Electric Field-Enhanced Ion Rejection Rate in Freeze Desalination.

Freeze desalination is an appealing method for seawater desalination through freezing seawater. The percentage of ions in the liquid phase, which is termed ion rejection rate, is a critical factor affecting the performance of freeze desalination. Improving the ion rejection rate is an important topic for freeze desalination. In this work, we investigate the effects of electric fields on the ion rejection rate during the freezing of seawater through molecular dynamics simulations. It is found that the ion rejection rate increases with increasing electric field strength. The enhanced ion rejection rate is due to the reduction of the energy barrier at the ice-water interface caused by the electric field, which affects the orientation of water molecules and ion-water interactions. However, the electric field hinders the ice growth rate, which affects the productivity of freeze desalination. Nevertheless, the finding in this work offers a new idea to improve the ion rejection rate. Practically, a trade-off needs to be found to optimize the overall performance of freeze desalination.

A Janus Textile Capable of Radiative Subambient Cooling and Warming for Multi-Scenario Personal Thermal Management.

Textiles with radiative cooling/warming capabilities provide a green and effective solution to personal thermal comfort in different climate scenarios. However, developing multiple-mode textiles for wearing in changing climates with large temperature variation remains a challenge. Here a Janus textile is reported, comprising a polyethersulfone (PES)-Al2 O3 cooling layer optically coupled with a Ti3 C2 Tx warming layer, which can realize sub-ambient radiative cooling, solar warming, and active Joule heating. Owing to the intrinsically high refractive index of PES and the rational design of the fiber topology, the nanocomposite PES textile features a record high solar reflectance of 0.97. Accompanied by an infrared (IR) emittance of 0.91 in the atmospheric window, sub-ambient cooling of 0.5-2.5 °C is achieved near noontime in humid summer under ≈1000 W m-2 solar irradiation in Hong Kong. The simulated skin covered with the textile is ≈10 °C cooler than that with white cotton. The Ti3 C2 Tx layer provides a high solar-thermal efficiency of ≈80% and a Joule heating flux of 66 W m-2 at 2 V and 15 °C due to its excellent spectral selectivity and electrical conductivity. The switchable multiple working modes enable effective and adaptive personal thermal management in changing environments.

A UV-Reflective Organic-Inorganic Tandem Structure for Efficient and Durable Daytime Radiative Cooling in Harsh Climates.

Radiative cooling shows great promise in eco-friendly space cooling due to its zero-energy consumption. For subambient cooling in hot humid subtropical/tropical climates, achieving ultrahigh solar reflectance (≥96%), durable ultraviolet (UV) resistance, and surface superhydrophobicity simultaneously is critical, which, however, is challenging for most state-of-the-art scalable polymer-based coolers. Here an organic-inorganic tandem structure is reported to address this challenge, which comprises a bottom high-refractive-index polyethersulfone (PES) cooling layer with bimodal honeycomb pores, an alumina (Al2 O3 ) nanoparticle UV reflecting layer with superhydrophobicity, and a middle UV absorption layer of titanium dioxide (TiO2 ) nanoparticles, thus providing thorough protection from UV and self-cleaning capability together with outstanding cooling performance. The PES-TiO2 -Al2 O3 cooler demonstrates a record-high solar reflectance of over 0.97 and high mid-infrared emissivity of 0.92, which can maintain their optical properties intact even after equivalent 280-day UV exposure despite the UV-sensitivity of PES. This cooler achieves a subambient cooling temperature up to 3 °C at summer noontime and 5 °C at autumn noontime without solar shading or convection cover in a subtropical coastal city, Hong Kong. This tandem structure can be extended to other polymer-based designs, offering a UV-resist but reliable radiative cooling solution in hot humid climates.

A Highly Transparent Photo-Electro-Thermal Film with Broadband Selectivity for All-Day Anti-/De-Icing.

