Nanostructured Anodic Aluminium Oxide (AAO) with Metal Coating Optimized for Passive Radiative Cooling

Currently, one third of the total energy consumption is already used for cooling in modern countries. An alternative way to achieve thermal comfort is becoming crucial to face this trend, and a passive cooling technology is a strong candidate that should be considered. Specially, when passive thermal management is achieved by using low-cost and easy-scalable to industry materials. In this sense, this study shows the possibilities of nanostructured anodic aluminium oxide (AAO) for passive radiative cooling: first, we analyse in detail the influence of all morphological parameters and the effect of the chemical structure on the optical response as well as on the passive radiative cooling performance; second, considering the most suitable kind of AAO nanostructures for passive cooling, we characterise different metal coating on the AAO nanostructures. Hence, we found the wavelength regions where the alumina thickness, the pore diameter, the interpore distance, the porosity and the incorporated counterions show the major impact in the optical response of the AAO nanostructures. We also improve the cooling performance of these AAO nanostructures by metal coating. A maximum temperature reduction of 11.7 K is experimentally measured under direct sunlight in a summer day in Spain. The results of this work demonstrate the enormous potential of AAO nanostructures to be used in thermal management applications and to contribute to a sustainable future energy.