Sub-ambient Temperatures Research Articles

Design of radiative cooler based on porous TiO2 for improving solar cells' performance.

It is widely known that the conversion efficiency and lifetime of solar cell modules decrease with higher operating temperatures. To maximize both efficiency and reliability, solar cell modules benefit greatly from the use of daytime passive radiative cooling techniques. In this study, we introduce a simple, low-cost, double-layer coating based on porous TiO2 as a daytime passive radiative cooling system to achieve sub-ambient operating temperatures in a solar cell module. The top and bottom layers of the implemented design are porous TiO2 and BK7 (glass), respectively. This solar cell/radiative cooling hybrid design is capable of achieving both high solar absorption in the photovoltaic conversion band 0.3-1.1 µm and high emissivity over 0.96 in the atmospheric transparency window 8-13 µm, while rejecting parasitic solar absorption. At 800W/m2 solar heating power, we found that adding the proposed cooling design on top of mono-crystalline silicon (m-Si), the solar cell panel lowered its operating temperature by 18.04°C, leading to a relative (effective) efficiency advantage of 21.56%. Additionally, at steady-state temperature (325 K), the power conversion efficiency of our radiative-cooler-coated m-Si solar cell is estimated to reach 20.46%, in contrast to 16.83% for an uncoated silicon solar cell. When compared with an uncoated silicon solar cell, optoelectronic simulations of our coated silicon solar cell show a short-circuit current density Jsc as high as 5.07mA/cm2, and the open circuit voltage Voc increased from 771.78 to 776.3 mV.

Molecular Recognition of the HPLC Whelk-O1 Selector towards the Conformational Enantiomers of Nevirapine and Oxcarbazepine.

The presence of stereogenic elements is a common feature in pharmaceutical compounds, and affording optically pure stereoisomers is a frequent issue in drug design. In this context, the study of the chiral molecular recognition mechanism fundamentally supports the understanding and optimization of chromatographic separations with chiral stationary phases. We investigated, with molecular docking, the interactions between the chiral HPLC selector Whelk-O1 and the stereoisomers of two bioactive compounds, the antiviral Nevirapine and the anticonvulsant Oxcarbazepine, both characterized by two stereolabile conformational enantiomers. The presence of fast-exchange enantiomers and the rate of the interconversion process were studied using low temperature enantioselective HPLC and VT-NMR with Whelk-O1 applied as chiral solvating agent. The values of the energetic barriers of interconversion indicate, for the single enantiomers of both compounds, half-lives sufficiently long enough to allow their separation only at critically sub-ambient temperatures. The chiral selector Whelk-O1 performed as a strongly selective discriminating agent both when applied as a chiral stationary phase (CSP) in HPLC and as CSA in NMR spectroscopy.

Enhanced thermal stability and monodomain growth in a 3D soft photonic crystal aided by graphene substrate

We report the growth of monodomain blue phase liquid crystal and its thermal stability on reduced graphene oxide-grown quartz substrates using optical reflection microscopy and spectroscopy. Optical textural images show that the graphene substrate enhances the thermal range of the blue phase by a factor of four compared to conventional ITO-coated glass substrate. The phase is stabilized down to sub-ambient temperatures (from 60 °C to 18 °C) with the blue phase domains remaining undistorted at ambient conditions for more than three months. Also, the graphene substrate aids the monodomain formation with the average BP platelet size being nearly two orders of magnitude larger compared to the ITO / bare quartz substrates. The enhanced thermal stability and single-crystal-like growth of the blue phase are due to the improved wettability and non-covalent π-π interaction between graphene layers and liquid crystal molecules, as confirmed from the contact angle and Raman spectroscopic measurements respectively. Thus, the room temperature stable, graphene layer-stabilized-blue phase is an ideal candidate for high-performance photonic applications.