A photo- and electro-thermal film can convert sunlight and electricity into heat to solve icing problems. Combination of them provides an efficient strategy for all-day anti-/de-icing. However, only opaque surfaces have been reported, due to the mutual exclusiveness between photon absorption and transmission. Herein, a highly transparent and scalable solution-processed photo-electro-thermal film is reported, which exhibits an ultra-broadband selective spectrum to separate the visible light from sunlight and a countertrend suppress of emission in longer wavelength. It absorbs ≈ 85% of invisible sunlight (ultraviolet and near-infrared) for light-heat conversion, meanwhile maintains luminous transmittance > 70%. The reflection of mid-infrared leads to low emissivity (0.41), which further preserves heat on the surface for anti-/de-icing purpose. This ultra-broadband selectivity enables temperature elevation > 40 °C under 1-sun illumination and the mutual support between photo-thermal and electro-thermal effects contributes to > 50% saving of electrical consumption under weak solar exposure (0.4-sun) for maintaining unfrozen surfaces at -35 °C environment. The reverberation from photo-electro-thermal and super-hydrophobic effects illustrates a lubricating removal of grown ice in short time (< 120 s). The self-cleaning ability and the durability under mechanical, electrical, optical, and thermal stresses render the film stable for long-term usage in all-day anti-/de-icing applications.

Nanoparticle-on-Mirror Metamaterials for Full-Spectrum Selective Solar Energy Harvesting.

Most broadband metamaterial absorbers are realized by patterning periodic arrays of plasmonic nanoparticles (>100 nm) on dielectric/metallic substrates to enable both electric and magnetic resonances. These metamaterials, however, require costly nanolithographic top-down techniques for fabrication. Here, we demonstrate new-concept nanoparticle-on-mirror (NoM) metamaterial absorbers by densely packing plasmonic nanoparticles of much smaller size (∼30 nm) on metal films directly. Such a simple but rational design enables the use of all-solution-based bottom-up processes. Because of the decoupling of electric and magnetic polarizations in these ultrasmall nanoparticles, excellent impedance match and near-perfect light absorption can be achieved in a broad band over the solar spectrum with weak thermal emission. Proof-of-concept large-area NoM metamaterial absorbers that offer a solar absorptance of 94% but a low IR emittance of 2% are experimentally demonstrated. The outstanding performance, bottom-up process, and great compatibility render the design promising for efficient and large-scale solar energy harvesting.

Experimental Evidence of Superdiffusive Thermal Transport in Si0.4Ge0.6 Thin Films.

Superdiffusive thermal transport represents a unique phenomenon in heat conduction, which is characterized by a size (L) dependence of thermal conductivity (κ) in the form of κ ∝ Lß with a constant ß between 0 and 1. Although superdiffusive thermal transport has been theoretically predicted for SiGe alloys, direct experimental evidence is still lacking. Here, we report on a systematic experimental study of the thickness-dependent thermal conductivity of Si0.4Ge0.6 thin films grown by molecular beam epitaxy. The cross-plane thermal conductivity of Si0.4Ge0.6 thin films spanning a thickness range from 20 to 1120 nm was measured in the temperature range 120-320 K via a differential three-omega method. Results show that the thermal conductivity follows a consistent κ ∝ t0.26 power law with the film thickness (t) at different temperatures, providing direct experimental evidence that alloy-scattering dominated thermal transport in SiGe is superdiffusive.

Self-Protecting Aqueous Lithium-Ion Batteries.

Capacity degradation and destructive hazards are two major challenges for the operation of lithium-ion batteries at high temperatures. Although adding flame retardants or fire extinguishing agents can provide one-off self-protection in case of emergency overheating, it is desirable to directly regulate battery operation according to the temperature. Herein, smart self-protecting aqueous lithium-ion batteries are developed using thermos-responsive separators prepared through in situ polymerization on the hydrophilic separator. The thermos-responsive separator blocks the lithium ion transport channels at high temperature and reopens when the battery cools down; more importantly, this transition is reversible. The influence of lithium salts on the thermos-responsive behaviors of the hydrogels is investigated. Then suitable lithium salt (LiNO3 ) and concentration (1 m) are selected in the electrolyte to achieve self-protection without sacrificing battery performance. The shut-off temperature can be tuned from 30 to 80 °C by adjusting the hydrophilic and hydrophobic moiety ratio in the hydrogel for targeted applications. This self-protecting LiMn2 O4 /carbon coated LiTi2 (PO4 )3 (LMO/C-LTP) battery shows promise for smart energy storage devices with high safety and extended lifespan in case of high operating temperatures.

