Tunable High-Performance Electromagnetic Interference Shielding of VO2 Nanowires-Based Composite.

The unique metal-insulator transition of VO2 is very suitable for dynamic electromagnetic (EM) regulation materials due to its sharp change in electrical conductivity. Here, we have developed an off/on switchable electromagnetic interference (EMI) shielding composite by interconnecting VO2 nanowires (NWs) in poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) to form conductive networks, resulting in outstanding performance at the X and Ku bands with maximum change values of 44.8 and 59.4 dB, respectively. The unique insulator-to-metal transition (IMT) of VO2 NWs has dominated the variation of polarization loss (εp″) and conductivity loss (εσ″) for the composites, which is the mechanism of EMI shielding switching between off and on states. Furthermore, the composite exhibits good cycling stability of the off/on switchable EMI shielding performance and has excellent mechanical properties, especially with 200 times abrasion resistance without obvious weight loss. This study provides a unique approach for dynamic switching of EM response with the potential to construct practical intelligent EM response systems for next-generation smart electromagnetic devices in various scenarios.

Unprecedented Spatial Manipulation and Transformation of Dynamic Thermal Radiation Based on Vanadium Dioxide.

Reconfigurable infrared (IR) materials have widespread applications in thermal management and smart IR concealment. Although various reconfigurable IR materials can be customized by positive or negative differential VO2-based resonators, their insightful mechanism remains unknown. Here, we comprehensively investigate the fundamental design rule of reconfigurable thermal radiation between positive and negative differential thermal radiation properties for the first time. Importantly, the skin depth of VO2 film in the metal state is investigated to clarify the transformation from positive to negative differential thermal radiation properties, and the critical thickness is further derived, providing important guidance in designing the reconfigurable thermal radiation regulator. Furthermore, the reconfigurable multistate thermal images had been presented into one plate. The resulting emittance variation (△ε8-14 µm) of the VO2-based resonator can change from 0.61 to -0.53, which consummates the ability for diverse demands such as infrared concealment, thermal illusion, and thermal management. This work constitutes a promising and universal route toward designing whole smart devices and may create new scientific and technological opportunities for platforms that can benefit from reconfigurable electromagnetic manipulation.

Rejuvenation of Electrochromic Devices.

Electrochromic devices (ECDs) are a hot pot due to their significant energy-saving effect in green buildings. However, the ECDs suffer from degradation induced by ion trapping during cycling, which restricts their further development. Here, it is demonstrated that the electrochromic performance of the degraded ECDs can be rejuvenated by heat treatment method The release mechanism of trapped ions in films is simulated and validated using three types of ECDs. The semi-solid-state ECD evinces a state of near-failure at low temperatures can regain its initial performance by heating. All-solid-state ECDs, including amorphous WO3 (a-WO3 ECD) and crystalline WO3 (c-WO3 ECD) as the electrochromic layer, can also release the trapped ions and regain the performance (97.3% and 95.5% of initial optical modulation) by annealing, regardless of the way of degradation. The research has extended the lifespan of multiple ECDs, providing significant practical value and promoting sustainable, and eco-friendly development.

Core-Shell-Structured Electrorheological Fluid with a Polarizability-Tunable Nanocarbon Shell for Enhanced Stimuli-Responsive Activity.

The incorporation of nanocarbon-based materials into electrorheological fluids has been shown to be an effective means of improving the electrorheological (ER) response. However, the mechanism of the sp2/sp3-hybridized carbon structure and high ER response is still under investigation. Herein, barium titanate@nanocarbon shell (BTO@NCs) composites are proposed and prepared by introducing carbonized polydopamine (C-PDA) into a shell. When the polymerization time of dopamine is tuned, the shell thickness, surface polar functional groups, and sp2/sp3-hybridized carbon can be effectively controlled. The maximum yield stress of the BTO@NCs-24 h ER fluid reaches 2.5 kPa under an electric field of 4 kV mm-1, which is attributed to the increased content of sp3 C-OH and oxygenous functional groups within the shell, resulting in a rapidly achievable polarization. Furthermore, the SiO2@NCs and TiO2@NCs ER fluids are also prepared with enhanced ER behavior in these phenomena, confirming an approach to high-performance ER fluids based on nanocarbon composites.

