Plasmonic AgAl Bimetallic Alloy Nanoparticle/Al2O3 Nanocermet Thin Films with Robust Thermal Stability for Solar Thermal Applications

Abstract

Developing plasmonic materials as cermet composites is desirable for selective solar absorbers. Silver nanoparticles/alumina (Ag‐Al2O3) cermet possesses reasonable resistance to high‐temperature oxidation; however, an inherent long‐range diffusion of Ag element limits their applications at elevated temperatures. In this work, a well‐designed AgAl‐Al2O3 nanocermet, after low‐temperature pretreatment in air, exhibits stable plasmonic absorption feature with negligible degradation at 500 °C for 990 h in nitrogen ambient. Based on this cermet, an Al2O3/low metal volume fraction AgAl‐Al2O3/high metal volume fraction AgAl‐Al2O3/Al2O3/AgAl tandem absorber was successfully constructed, demonstrating a high solar absorptance of ≈95% and a low infrared emittance of ≈11%@673 K after annealing at 500 °C for 1002 h in nitrogen ambient. It is believed that thermal‐induced out‐diffusion of Al atoms from AgAl bimetallic nanoparticles and their consequent oxidation afford an opportunity to generate self‐organized alumina‐capped Ag nanoparticles. The alumina‐capped Ag particles and unalloyed Ag agglomerations are mixed together to form mosaic structure, suppressing the long‐distance diffusion of active Ag and wild growth of particle agglomerations so as to guarantee the microstructural integrity and plasmon absorption stability. These results demonstrate that the proposed AgAl‐Al2O3‐based solar absorber is remarkably promising to be used in high‐temperature solar thermal conversion.