Optimization and performance analysis of a multilayer structure for daytime radiative cooling

Daytime radiative cooling has drawn much attention recently because a target surface can be passively maintained at sub-ambient temperature. In order to implement a daytime radiative cooling device (simply ‘radiative cooler’), strong thermal emission should be focused in the mid-infrared regime (8–13 µm), called ‘atmospheric transparent window’. At the same time, absorption of the solar irradiation should be minimized. In the present study, for optimal performance of daytime radiative cooling, a mixed-integer genetic algorithm was employed to achieve maximal infrared emission as well as minimal solar absorption. The combination of total number of layer, materials, and thickness of each layer in the multilayered radiative cooler were determined through optimization. The optimized multilayer structure exhibited the spectrally-averaged (in the 8–13 µm wavelength range) normal emissivity value of 0.96 and the solar-weighted absorptivity of 0.03. The corresponding net cooling power was found to be 101.0 W/m2, and a sub-ambient cooling temperature of 11.2∘C (i.e., below ambient temperature) was predicted in daytime at air-mas 1.5 condition. Besides, the mechanism of enhanced emission in the infrared region and suppressed absorption in the solar spectrum were thoroughly investigated. We also derived the expected performance of the optimized radiative cooler for various conditions of the environmental parameters, such as convection heat transfer coefficient, ambient temperature, and precipitable water level.

Passive Sub-Ambient Cooling from a Transparent Evaporation-Insulation Bilayer

<h2>Summary</h2> Hydrogel-based evaporative cooling, which mimics perspiration of mammals, provides great potential to reduce energy consumption for thermal regulation. Yet, environmental heat gain presents a critical challenge to this cooling strategy at sub-ambient temperatures. Herein, inspired by the fur layer of desert animals, we propose an evaporation-insulation cooling design based on hydrogels and aerogels. Our transparent bilayer structure relies on water evaporation from hydrogels through highly porous aerogels that are of ultralow thermal conductivity and minimize heating from the surroundings. Consequently, this bilayer design allows for optimization between the temperature drop from the ambient and the effective cooling time, which we demonstrated through both modeling and experiments. We show that our hydrogel-aerogel structure can extend the lifetime of the cooling package by 400% compared with the conventional single-layer design. We further provide design guidelines for various cooling applications, including thermal regulation of food, pharmaceuticals, and buildings.

Daytime radiative cooler using porous TiO2: new approach.

Passive daytime radiative cooling remains a topic of intense interest that has gained great attention recently, mainly due to its important applications, such as electronic heat dissipation, solar cells, and photo-thermal technologies. In order to achieve the daytime radiative cooling for thermal management applications, a new smart shield should be designed to have both a low absorptivity in the solar range of 0.3-2.5 µm and high emissivity in the atmospheric transparency windows of 8-13 µm and 16-26 µm. In this work, we propose and analyze a new, inexpensive, and highly scalable double-layer coating to reach an efficient passive daytime radiative cooling. Double-layer coatings consisting of a top TiO2 porous adsorbent layer and a bottom providing excellent transmittance in the solar spectrum are achieved properly by borosilicate-crown glass (BK7). We have shown that the proposed device preserves an average absorptivity/emissivity well below 7% in the entire solar spectrum and almost 95% in the atmospheric transparency windows. Besides, our design allows for sub-ambient temperature drops of 45° and diurnal cooling power output of 133W/m2, even in the case of solar irradiance up to 1000W/m2. The cooling performance persists under high humidity, even when taking the non-radiative heat exchange progress into account. The results revealed that the proposed design can be easily applied to a large area and promotes a significant step towards achieving large scale application in solar cells and related systems.