Polyaniline-Based Infrared Dynamic Patterned Encoder with Multiple Thermal Radiation Characteristics.

A high-level infrared dynamic patterned encoder (IR-DPE) possesses prospective applications for energy-harvesting and information, but a simple and reliable method for fabrication remains challenging. Herein, we first report an IR-DPE with multiple thermal radiation characteristics based on polyaniline (PANI). Specifically, the electron-beam evaporation technique is introduced to obtain the divanadium pentoxide (V2O5) coating, and then the V2O5 film acts as an oxidant to drive in situ polymerization of the PANI film. During the process, we experimentally explore the relationship between the thickness of V2O5 and the emissivity of PANI to obtain up to six emissivity levels and achieve the IR pattern integrated into multiple thermal radiation characteristics. The device shows multiple thermal radiation characteristics at the oxidized state, realizing a pattern visible with the IR camera and the same thermal radiation properties at the reduced state, leading to the pattern concealed in the IR regime. In addition, the highest emissivity tunability of the device is to be tuned from 0.40 to 0.82 (Δε = 0.42) at 2.5-25 µm. Meanwhile, the device exhibits a maximum temperature control of up to 5.9 °C. The results show the enormous potential of IR-DPEs for IR information transfer and thermal management.

Oxygen vacancy modulated amorphous tungsten oxide films for fast-switching and ultra-stable dual-band electrochromic energy storage smart windows.

Dual-band electrochromic energy storage (DEES) windows, which are capable of selectively controlling visible (VIS) and near-infrared (NIR) light transmittance, have attracted research attention as energy-saving devices that integrate electrochromic (EC) and energy storage functions. However, there are few EC materials with spectrally selective modulation. Herein, oxygen vacancy modulated amorphous tungsten oxide (a-WO3-x-OV) is firstly shown to be a potential material for DEES windows. Furthermore, experimental results and density functional theory (DFT) calculations demonstrate that an oxygen vacancy not only enables the a-WO3-x-OV films to modulate NIR light transmittance selectively, but also enhances ion adsorption and diffusion in the a-WO3-x host to obtain excellent EC performance and a large energy storage capacity. Consequently, the a-WO3-x-OV film can selectively control VIS and NIR light transmittance with a state-of-the-art EC performance, including high optical modulation (91.8% and 80.3% at 633 and 1100 nm, respectively), an unprecedentedly fast switching speed (tb/tc = 4.1/5.3 s), high coloration efficiency (167.96 cm2 C-1), high specific capacitance (314 F g-1 at 0.5 A g-1), and ultra-robust cycling stability (83.3% optical modulation retention after 8000 cycles). The fast-switching and ultra-stable dual-band EC properties with efficient energy recycling are also successfully demonstrated in a DEES prototype. The results demonstrate that the a-WO3-x-OV films show great potential for application in high-performance DEES smart windows.

Electrostatic Interfacial Cross-Linking and Structurally Oriented Fiber Constructed by Surface-Modified 2D MXene for High-Performance Flexible Pseudocapacitive Storage.

Fiber supercapacitors are promising power supplies suitable for wearable electronics, but the internally insufficient cross-linking and random structure of fiber electrodes restrict their performance. This study describes how interfacial cross-linking and oriented structure can fabricate an MXene fiber with high flexibility and electrochemical performance. The continuous and highly oriented macroscopic fibers were constructed by 2D MXene sheets via a liquid-crystalline wet-spinning assembly. The oxyanion-enriched terminations of surface-modified MXene in situ could reinforce the interfacial cross-linking by electrostatic interactions while mediating the sheet-to-sheet lamellar structure within the fiber. The resultant MXene fiber exhibits high electrical conductivity (3545 S cm-1) and mechanical strength (205.5 MPa) and high pseudocapacitance charge storage capability up to 1570.5 F cm-3. Notably, the assembled fiber supercapacitor delivers an energy density of 77.6 mWh cm-3 at 401.9 mW cm-3, exceptional flexibility and stability exhibiting ∼99.5% capacitance retention under mechanical deformation, and can be integrated into commercial textiles to power microelectronic devices. This work provides insight into the fabrication of an advanced MXene fiber and the development of high-performance flexible fiber supercapacitors.

