Electroplated $${\hbox {Co}₃}{\hbox {O}_{{4}}}$$ selective coatings for high-temperature solar thermal applications

This communication presents the optical characterization of (hbox {Co}_{{3}}hbox {O}_{{4}}) films electroplated on Cu- and Ni-coated Cu substrates. (hbox {Co}_{{3}}hbox {O}_{{4}}) films were successfully deposited by using the electrochemical deposition method with cobalt acetate tetrahydrate as a cobalt precursor followed by annealing at (350^circ hbox {C}). The as-prepared films were characterized using X-ray diffraction, UV–visible spectroscopy, Fourier transform infrared spectroscopy, scanning electron microscopy and stagnation temperature test. The characterization shows the presence of only the cubic spinal (hbox {Co}_{{3}}hbox {O}_{{4}}) phase in all films. The morphological analysis revealed the generation of unique fish-shaped (hbox {Co}_{{3}}hbox {O}_{{4}}) particles with uniform size distribution for the films obtained on the Ni-coated Cu substrate. The Cu substrate with and without nickel plating used for deposition has shown a profound effect on the optical characteristics of films. The solar absorbance as high as 0.96 and thermal emittance as low as 0.02 were obtained for the films deposited on the Ni-coated Cu substrate. The highest value of the figure of merit ((F_{{1}})) of (sim )0.34 and extrapolated stagnation temperature of (sim )362(^circ hbox {C}) were realized for films having better optical characteristics. The results obtained indicate very good potential of the deposited films for solar thermal applications.