Unlocking the High Capacity Ammonium-Ion Storage in Defective Vanadium Dioxide.

Aqueous ammonium-ion storage has been considered a promising energy storage competitor to meet the requirements of safety, affordability, and sustainability. However, ammonium-ion storage is still in its infancy in the absence of reliable electrode materials. Here, defective VO2 (d-VO) is employed as an anode material for ammonium-ion batteries with a moderate transport pathway and high reversible capacity of ≈200 mAh g-1 . Notably, an anisotropic or anisotropic behavior of structural change of d-VO between c-axis and ab planes depends on the state of charge (SOC). Compared with potassium-ion storage, ammonium-ion storage delivers a higher diffusion coefficient and better electrochemical performance. A full cell is further fabricated by d-VO anode and MnO2 cathode, which delivers a high energy density of 96 Wh kg-1 (based on the mass of VO2 ), and a peak energy density of 3254 W kg-1 . In addition, capacity retention of 70% can be obtained after 10 000 cycles at a current density of 1 A g-1 . What's more, the resultant quasi-solid-state MnO2 //d-VO full cell based on hydrogel electrolyte also delivers high safety and decent electrochemical performance. This work will broaden the potential applications of the ammonium-ion battery for sustainable energy storage.

Responses of soil enzyme activities and plant growth in a eucalyptus seedling plantation amended with bacterial fertilizers.

Plant growth-promoting rhizobacteria (PGPR) are widely used to improve plant nutrient uptake and assimilation and soil physicochemical properties. We investigated the effects of bacterial (Bacillus megaterium strain DU07) fertilizer applications in a eucalyptus (clone DH32-29) plantation in Guangxi, China in February 2011. We used two types of organic matter, i.e., fermented tapioca residue ("FTR") and filtered sludge from a sugar factory ("FS"). The following treatments were evaluated: (1) no PGPR and no organic matter applied (control), (2) 3 × 109 CFU/g (colony forming unit per gram) PGPR plus FS (bacterial fertilizer 1, hereafter referred to as BF1), (3) 4 × 109 CFU/g plus FS (BF2), (4) 9 × 109 CFU/g plus FS (BF3), (5) 9 × 109 CFU/g broth plus FTR (BF4). Soil and plant samples were collected 3 months (M3) and 6 months (M6) after the seedlings were planted. In general, bacterial fertilizer amendments significantly increased plant foliar total nitrogen (TN) and soil catalase activity in the short term (month 3, M3); whereas, it significantly increased foliar TN, chlorophyll concentration (Chl-ab), proline; plant height, diameter, and volume of timber; and soil urease activity, STN, and available N (Avail N) concentrations in the long term (month 6, M6). Redundancy analysis showed that soil available phosphorus was significantly positively correlated with plant growth in M3, and soil Avail N was negatively correlated with plant growth in M6. In M3, soil catalase was more closely correlated with plant parameters than other enzyme activities and soil nutrients, and in M6, soil urease, polyphenol oxidase, and peroxidase were more closely correlated with plant parameters than other environmental factors and soil enzyme activities. PCA results showed that soil enzyme activities were significantly improved under all treatments relative to the control. Hence, photosynthesis, plant growth, and soil N retention were positively affected by bacterial fertilizer in M6, and bacterial fertilizer applications had positive and significant influence on soil enzyme activities during the trial period. Thus, bacterial fertilizer is attractive for use as an environmentally friendly fertilizer in Eucalyptus plantations following proper field evaluation.

