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Abstract Constructing crossmodal in-sensor processing system based on high-performance flexible devices is of great significance for the development of wearable human-machine interfaces. A bio-inspired crossmodal in-sensor computing system can perform real-time energy-efficient processing of multimodal signals, alleviating data conversion and transmission between different modules in conventional chips. Here, we report a bio-inspired crossmodal spiking sensory neuron (CSSN) based on a flexible VO2 memristor, and demonstrate a crossmodal in-sensor encoding and computing system for wearable human-machine interfaces. We demonstrate excellent performance in the VO2 memristor including endurance (>1012), uniformity (0.72% for cycle-to-cycle variations and 3.73% for device-to-device variations), speed (

Passive daytime radiative cooling has emerged as a promising sustainable technique for meeting ever-growing demand for cooling across multiple sectors. Although a number of review articles have reported fundamental mechanisms and materials developments of daytime radiative cooling, reviews on its current and potential applications have been limited to specific scenarios such as building energy saving. Thus, to the best of our knowledge, here we summarize and discuss a comprehensive list of most current and potential applications of passive daytime radiative cooling to broaden horizons in this technology. First, from a materials perspective, we briefly summarize approaches to creating high solar reflectance and high emissivity in the atmospheric window of 8–13 µm. We then present applications in five major categories, each with several sub-categories, and discus each application with selective articles. Based on the availability of real-world demonstrations and developments in commercialization, we qualitatively assess the technology readiness levels of these applications, highlighting future directions that need more attention. This review offers one-stop access to a comprehensive summary of passive radiative cooling applications along with recent progress and future opportunities.

Abstract Interlayer decoupling plays an essential role in realizing unprecedented properties in atomically thin materials, but it remains relatively unexplored in the bulk. It is unclear how to realize a large crystal that behaves as its monolayer counterpart by artificial manipulation. Here, we construct a superlattice consisting of alternating layers of NbSe2 and highly porous hydroxide, as a proof of principle for realizing interlayer decoupling in bulk materials. In (NaOH)0.5NbSe2, the electric decoupling is manifested by an ideal 1D insulating state along the interlayer direction. Vibration decoupling is demonstrated through the absence of interlayer models in the Raman spectrum, dominant local modes in heat capacity, low interlayer coupling energy and out-of-plane thermal conductivity (0.28 W/mK at RT) that are reduced to a few percent of NbSe2’s. Consequently, a drastic enhancement of CDW transition temperature (>110 K) and Pauling-breaking 2D superconductivity is observed, suggesting that the bulk crystal behaves similarly to an exfoliated NbSe2 monolayer. Our findings provide a route to achieve intrinsic 2D properties on a large-scale without exfoliation.

Abstract Recently, PbSnSe2 alloy was found to exhibit a large hysteresis effect on transport properties, demonstrating its significant potential for thermoelectric applications. Using ab initio approaches, we studied the carrier transport properties of PbSnSe2 crystal, which is a special case of the alloy with the shortest‐range order. A peak power factor of 134.2 μW cm−1 K−2 was found along the cross‐plane direction in the n‐type PbSnSe2 at a doping concentration of 7 × 1020 cm−3 at 700 K. This high power factor originates from delocalized p electrons between intra‐plane Pb–Se pairs and between cross‐plane Sn–Se pairs that can build up transport channels for conducting electrons, leading to a high electrical conductivity of 5.9 × 105 S m−1. Introducing Pb atoms into Pnma phase SnSe can decrease the phonon group velocities and enhance the phonon–phonon scatterings, leading to a low thermal conductivity of 0.53 W m−1 K−1 at 700 K along the cross‐plane direction. The calculated peak ZT of ~3 along the cross‐plane direction at an n‐type doping concentration of around 5 × 1019 cm−3, which represents a theoretical upper limit for an idealized PbSnSe2 crystal. This work interprets the origins of three‐dimensional charge and two‐dimensional phonon transport behavior in PbSnSe2 and demonstrates that such crystals are promising high‐performance thermoelectric semiconductors.

Abstract Developing redox electrolytes with high thermopower is the key to making efficient thermogalvanic batteries for harvesting low‐grade heat. This work applies molecular dynamics simulations to predict the thermopower (i.e. thermogalvanic temperature coefficient) α of the redox pairs Fe(CN)63−/Fe(CN)64− and Fe3+/Fe2+, showing excellent agreement with experimental values. We showed that α of the Fe3+/Fe2+ redox pair can be increased from 1.7±0.4 mV/K to 3.8±0.5 mV/K with the increased acetone to water fraction. We discovered a significant change in the variance of solvent dipole orientation between Fe3+ and Fe2+, which can serve as a microscopic indicator for large α. In mixed acetone‐water solvent, α of Fe3+/Fe2+ showed a rapid increase at high acetone fractions, due to the intercalation of acetone molecules into the first solvation shell of the Fe2+ at high acetone fractions. Our discovery provides insights into how solvation shell order can be engineered to develop electrolytes with high α.