Effect of microstructural and environmental variables on ductility of austenitic stainless steels

Austenitic stainless steels are used extensively in harsh environments, including for high-pressure gaseous hydrogen service. However, the tensile ductility of this class of materials is very sensitive to materials and environmental variables. While tensile ductility is generally insufficient to qualify a material for hydrogen service, ductility is an effective tool to explore microstructural and environmental variables and their effects on hydrogen susceptibility, to inform understanding of the mechanisms of hydrogen effects in metals, and to provide insight to microstructural variables that may improve relative performance. In this study, hydrogen precharging was used to simulate high-pressure hydrogen environments to evaluate hydrogen effects on tensile properties. Several austenitic stainless steels were considered, including both metastable and stable alloys. Room temperature and subambient temperature tensile properties were evaluated with three different internal hydrogen contents for type 304L and 316L austenitic stainless steels and one hydrogen content for XM-11. Significant ductility loss was observed for both metastable and stable alloys, suggesting the stability of the austenitic phase is not sufficient to characterize the effects of hydrogen. Internal hydrogen does influence the character of deformation, which drives local damage accumulation and ultimately fracture for both metastable and stable alloys. While a quantitative description of hydrogen-assisted fracture in austenitic stainless steels remains elusive, these observations underscore the importance of the hydrogen-defect interactions and the accumulation of damage at deformation length scales.

Minimizing lithium deactivation during high-rate electroplating via sub-ambient thermal gradient control

The reversibility of Li electrodeposits must be significantly improved for Li metal anodes to be realized for next-generation, high energy density batteries. The most commonly tested thermal condition in the Li metal battery literature is isothermal ~20 °C (ambient). Elevating the cell temperature (40 °C) improves Li metal stability by suppressing dendritic growth at the expense of augmenting solid electrolyte interphase growth. However, at the high current density and areal capacity tested in this work (10 mA cm−2, 3.0 mA h cm−2), dendritic growth is inevitable and Li metal electrodes succumb to extensive degradation due to Li deactivation. To overcome these shortcomings of isothermal cycling, we expand on our concept of an interelectrode thermal gradient, which enhances Li surface diffusion to homogenize Li electroplating. With mean temperatures near ambient, a thermal gradient (ΔTwarm: 22.6 °C negative electrode, 21.4 °C positive electrode) delays failure compared with isothermal control (20 °C). The greatest benefit of the thermal gradient is unlocked at sub-ambient electrode temperatures. By applying the thermal gradient at low temperatures (ΔTcold: 3.7 °C negative electrode, 2.0 °C positive electrode), SEI growth stifles, dendrite propagation suppresses, and Li deactivation minimizes, stabilizing high-rate Li electroplating and stripping. After 100 cycles, ΔTcold reduces voltage hysteresis and electrode resistance by 51% and 77%, respectively, compared with the most promising isothermal condition (40 °C). Operando optical visualization confirms more reversible and dense Li electrodeposition via sub-ambient thermal gradient control with higher first-cycle Coulombic efficiency in an anode-free configuration. By contrast, isothermal 20 °C control exacerbates porous and dendritic Li electrodeposition with low reversibility.

Waterborne coatings with sub-ambient cooling under direct sunlight–part I: Optical properties and cooling effect measurements

The conventional way to fabricate current sub-ambient daytime radiative cooling (SDRC) systems is to maximally suppress the cooler's solar absorption and substantially improve its selective emissivity only in the atmospheric transparency window. This greatly limits the selection of materials and their practical applications. In this paper, an alternative method, which combines sunlight-triggered fluorescent cooling, particle scattering, and broadband infrared radiation, was presented for creating serial eco-friendly coatings with the SDRC effect with conventional cost-effective building materials. The presence of conventional fluorescent pigments in the coating composition increased the effective direct-normal solar reflectance via sunlight-excited fluorescent emissions to the level required for SDRC. When applied to various substrates, the serial coatings exhibited distinct SDRC effects under direct and strong sunlight in typical temperate monsoon climate regions such as Beijing. The observed sub-ambient temperature reduction of the coating with yellow–green fluorescence over an aluminium plate was 3.5 °C under a peak solar intensity of 996 W/m2, yielding a cooling power of 45.7 W/m2 under a peak solar intensity of 981 W/m2. Compared with the conventional cool white coatings, the large-scale application of the coating to urban surfaces is predicted to reduce a city's air temperature by approximately 1 °C and thereby decrease the Heat Island Intensity. Additionally, the method proposed in this paper was generic and expanded the SDRC design paradigm, thereby promoting SDRC as a viable energy-efficient technology.