Enhancing sodium ionic conductivity in tetragonal-Na3PS4 by halogen doping: a first principles investigation.

Tetragonal Na3PS4 (t-Na3PS4) has been demonstrated as a very promising candidate for a solid-state sodium-ion electrolyte with high Na ionic conductivity at ambient temperature. In this paper, we systematically investigated the Na ionic conductivity in pristine and halogen (F, Cl, Br, and I) doped tetragonal-Na3PS4 superionic conductors using first-principles calculations. The Na ionic conductivity of pristine t-Na3PS4 is calculated to be about 0.01 mS cm-1, while much higher Na ionic conductivities could be achieved by introducing Na ion vacancies via a halogen doping strategy. The calculated Na ionic conductivity of t-Na3PS4 doped with 1.56% Cl is 1.07 mS cm-1 at ambient temperature. Among different halogen-doped t-Na3PS4, Br-doped t-Na3PS4 shows the lowest activation energy and the highest Na ionic conductivity, which reaches 2.37 mS cm-1 at 300 K. The low activation energy and high Na ionic conductivity in Br-doped t-Na3PS4 are due to a relatively lower defect binding energy of the defect pair of halogen substitution and a Na ion vacancy. Our results suggest Br-doped t-Na3PS4 may serve as a very promising Na-ion solid-state superionic conductor.

Generalized Two-Temperature Model for Coupled Phonons in Nanosized Graphene.

The design of graphene-based composite with high thermal conductivity requires a comprehensive understanding of phonon coupling in nanosized graphene. We extended the two-temperature model to coupled groups of phonons. The study give new physical quantities, the phonon-phonon coupling factor and length, to characterize the couplings quantitatively. Besides, our proposed coupling length has an obvious dependence on system size. Our studies can not only observe the nonequilibrium between different groups of phonons but explain theoretically the thermal resistance inside nanosized graphene.

Stress-Induced Cubic-to-Hexagonal Phase Transformation in Perovskite Nanothin Films.

The strong coupling between crystal structure and mechanical deformation can stabilize low-symmetry phases from high-symmetry phases or induce novel phase transformation in oxide thin films. Stress-induced structural phase transformation in oxide thin films has drawn more and more attention due to its significant influence on the functionalities of the materials. Here, we discovered experimentally a novel stress-induced cubic-to-hexagonal phase transformation in the perovskite nanothin films of barium titanate (BaTiO3) with a special thermomechanical treatment (TMT), where BaTiO3 nanothin films under various stresses are annealed at temperature of 575 °C. Both high-resolution transmission electron microscopy and Raman spectroscopy show a higher density of hexagonal phase in the perovskite thin film under higher tensile stress. Both X-ray photoelectron spectroscopy and electron energy loss spectroscopy does not detect any change in the valence state of Ti atoms, thereby excluding the mechanism of oxygen vacancy induced cubic-to-hexagonal (c-to-h) phase transformation. First-principles calculations show that the c-to-h phase transformation can be completed by lattice shear at elevated temperature, which is consistent with the experimental observation. The applied bending plus the residual tensile stress produces shear stress in the nanothin film. The thermal energy at the elevated temperature assists the shear stress to overcome the energy barriers during the c-to-h phase transformation. The stress-induced phase transformation in perovskite nanothin films with TMT provides materials scientists and engineers a novel approach to tailor nano/microstructures and properties of ferroelectric materials.

Size- and temperature-dependent Young's modulus and size-dependent thermal expansion coefficient of thin films.

