A multilayered black Ni-P solar absorbent material with double physical vapor deposited Ag and Al selective nanocoatings

This study presents a single proposed sample type designed to combine high solar absorption efficiency and enhanced corrosion resistance, a multilayer solar absorber material comprising a black nickel-phosphorus base layer, for absorption in the visible to short-wavelength infrared. It was covered with nanometric Ag (∼7 nm) and Al (∼5 nm) thin films proposed as complementary selective layers to reflect in the mid- and long-wavelength infrared to avoid losing energy in hot surfaces by radiation. This multilayer optimizes solar absorption but also possesses corrosion resistance with the Al₂O₃ self-passivating layer of Al, albeit with limitations due to heterogeneity and the topography of the underlying black Ni-P layer. The Al layer reduced the corrosion rate from 0.28 for steel to 0.19 mmpy for the full multilayer system, despite introducing microgalvanic interactions in chloride-rich environments that increased localized corrosion signals. The multilayer absorption system achieved total absorptions of about 91 % for steel/Ni-P/Ag and about 93 % for steel/Ni-P/Ag/Al/Al₂O₃ in the visible/near-wavelength/short-wavelength infrared, with an overall absorption of up to 99 %. This work highlights the required balance between optical performance and electrochemical stability attained with multilayer systems, making them a promising solution for sustainable solar energy applications.