Skutterudite Unicouple Characterization for Energy Harvesting Applications

Skutterudites are promising thermoelectric materials because of their high figure of merit, ZT, and good thermomechanical properties. This work reports the effective figure of merit, ZT_eff, and the efficiency of skutterudite legs and a unicouple working under a large temperature difference. The p‐ and n‐type legs are fabricated with electrodes sintered directly to the skutterudite during a hot pressing process. CoSi₂ is used as the electrode for the n‐type skutterudite (Yb_0.35Co₄Sb₁₂) and Co₂Si for the p‐type skutterudite (NdFe_3.5Co_0.5Sb₁₂). A technique is developed to measure the ZT_eff of individual legs and the efficiency of a unicouple. An ZT_eff of 0.74 is determined for the n‐type legs operating between 52 and 595 °C, and an ZT_eff of 0.51 for the p‐type legs operating between 77 and 600 °C. The efficiency of the p–n unicouple is determined to be 9.1% operating between ～70 and 550 °C.     

Optimization Design of a Multi-slot Nanoantenna Based on Genetic Algorithm for Energy Harvesting

A new genetic algorithm (GA)-based multi-slot nanoantenna is proposed for energy harvesting, which consists of two element nanoantennas with rectangular shape and with double bowtie double ring (DBDR) slot. The DBDR slot structure can enhance the electric field to increase the absorptivity of nanoantennas; however, the larger parameter space of multi-slot is more hardly controlled. Therefore, we use GA to optimize the parameters of the DBDR slot nanoantenna and the Finite-Difference Time-Domain method to calculate the absorptivity. It is found that absorptivity of the optimized nanoantenna is over 77% in 400–1800 nm waveband. We attribute the better absorbing property of the nanoantenna to the synergistic effect of the localized surface plasmon resonance enhancement and coupling between slots.

     

Energy Harvesting Technologies for Tire Pressure Monitoring Systems

Tire pressure monitoring systems (TPMS) are becoming increasingly important to ensure safe and efficient use of tires in the automotive sector. A typical TPMS system consists of a battery powered wireless sensor, as part of the tire, and a remote receiver to collect sensor data, such as pressure and temperature. In order to provide a maintenance‐free and battery‐less sensor solution there is growing interest in using energy harvesting technologies to provide power for TPMS. This paper summarizes the current literature and discusses the use of piezoelectric, electromagnetic, electret and triboelectric materials in a variety of harvesting systems.     

Metamaterial-Based Energy Harvesting for Detectivity Enhanced Infrared Detectors

Plasmonics - In this paper, we propose new detectivity enhanced infrared detectors in which metamaterial cells are used to harvest the IR energy. Analytical models are developed and numerically...     

A Highly-Flexible and Breathable Photo-Thermo-Electric Membrane for Energy Harvesting

Photo-thermo-electric (PTE) technology is a simple but sustainable method that directly converts solar energy into electricity. However, the manufacturing of flexible and breathable PTE generators for practical applications, such as intelligent wearable and self-powered sensors, poses significant challenges due to the rigid thermoelectric materials and unbreathable substrates. Here, a highly-flexible and breathable photo-thermal-electric membrane (FB-PTEM) is developed by magnetron sputtering (MS) on a photo-thermal nanofiber membrane. A single unit of FB-PTEM produced an open-circuit voltage of 0.52 V under 1 sun (100 mW cm⁻²) and 0.2 V under LED illumination, making it suitable for all-weather use. The photo-thermal nanofiber membrane exhibited high photo-thermal conversion capacity of reaching 70 °C within 50 s under 1 sun irradiation. The FB-PTEM with a thickness of 0.35 mm achieved a self-temperature difference of 20.6 °C under 1 sun with the low thermal conductivity of the nanofiber membrane. Furthermore, it has a vapor permeability of 14.6 kg m⁻² d⁻¹ due to the inherent high porosity of the nanofiber membranes. The FB-PTEM demonstrates great potential for the development of highly flexible thermoelectric materials, as it encompasses various advantageous features such as self-temperature difference, lightweight design, high breathability, and all-weather suitability.     

