Nickel doped cobaltite spinel as a solar selective absorber coating for efficient photothermal conversion with a low thermal radiative loss at high operating temperatures

Abstract

Concentrated Solar Thermal (CST) system efficiency depends mainly on the operating temperature. One of the key components in the CST system is the receiver tube to attain higher temperatures, where the challenge remains on developing a solar absorber coating with high photothermal conversion and thermal stability at high temperatures. Nickel doped cobaltite (NixCo3-xO4; 0 ≤ x ≥ 1) thin film has been developed with spinel oxide phase on top of stainless steel substrates using a simple wet-chemical dip coating method as a base absorber layer (absorptance, α = 0.92; emittance, ε = 0.14). On top of the base absorber layer, coating integrated with silica (SiO2) as an optical enhancement layer (OPEL) has been deposited to make the coating more selective (α = 0.94 and ε = 0.13). A thorough investigation has been done to characterize the samples through UV–Vis–NIR spectrophotometer, Fourier transform infra-red spectroscopy, X-ray diffraction, transmission electron microscopy and thermogravimetric analyzer for the optical and physiochemical properties. Besides, the optimized spinel coating exhibits a low radiative loss with a minimum thermal emissivity of 0.07 at 100 °C and 0.18 at 500 °C, which indicates that the nickel cobaltite spinels are a very good candidate for high temperature solar selective applications.