Aqueous solution-chemical derived Ni–Al2O3 solar selective absorbing coatings

Here we report the preparation of Ni–Al2O3 absorbing coatings by a facile aqueous solution-chemical method. In this approach, aluminum nitrate and nickel nitrate were simply mixed in water as precursor solution together with a chelating agent and a wetting agent, all of which were of low cost and available commercially. At high temperature and in N2 atmosphere, aluminum ions were converted into an Al2O3 matrix and nickel ions were in situ reduced into nano-size nickel particles embedded in the Al2O3 matrix. The optimum single layer attained a high normal solar absorptance of 0.85 and a low normal thermal emittance of 0.03. A three-layer coating, i.e. double absorption layers together with one top anti-reflection layer, exhibited better optical properties of absorptance/thermal emittance=0.93/0.05, respectively, and was stable in air up to 300 °C.