Time-modulated near-field radiative heat transfer.

Near-field radiative heat transfer has recently attracted increasing interests for its applications in energy technologies, such as thermophotovoltaics. Existing works, however, are restricted to time-independent systems. Here, we explore near-field radiative heat transfer between two bodies under time modulation by developing a rigorous fluctuational electrodynamics formalism. We demonstrate that time modulation can result in the enhancement, suppression, elimination, or reversal of radiative heat flow between the two bodies, and can be used to create a radiative thermal diode with an infinite contrast ratio, as well as a near-field radiative heat engine that pumps heat from the cold to the hot bodies. The formalism reveals a fundamental symmetry relation in the radiative heat transfer coefficients that underlies these effects. Our results indicate the significant capabilities of time modulation for managing nanoscale radiative heat flow.

An integrated RF energy-harvesting system with broad input voltage range and high power conversion efficiency.

By 2050, countries around the world are expected to be gradually phasing out fossil fuels and implementing greener energy technologies. In this work, we present a system employing Energy harvesting, a self-powered technology that can recycle energy from the surrounding environment. A high-efficiency radio frequency (RF) energy-harvesting chip was designed and fabricated. With an off-chip antenna and rectifier, the system scavenges ambient RF energy and converts it into usable energy, which is then stored in energy storage elements (such as a supercapacitor or a rechargeable battery). The system can further be implemented as an energy source for charging smart devices. The system-on-chip design consists of a cold start block, a boost converter with maximum power point tracking functionalities, and a charging block. The chip was fabricated using AMS 350 nm technology. Although the system was optimized for harvesting RF energy, it can be easily adapted to harvest other energy sources (i.e., mechanical and thermal energy sources). Using an optimized cold start architecture, the circuit has a cold start voltage of 380 mV. With an improved control strategy of power conversion, the system is capable of continuously charging up to 4.5 V with a broad input voltage range of 100 mV to 10 V and has a peak charging efficiency of 82%.

Direct Electron Transfer-Type Oxidoreductases for Biomedical Applications.

Among the various types of enzyme-based biosensors, sensors utilizing enzymes capable of direct electron transfer (DET) are recognized as the most ideal. However, only a limited number of redox enzymes are capable of DET with electrodes, that is, dehydrogenases harboring a subunit or domain that functions specifically to accept electrons from the redox cofactor of the catalytic site and transfer the electrons to the external electron acceptor. Such subunits or domains act as built-in mediators for electron transfer between enzymes and electrodes; consequently, such enzymes enable direct electron transfer to electrodes and are designated as DET-type enzymes. DET-type enzymes fall into several categories, including redox cofactors of catalytic reactions, built-in mediators for DET with electrodes and by their protein hierarchic structures, DET-type oxidoreductases with oligomeric structures harboring electron transfer subunits, and monomeric DET-type oxidoreductases harboring electron transfer domains. In this review, we cover the science of DET-type oxidoreductases and their biomedical applications. First, we introduce the structural biology and current understanding of DET-type enzyme reactions. Next, we describe recent technological developments based on DET-type enzymes for biomedical applications, such as biosensors and biochemical energy harvesting for self-powered medical devices. Finally, after discussing how to further engineer and create DET-type enzymes, we address the future prospects for DET-type enzymes in biomedical engineering.

High Performance Indium-Tin-Oxide Schottky Diodes for Terahertz Band Operation.

Schottky diode, capable of ultrahigh frequency operation, plays a critical role in modern communication systems. To develop cost-effective and widely applicable high-speed diodes, researchers have delved into thin-film semiconductors. However, a performance gap persists between thin-film diodes and conventional bulk semiconductor-based ones. Featuring high mobility and low permittivity, indium-tin-oxide has emerged to bridge this gap. Nevertheless, due to its high carrier concentration, indium-tin-oxide has predominantly been utilized as electrode rather than semiconductor. In this study, a remarkable quantum confinement induced dedoping phenomenon was discovered during the aggressive indium-tin-oxide thickness downscaling. By leveraging such a feature to change indium-tin-oxide from metal-like into semiconductor-like, in conjunction with a novel heterogeneous lateral design facilitated by an innovative digital etch, we demonstrated an indium-tin-oxide Schottky diode with a cutoff frequency reaching terahertz band. By pushing the boundaries of thin-film Schottky diodes, our research offers a potential enabler for future fifth-generation/sixth-generation networks, empowering diverse applications.

Lightweight and Strong Cellulosic Triboelectric Materials Enabled by Cell Wall Nanoengineering.