A Multifunctional Flexible Electronic Skin for Dynamic Thermal Radiation Regulation and Electromagnetic Interference Shielding.

A multifunctional electronic skin with thermal radiation regulation and electromagnetic interference (EMI) shielding is urgent for electronic systems because of the thermal radiation emission and electromagnetic wave pollution. Herein, a flexible electronic skin was designed and fabricated, where the polyaniline (PANI) served as the functional layer and Ti3C2Tx MXene was employed as the conductive electrode. The transformation of emeraldine salt (ES) and leucoemeraldine base (LB) of PANI makes the skin achieve an infrared emissivity modulation, and the electromagnetic loss of PANI and ultrahigh electrical conductivity of Ti3C2Tx MXene make it exhibit EMI shielding ability. Benefiting from the special structural design, the multifunctional skin with a small thickness (0.3 mm) and low surface density (0.06 g/cm2) exhibits an excellent infrared emissivity modulation ability (Δε) of 0.32 with emissive power of 119.1 W/m2 at the wavelength range of 2.5-25 µm and total shielding effectiveness (SET) of 36.3 dB over the X-band (8.2-12.4 GHz). Meanwhile, the multifunctional skin remains black in the visible spectrum but a changeable color in the infrared spectrum. Even after repeated bending and twisting, the multifunctional skin still maintains a good emissivity adjustment. The simultaneous realization of dynamic thermal radiation regulation and EMI shielding endows the skin promising potential for various fields, such as adaptive infrared camouflage, thermal regulation, anticounterfeiting, and EMI shielding-related crossing field.

Copper ferrite and cobalt oxide two-layer coated macroporous SiC substrate for efficient CO2-splitting and thermochemical energy conversion.

CO2-splitting and thermochemical energy conversion effectiveness are still challenged by the selectivity of metal/metal oxide-based redox materials and associated chemical reaction constraints. This study proposed an interface/substrate engineering approach for improving CO2-splitting and thermochemical energy conversion through CuFe2O4 and Co3O4 two-layer coating SiC. The newly prepared material reactive surface area available for gas-solid reactions is characterized by micro-pores CuFe2O4 alloy easing inter-layer oxygen micro mass exchanges across a highly stable SiC-Co3O4 layer. Through a thermogravimetry analysis, oxidation of the thermally activated oxygen carriers exhibited remarkably CO2-splitting capacities with a total CO yield of 1919.33 µmol/g at 1300 °C. The further analysis of the material CO2-splitting performance at the reactor scale resulted in 919.04 mL (788.94 µmol/g) of CO yield with an instantaneous CO production rate of 22.52 mL/min and chemical energy density of 223.37 kJ/kg at 1000 °C isothermal redox cycles. The reaction kinetic behavior indicated activation energy of 30.65 kJ/mol, which suggested faster CO2 activation and oxidation kinetic on SiC-Co3O4-CuFe2O4 O-deficit surfaces. The underlying mechanism for the remarkable thermochemical performances was analyzed by combining experiment and density functional theory (DFT) calculations. The significance of exploiting the synergy between CuFe2O4 and Co3O4 layers and stoichiometric reaction characteristics provided fundamental insights useful for the theoretical modeling and practical application of the solar thermochemical process.

Iridescent Daytime Radiative Cooling with No Absorption Peaks in the Visible Range.

Coatings for passive radiative cooling applications must be highly reflected in the solar spectrum, and thus can hardly support any coloration without losing their functionality. In this work, a colorful daytime radiative cooling surface based on structural coloration is reported. A designed radiative cooler with a bioinspired array of truncated SiO2 microcones is manufactured via a self-assembly method and reactive ion etching. Complemented with a silver reflector, the radiative cooler exhibits broadband iridescent coloration due to the scattering induced by the truncated microcone array while maintaining an average reflectance of 95% in the solar spectrum and a high thermal emissivity (ε) of 0.95, owing to the reduced impedance mismatch provided by the patterned surface at infrared wavelengths, reaching an estimated cooling power of ≈143 W m-2 at an ambient temperature of 25 °C and a measured average temperature drop of 7.1 °C under direct sunlight. This strong cooling performance is attributed to its bioinspired surface pattern, which promotes both the aesthetics and cooling capacity of the daytime radiative cooler.

