Effects of Metal Dopings on CuCr₂O₄ Pigment for Use in Concentrated Solar Power Solar Selective Coatings

The process of fabricating the solar absorbing spinel-structured CuCr2O4 black oxide pigment doped with different metals (Mn, Ni, Co, Al, Zn, and Sn) was discovered to improve the solar selective property. Manganese stands out as an ideal dopant to copper chromite (CuCr2O4) for highly solar absorptive pigments compared to the other metal dopings. XRD analysis confirmed that various molar ratios of CuCr(2–x)MnxO4 spinel black oxides were successfully fabricated. Mn-doped black oxide has the highest absorptivity (the lowest band gap value of 1.35 eV) among various metal doped black oxides produced by the hydrothermal synthesis. Manganese is the only dopant that suppresses reflectance peaks exhibited by the copper chromium oxide at 1 and 1.5 μm in the light spectrum, raising the solar absorptivity of the pigment. Different manganese doping compositions are introduced to CuCr(2–x)MnxO4 where x = 0.1, 0.25, 0.5, 1, 1.5, 1.75, and 1.9. The high selective solar absorptivity appears after 100% (x = 1) manganese doping with solar absorbance 0.9874 and a figure of merit (FOM) value of 0.9284.