Natural Leaf Made Triboelectric Nanogenerator for Harvesting Environmental Mechanical Energy

Distributed environmental mechanical energy is rarely collected due to its fluctuating amplitudes and low frequency, which is usually attributed as “random” energy. Considering the rapid development of the Internet of things (IoT), there is a great need for a large number of distributed and sustainable power sources. Here, a natural leaf assembled triboelectric nanogenerator (Leaf‐TENG) is designed by utilizing the green leaf as an electrification layer and electrode to effectively harvest environmental mechanical energy. The Leaf‐TENG with good adaptability has the maximum output power of ≈45 mW m^?2, which is capable of driving advertising LEDs and commercial electronic temperature sensors. Besides, a tree‐shaped energy harvester is integrated with natural Leaf‐TENG to harvest large‐area environmental mechanical energy. This work provides a new prospect for distributed and environmental‐friendly power sources and has potential applications in the IoT and self‐powered systems.     

Design and Analysis of Ultra Broadband Nano-absorber for Solar Energy Harvesting

In this paper, we propose a metamaterial based ultra broadband nano-absorber (UBNA) for solar energy harvesting, whose elements consist of a ring column and dual hexagon pillar at the center. In this absorber, the light of shorter wavelengths is harvested at ring column, while the light of longer wavelengths is trapped by dual hexagon pillar. It is found that the average absorptivity of the UBNA is as high as 96% in 300–1300 nm waveband and the UBNA can maintain 95% in the whole visible and near-infrared waveband ranging from 300 to 2000 nm. In addition, the perfect light absorbing capability of the UBNA is independent of the incident light polarization state in the waveband of 300–1300 nm, and it can keep up an average absorptivity of 91% with an large incident angle varying between ?60^° and 60^°. We attribute the perfect absorbing property of UBNA to the synergistic effect of the slow wave effect, Fabry-Perot resonance and the localized surface plasmon resonance enhancement.     

Comprehensive Surface-Wave Description for the Nano-scale Energy Concentration with Resonant Dipole Antennas

Resonant optical dipole nano-antennas allow giant field enhancement within nano-gaps. To show how the energy of external illumination waves is delivered and concentrated in nano-gaps, we build up a model by considering the dynamical launching and multiple scattering processes of surface plasmon polaritions (SPPs) on both antenna arms. The model captures the main feature of the antenna resonance as evidenced by comparison of the model prediction with fully vectorial numerical results and provides an intuitive picture that the energy of external wave is initially transferred into SPP and is then coupled into the nano-gap. The enhanced field in the nano-gap oscillates quasi-periodically with the increase of the antenna-arm length, and the resonance peaks can be predicted with a phase-matching condition derived from the model, showing that antenna resonance is due to a constructive interference of the multiple-scattered SPPs. Analytical equation for determining the complex resonance wavelength and the quality factor of the resonant modes is obtained. The model however exhibits observable deviation from fully vectorial numerical results for the lowest resonance order (for antenna with the shortest arms), evidencing that, for this case, surface waves other than SPPs contribute to the antenna resonance. The present results are helpful for clarifying the underlying physics for the energy concentration with resonant dipole antennas and may provide recipes for intuitive design of antenna devices, such as those used for optical nonlinearity enhancement and biochemical sensing.     

Low-Friction Graphene Oxide-Based Ion Selective Membrane for High-Efficiency Osmotic Energy Harvesting

Graphene-based laminate membranes with selective ion-transport capability show great potential in renewable osmotic energy harvesting. One of the great challenges is to reduce the overall energy barriers while remain the high ion selectivity in the transmembrane ion transport process. Here, a strategy is proposed to break the trade-off between ion selectivity and permeability in laminar nanochannels using amphiphilic molecules as modifier, which enhances the surface charge density of nanochannel by loading more ion polymer with polar head and lows the frictional force of ion transport with hydrophobic tail. The conversion efficiency can reach to 32% in osmotic energy harvesting (0.5 m /0.01 m concentration gradient) after adopting this modifier. During the process of mixing real river water and seawater, the maximum power density can reach to 13.38 W m⁻². The amphiphilic molecules also bind adjacent nanosheets, endowing the membrane's strong mechanical strength and high stability in aqueous solution. This work can open up a new way to regulate the transmembrane ion transport in 2D laminate membranes.     

