Oxidation-resistant, solution-processed plasmonic Ni nanochain-SiO_x (x < 2) selective solar thermal absorbers

Metal oxidation at high temperatures has long been a challenge in cermet solar thermal absorbers, which impedes the development of atmospherically stable, high-temperature, high-performance concentrated solar power (CSP) systems. In this work, we demonstrate solution-processed Ni nanochain-SiO_x (x < 2) and Ni nanochain-SiO₂ selective solar thermal absorbers that exhibit a strong anti-oxidation behavior up to 600 °C in air. The thermal stability is far superior to previously reported Ni nanoparticle-Al₂O₃ selective solar thermal absorbers, which readily oxidize at 450 °C. The SiO_x (x < 2) and SiO₂ matrices are derived from hydrogen silsesquioxane and tetraethyl orthosilicate precursors, respectively, which comprise Si-O cage-like structures and Si-O networks. Fourier transform infrared spectroscopy shows that the dissociation of Si-O cage-like structures and Si-O networks at high temperatures have enabled the formation of new bonds at the Ni/SiO_x interface to passivate the surface of Ni nanoparticles and prevent oxidation. X-ray photoelectron spectroscopy and Raman spectroscopy demonstrate that the excess Si in the SiO_x (x < 2) matrices reacts with Ni nanostructures to form silicides at the interfaces, which further improves the anti-oxidation properties. As a result, Ni-SiO_x (x < 2) systems demonstrate better anti-oxidation performance than Ni-SiO₂ systems. This oxidation-resistant Ni nanochain-SiO_x (x < 2) cermet coating also exhibits excellent high-temperature optical performance, with a high solar absorptance of ∼90% and a low emittance ∼18% measured at 300 °C. These results open the door towards atmospheric stable, high temperature, high-performance solar selective absorber coatings processed by low-cost solution-chemical methods for future generations of CSP systems.