New progress has been made in composite ceramic-based solar absorbing coatings

Extracting energy from inexhaustible solar radiation and converting it into thermal energy for use is a forward-looking strategy to deal with the energy crisis and environmental pollution and accelerate the transition to a sustainable, low-carbon world. As an important part of photothermal conversion technology, solar selective absorption coatings require high absorption rate in the solar spectral band (0.3-2.5 μm) and low emissivity in the mid-infrared band (2.5-20 μm), so that they show higher photothermal conversion efficiency, whether in the field of high-temperature solar thermal utilization, such as solar thermal power generation, or low-temperature solar thermal utilization, such as photothermal sterilization, de-icing, seawater desalination, can show great application prospects. However, most of the current solar absorbing coatings have a thermal stability of less than 650 °C under vacuum conditions, limiting their application at high temperatures. Therefore, it is of great significance to develop a solar absorption coating with excellent thermal stability (greater than 700 °C), scalable, simple structure and easy preparation.

Recently, Gao Xianghu, associate researcher of the Low Carbon Energy Materials Group of the Laboratory of Clean Energy Chemistry and Materials, Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, and Researcher Liu Gang have developed a high-temperature solar selective absorption coating based on the bilayer structure of composite ceramics, with composite ceramics (TiB2-HfB2) as the absorption layer and Al2O3 as the anti-reflective layer (Figure 1).

After the low temperature annealing treatment of the material, the absorption rate of the coating can be increased to 93.2%, and the emissivity can be reduced to 8.9%, which is due to the formation of a new intermediate layer between the composite ceramic layer and the anti-reflective layer, and a solar absorption coating with a three-layer optical gradient structure is obtained, thereby enhancing the optical properties of the coating material. Moreover, the absorption rate of the absorbent coating is not sensitive to the angle of incident light, and can achieve efficient solar conversion in the range of 0-60 ° angle of incidence, which is of great significance for reducing the operating cost of solar tracking system.

Figure 1. Reflection spectra and structural characterization of composite ceramic-based solar selective absorption coatings

Figure 2. Thermal stability study of solar selective absorption coatings, comparison of photothermal conversion efficiency and failure analysis

In addition, the absorption coating after low temperature annealing treatment has excellent thermal stability (Figure 2). Annealed for 240 h under vacuum conditions at 800 °C, the reflectance spectra of the absorption coating did not change significantly, and still showed good optical properties. At an operating temperature of 800 °C and a light intensity of 100 suns, the photothermal conversion efficiency of the solar energy is 68.6%.

The composite ceramic (TiB2 – HfB2) based solar selective absorption coating developed by the researchers has the advantages of good photothermal conversion efficiency, excellent thermal stability, simple structure, easy preparation, etc., which is expected to promote the development of solar thermal heat in different temperature fields of the material. The research was published in Materials Today Physics under the title “Reinforcement optical performance and thermal tolerance in a TiB2-HfB2-based double-layer spectral selective absorber via a pre-annealing strategy” ( on. Dr. Qiu Xiaoli is the first author of the paper, and Associate Researcher Gao Xianghu and Dr. He Chengyu are the corresponding authors.

The work has been supported by the Chinese Academy of Sciences Youth Innovation Promotion Association, the regional key project of the Chinese Academy of Sciences Science and Technology Service Network Program, and the major science and technology projects in Gansu Province. (Source: Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences)

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