High Efficiency Half‐Heusler Thermoelectric Materials for Energy Harvesting

Half‐Heusler (HH) compounds have gained ever‐increasing popularity as promising high temperature thermoelectric materials. High figure of merit zT of ≈1.0 above 1000 K has recently been realized for both n‐type and p‐type HH compounds, demonstrating the realistic prospect of these high temperature compounds for high efficiency power generation. Here, recent progress in advanced fabrication techniques and the intrinsic atomic disorders in HH compounds, which are linked to the understanding of the electrical transport, is discussed. Thermoelectric transport features of n‐type ZrNiSn‐based HH alloys are particularly emphasized, which is beneficial to further improving thermoelectric performance and comprehensively understanding the underlying mechanisms in HH thermoelectric materials. The rational design and realization of new high performance p‐type Fe(V,Nb)Sb‐based HH compounds are also demonstrated. The outlook for future research directions of HH thermoelectric materials is also discussed.     

Application of Nanoparticle Antioxidants to Enable Hyperstable Chloroplasts for Solar Energy Harvesting

The chloroplast contains densely stacked arrays of light‐harvesting proteins that harness solar energy with theoretical maximum glucose conversion efficiencies approaching 12%. Few studies have explored isolated chloroplasts as a renewable, abundant, and low cost source for solar energy harvesting. One impediment is that photoactive proteins within the chloroplast become photodamaged due to reactive oxygen species (ROS) generation. In vivo, chloroplasts reduce photodegradation by applying a self‐repair cycle that dynamically replaces photodamaged components; outside the cell, ROS‐induced photodegradation contributes to limited chloroplast stability. The incorporation of chloroplasts into synthetic, light‐harvesting devices will require regenerative ROS scavenging mechanisms to prolong photoactivity. Herein, we study ROS generation within isolated chloroplasts extracted from Spinacia oleracea directly interfaced with nanoparticle antioxidants, including dextran‐wrapped nanoceria (dNC) previously demonstrated as a potent ROS scavenger. We quantitatively examine the effect of dNC, along with cerium ions, fullerenol, and DNA‐wrapped single‐walled carbon nanotubes (SWCNTs), on the ROS generation of isolated chloroplasts using the oxidative dyes, 2’,7’‐ dichlorodihydrofluorescein diacetate (H₂DCF‐DA) and 2,3‐bis(2‐methoxy‐4‐nitro‐5‐sulfophenyl)‐2H‐tetrazolium‐5‐carboxanilide sodium salt (XTT). Electrochemical measurements confirm that chloroplasts processed from free solution can generate power under illumination. We find dNC to be the most effective of these agents for decreasing oxidizing species and superoxide concentrations whilst preserving chloroplast photoactivity at concentrations below 5 μM, offering a promising mechanism for maintaining regenerative chloroplast photoactivity for light‐harvesting applications.     

Roles of the Excitation in Harvesting Energy from Vibrations

The study investigated the role of excitation in energy harvesting applications. While the energy ultimately comes from the excitation, it was shown that the excitation may not always behave as a source. When the device characteristics do not perfectly match the excitation, the excitation alternately behaves as a source and a sink. The extent to which the excitation behaves as a sink determines the energy harvesting efficiency. Such contradictory roles were shown to be dictated by a generalized phase defined as the instantaneous phase angle between the velocity of the device and the excitation. An inductive prototype device with a diamagnetically levitated seismic mass was proposed to take advantage of the well established phase changing mechanism of vibro-impact to achieve a broader device bandwidth. Results suggest that the vibro-impact can generate an instantaneous, significant phase shift in response velocity that switches the role of the excitation. If introduced properly outside the resonance zone it could dramatically increase the energy harvesting efficiency.     

Multiband Metamaterial Absorber Design Based on Plasmonic Resonances for Solar Energy Harvesting

A new metamaterial absorber is designed and characterized numerically for the harvesting of solar energy. The design is composed of three layers in which the interaction among them gives rise to the plasmonic resonances. The main operation frequency range of the proposed structure is chosen to be the visible regime. However, the design is also analyzed for the infrared and ultraviolet regimes. In order to characterize the absorber, some parametric studies with respect to the dimensions of the structure are carried out. According to the results, it is found that the proposed metamaterial absorber has 98.2 % absorption capability at 445.85 THz and 99.4 % absorption capability between 624 and 658.3 THz. Moreover, the polarization dependency of the structure is examined and it is found that the design operates well as a perfect absorber with polarization independency for the studied frequency range. As a result, the proposed metamaterial absorber can be used for solar energy harvesting as it provides multiple perfect absorption bands in the visible regime.     

