High-entropy carbides (HECs) have attracted growing attention as promising noble-metal catalyst alternatives for the hydrogen evolution reaction. Nevertheless, the reported HEC nanocrystals remain confined to dense solid structures with metallic components limited to groups IVB-VIB. The first synthesis of hollow nanostructured high-entropy carbides (HfNbTaTiZr)C, (HfNbTaTiZrRE)C (RE=Gd, Ce, Y) and (HfNbTaTiZrCeY)C was achieved by a direct electroreduction process. Electrolysis was conducted at 3.1 V using a graphite anode and a cathode prepared from mixed oxides/carbon additive powders in molten CaCl₂-NaCl at 800 °C. The effects of carbon sources on the microstructure of the product were systematically investigated. The results show that the microstructure of HECs can be easily tailored from solid to hollow particles by selecting different carbon sources. All as-synthesized HECs exhibit a single face-centered cubic phase and compositional homogeneity from the nanoscale to the microscale. It was found that the engineered hollow nanostructure, coupled with the incorporation of rare-earth elements, significantly enhanced electrocatalytic performance of HECs for hydrogen evolution in an alkaline electrolyte. Specifically, the HECs incorporated with dual rare-earth elements exhibited superior performance to those with a single element. Among them, (HfNbTaTiZrCeY)C demonstrates superior hydrogen evolution reaction performance with a low overpotential of 167 mV, a small Tafel slope of 58.8 mV·dec^-1, and a low charge transfer resistance of 2.7 Ω. This work not only establishes a facile method for synthesizing various hollow rare-earth-containing high-entropy carbide nanoparticles, but also provides a novel strategy for the design of high-performance non-noble metal-based catalysts.

As global energy consumption rises, developing efficient energy-saving materials is crucial for alleviating energy pressure. Passive daytime radiative cooling materials are promising for energy-free refrigeration. The wide band gap and the absorption of infrared photons through lattice vibrations of the SrZrO₃ crystal make it a potential passive radiative cooling material, but its solar reflectivity and atmospheric window emissivity can be further enhanced. For this purpose, a series of Zn-doped SrZrO₃ crystals were prepared by the sol–gel method combined with the solid-phase synthesis method. The effects of Zn doping on the phase structure, electronic structure, spectral radiative characteristics, and passive daytime radiative cooling performance of SrZrO₃ crystals were investigated by experiments and theoretical calculations. The results show that, on one hand, the changes in the grain morphology and electronic structure caused by Zn doping jointly improved the reflection performance of the crystals in the wavelength of 0.3–2.5 μm. On the other hand, the lattice distortion and decrease in the lattice symmetry caused by Zn doping lead to an increase in the photon emissivity for the 8–13 μm band. The solar reflectivity of the SrZr_0.75Zn_0.25O_2.75 crystal powder can reach 0.892, whereas the atmospheric window emissivity can reach 0.954, both of which are greater than that of SrZrO₃. The coating prepared with the SrZr_0.75Zn_0.25O_2.75 crystal powder as the radiative refrigerant can reach a maximum radiative cooling temperature of 15.3 °C under a solar irradiation of 654 W·m⁻², and the maximum net radiative power is 64.7 W·m⁻². These results indicate that SrZr_0.75Zn_0.25O_2.75 is an excellent passive daytime radiative cooling material.

Thermal barrier coating has good thermal insulation effect and high temperature oxidation resistance, which can significantly increase the service temperature and life of high temperature components in aeroengines. The development of advanced aeroengine has put forward higher requirements for the protective effect and service life of ceramic thermal barrier coating materials. The research progress of thermal barrier coating system for advanced aeroengine is reviewed. The ceramic layer and bond layer material system and preparation technology of thermal barrier coating at home and abroad in recent years are described in detail, while the failure of coating is analyzed. The research and application prospect of the next generation high-performance thermal barrier coatings for aeroengine are prospected.

Developing new high-entropy rare-earth zirconate (HE-RE₂Zr₂O₇) ceramics with low thermal conductivity is essential for thermal barrier coating materials. In this work, the average atomic spacings, interatomic forces, and average atomic masses of 16 rare-earth elements occupying the A site of the cubic A₂B₂O₇ crystal structure were calculated by density functional theory. These three physical qualities, as vectors, characterize the corresponding rare-earth elements. The distance between two vectors quantitatively describes the difference between two rare-earth elements. For greater differences between two rare-earth elements, the disorder degree of HE-RE₂Zr₂O₇ is greater, and therefore, the thermal conductivity is lower. According to the theoretical calculations, the thermal conductivity of the ceramics gradually increases in the order of (Sc_0.2Y_0.2La_0.2Ho_0.2Yb_0.2)₂Zr₂O₇, (Sc_0.2Ce_0.2Nd_0.2Eu_0.2Gd_0.2)₂Zr₂O₇, (Sc_0.2Y_0.2Tm_0.2Yb_0.2Lu_0.2)₂Zr₂O₇, and (Sc_0.2Er_0.2Tm_0.2Yb_0.2Lu_0.2)₂Zr₂O₇. Using the solution precursor plasma spray method and pressureless sintering method, four types of HE-RE₂Zr₂O₇ powder and bulk samples were prepared. The samples all showed a single defective fluorite structure with a uniform distribution of the elements and a stable phase structure. The thermal conductivities of the sintered HE-RE₂Zr₂O₇ bulk samples ranged from 1.30 to 1.45 W·m⁻¹·K⁻¹ at 1400 °C, and their differences were consistent with the theoretical calculation results. Among the ceramics, (Sc_0.2Y_0.2La_0.2Ho_0.2Yb_0.2)₂Zr₂O₇ had the lowest thermal conductivity (1.30 W∙m⁻¹∙K⁻¹, 1400 °C), highest thermal expansion coefficient (10.19×10⁻⁶ K⁻¹, 200–1400 °C), highest fracture toughness (1.69±0.28 MPa∙m^1/2), and smallest brittleness index (3.03 μm^−1/2). Therefore, (Sc_0.2Y_0.2La_0.2Ho_0.2Yb_0.2)₂Zr₂O₇ is considered to be an ideal candidate material for next-generation thermal barrier coating applications.