Abstract SnTe possesses a single- to double-valley transition in the conduction band minimum when a compressive strain is applied. Through a tight-binding analysis, it is shown that the variation of the band structure is attributed to the strain-induced delocalization of both the Sn-5s orbitals and Te-5p orbitals with different angular momenta. This effect can largely increase the electron density of states near the band edge and thus keep the Fermi level of the compressed SnTe closer to it, where the electrons have lower scattering rates. The strain-induced double valleys lead to simultaneous increases in the electrical conductivity and the Seebeck coefficient and thereby nearly four times the enhancement of the power factor at the doping concentration of 5×1019 cm–3. This work suggests a feasible concept that can be employed to promote the power factor of a Dirac semiconductor via manipulating the valley degeneracy in the conduction band minimum.

Abstract Cost-effective CO2 capture is essential for decarbonized cement production since it is one of the largest CO2 emission sources, where 60% of direct emissions are from CaCO3 decomposition and 40% are from fuel combustion. This work presents a low-carbon cement manufacturing process by integrating it with renewable energy for electric heating and thermal storage to replace the burning of fossil fuels in the conventional calciner. The low-carbon renewable energy reduces the indirect CO2 emissions from electricity consumption. The high-temperature CO2 is employed as the heat transfer fluid between the energy storage system and the calciner. In the proposed basic manufacturing process, the CO2 from the CaCO3 decomposition can be directly collected without energy-consuming separation since no impurities are introduced. Furthermore, the remaining CO2 from fuel combustion in the kiln can be captured through monoethanolamine (MEA) absorption using waste heat. In the two situations, the overall CO2 emissions can be reduced by 69.7% and 83.1%, respectively, including the indirect emissions of electricity consumption. The economic performance of different energy storage materials is investigated for materials selection. The proposed manufacturing process with a few high-temperature energy storage materials (BaCO3/BaO, SrCO3/SrO, Si, etc.) offers a higher CO2 emission reduction and lower cost than alternative carbon capture routes, i.e., oxyfuel. The cost of CO2 avoided as low as 39.27 $/t can be achieved by thermochemical energy storage with BaCO3/BaO at 1300 °C, which is superior to all alternative technologies evaluated in recent studies.

Concentrated solar power (CSP) plants are generally located in solar-abundant yet hot and water-stressed locations. In such circumstances, efficient but water-intensive once-through wet cooling and water-free but inefficient air cooling are both unfavorable. Considering both thermal efficiency and water availability/temperature, recirculating evaporative cooling is a better alternative. However, evaporative cooling still loses large amounts of water into the atmosphere and thus requires a nonstop water supply. Therefore, simultaneously reducing water loss and maintaining thermal efficiency requires efficient means of supplemental cooling for CSP plants. Following our previous work on scalable radiative cooling films and a kW-scale radiative cooling system, we explore the potential of consumptive water use reduction in recirculating wet-cooled CSP plants by integrating supplemental radiative cooling and cold storage. Through modeling of a reference CSP plant with a supplemental radiative cooling system as large as the plant solar field, the results show that 40%–60% of the annual consumptive water use can be potentially reduced in the hot southwestern U.S. region with daytime-only radiative cooling, whereas the annual potential water saving can be as much as 65%–85% if the radiative cooling system works both day and night with cold storage.

Abstract Thermoelectric cooling (TEC) is critically important in thermal management of laser modules or chips and potentially for personalized thermoregulation. The formulae for efficiency in standard textbooks can only describe the performance of a TEC module with ideal thermal conditions, that is, fixed terminal temperatures, but are unable to deal with a real TEC system where heat transfer at its interfaces with the heat source and sink are finite and with thermal resistances. Here, we define the TEC system‐level performance indices, that is, the maximum cooling power, temperature difference, and coefficient of performance, by introducing a set of explicit formulae. The external heat transfer conditions are taken into account as dimensionless thermal resistance parameters. With these formulae, the TEC system performances are evaluated elegantly with errors well within ±5% over broad operating conditions. We further optimize the cooling power and the coefficient of performance in practical scenarios and establish a general White–Box design procedure for TEC systems, which enables a transparent design process and straightforward analysis of performance bottlenecks. A set of cooling experiments are performed to validate the analytical model and to illustrate the dependence of system design on realistic thermal conditions. By choosing the suitable TEC module parameter under given external heat transfer conditions, the cooling power can be improved by more than 100%. This work sheds some light on the integral design of TEC systems for broad applications to take full advantage of the advanced thermoelectric materials in the cooling field.

