Highly Enhanced Thermal Robustness and Photothermal Conversion Efficiency of Solar-Selective Absorbers Enabled by High-Entropy Alloy Nitride MoTaTiCrN Nanofilms

A Janus Textile with Tunable Heating Modes toward Precise Personal Thermal Management in Cold Conditions

Passive heating textiles (PHTs) have drawn increasing attention due to the advantages of energy-conservation heating. However, the heating capabilities of current PHTs are typically static and non-tunable, presenting poor adaptation to dynamic winter. Herein, a novel Janus textile with tunable heating modes is developed by constructing a customized structure with asymmetric optical properties. This Janus textile is created by coating one side of a cotton fabric with silver nanowires (AgNWs) and then applying transition metal carbides/nitrides (MXene) to the other side. The MXene side exhibits high solar absorptivity and low mid-infrared emissivity, while the AgNWs side has moderate solar absorptivity and mid-infrared emissivity. This structure ensures that the solar and radiative heating temperatures of the MXene side are 16 °C and 1.7 °C higher than those of the AgNWs side. This distinction allows for on-demand, accurate adjustments in solar and radiative heating capabilities by flipping the textile according to ambient temperature. Furthermore, this innovative design also features desired electric heating, thermal camouflage, self-cleaning and antibacterial properties, electromagnetic interference shielding, durability, and wearability. The Janus textile enables precise thermoregulation of the human body to adapt to variable cold weather, making it essential for optimal personal thermal management and climate change mitigation.

High-Entropy Photothermal Materials

High-entropy (HE) materials, celebrated for their extraordinary chemical and physical properties, have garnered increasing attention for their broad applications across diverse disciplines. The expansive compositional range of these materials allows for nuanced tuning of their properties and innovative structural designs. Recent advances have been centered on their versatile photothermal conversion capabilities, effective across the full solar spectrum (300-2500 nm). The HE effect, coupled with hysteresis diffusion, imparts these materials with desirable thermal and chemical stability. These attributes position HE materials as a revolutionary alternative to traditional photothermal materials, signifying a transformative shift in photothermal technology. This review delivers a comprehensive summary of the current state of knowledge regarding HE photothermal materials, emphasizing the intricate relationship between their compositions, structures, light-absorbing mechanisms, and optical properties. Furthermore, the review outlines the notable advances in HE photothermal materials, emphasizing their contributions to areas, such as solar water evaporation, personal thermal management, solar thermoelectric generation, catalysis, and biomedical applications. The review culminates in presenting a roadmap that outlines prospective directions for future research in this burgeoning field, and also outlines fruitful ways to develop advanced HE photothermal materials and to expand their promising applications.

Thermal Stability and Weather Resistance of a Bionic Lotus Multiscale Micro-Nanostructure TiC/TiN-Ni/Mo Spectral Selective Absorber Based on Laser Cladding-Induced Melt Foaming

As the core of a solar collector, a solar selective absorbing coating has become the key material for efficient utilization and development of solar energy. In order to overcome the core scientific problem of poor high-temperature stability of optical properties caused by atomic diffusion between layers in the high-temperature environment of traditional multilayer solar absorption coatings, the multiscale lotus bionic porous structure was constructed by using a TiC/TiN-Ni/Mo material system with excellent intrinsic absorption performance. The melt foam method and laser cladding technology were combined to deposit the multiscale bionic porous structure solar selective absorption coating in situ by a laser-induced melt foaming strategy. It was found that the bubbles in the molten pool were affected by Marangoni force, gravity, buoyancy, and surface tension. The unescaped bubbles formed pores near the surface of the coating and showed a bimodal distribution. For the multiscale addition of 1.8 and 0.4 μm pore-forming agents with a mass fraction of 15 wt %, the multiscale pores enhance the scattering and secondary absorption of light and reduce the amplitude of electromagnetic wave to electron vibration; at the same time, the small-size conductor effect formed by the hole increases the surface electron concentration, strengthens the absorption of light, and enhances the magnetic field strength at the hole, and the structural absorbing effect is significant. The coating absorptivity α reaches 85%, and the temperature stability is excellent. Compared with the substrate, the coating has a smaller corrosion current density, larger polarization resistance, and strong corrosion resistance. The research shows that the laser-induced multiscale bionic porous structure coating obtains the intrinsic absorption-structural absorption composite absorption mechanism and realizes the integration of flexible design and efficient manufacturing of high-temperature solar absorption coatings.

