Electrodeposition of Selective Absorber Coatings Based on Black Nickel for Solar - Thermal Energy Conversion

Solar energy is the most abundant, renewable and clean energy source, and several systems exist to convert solar energy into a useful form for specific applications. One of them is the development of solar collectors based on selective coatings, with a high absorptivity in the visible and low emissivity in the near to mid infrared regions of the solar spectrum. The use of selective coatings has been widely established as an industrial practice to improve the efficiency in solar energy collection. For practical applications, a solar absorber coating with selective optical properties should be easily applicable with easy scale-up, low cost and short time of synthesis. These coatings can be applied to the collector substrate by various techniques including vacuum deposition, spray methods, sol-gel chemistry, and electrodeposition.

In this work, bright and black nickel coatings were electrodeposited onto copper and stainless steel substrates with an area of 16 cm². The experiments were performed at room temperature using electrolytes from nickel sulfate and nickel chloride salts. For the characterization of the coatings, several techniques were used, as profilometry, scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The optical properties of the coatings were measured by reflectance spectroscopy. For the evaluation of the energy conversion efficiency, the electrodeposited coatings were irradiated at 1 sun and the heating of an aqueous was measured as a function of film properties.