using only publications in the natural and life sciences), we find increasing inequality for those countries, which used NPM during the 1990s, but not during the 2000s. Our findings suggest that increased output steering from the policy side leads to a global conformation to performance standards.