Greatly enhanced anticorrosion of Al-AlNxOy nanocermet films with self-passivated Al nanoparticles for enduring solar-thermal energy harvesting

Metal-dielectric (cermet) solar selective absorber coatings (SSACs), in which metal NPs are embedded in dielectric matrices, have been widely used in the photothermal conversion field due to their strong broadband absorption characteristics. However, metal nanoparticles (NP) always possess some inherent activity (i.e. diffusion, agglomeration or oxidation) that decreases their surface energy. Therefore, cermet-based SSACs are not corrosion-resistant and show poor thermal stability. Here, Al NPs were selected as the doped metal and AlNxOy as the dielectric matrices; with the aid of self-passivating Al NPs in the newly formed Al-enriched AlxOy/Al2O3/AlxOy(OH), Al-AlNxOy SSACs possessed unprecedented anticorrosion and outstanding thermal stability (up to 400 degrees C). The corrosion tolerance of the Al-AlNxOy SSACs film significantly surpasses those of reported commercial and laboratorial films. The film still displayed desirable solar absorptance (0.924) and low thermal emissivity (0.116) after 5.0 wt% NaCl salt spray for 2000 h. More importantly, the fabrication of the Al-AlNxOy SSACs is simple, cost-effective, and highly suitable for large scale production. A self-developed industrial-scale air-to-air sputtering line was fabricated for continuous production of Al-AlNxOy SSACs on 1000 mm wide aluminum strips. Based on the above high performance, Al-AlNxOy SSACs are promising absorbers for enduring photothermal utilization in high-salinity environments.