Nanomaterials possess a high surface/volume ratio and surfaces play an essential role in size-dependent material properties. In the present study, nanometer-thick thin films were taken as an ideal system to investigate the surface-induced size- and temperature-dependent Young's modulus and size-dependent thermal expansion coefficient. The surface eigenstress model was further developed with the consideration of thermal expansion, leading to analytic formulas of size- and temperature-dependent Young's modulus, and size-dependent thermal expansion coefficient of thin films. Molecular dynamics (MD) simulations on face-centered cubic (fcc) Ag, Cu, and Ni(001) thin films were conducted at temperatures ranging from 300 K to 600 K. The MD simulation results are perfectly consistent with the theoretical predictions, thereby verifying the theoretical approach. The newly developed surface eigenstress model will be able to attack similar problems in other types of nanomaterials.

Unusual Enhancement in Intrinsic Thermal Conductivity of Multilayer Graphene by Tensile Strains.

Using the Boltzmann-Peierls equation for phonon transport approach with the inputs of interatomic force constants from the self-consistent charge density functional tight binding method, we calculate the room-temperature in-plane lattice thermal conductivities k of multilayer graphene (up to four layers) and graphite under different isotropic tensile strains. The calculated in-plane k of graphite, finite monolayer graphene and 3-layer graphene agree well with previous experiments. For unstrained graphene systems, both the intrinsic k and the extent of the diffusive transport regime present a drastic dimensional transition in going from monolayer to 2-layer graphene and thereafter a gradual transition to the graphite limit. We find a peak enhancement of intrinsic k for multilayer graphene and graphite with increasing strain with the largest enhancement amplitude ∼40%. Competition between the decreased mode heat capacities and the increased lifetimes of flexural phonons with increasing strain contribute to this k behavior. Similar k behavior is observed for 2-layer hexagonal boron nitride systems. This study provides insights into engineering k of multilayer graphene and boron nitride by strain and into the nature of thermal transport in quasi-two-dimensional and highly anisotropic systems.

Solid-state semiconductor optical cryocooler based on CdS nanobelts.

We demonstrate the laser cooling of silicon-on-insulator (SOI) substrate using CdS nanobelts. The local temperature change of the SOI substrate exactly beneath the CdS nanobelts is deduced from the ratio of the Stokes and anti-Stokes Raman intensities from the Si layer on the top of the SOI substrate. We have achieved a 30 and 20 K net cooling starting from 290 K under a 3.8 mW 514 nm and a 4.4 mW 532 nm pumping, respectively. In contrast, a laser heating effect has been observed pumped by 502 and 488 nm lasers. Theoretical analysis based on the general static heat conduction module in the Ansys program package is conducted, which agrees well with the experimental results. Our investigations demonstrate the laser cooling capability of an external thermal load, suggesting the applications of II-VI semiconductors in all-solid-state optical cryocoolers.

Stepless IR Chromism in Ti3 C2 Tx MXene Tuned by Interlayer Water Molecules.

Real-time control over infrared (IR) radiation of objects is highly desired in a variety of areas such as personal thermal regulation and IR camouflage. This requires the dynamic modulation of IR emissivity in a stepless manner over a wide range (>50%), which remains a daunting challenge. Here, an emissivity modulation phenomenon is reported in stacked 2D Ti3 C2 Tx MXene nanosheets, from 12% to 68% as the intercalation/discharging of water molecules within the interlayers. The intercalation of water molecules dynamically changes the electronic properties and the complex permittivity in IR frequencies of Ti3 C2 Tx . This emissivity modulation is a stepless and reversible process without the assistance of any external energy input. Further, intercalating cellulose nanofibers into the Ti3 C2 Tx interlayers makes this dynamic process highly repeatable. Last, a sweat-responsive adaptive textile that can improve thermal comfort of human body under changes in metabolic rates and environmental conditions is demonstrated, showing great potential of this mechanism in passive on-demand radiation modulation.

Mask-inspired moisture-transmitting and durable thermochromic perovskite smart windows.