Abstract Solid particles are generally considered to be the most suitable heat transfer fluid (HTF) and thermal energy storage (TES) materials for the next‐generation concentrated solar power (CSP) plant. The operating temperature of the solar receiver can be raised to exceed 800°C by the application of appropriate solid particles. In this way, power conversion efficiencies greater than 50% can be achieved with the supercritical carbon dioxide (sCO2) Brayton cycle. Solid particle solar receiver (SPSR) is the key equipment to absorb the concentrated solar flux, and its thermal performance is remarkably affected by receiver system designs, particle flow characteristics, and properties of solid particulate materials. This paper provides an in‐depth review of various SPSR technologies, as well as pertinent solid particle selections, optimization of the receiver system structures, particle flow characteristics, and heat transfer characteristics. The technical drawbacks, the large‐scale development prospects, and the potential optimization strategies of the various SPSR designs are highlighted by the comparative analysis of multiple parameters.

A transparent radiative cooling (T-RC) film with low transmittance in solar spectra and selectively high emissivity in the atmospheric window (8–13 μm) is applied on roof glazing for building energy saving. To evaluate the performance of the T-RC film, two identical model boxes (1.0 m × 0.6 m × 1.2 m, L × W × H) were constructed and the inside air temperatures were measured in August in Ningbo, China. Results show that the maximum temperature difference between the two model boxes with and without the T-RC film was 21.6 °C during the experiment. A whole building model was built in EnergyPlus for the model box. With a good agreement achieved between the calculation results and the measured temperature data, the experimentally validated EnergyPlus model was then extended to an 815.1 m2 exhibition building with roof glazing to analyze the annual air conditioning (AC) energy consumption. The results show that by incorporating both the T-RC film's cooling benefit in summer and heating penalty in winter, the annual AC energy consumption of the exhibition building can be reduced by 40.9–63.4%, varying with different climate conditions.

Summary: Many of the advanced technologies, e.g., microprocessors, laser and radar, and power transmitters and amplifiers, are becoming increasingly dependent on the ability to dissipate the enormous amount of waste heat in extremely small areas. Two-phase heat spreaders utilizing the liquid-vapor phase change are appealing due to the high performance and potentially low cost. However, thin film evaporation is limited by the capillary dry-out of wicking structures. We demonstrate here an ultra-high thermal conductance and high flux heat spreader enabled by a capillary-driven liquid film boiling process on a hierarchical mesh wicking structure. By manipulating liquid wicking flow and vapor bubble escape, liquid film boiling is demonstrated to have a heat removal capability of 552 W/cm2 from an area of 25 mm2 with a temperature increase of less than 8 K, corresponding to a heat transfer coefficient of 732.5 kW/m2·K. The effective thermal conductivity of the 1-mm-thick two-phase heat spreader is larger than 104 W/m·K.

Summary: Evaporation, boiling, and condensation are fundamental liquid-vapor phase-change heat transfer processes and have been utilized in many conventional and emerging energy systems. Recent advances in the manipulation of interface wetting and heterogeneous nucleation using micro/nano-structured surfaces have enabled exciting two-phase flow dynamics and heat transfer enhancement. However, independently manipulating droplets, bubbles, or liquid films through surface modification has encountered bottlenecks. In this Perspective, we discuss an emerging strategy where droplets/bubbles are coupled with a liquid film to control fluid dynamics for minimizing the thermal resistance between the liquid-vapor interface and solid substrate, thus significantly enhancing the heat transfer performance beyond the state of the art.

To further improve the mechanical properties of H13 steel at room and high temperatures, its precipitates were regulated based on the Thermo-Calc results. Scanning electron microscope (SEM), electron backscattering diffraction (EBSD), transmission electron microscope (TEM), and X-ray diffraction (XRD) Rietveld refinement were used to study the effect of the intercritical annealing on the microstructure and mechanical properties of H13 steel. The results show that the intercritical annealing at 850~95 °C increased the VC volume fraction from 2.23 to 3.03~3.48%. Increasing the VC volume fraction could inhibit the M7C3 precipitation from 10.01 to 6.63~5.72% during tempering. A large amount of VC also promoted the M23C6 precipitation during tempering at higher dislocation densities. The intercortical annealing simultaneously increased the elongation of H13 steel. An excellent combination (room temperature: ultimate tensile strength (UTS) of 898 MPa and total elongation (TEL) of 19.35%, 650 °C: UTS of 439 MPa, and TEL of 27.80%) could be obtained when intercritical annealing is performed at 900 °C. Meanwhile, after aging at 650 °C for 128 h, the room temperature UTS and TEL decreased by only 31 MPa and 0.52%, respectively.

