Study on the solar selectivity and air thermal stability of cobalt–nickel–iron oxide coating fabricated by spraying method

Abstract Solar selective absorber coatings (SSACs) with transition metal spinel structure were fabricated with Fe-, Ni- and Co-based nitrate salts by facile sol-gel method and fast spraying process that facilitates large-area coating preparation. By optimizing the doping ratio of three transition metal nitrates, the number of spraying layers and the annealing temperature, the SSAC with solar absorptance of 0.93 and vertical emittance of 0.11 were achieved. The actual and comprehensive heat collection performance was studied by placing the coating samples directly in the sun. The surface temperature of the coating reached 72.8 °C when the outdoor temperature was 33 °C and the sunshine duration was 30 min. The thermal stability of the two-layer Ni0·9Fe0·1Co2Oy coatings was evaluated by continuously heating at 500 °C in the air for 48 h. The solar absorptance remained basically unchanged at 0.93, while the emissivity gradually increased from 0.11 to 0.30. The experimental results also show that the sintering temperature has a great influence on the absorptance of the coating, while the heating duration time has a greater influence on the vertical emittance. It indicates that the Ni0·9Fe0·1Co2Oy coating prepared by fast sol-gel spraying method is a promising SSAC which is easily prepared and applied on complex surface.