Controlling Human Rabies: The Development of an Effective, Inexpensive and Locally Made Passive Cooling Device for Storing Thermotolerant Animal Rabies Vaccines.

Thermotolerant vaccines greatly improved the reach and impact of large-scale vaccination programs to eliminate diseases such as smallpox, polio and rinderpest. A recent study demonstrated that the potency of the Nobivac® Canine Rabies vaccine was not impacted following experimental storage at 30 °C for three months. We conducted a study to develop a passive cooling device (PCD) that could store thermotolerant vaccines under fluctuating subambient temperatures. Through a participatory process with local communities in Northern Tanzania, we developed innovative PCD designs for local manufacture. A series of field experiments were then carried out to evaluate the effectiveness of five PCDs for vaccine storage under varying climatic conditions. Following iterative improvement, a final prototype “Zeepot Clay” was developed at the cost of US$11 per unit. During a further field-testing phase over a 12-month period, the internal temperature of the device remained below 26 °C, despite ambient temperatures exceeding 42 °C. Our study thus demonstrated that locally designed PCDs have utility for storing thermotolerant rabies vaccines at subambient temperatures. These results have application for the scaling up of mass dog vaccination programs in low-and-middle income countries, particularly for hard-to-reach populations with limited access to power and cold-chain vaccine storage.

Recent development and research priorities on cool and super cool materials to mitigate urban heat island

The urban heat island is increasing the temperature of cities up to 10 °C and has a very important impact on energy, environmental quality and health. Materials used in the building and urban fabric affect the urban thermal balance and contribute highly to urban overheating. The article presents the progress achieved on the design, development and implementation of mitigation materials presenting a low and very low surface temperature. The recent technological progress and developments concerning natural, light colour, IR reflective, PCM doped, thermochromic, fluorescent, photonic and plasmonic materials is presented. Experimental results on the cooling capacity and the thermal performance of conventional and advanced materials are described in a comparative way. It is demonstrated that innovative materials can exhibit sub-ambient surface temperatures and contribute highly to mitigate urban overheating. • New innovative mitigation materials are recently developed. • Innovative advanced materials present a superior performance. • New materials contribute to counterbalance urban overheating. • Super cool materials operate under sub ambient surface temperatures.

Microstructural characterization and toughness evaluation of 10 wt% Ni steel weld metal gas tungsten arc and gas metal arc weld fusion zones

A novel 10 wt% Ni steel weld metal under development for use in high strength/high toughness applications was used to fabricate gas tungsten arc (GTAW) and gas metal arc (GMAW) welds. Both welds exhibit excellent toughness at sub-ambient temperatures, yet the toughness of the GTAW is superior to the GMAW. Using scanning electron microscopy, three differences in microstructure were identified in the GMAW compared to the GTAW, all of which are known to be detrimental to toughness: (1) an overall coarser effective grain size of the martensitic microstructure, (2) a larger presence of a coarse martensite constituent, and (3) a higher number density of oxide inclusions. The difference in the effective grain size of the two welds is rationalized based on inherent differences in the welding processes that produces much larger weld beads and a finger penetration profile in the GMAW thereby limiting the amount of reheating each bead receives. The higher number density of oxide inclusions in the GMAW is from the use of a 98% Ar/2% O2 shielding gas, as compared to 100% Ar used in the GTAW. A GMAW produced using 100% Ar as the shielding gas demonstrated improvements in toughness because of smaller oxide inclusions, yet the toughness was not as high as the GTAW, demonstrating the complexity of the interactions of the three different toughness influences. These results are significant in that they allow modifications to be made to the alloy composition and/or welding process parameters based on a sound scientific basis.