Novel Transparent TiO2/AgNW-Si(NH2)/PET Hybrid Films for Flexible Smart Windows.

The application of flexible indium tin oxide (ITO)-free electrochromic devices (FCDs) has always been a research hotspot in flexible electronics. Recently, a silver nanowire (AgNW)-based transparent conductive film has raised great interest as an ITO-free substrate for FCDs. However, several challenges, such as the weak binding of AgNWs to the substrate, high junction resistance, and oxidation of AgNWs, remain. In this paper, a novel method for surface modification of AgNWs with N-aminoethyl-γ-aminopropyltrimethoxysilane [Si(NH2)] solution is proposed to enhance the bonding with the flexible substrates and the active materials, thereby inhibiting the delamination of AgNWs from the substrate and reducing the high junction resistance between nanowires. The TiO2/AgNW-Si(NH2)/poly(ethylene terephthalate) (PET) films show outstanding mechanical properties, of which the resistance remains almost unchanged after mechanical bending of 5000 cycles (ΔR/R0 ≈ 3.6%) and repeated peeling off cycles with 3M tape 100 times (ΔR/R0 ≈ 6.0%). In addition, we found that the oxygen-containing groups on the TiO2/AgNW-Si(NH2)/PET surface form hydrogen bonds with the TiO2 sol, resulting in tight contact between the TiO2 sol and the AgNWs, which prevents the AgNWs from oxidation. As a result, the TiO2/AgNW-Si(NH2)/PET film exhibited long-time aging (ΔR/R0 ≈ 4.9% in the air for 100 days) stability. A FCD was constructed with the TiO2/AgNW-Si(NH2)/PET film, which showed excellent electrochromic performance (94% retention) after 5000 bending cycles, indicating high stability and mechanical flexibility. These results present a promising solution to the transparent conductive films for flexible energy devices.

Passive and Dynamic Phase-Change-Based Radiative Cooling in Outdoor Weather.

Radiative cooling has attracted considerable attention due to its tremendous potential in exploiting the cold reservoir of deep sky. However, overcooling always occurs in the conventional static radiative coolers because they operate only in the cooling mode in both hot and cold. Therefore, a dynamic radiative cooler based on phase change materials is highly desired. Nevertheless, the practical outdoor phase-change-based dynamic radiative cooling has not yet been experimentally demonstrated. To satisfy the stringent requirement of the phase-change-based radiative cooler in outdoor weather conditions, we engineered the phase-change material (VO2) to possess the room-temperature phase-transition capability for typical weather conditions. Second, the reconfigurable cavity consists of the lossless spacer to ensure the magnitude of thermal modulation and suppress the solar absorption simultaneously. Third, the practical selective-filtering method is devised to shield the solar irradiance while permitting the thermal emission. Our experiment demonstrates that these materials and photonic measures can work together to realize the dynamic radiative cooling in actual weather conditions, which shows a self-adaptive switch between the ON-cooling state in hot daytime and the OFF-cooling state in cold nighttime. The study pushes the radiative cooler toward multifunctionality and provides beneficial guidance for the phase-change-based intelligent thermal control.

VO2-Based Infrared Radiation Regulator with Excellent Dynamic Thermal Management Performance.

