High-Entropy Alloy-Based Coatings

Coatings Based on High-Entropy Alloys As a new player in the world of alloy materials, high-entropy alloys, containing more than five elements, exceed expectations in conventional alloy design concepts and typically exhibit a simple solid solution structure due to their high configurational entropies. With excellent mechanical properties, heat resistance, and resistance to wear, corrosion and irradiation, high-entropy alloys have significant potential for advancement in the renewable energy industry. Recently, a research team led by Associate Professor GAO Xianghu and Professor LIU Gang at the Lanzhou Institute of Chemical Physics of the Chinese Academy of Sciences (CAS) prepared a series of high-entropy alloy-based, high-temperature, solar-selective absorber coatings through component modulation, conformational entropy optimization and structural design using high-entropy nitrides. The researchers designed a solar-selective absorber coating consisting of an infrared-reflective aluminum layer, high-entropy alloy nitride, high-entropy alloy nitrogen oxide and silicon dioxide, which provided high solar absorption of 93.5% and thermal emittance of less than 10%. Subsequently, they found that a single high-entropy alloy nitride ceramic layer also possessed good intrinsic absorption properties and therefore prepared a coating with a simple structure. They used high-entropy alloy nitride as the absorption layer and SiO2 or Si3N4 as the antireflection layer, and obtained a coating with 92.8% absorption and less than 7% emittance that demonstrated appropriate thermal stability at 650 degrees Celsius in vacuum for 300 hours. To further increase the absorption capacity of the absorber, the researchers created a structure with stainless steel as the substrate, low-nitrogen-content high-entropy alloy films as the main absorption layer, high-nitrogen-content high-entropy alloy films as the extinction interference layer, and SiO2, Si3N4 or Al2O3 as the antireflection layer, with optical constants gradually decreasing from the bottom layer to the surface. To increase preparation efficiency, a combination of optical simulation and magnetron sputtering methods was used, which contributed to excellent solar absorption of 96% and low thermal emittance lower than 10%. Subsequently, they investigated the light absorption mechanism using finite-difference time-domain simulation. After annealing at 600 degrees Celsius in vacuum for 168 hours, the high-entropy alloy nitride-based absorber retained its good optical properties, demonstrating exceptional thermal stability. The photothermal conversion efficiency of the absorber was calculated at different operating temperatures and concentration ratios, and the efficiency reached 90.1% when the operating temperature was 550 degrees Celsius and the solar concentration was 100. When compared with the latest state-of-the-art absorber recently reported, the high-entropy alloy-based absorber exhibited both excellent photothermal conversion efficiency and thermal stability. The absorbers were deposited on different substrate materials, maintaining excellent optical properties and providing large-scale preparation on aluminum foil. Through examination of absorption spectra at different incident angles, it was found that the absorption coating had good absorption in the incident light angle range of 0-60°. Under radiation from simulated sunlight, the temperature of the coating surface exceeded 100 degrees Celsius, demonstrating significant potential for the material to be applied in the interfacial water evaporation field. Sources and Further Information: • Hui-Xia Guo et al, A novel multilayer high temperature colored solar absorber coating based on high-entropy alloy MoNbHfZrTi: Optimized preparation and chromaticity investigation, Solar Energy Materials and Solar Cells (2020). DOI: 10.1016/j.solmat.2020.110444 • Cheng-Yu He et al, Further investigation of a novel high entropy alloy MoNbHfZrTi based solar absorber coating with double antireflective layers, Solar Energy Materials and Solar Cells (2020). DOI:10.1016/j.solmat.2020.110709 • Cheng-Yu He et al, Scalable and highly efficient high temperature solar absorber coatings based on high entropy alloy nitride AlCrTa- TiZrN with different antireflection layers, Journal of Materials Chemistry A (2021). DOI: 10.1039/D0TA09988K • Cheng-Yu He et al, Highly Enhanced Thermal Robustness and Photothermal Conversion Efficiency of Solar-Selective Absorbers Enabled by High-Entropy Alloy Nitride MoTaTiCrN Nanofilms, ACS Applied Materials & Interfaces (2021). DOI: 10.1021/acsami.0c23011 • Cheng-Yu He et al, Toward a Scalable and Cost-Conscious Structure in Spectrally Selective Absorbers: Using High-Entropy Nitride TiVCrAlZrN, ACS Applied Energy Materials (2021). DOI: 10.1021/acsaem.1c00918 • Cheng-Yu He et al, Scalable and Ultrathin High‐Temperature Solar Selective Absorbing Coatings Based on the High‐Entropy Nanoceramic AlCrWTaNbTiN with High Photothermal Conversion Efficiency, Solar RRL (2021). DOI: 10.1002/solr.202000790 • Cheng-Yu He et al, Greatly enhanced solar absorption via high entropy ceramic AlCrTaTiZrN based solar selective absorber coatings, Journal of Materiomics (2020). DOI: 10.1016/j.jmat.2020.11.010 • Journal information: Solar Energy Materials and Solar Cells , Journal of Materials Chemistry A , ACS Applied Materials and Interfaces. • https://phys.org/news/2021-10-high-entropy-alloysbased-hightemperature-solar-absorption-coatings.html