High-temperature stable refractory nanoneedles with over 99% solar absorptance

Abstract

Solar absorber coatings have widely been investigated for solar-thermal technologies including concentrated solar power and solar thermochemistry. While various nanostructures such as nanowires and nanotubes have been commonly used for high solar absorptance owing to their potent light trapping effect, the high temperature stability of these nanostructures has yet to be established due to either coarsening of nanostructures or oxidation of certain materials in air (e.g., Si and C). In this work, we developed a nanostructured solar absorber from a family of high-temperature refractory spinel oxides, Co3O4 and CuCo2O4, with ultra-high solar absorptance over 99%. Once coated with a thin layer of HfO2 or SiO2 through atomic layer deposition, the Co3O4 and CuCo2O4 nanoneedles preserve their high aspect ratio and sharp tips, allowing the solar absorbers to maintain the superior absorptivity and excellent thermal stability at an elevated temperature for an extended period (650 °C and 800 °C for 100 h for passivated Co3O4 and Cu1Co2O4, respectively). These results suggest that solar absorbers made from refractory spinel oxide nanoneedles can be used for high-temperature solar thermal applications with ultrahigh absorptance.