Electrodeposition and Characterization of Selective Coatings Based on Black Cobalt for Solar-to-Thermal Energy Conversion

Solar-thermal energy conversion is achieved by selective coatings on a metallic substrate. The selective coating consist of a thin selectively absorbing film on a highly IR reflective underlying metal. The optical performance of the selective coating depends on the thickness of the respective films, which can be controlled through the electric charge applied during the electrodeposition process. Selective coatings have been deposited on copper substrates by the electrodeposition method. The coating consists of an intermediate reflective layer of electrodeposited bright nickel and an absorbing film of black cobalt. Different times were used for the galvanostatic deposition of black cobalt in order to optimize the optical properties. In order to evaluate the thermal stability, the coatings were exposed to temperature of 300^oC.  The coatings were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The visible and IR film reflectance was evaluated before and after the thermal treatment through UV-Vis-NIR spectrophotometer and a Perkin Elmer FTIR spectrophotometer (Frontier MIR/NIR) with an integrating sphere from 2 µm to 15 µm.   The spectrophotometry results showed little change in the film reflectance after of the thermal treatment, suggesting a good thermal stability.