Dynamic thermal management materials attract fast-increasing interest due to their adaptability to changing environments and greater energy savings as compared to static materials. However, the high transition temperature and the low emittance tunability of the vanadium dioxide (VO2)-based infrared radiation regulators limit their practical applications. This study addresses these issues by proposing a smart infrared radiation regulator based on a Fabry-Pérot cavity structure (VO2/HfO2/Al), which is prepared by high-power impulse magnetron sputtering (HiPIMS) and has the potential for large-scale production. Remarkably, the outstanding emittance tunability reaches 0.51, and the phase transition temperature is lowered to near a room temperature of 27.5 °C by tungsten (W) doping. In addition, a numerical thermal management power of 196.3 W/m2 (at 8-14 µm band) can be obtained from 0 to 60 °C. As a proof-of-concept, the demonstrated capabilities of the VO2 infrared radiation regulator show great potentials in a wide range of applications for the thermal management of buildings and vehicles.

Smart Materials for Dynamic Thermal Radiation Regulation.

Thermal radiation in the mid-infrared region profoundly affects human lives in various fields, including thermal management, imaging, sensing, camouflage, and thermography. Due to their fixed emissivities, radiance features of conventional materials are usually proportional to the quadruplicate of surface temperature, which set the limit, that one type of material can only present a single thermal function. Therefore, it is necessary and urgent to design materials for dynamic thermal radiation regulations to fulfill the demands of the age of intelligent machines. Recently, the ability of some smart materials to dynamically regulate thermal radiation has been evaluated. These materials are found to be competent enough for various commands, thereby, providing better alternatives and tremendously promoting the commercial potentials. In this review, the dynamic regulatory mechanisms and recent progress in the evaluation of these smart materials are summarized, including thermochromic materials, electrochromic materials, mechanically and humidity responsive materials, with the potential applications, insufficient problems, and possible strategies highlighted.

Effect of Unit Cell Shape on Switchable Infrared Metamaterial VO2 Absorbers/Emitters.

Metamaterial absorber/emitter is an important aspect of infrared radiation manipulation. In this paper, we proposed four simple switchable infrared metamaterial absorbers/emitters with Ag/VO2 disks on the Ag plane employing triangle, square, hexagon, and circle unit cells. The spectral absorption peaks whose intensities are above 0.99 occur at ~4 µm after structure optimization when VO2 is in insulating state and disappear when VO2 becomes metallic state. The simulated electromagnetic field reveals that the spectral absorption peaks are attributed to the excitation of magnetic polariton within the insulating VO2 spacer layer, whose values exceed 1.59 orders of magnitude higher than the incident magnetic field. Longer resonant wavelength would be excited in square arrays because its configuration is a better carrier of charges at the same spans. For absorption stability, the absorbers/emitters with square and circular structures do not have any change with the polarization angles changing from 0° to 90°, due to the high rotational symmetric structure. And four absorbers/emitters reveal similar shifts and attenuations under different incident angles. We believed that the switchable absorber/emitter demonstrates promising applications in the sensing technology and adaptive infrared system.

S, O dual-doped porous carbon derived from activation of waste papers as electrodes for high performance lithium ion capacitors.

To circumvent the imbalances of electrochemical kinetics and charge-storage capacity between Li+ ion battery anodes and capacitive cathodes in lithium-ion capacitors (LICs), dual carbon based LICs are constructed and investigated extensively. Herein, S, O dual-doped 3D net-like porous carbon (S-NPC) is prepared using waste paper as the carbon source through a facile solvothermal treatment and chemical activation. Benefiting from the combination effect of the rich S,O-doping (about 2.1 at% for S, and 9.0 at% for O), high surface area (2262 m2 g-1) and interconnected porous network structure, the S-NPC-40 material exhibits excellent electrochemical performance as both cathode material and anode material for LICs. S, O doping not only increases the pseudocapacity but also improves the electronic conductivity, which is beneficial to reduce the mismatch between the two electrodes. The S-NPC-40//S-NPC-40 LIC delivers high energy densities of 176.1 and 77.8 W h kg-1 at power densities of 400 and 20 kW kg-1, respectively, as well as superior cycling stability with 82% capacitance retention after 20 000 cycles at 2 A g-1. This research provides an efficient method to convert waste paper to porous carbon electrode materials for high performance LIC devices.

Bioinspired Microstructured Materials for Optical and Thermal Regulation.