Efficient Warming Textile Enhanced by a High-Entropy Spectrally Selective Nanofilm with High Solar Absorption

Solar and radiative warming are smart approaches to maintaining the human body at a metabolically comfortable temperature in both indoor and outdoor scenarios. Nevertheless, existing warming textiles are ineffective in frigid climates because the solar absorption of selective absorbing coating is significantly reduced when coated on rough textile surface. Herein, for the first time, high-entropy nitrides based spectrally selective film (SSF) is introduced on common cotton through a one-step magnetron sputtering method. The well-designed refractive index gradient enables destructive interference effects, offering a roughness-insensitive high solar absorptance (92.8%) and low thermal emittance (39.2%). Impressively, the solar absorptance is 9.1% higher than the reported best-performing selective nanofilm-based textile. As a result, such a textile achieves a record-high photothermal conversion efficiency (82.2% under 0.6 suns, at 0 °C). This textile yields a 3.5 °C drop in the set-point of indoor air-conditioner temperature. Besides, in a winter morning with an air temperature of 7.5 °C, it warms up the human skin by as large as 12 °C under weak sunlight (350 W m^-2 ). More importantly, such a superior radiative warming performance is achieved by engineering the widely used cotton without compromising its breathability and durability, showing great potential for practical applications.

Enabling Highly Enhanced Solar Thermoelectric Generator Efficiency by a CuCrMnCoAlN-Based Spectrally Selective Absorber

Harvesting solar energy to enhance thermoelectric generator efficiency is a highly effective strategy. However, it is a grand challenge but essential to increase solar-thermal conversion efficiency. A spectrally selective absorber, which is capable of boosting solar absorptance (α) while suppressing thermal emittance (ε), shows great potential to elevate the solar-thermal conversion efficiency. Herein, we fabricate a multilayer spectrally selective absorber with the assistance of high-entropy nitrides, which shows outstanding spectral selectivity (α/ε = 95.2/10.9%). Benefitting from the high-entropy nitrides, it is experimentally demonstrated that the as-deposited absorber exhibits superior thermal stability, which is crucial to ensure service life. Under 1000 W·m-2 simulated solar illumination, it achieves a very high surface temperature of 109.6 °C, making it suitable to enhance the efficiency of solar thermoelectric generators. Impressively, the integration of the proposed absorber with a commercial thermoelectric generator efficiently reinforces thermoelectric performance, offering a high output power of 1.99 mW. More importantly, by taking advantage of a thermal concentration strategy, it enables a further increase of the output power by 2.98 mW. This work provides a promising solar-thermal material to boost high thermoelectric performance and extends the application category of high-entropy nitrides.

Near-perfect spectrally-selective metasurface solar absorber based on tungsten octagonal prism array

Solar selective absorbers influence the photothermal efficiency of high-temperature solar thermal applications directly and significantly. In present work, a metasurface absorber consisting of an octagonal prism array is proposed, optimized and analyzed. Firstly, the structure parameters of the absorber are optimized, finding the optimal absorber achieves near-perfect spectrally-selectivity compared with the perfect solar absorber. The high solar absorptivity of 0.9591, low emissivity of 0.1594–0.3694, and high photothermal efficiency of 94.72–83.10% are achieved at 1073–1573 K and 1000 suns. Then, the mechanisms leading to the excellent spectral selectivity are investigated, suggesting that the coupling effects of multi-plasmon resonance modes and the impedance matching lead to the high solar absorptivity. Meanwhile, the impedance mismatching is the mechanism to minimize the emissivity in the mid-IR region. Moreover, whether the spectral absorptivity can be changed by structural parameters is investigated, suggesting that the excircle diameter of the first tungsten octagonal prism and the height of SiO₂ under the octagonal prism can influence the spectral absorptivity obviously. Finally, the metasurface absorber is demonstrated to be highly insensitive to both polarization and incident angles. These results suggest that the proposed metasurface absorber should be suitable for high-temperature solar thermal devices.

A metamaterial absorber that can achieve near-perfect spectral selectivity with simple structure is proposed for high-temperature solar energy harvesting.

Entropy-Assisted High-Entropy Oxide with a Spinel Structure toward High-Temperature Infrared Radiation Materials

Developing advanced materials with a high-entropy concept is one of the hot trends in materials science. The configurational entropy of high-entropy materials can be tuned by introducing different atomic species, which can also impart a result in excellent physical and chemical properties. In this work, we synthesized a solid-solution oxide (Cu, Mn, Fe, Cr)₃O₄ by a simple and scalable solid-phase synthesis method. We extensively investigated the microstructure and chemical composition, indicating that (Cu, Mn, Fe, Cr)₃O₄ has a single-phase spinel structure. Simultaneously, we reasonably evaluated the position occupied by the elements of (Cu, Mn, Fe, Cr)₃O₄ in a spinel structure as (Cu_0.75Fe_0.25)(Fe_0.25Cr_0.375Mn_0.375)₂O₄. Here, we first evaluated the infrared radiation performance of (Cu, Mn, Fe, Cr)₃O₄. The new, high-entropy oxide (HEO) (Cu, Mn, Fe, Cr)₃O₄ powder exhibits high infrared emissivity values of 0.879 and 0.848 in the wavelengths of 0.78-2.5 and 2.5-16 μm, respectively, and has excellent thermal stability. More importantly, the infrared emissivity values of as-prepared HEO coating reach 0.955 (0.78-2.5 μm) at room temperature and 0.936 (3-16 μm) at 800 °C. This work provides a viable strategy toward the laboratory mass production of this HEO for infrared radiation materials, which shows great potential in the energy-related applications.