As intelligent technology surges forward, wearable electronics have emerged as versatile tools for monitoring health and sensing our surroundings. Among these advancements, porous triboelectric materials have garnered significant attention for their lightness. However, these materials face the challenge of improving structural stability to further enhance the sensing accuracy of triboelectric sensors. In this study, a lightweight and strong porous cellulosic triboelectric material is designed by cell wall nanoengineering. By tailoring of the cell wall structure, the material shows a high mechanical strength of 51.8 MPa. The self-powered sensor constructed by this material has a high sensitivity of 33.61 kPa-1, a fast response time of 36 ms, and excellent pressure detection durability. Notably, the sensor still enables a high sensing performance after the porous cellulosic triboelectric material exposure to 200 °C and achieves real-time feedback of human motion, thereby demonstrating great potential in the field of wearable electronic devices.

Alternatives to Fluoropolymers for Motion-Based Energy Harvesting: Perspectives on Piezoelectricity, Triboelectricity, Ferroelectrets, and Flexoelectricity.

Fluoropolymers, including polytetrafluoroethylene (PTFE, Teflon), polyvinylidene difluoride (PVDF), and fluorine kautschuk materials (FKMs, Viton) are critical polymers for applications ranging from non-stick coatings, corrosion resistant seals, semiconductor manufacturing, membranes, and energy harvesting technologies. However, the synthesis of these fluoropolymers requires the use of per- and polyfluorinated alkyl substances (PFAS) known colloquially as "forever chemicals," and as such there is a pressing need to develop alternative technologies that can serve the end-use of fluoropolymers without the environmental cost of using PFAS. Further, fluoropolymers themselves fall under the PFAS umbrella. Here, alternative mechanical-to-electrical energy harvesting polymers are reviewed and benchmarked against the leading fluoropolymer energy harvesters. These alternative technologies include nonfluoropolymer piezoelectric polymers, triboelectric nanogenerators (TENGs), ferroelectric elastomers, and flexoelectric polymers. A vision towards sustainable, non-fluoropolymer-based energy harvesting is provided.

Dynamic Thermostable Cellulosic Triboelectric Materials from Multilevel-Non-Covalent Interactions.

Triboelectric materials present great potential for harvesting huge amounts of dispersed energy, and converting them directly into useful electricity, a process that generates power more sustainably. Triboelectric nanogenerators (TENGs) have emerged as a technology to power electronics and sensors, and it is expected to solve the problem of energy harvesting and self-powered sensing from extreme environments. In this paper, a high-temperature-resistant triboelectric material is designed based on multilevel non-covalent bonding interactions, which achieves an ultra-high surface charge density of 192 µC m-2 at high temperatures. TENGs based on the triboelectric material exhibit more than an order of magnitude higher power output (2750 mW m-2 at 200 °C) than the existing devices at high temperatures. These remarkable properties are achieved based on enthalpy-driven molecular assembly in highly unbonded states. Thus, the material maintains bond strength and ultra-high surface charge density in entropy-dominated high-temperature environments. This molecular design concept points out a promising direction for the preparation of polymers with excellent triboelectric properties.

Organic-Inorganic Rare-Earth Double Perovskite Ferroelectric with Large Piezoelectric Response and Ferroelasticity for Flexible Composite Energy Harvesters.

Hybrid organic-inorganic perovskite (HOIP) ferroelectric materials have great potential for developing self-powered electronic transducers owing to their impressive piezoelectric performance, structural tunability and low processing temperatures. Nevertheless, their inherent brittle and low elastic moduli limit their application in electromechanical conversion. Integration of HOIP ferroelectrics and soft polymers is a promising solution. In this work, a hybrid organic-inorganic rare-earth double perovskite ferroelectric, [RM3HQ]2RbPr(NO3)6 (RM3HQ = (R)-N-methyl-3-hydroxylquinuclidinium) is presented, which possesses multiaxial nature, ferroelasticity and satisfactory piezoelectric properties, including piezoelectric charge coefficient (d33) of 102.3 pC N-1 and piezoelectric voltage coefficient (g33) of 680 × 10-3 V m N-1. The piezoelectric generators (PEG) based on composite films of [RM3HQ]2RbPr(NO3)6@polyurethane (PU) can generate an open-circuit voltage (Voc) of 30 V and short-circuit current (Isc) of 18 µA, representing one of the state-of-the-art PEGs to date. This work has promoted the exploration of new HOIP ferroelectrics and their development of applications in electromechanical conversion devices.

Fabrication of Electronically Conductive Protein-Heme Nanowires for Power Harvesting.