GaSb‐Based Solar Cells for Full Solar Spectrum Energy Harvesting

In this work, a multijunction solar cell is developed on a GaSb substrate that can efficiently convert the long‐wavelength photons typically lost in a multijunction solar cell into electricity. A combination of modeling and experimental device development is used to optimize the performance of a dual junction GaSb/InGaAsSb concentrator solar cell. Using transfer printing, a commercially available GaAs‐based triple junction cell is stacked mechanically with the GaSb‐based materials to create a four‐terminal, five junction cell with a spectral response range covering the region containing >99% of the available direct‐beam power from the Sun reaching the surface of the Earth. The cell is assembled in a mini‐module with a geometric concentration ratio of 744 suns on a two‐axis tracking system and demonstrated a combined module efficiency of 41.2%, measured outdoors in Durham, NC. Taking into account the measured transmission of the optics gives an implied cell efficiency of 44.5%.     

Bioinspired Ultrastrong Nanocomposite Membranes for Salinity Gradient Energy Harvesting from Organic Solutions

Efforts to extract energy from waste organic solutions can not only support clean environments but also help to alleviate the energy crisis. Here, a bioinspired ultrastrong nanocomposite membrane is developed via the layer‐by‐layer method based on aramid nanofiber‐graphene oxide (AGO) with good mechanical properties for salinity gradient energy harvesting from organic solutions. Benefiting from the 1D and 2D network interlocking arrangement, the AGO membrane shows an unprecedented mechanical stress of 688 MPa and maintains its integrity after soaking in organic solvents for 24 h. Impressively, when LiCl is diluted in methanol, the AGO membrane device with a working area of 113 mm² produces a current and a measured power generation of 28 ± 11 µA and 3140 ± 960 nW (C_feed = 2 mol L^?1), respectively. Thus, the working area of the AGO membrane for salinity gradient energy harvesting and temperature‐related energy harvesting enables its use in practical applications. In addition, 14 cells with the methanol‐LiCl solution (C_feed = 1 mol L^?1) can produce a voltage up to 1.82 V to light a liquid crystal display. Therefore, this AGO nanocomposite membrane presents a promising avenue to harvest salinity gradient energy from organic solutions.     

Oblate Spheroidal Triboelectric Nanogenerator for All‐Weather Blue Energy Harvesting

Triboelectric nanogenerators (TENGs) provide one of the most promising techniques for large‐scale blue energy harvesting. However, lack of reasonable designs has largely hindered TENG from harvesting energy from both rough and tranquil seas. In this paper, an oblate spheroidal TENG assembled by two novel TENG parts is elaborately designed for both situations. The TENG in the upper part is based on spring steel plates without other substrate materials, which makes it possible to output considerable power in rough seas and occupy small space. The TENG in the lower part consists of two copper‐coated polymer films and a rolling ball which can capture small wave energy from tranquil seas. The working mechanism and output performance are systematically studied. A maximum open‐circuit voltage of 281 V and a short‐circuit current of 76 µA can be achieved by one upper part, enough to charge a commercial capacitor for potential applications. More important, the proposed oblate spheroidal shell not only guarantees high sensitivity of the TENG in the lower part, but also qualifies the TENG with unique self‐stabilization and low consumables for the next generation of TENGs with new structural design toward all‐weather blue energy harvesting.     

Rational Structure Optimized Hybrid Nanogenerator for Highly Efficient Water Wave Energy Harvesting

Water wave energy is a promising renewable energy source that may alleviate the rising concerns over current resource depletion, but it is rarely exploited due to the lack of efficient energy harvesting technologies. In this work, a hybrid system with a triboelectric nanogenerator (TENG) and an electromagnetic generator (EMG) based on an optimized inner topological structure is reported to effectively harvest water wave energy. The TENG with etched polytetrafluoroethylene films and Cu electrodes utilizing the contact‐freestanding mode is designed into a cubic structure, in which the EMG is well hybridized. An integration of TENG and EMG achieves mutual compensation of their own merits, enabling the hybrid system to deliver satisfactory output over a broad range of operation frequency. The output performance of TENG with varied inner topological structures is experimentally and theoretically compared, and a concept is proposed to further clarify the energy conversion efficiency, which should be considered in designing energy harvesting devices. The influences of oscillation frequency, amplitude, and dielectric materials on the output performance of the hybrid system are comprehensively studied on different platforms. Furthermore, the optimum operation frequency ranges for TENG and EMG are concluded. The proposed hybrid nanogenerator renders an effective approach toward large‐scale blue energy harvesting over a broad frequency range.