Waterborne coatings with sub-ambient cooling under direct sunlight–Part II: Cooling effect under real working conditions and key physical properties

Current sub-ambient daytime radiative cooling (SDRC) designs are generally evaluated in a well-insulated apparatus to suppress heat convection and conduction with the surrounding environment. In a companion study, we experimentally demonstrated that serial waterborne coatings, which combined particle scattering, sunlight-excited fluorescence, and mid-infrared broadband radiation, exhibited pronounced SDRC effects on various substrates installed on a well-designed rooftop setup under different climatic conditions. In this study, we experimentally show that the coating with yellow-green fluorescence (termed as the FR coating) can achieve meaningful SDRC under real working conditions. When applied to a concrete scale-model building, the FR coating showed a significant SDRC effect compared with other substrates installed on the rooftop cooling device and an assembled corrugated steel house. The average decrease in sub-ambient temperature under direct sunlight was 10.1 ± 1.4 °C with a maximum value of 12.4 °C under a peak solar intensity of 999 W/m2. Moreover, during the coldest day in winter, the maximum sub-ambient temperature reduction during the midday hours was 5.3 °C. The maximum difference between the lowest temperatures of the coated and uncoated scale-model buildings’ room interiors was 1.5–1.6 °C. Therefore, excessive heating energy consumption in the winter might be completely compensated for or exceeded by the cooling energy savings in the summer in areas that require both heating and cooling depending on the season. Additionally, the coating possesses excellent weather and salt spray resistance, self-cleaning capabilities, and excellent visible appearance, which are essential for practical applications.

Mechanistic insights and consequences of intrapore liquids in ethene, propene, and butene dimerization on isolated Ni2+ sites grafted within aluminosilicate mesopores

The stability, selectivity, and reactivity conferred by intrapore liquids onto Ni2+ species grafted within mesoporous aluminosilicates for the dimerization of C2-C4 alkenes are reported and interpreted by the preferential stabilization of dimer desorption transition states, which inhibit further growth during the surface sojourn that forms these dimers. The marked decrease in deactivation rate constants leads to catalyst half-lives > 600 h for all alkenes and to turnover rates (per Ni) at sub-ambient temperatures (240–260 K) that exceed those at the higher temperatures previously used for Ni-based solid catalysts (350–500 K). These effects appear at the relative pressures required for alkene capillary condensation within Ni-Al-MCM-41 catalysts with different mesopore diameters and are also evident when the intrapore liquids consist of unreactive alkanes, indicative of solvation effects conferred by non-covalent interactions mediated by dispersion forces. For all alkenes, turnover rates (per Ni) are unaffected by Ni content until each acidic proton in the Al-MCM-41 is replaced by one Ni atom, consistent with the involvement of grafted (Ni-OH)+ monomers as active centers and excess Ni leading to inactive NiO species. The stable nature of these catalysts allows accurate mechanistic assessments and a demonstration of the kinetic relevance of the CC coupling elementary steps on essentially bare (Ni-OH)+ centers, leading to rates described by second-order dimerization constants (αn′) and adsorption constants (βn′) for each alkene (Cn); these parameters are influenced only slightly by intrapore liquids, because they reflect free energies of formation of surface-bound species and transition states from gaseous precursors. These αn′ and βn′ parameters increase with alkene size, with the enthalpic component of αn′ increasing from 21 to 46 kJ mol−1 and the activation entropy becoming more negative (−103 to −187 J (mol K)−1), consistent with CC coupling transition states that occur late along the reaction coordinate and resemble its bound dimer product. The low C3n/C2n ratios observed in the presence of intrapore liquids (<0.04, for n = 2–4) reflect the endothermic nature of dimer desorption events, for which product-like transition states benefit from the solvation of desorbing products by a non-polar liquid phase, thus allowing detachment from Ni centers before subsequent growth. The inhibition of such growth events accounts not only for the unique dimer selectivity observed, but also for the unprecedented stability conferred by intrapore liquids by inhibiting the formation of oligomers that bind more strongly with increasing chain size, as evident from the βn′ values reported here for alkene reactants.

