Black oxide nanoparticles as durable solar absorbing material for high-temperature concentrating solar power system

• Co3O4 nanoparticles for light absorbing coatings of CSP systems.
• Co3O4 coating with light-trapping structures leading to high thermal efficiency.
• Durable structure and stable thermal efficiency after 1000-h exposure to 750 °C air.

Concentrating solar power is becoming an increasingly important part of the renewable energy portfolio. However, further cost reduction is desired to make CSP competitive with traditional energy technologies. Higher operating temperature is considered an attractive avenue leading to higher power conversion efficiency and lower cost, but tremendous technical challenges exist with higher temperature operation of CSP, with one of the main issues being the lack of a high-performance solar absorbing material that is durable at 750 °C or above. In this work, a black oxide material, made of cobalt oxide nanoparticles, is synthesized and utilized as a high-temperature solar absorbing material. The nanoparticles are embedded in a dielectric matrix through a scalable spray coating process. The top layer of the coating is further improved with light-trapping structures using sacrificial fillers introduced from the same coating process. After the surface modification of cobalt oxide coating, we achieved a high thermal efficiency of 88.2%. More importantly, the coating shows no degradation after 1000-h annealing at 750 °C in air, while the existing commercial light absorbing coating was reported to degrade by long-term exposure at high temperature. Our findings suggest that the materials and processes developed here are promising for solar absorbing coating for future high-temperature CSP systems.