Thermochromic perovskite smart windows (TPWs) are a cutting-edge energy-efficient window technology. However, like most perovskite-based devices, humidity-related degradation limits their widespread application. Herein, inspired by the structure of medical masks, a unique triple-layer thermochromic perovskite window (MTPW) that enable sufficient water vapor transmission to trigger the thermochromism but effectively repel detrimental water and moisture to extend its lifespan is developed. The MTPW demonstrates superhydrophobicity and maintains a solar modulation ability above 20% during a 45-day aging test, with a decay rate 37 times lower than that of a pristine TPW. It can also immobilize lead ions and significantly reduce lead leakage by 66 times. Furthermore, a significant haze reduction from 90% to 30% is achieved, overcoming the blurriness problem of TPWs. Benefiting from the improved optical performance, extended lifespan, suppressed lead leakage, and facile fabrication, the MTPW pushes forward the wide applications of smart windows in green buildings.

Robust All-Day Frostphobic Surfaces.

The application of solar-thermal surfaces for antifrosting and defrosting has emerged as a passive and environmentally friendly approach to mitigate the negative consequences of frost formation, such as structural damage and reduced heat transfer efficiency. However, achieving robust all-day frostphobicity solely through interfacial modification and solar-thermal effects is challenging in practical applications: The thick frost that accumulates at night strongly scatters solar radiation, rendering the solar-thermal coatings ineffective during the daytime. Additionally, these nanostructured coatings are susceptible to wear and tear when exposed to the outdoors for extended periods of time. To address these challenges, we present an innovative frostphobic surface that incorporates V-grooved structures with superhydrophobic solar-thermal layers (VSSs). The out-of-plane gradient structures facilitate spatially regulated vapor diffusion, an enhanced photothermal effect, and robust water repellency. These features not only prevent frost from covering the entire surface overnight, enabling effective solar-thermal defrosting during the daytime, but also protect the surface from deterioration. The combined merits ensure robust all-day frostphobicity and exceptional durability, making the VSS surface promising for practical applications and extending the lifespan in extreme environments.

Shear-Enhanced Ion Rejection during Seawater Freezing.

Ion rejection during seawater freezing is the basis for freeze desalination. A high ion rejection rate is desired for improving the performance of freeze desalination. In this work, we propose a method to enhance the ion rejection rate through external shear, which is demonstrated through molecular dynamics (MD) simulations and experiments. MD simulations show that the ion rejection rate increases with an increasing shear rate. This is attributed to the disruption of the hydration bonds between ions and water molecules in the hydration shell caused by the shear. Consequently, the mobility of ions is increased, and the energy barrier is reduced at the ice-water interface such that ions have a greater chance of diffusing into the aqueous solution, leading to an enhanced ion rejection rate. The MD results in this work are qualitatively confirmed by experiments and provide insights into the enhancement of the ion rejection rate through external parameters.

Ultrasensitive Flexible Thermal Sensor Arrays based on High-Thermopower Ionic Thermoelectric Hydrogel.

Ionic circuits using ions as charge carriers have demonstrated great potential for flexible and bioinspired electronics. The emerging ionic thermoelectric (iTE) materials can generate a potential difference by virtue of selective thermal diffusion of ions, which provide a new route for thermal sensing with the merits of high flexibility, low cost, and high thermopower. Here, ultrasensitive flexible thermal sensor arrays based on an iTE hydrogel consisting of polyquaternium-10 (PQ-10), a cellulose derivative, as the polymer matrix and sodium hydroxide (NaOH) as the ion source are reported. The developed PQ-10/NaOH iTE hydrogel achieves a thermopower of 24.17 mV K-1 , which is among the highest values reported for biopolymer-based iTE materials. The high p-type thermopower can be attributed to thermodiffusion of Na+ ions under a temperature gradient, while the movement of OH- ions is impeded by the strong electrostatic interaction with the positively charged quaternary amine groups of PQ-10. Flexible thermal sensor arrays are developed through patterning the PQ-10/NaOH iTE hydrogel on flexible printed circuit boards, which can perceive spatial thermal signals with high sensitivity. A smart glove integrated with multiple thermal sensor arrays is further demonstrated, which endows a prosthetic hand with thermal sensation for human-machine interaction.