The direct synthesis of hydrogen peroxide from H2 and O2 using Pd-Ni/TiO2 catalysts.

The direct synthesis of hydrogen peroxide (H2O2) from molecular H2 and O2 offers an attractive, decentralized alternative to production compared to the current means of production, the anthraquinone process. Herein we evaluate the performance of a 0.5%Pd-4.5%Ni/TiO2 catalyst in batch and flow reactor systems using water as a solvent at ambient temperature. These reaction conditions are considered challenging for the synthesis of high H2O2 concentrations, with the use of sub-ambient temperatures and alcohol co-solvents typical. Catalytic activity was observed to be stable to prolonged use in multiple batch experiments or in a flow system, with selectivities towards H2O2 of 97% and 85%, respectively. This study was carried out in the absence of halide or acid additives that are typically used to inhibit sequential H2O2 degradation reactions showing that this Pd-Ni catalyst has the potential to produce H2O2 selectively. This article is part of a discussion meeting issue 'Science to enable the circular economy'.

Effect of the spectrally selective features of the cover and emitter combination on radiative cooling performance

Radiative cooling (RC) shows good potential for building energy saving by throwing waste heat to the cosmos in a passive and sustainable manner. However, most available radiative coolers suffer from low cooling flux. The situation becomes even deteriorated in the daytime when radiative coolers are exposed to direct sunlight. To tackle this challenge, an idea of employing both a spectrally selective cover and a spectrally selective emitter is proposed in this study as an alternative approach. A comparative study is conducted among four RC modules with different spectral characteristics for the demonstration of how the spectral profiles of the cover and the emitter affects the RC performance. The results under given conditions show that the RC module with a spectrally selective cover and a spectrally selective emitter (SC/SE) reaches a net RC power of 62.4 W/m2 when the solar radiation is 800 W/m2, which is about 1.8 times that of the typical RC module with a spectrally non-selective cover and a spectrally selective emitter (n-SC/SE). When the ambient temperature is 30 °C, the SC/SE based RC module realizes a daytime sub-ambient temperature reduction of 20.0 °C, standing for a further temperature decrement of 9.2 °C compared to the n-SC/SE based RC module.

Comprehensive evaluation of thermal and energy performance of radiative roof cooling in buildings

This paper newly established a radiative roof cooling performance model to conduct thorough parametric studies on pivotal factors governing achievable equilibrium temperature and net cooling power in building roofs. A detailed building model integrated with radiative roof cooling considering typical climate regions in China was correspondingly developed to evaluate building thermal response and energy efficiency. The results indicate that compared with broadband and transmittance based adaptive emitters as roof surfaces, atmospheric window based selective emitter can achieve the minimum sub-ambient equilibrium temperature. Net cooling powers are reduced by 13–33.6 W/m2 and sub-ambient equilibrium temperatures are weakened by 7.1–13.5 °C with atmospheric precipitable water vapor increasing from 2.3 to 10 mm. The cooler degree of roof top temperature can reach over 30 °C under radiative roof surface which is conducive to avoiding thermal shock. The roof bottom temperature reduction noticeably reaches up to 13.8 °C for non-air-conditioned buildings, guaranteeing a more thermally comfortable built environment. The annual energy savings turn out to be positive for five typical cities, where cooling load dominant regions exhibit the most saving potentials with the saving rates of 7.1% for Hong Kong and 9.3% for Kunming respectively. With the application of a radiative roof cooling surface, the heat resistance layer can be removed from the thermal perspective for cost savings. The study sheds light on the promising benefits of radiative roof cooling for achieving energy efficient buildings in China.