Electronically conductive protein-based materials can enable the creation of bioelectronic components and devices from sustainable and nontoxic materials, while also being well-suited to interface with biological systems, such as living cells, for biosensor applications. However, as proteins are generally electrical insulators, the ability to render protein assemblies electroactive in a tailorable manner can usher in a plethora of useful materials. Here, an approach to fabricate electronically conductive protein nanowires is presented by aligning heme molecules in proximity along protein filaments, with these nanowires also possessing charge transfer abilities that enable energy harvesting from ambient humidity. The heme-incorporated protein nanowires demonstrate electron transfer over micrometer distances, with conductive atomic force microscopy showing individual nanowires having comparable conductance to other previously characterized heme-based bacterial nanowires. Exposure of multilayer nanowire films to humidity produces an electrical current, presumably through water molecules ionizing carboxyl groups in the filament and creating an unbalanced total charge distribution that is enhanced by the heme. Incorporation of heme and potentially other metal-center porphyrin molecules into protein nanostructures could pave the way for structurally- and electrically-defined protein-based bioelectronic devices.

Enhancing the Humidity Resistance of Triboelectric Nanogenerators: A Review.

Triboelectric nanogenerators (TENGs) are sustainable energy resources for powering electronic devices from miniature to large-scale applications. However, their output performance and stability can deteriorate significantly when TENGs are exposed to moisture or humidity caused by the ambient environment or human physiological activities. This review provides an overview of the recent research advancements in enhancing the humidity resistance of TENGs. Various approaches have been reviewed including encapsulation techniques, surface modification of triboelectric materials to augment hydrophobicity or superhydrophobicity, the creation of fibrous architectures for effective moisture dissipation, leveraging water assistance for TENG performance enhancement, and other strategies like charge excitation. These research efforts contribute to the improvement of environmental adaptability and lead to expanded practical TENG applications both as energy harvesters and self-powered sensors. The efficacy of these strategies and future challenges are also discussed to facilitate the continued development of resilient TENGs in high humidity environments.

High Efficiency Breathable Thermoelectric Skin Using Multimode Radiative Cooling/Solar Heating Assisted Large Thermal Gradient.

This study proposes a Janus structure-based stretchable and breathable thermoelectric skin with radiative cooling (RC) and solar heating (SH) functionalities for sustainable energy harvesting. The challenge of the wearable thermoelectric generator arises from the small temperature difference. Thus, this dual-sided structure maximizes the thermal gradient between the body and the surrounding environment, unlike the previous works that rather concentrate on the efficiency of the thermoelectric generator itself. The Janus structure allows the device to switch to the other mode, optimizing electricity generation from a given weather condition. For these functionalities, for the first time, boron nitride-polydimethylsiloxane (BP) and graphene nanoplatelet-polydimethylsiloxane (GP) nanofiber (NF) are developed as substrates. The BP NF generates the RC capability of ΔTcooling  = 4 °C, and the high solar absorbance of the GP NF enables it to be photothermally heated. The flip-overable thermoelectric skin (FoTES) achieves a maximum power output (Pmax ) of 5.73 µW cm-2 in RC mode, surpassing SH mode by 5.55 µW cm-2 in the morning. In the afternoon, it generates a Pmax of 18.59 µW cm-2 in SH mode, outperforming RC mode by 15.56 µW cm-2 . This work contributes to the advancement of wearable electronics, offering a sustainable power source in a wearable form.

Highly Stretchable, Knittable, Wearable Fiberform Hydrovoltaic Generators Driven by Water Transpiration for Portable Self-Power Supply and Self-Powered Strain Sensor.

The development of excellently stretchable, highly mobile, and sustainable power supplies is of great importance for self-power wearable electronics. Transpiration-driven hydrovoltaic power generator (HPG) has been demonstrated to be a promising energy harvesting strategy with the advantages of negative heat and zero-carbon emissions. Herein, this work demonstrates a fiber-based stretchable HPG with the advantages of high output, portability, knittability, and sustainable power generation. Based on the functionalized micro-nano water diffusion channels constructed by the discarded mask straps (MSs) and oxidation-treated carbon nanomaterials, the applied water can continuously produce electricity during the spontaneous flow and diffusion. Experimentally, when a tiny 0.1 mL of water encounters one end of the proposed HPG, the centimeter-length device can yield a peak voltage of 0.43 V, peak current of 29.5 µA, and energy density of 5.833 mW h cm-3. By efficiently integrating multiple power generation units, sufficient output power can be provided to drive commercial electronic devices even in the stretched state. Furthermore, due to the reversibility of the electrical output during dynamic stretching-releasing, it can passively convert physiological activities and motion behaviors into quantifiable and processable current signals, opening up HPG's application in the field of self-powered wearable sensing.