The concept of a novel integrated greenhouse is introduced in which a spectral-splitting material is employed to reduce heat transfer to the greenhouse by utilizing part of the solar spectrum for heating a water solar collector. The irradiating solar spectrum is also shifted to wavelengths propitious for plant growth. The solar collector is part of an integrated humidification-dehumidification system that can produce freshwater for plant irrigation from a variety of compromised water sources. In order to evaluate the performance of the proposed integrated greenhouse, a multivariable thermal model is presented which includes the solar collector, the desalination system, and the greenhouse (accounting for the air, the soil, the plants, and the ground). A representative greenhouse is modeled and the results are used to estimate freshwater production and associated reduction in cooling or heating loads. The results of the model are used for evaluating the performance of the representative integrated greenhouse in various locations across the United States. Results suggest that the proposed greenhouse in Phoenix (Arizona, USA) can produce about 85% of required water for tomato growth, while reducing the cooling load by more than 25%.

Thanks to recent advances in nanophotonics and scalable manufacturing of metamaterials, radiative sky cooling has emerged as a “self-reliant” cooling technology with various potential applications. However, not every region across the globe is well suited for the adoption of radiative cooling technologies, depending on the local climate, population density, cooling demand, air conditioning saturation, economic prosperity, etc. Because the atmospheric downward longwave radiation, especially the portion from the atmospheric window (8–13 µm), is substantially affected by weather conditions, the performance of a well-designed radiative cooler can be vastly different across regions and seasons. Here, we first map the global radiative sky cooling potential in the form of net cooling power density. We then further evaluate it based on the global population density and cooling demand. In terms of the adjusted potential, we show that geographically and demographically “transitional” regions, located between wet and dry climates as well as sparsely and densely populated regions, are better suited for the adoption of radiative cooling technologies because of their temperate climate and moderate population density. Even in densely populated and humid regions, the cumulative impact and other accompanying benefits must not be ignored.

Hybrid inorganic-organic superlattices show promise for flexible thermoelectric applications, yet they suffer from limited performance. Here, the authors devise a strategy for carrier optimization in a hybrid inorganic-organic superlattice of TiS2[tetrabutylammonium] x [hexylammonium] y , achieving an ultrahigh power factor of 904 μW m−1 K−2.

In order to reduce the residual stress of the GH4169 alloy, the effect and micro-mechanism of the tensile deformation were studied. The residual stress, dislocation density, and distribution of the GH4169 alloy were analyzed by X-ray residual stress tester, X-ray diffractometer (XRD), and electron backscatter diffraction (EBSD). The results show that: with the increase of tensile deformation, the residual stress relief first increases and then decreases. When the tensile deformation is 3%, the reduction rate of residual stress reaches the maximum, which is 90%. The mechanism of residual stress relief by the tensile treatment is that the dislocation group in the alloy is activated by tensile treatment, and the dislocation distribution in the alloy is more uniform by dislocation movement, multiplication, and annihilation so that the residual stress can be eliminated.

We theoretically investigate the enhancement of thermoelectric cooling performance in thermoelectric refrigerators made of materials with inhomogeneous thermal conductivity, beyond the usual practice of enhancing thermoelectric figure of merit (ZT) of materials. The dissipation of the Joule heat in such thermoelectric refrigerators is asymmetric which can give rise to better thermoelectric cooling performance. Although the thermoelectric figure of merit and the coefficient-of-performance are slightly enhanced, both the maximum cooling power and the maximum cooling temperature difference can be enhanced significantly. This finding can be used to increase the heat absorption at the cold end. We further find that the asymmetric dissipation of Joule heat leads to thermal rectification.

Thermoelectric (TE) devices are solid-state energy converters that can be used for power generation through the Seebeck effect and TE cooling through the Peltier effect. Nanostructures give great opportunities to engineer TE energy conversion efficiency. In this work, we investigate TE transport properties in structured nanowires (NWs) in the ballistic transport regime, where the NWs are bent, kinked, stubbed and segmented like a superlattice nanowire using the Green’s function method and the Landauer–Büttiker formula. A large Seebeck coefficient is found when the transmission gap appears due to the quantum interference effect of electrons. The sign of the Seebeck coefficient can be controlled by the geometries of these structured NWs. This finding is helpful for the design of nanoscale TE devices, such as thermocouple, with the same type of material doping rather than those comprised of n -type and p -type materials.