Nitrogen-doped porous carbon with interconnected tubular structure for supercapacitors operating at sub-ambient temperatures

Operation of supercapacitors at sub-zero temperatures with reasonable performance is of great importance for their outdoor applications. Herein, the sub-zero performance of supercapacitors assembled from nitrogen-doped porous carbon electrodes with interconnected tubular structure using ionic liquid as electrolyte is reported. The carbon-based electrode materials are synthesized by pyrolysis of poly(1-vinylimidazole) networks in the presence of titanate nanotubes and potassium nitrate, followed by removal of titanate nanotubes. Benefiting from the interconnected hierarchically porous structure and large surface area, the synthesized electrode materials exhibits a gravimetric capacitance of 333 F·g−1 under 1 A·g−1 in a three-electrode system in 6.0 mol·L−1 KOH aqueous solution at room temperature. Symmetric supercapacitors assembled from the synthesized electrode deliver a specific energy of 32.7 Wh·kg−1 under 1.30 W·kg−1 using ionic liquid as electrolyte at room temperature. At −40 °C, the assembled device using ionic liquid as electrolyte possesses a specific energy of 48.3 Wh·kg−1 under 1.75 kW·kg−1 and 18.6 Wh·kg−1 under 35.0 kW·kg−1. In addition, the device retains 53.5% of its initial capacitance after 10,000 charge-discharge cycles at −40 °C under 10 A·g−1.

Biologically inspired flexible photonic films for efficient passive radiative cooling

Temperature is a fundamental parameter for all forms of lives. Natural evolution has resulted in organisms which have excellent thermoregulation capabilities in extreme climates. Bioinspired materials that mimic biological solution for thermoregulation have proven promising for passive radiative cooling. However, scalable production of artificial photonic radiators with complex structures, outstanding properties, high throughput, and low cost is still challenging. Herein, we design and demonstrate biologically inspired photonic materials for passive radiative cooling, after discovery of longicorn beetles' excellent thermoregulatory function with their dual-scale fluffs. The natural fluffs exhibit a finely structured triangular cross-section with two thermoregulatory effects which effectively reflects sunlight and emits thermal radiation, thereby decreasing the beetles' body temperature. Inspired by the finding, a photonic film consisting of a micropyramid-arrayed polymer matrix with random ceramic particles is fabricated with high throughput. The film reflects ∼95% of solar irradiance and exhibits an infrared emissivity >0.96. The effective cooling power is found to be ∼90.8 W⋅m-2 and a temperature decrease of up to 5.1 °C is recorded under direct sunlight. Additionally, the film exhibits hydrophobicity, superior flexibility, and strong mechanical strength, which is promising for thermal management in various electronic devices and wearable products. Our work paves the way for designing and fabrication of high-performance thermal regulation materials.

Study on low-temperature performances of Nb16W5O55 anode for lithium-ion batteries

Niobium tungsten oxide Nb16W5O55 is a competitive anode for lithium-ion batteries, while seldom research on low-temperature electrochemical properties. In this paper, Nb16W5O55 is synthesized by solid phase reaction and the effects of operation temperature (25, 0 and −20 °C) on the coulombic efficiency, cycling stability, rate capacity and crystal structure are studied in detail. At 25 °C, Nb16W5O55 electrode can give good cycling stability of 184 mAh g−1 after 404 cycles and rate capacity of 101 mAh g−1 at 4000 mA g−1. By contrast, the electrochemical properties decrease obviously at subambient temperatures. Electrochemical impedance spectroscopy reveal that the sharp increase of the charge-transfer impedance and the decrease of the solid-phase Li+ diffusion coefficient are the essential factors leading to the deterioration of low temperature performances. However, the low temperature mainly affects specific capacities and rate performances, but has little effect on cyclic stability and crystal structure of Nb16W5O55 electrode, indicated by ex-situ X-ray diffraction analysis. These results provide some new insights for the practical application of Nb16W5O55 anode.