Precise optical and thermal regulatory systems are found in nature, specifically in the microstructures on organisms' surfaces. In fact, the interaction between light and matter through these microstructures is of great significance to the evolution and survival of organisms. Furthermore, the optical regulation by these biological microstructures is engineered owing to natural selection. Herein, the role that microstructures play in enhancing optical performance or creating new optical properties in nature is summarized, with a focus on the regulation mechanisms of the solar and infrared spectra emanating from the microstructures and their role in the field of thermal radiation. The causes of the unique optical phenomena are discussed, focusing on prevailing characteristics such as high absorption, high transmission, adjustable reflection, adjustable absorption, and dynamic infrared radiative design. On this basis, the comprehensive control performance of light and heat integrated by this bioinspired microstructure is introduced in detail and a solution strategy for the development of low-energy, environmentally friendly, intelligent thermal control instruments is discussed. In order to develop such an instrument, a microstructural design foundation is provided.

Influence of Coagulation Bath Temperature on the Structure and Dielectric Properties of Porous Polyimide Films in Different Solvent Systems.

In this work, the effect of coagulation bath temperature in different solvent systems [1,4-butyrolactone (GBL)/N,N-dimethylacetamide (DMAC)] on the structure and dielectric properties of polyimide (PI) films was investigated for the first time. The solubility parameter was introduced to explain the formation process of porous PI films. The results showed that the changed tendency of the dielectric constant versus temperature is opposite for the single-solvent system and cosolvent system. For a single DMAC and GBL solvent, the dielectric constants of the films decreased with increasing temperature. In contrast, the dielectric constants increased with the increase in temperature for the GBL/DMAC cosolvent system. Moreover, the measured porosities were applied to estimate the dielectric constants of the PI films. This showed that the porosity increased with increasing temperature for a single-solvent system, while it decreased for a cosolvent system. Scanning electron microscopy images suggested that the variation trends are derived from the different influences of the temperature on the structure and morphology. Thus, this study reveals the effect of coagulation bath temperature on the structure and dielectric properties of porous PI films and provides the guidance for the design and optimization of architectures for high-performance porous films.

An electrochromic supercapacitor based on an MOF derived hierarchical-porous NiO film.

Nickel oxide (NiO) is a promising candidate for future electrochromic supercapacitors due to its pronounced electrical properties and low cost. Unfortunately, the weak interaction between NiO films and conductive substrates results in poor cycling stability. In addition, the long color-switching time and low capacitance by the small lattice spacing in dense NiO impede its practical applications seriously. Herein, a hierarchical porous NiO film/ITO glass bifunctional electrode has been prepared via the solvothermal and subsequent calcination process of growing MOF-74 in situ on ITO, which shows outstanding cycle reversibility, excellent capacitance, high coloration efficiency and short color-switching time. Because of the strong binding force between the NiO film and substrate, and large surface areas with a hierarchical porous structure which are beneficial to the ion transport, the NiO film demonstrates perfect capacitive and electrochromic properties. As a bifunctional electrode, the NiO film shows a specific capacitance of 2.08 F cm-2 at 1 mA cm-2, large optical modulation of 41.08% and about 86% of optical modulation retention after 10 000 cycles. Furthermore, we assembled a bifunctional device whose energy condition can be roughly estimated according to the color state of the device. This finding can provide us with a new application of MOFs in the dual device of electrochromic supercapacitors.

All solid state electrochromic devices based on the LiF electrolyte.

The unsafe deposition process and slow deposition rate of the electrolyte layers are the main obstacles for electrochromic devices (ECDs) toward commercial application. In this work, an ECD with a structure of glass/ITO/WO3/LiF/NiO/ITO has been prepared by electron beam and resistance evaporation methods. The LiF electrolyte is deposited by resistance evaporation with the LiF particles and shows promising potential as the Li+ based electrolyte in ECDs owing to its high transparency and good ionic conductivity. The ECD shows a fast response (4.0 s for bleaching and 9.6 s for coloring), large optical transmittance modulations (∼58.9% at 625 nm, 100 s for coloring), good stability and high coloration efficiency (88.5 cm2 C-1). This work not only indicates that LiF can be used as a Li+ based electrolyte in an ECD, but also paves a new way to fast and safe preparation of ECDs with high performance.