Durable Roller-Based Swing-Structured Triboelectric Nanogenerator for Water Wave Energy Harvesting.

Ocean energy is a kind of clean and renewable energy source, but it cannot be efficiently harvested by traditional electromagnetic generators, due to its low-frequency characteristic. The emergence of triboelectric nanogenerators provides a more promising technology for collecting ocean energy. In this work, a durable roller-based swing-structured triboelectric nanogenerator (RS-TENG) is designed and fabricated for low-frequency water wave energy harvesting. The rolling structure reduces the wear between triboelectric materials and improves the device's durability. After a continuous operation of 1 260 000 cycles, the attenuation of the electrical outputs of the RS-TENG is below 1.6%, exhibiting excellent durability. At the same time, the output current can arrive at 53.2 µA. Under the triggering of water waves, the RS-TENG can generate an output power of 4.27 mW, corresponding to a power density of 1.16 W m-3. After the arraying, the output performance can be doubled, so that the TENG can successfully power an environmental monitoring sensor and ensure long-term stable operation of the sensor. This work provides an effective strategy for improving the device durability, which benefits the practical applications of the TENGs in large-scale blue energy harvesting.

A Self-Sensing and Self-Powered Wearable System Based on Multi-Source Human Motion Energy Harvesting.

Wearable devices play an indispensable role in modern life, and the human body contains multiple wasted energies available for wearable devices. This study proposes a self-sensing and self-powered wearable system (SS-WS) based on scavenging waist motion energy and knee negative energy. The proposed SS-WS consists of a three-degree-of-freedom triboelectric nanogenerator (TDF-TENG) and a negative energy harvester (NEH). The TDF-TENG is driven by waist motion energy and the generated triboelectric signals are processed by deep learning for recognizing the human motion. The triboelectric signals generated by TDF-TENG can accurately recognize the motion state after processing based on Gate Recurrent Unit deep learning model. With double frequency up-conversion, the NEH recovers knee negative energy generation for powering wearable devices. A model wearing the single energy harvester can generate the power of 27.01 mW when the movement speed is 8 km h-1, and the power density of NEH reaches 0.3 W kg-1 at an external excitation condition of 3 Hz. Experiments and analysis prove that the proposed SS-WS can realize self-sensing and effectively power wearable devices.

A Triboelectric-Electromagnetic Hybrid Nanogenerator with Magnetic Coupling Assisted Waterproof Encapsulation for Long-Lasting Energy Harvesting.

Ocean energy harvesting based on a triboelectric nanogenerator (TENG) has great application potential, while the encapsulation of triboelectric devices in water poses a critical issue. Herein, a triboelectric-electromagnetic hybrid nanogenerator (TE-HNG) consisting of TENGs and electromagnetic generators (EMGs) is proposed to harvest water flow energy. A magnetic coupling transmission component is applied to replace traditional bearing structures, which can realize the fully enclosed packaging of the TENG devices and achieve long-lasting energy harvesting from water flow. Under the intense water impact, magnetic coupling reduces the possibility of internal gear damage due to excessive torque, indicating superior stability and robustness compared to conventional TENG. At the waterwheel rotates speed of 75 rpm, the TE-HNG can generate an output peak power of 114.83 mW, corresponding to a peak power density of 37.105 W m-3. After 5 h of continuous operation, the electrical output attenuation of TENG is less than 3%, demonstrating excellent device durability. Moreover, a self-powered temperature sensing system and a self-powered cathodic protection system based on the TE-HNG are developed and illustrated. This work provides a prospective strategy for improving the output stability of TENGs, which benefits the practical applications of the TENGs in large-scale blue energy harvesting.

Tunable Surface Charge of Layered Double Hydroxide Membranes Enabling Osmotic Energy Harvesting from Anion Transport.

Membrane-based osmotic energy harvesting is a promising technology with zero carbon footprint. High-performance ion-selective membranes (ISMs) are the core components in such applications. Recent advancement in 2D nanomaterials opens new avenues for building highly efficient ISMs. However, the majority of the explored 2D nanomaterials have a negative surface charge, which selectively enhances cation transport, resulting in the underutilization of half of the available ions. In this study, ISMs based on layered double hydroxide (LDH) with tunable positive surface charge are studied. The membranes preferentially facilitate anion transport with high selectivity. Osmotic energy harvesting device based on these membranes reached a power density of 2.31 W m-2 under simulated river/sea water, about eight times versus that of a commercial membrane tested under the same conditions, and up to 7.05 W m-2 under elevated temperature and simulated brine/sea water, and long-term stability with consistent performance over a 40-day period. A prototype reverse electrodialysis energy harvesting device, comprising a pair of LDH membranes and commercial cation-selective membranes, is able to simultaneously harvest energy from both cations and anions achieving a power density of 6.38 W m-2 in simulated river/sea water, demonstrating its potential as building blocks for future energy harvesting systems.

Enhancing the Output Performance of Triboelectric Nanogenerator Through Regulation of its Internal Nano-Architecture.

Triboelectric Nanogenerator (TENG) has proven highly effective in converting mechanical energy into electrical energy. Previous research on manipulating microstructure for performance enhancement primarily focused on the surface of TENGs. In this study, an innovative bottom-up strategic design to control the internal nano-architecture for the enhanced output of TENG is proposed. This multiscale structural design strategy consists of defect chemistry (angstrom-scale), surface modification (nano-scale), and spatial regulation of nanoparticles (meso-scale), which helps explore the optimal utilization of TENG's internal structure. After fine-tuning the nano-architecture, the output voltage is significantly increased. This optimized TENG serves as a robust platform for developing self-powered systems, including self-powered electrochemical chlorination systems for sterilization. Additionally, through the utilization of multiscale simulations (density functional theory, all-atom molecular dynamics, and dissipative particle dynamics), the underlying mechanisms governing how the optimized nanoparticle-polymer interface and spatial arrangement of nanoparticles influence the storage and transfer of charges are comprehensively elucidated. This study not only demonstrates the effectiveness of manipulating internal nano-architecture to enhance TENG performance for practical applications but also provides invaluable insights into structural engineering for TENG advancement.

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.

Self-Powered Traffic Lights Through Wind Energy Harvesting Based on High-Performance Fur-Brush Dish Triboelectric Nanogenerators.

Traffic lights play vital roles in urban traffic management systems, providing clear directional guidance for vehicles and pedestrians while ensuring traffic safety. However, the vast quantity of traffic lights widely distributed in the transportation system aggravates energy consumption. Here, a self-powered traffic light system is proposed through wind energy harvesting based on a high-performance fur-brush dish triboelectric nanogenerator (FD-TENG). The FD-TENG harvests wind energy to power the traffic light system continuously without needing an external power supply. Natural rabbit furs are applied to dish structures, due to their outstanding characteristics of shallow wear, high performance, and resistance to humidity. Also, the grid pattern of the dish structure significantly impacts the TENG outputs. Additionally, the internal electric field and the influences of mechanical and structural parameters on the outputs are analyzed by finite element simulations. After optimization, the FD-TENG can achieve a peak power density of 3.275 W m-3. The portable and miniature features of FD-TENG make it suitable for other natural environment systems such as forests, oceans, and mountains, besides the traffic light systems. This study presents a viable strategy for self-powered traffic lights, establishing a basis for efficient environmental energy harvesting toward big data and Internet of Things applications.

Sodium Niobate Nanowires Embedded PVA-Hydrogel-Based Triboelectric Nanogenerator for Versatile Energy Harvesting and Self-Powered CO Gas Sensor.

The surging demand for sustainable energy solutions and adaptable electronic devices has led to the exploration of alternative and advanced power sources. Triboelectric Nanogenerators (TENGs) stand out as a promising technology for efficient energy harvesting, but research on fully flexible and environmental friendly TENGs still remain limited. In this study, an innovative approach is introduced utilizing an ionic-solution modified conductive hydrogel embedded with piezoelectric sodium niobate nanowires-based Triboelectric Nanogenerator (NW-TENG), offering intrinsic advantages to healthcare and wearable devices. The synthesized NW-TENG, with a 12.5 cm2 surface area, achieves peak output performance, producing ≈840 V of voltage and 2.3 µC of charge transfer, respectively. The rectified energy powers up 30 LEDs and a stopwatch; while the NW-TENG efficiently charges capacitors from 1µF to 100 µF, reaching 1 V within 4 to 65 s at 6 Hz. Integration with prototype carbon monoxide (CO) gas sensor transform the device into a self-powered gas sensory technology. This study provides a comprehensive understanding of nanowire effects on TENG performance, offering insights for designing highly flexible and environmentally friendly TENGs, and extending applications to portable self-powered gas sensors and wearable devices.