Efficient solar steam generation by using metal-versatile hierarchical nanostructures for nickel and gold with aerogel insulator

Metallic nanostructure-based solar absorbers are widely used owing to their controllable range of absorption wavelengths and various potential applications. Metal-versatile solar absorbers that are not limited to noble metals are essential to reduce production costs. In this study, broadband solar absorbing surfaces were fabricated based on Ni or Au-deposited self-aggregated alumina nanowire structures. A high solar absorptance was obtained for both the Ni-deposited nanowire structures (~0.90) and Au-deposited nanowire structures (~0.92), indicating the advantage of using nickel instead of the noble metal. These high solar absorptance were theoretically analysed by comparing the electric field distributions obtained from finite-difference time-domain (FDTD) simulations and the dielectric functions of Ni and Au. In addition, efficient solar steam generation platform was designed using these broadband solar absorbers and aerogel thermal insulator. The solar steam generation efficiency was improved through heat localisation using an aerogel as a thermal insulator and a polyvinyl alcohol (PVA) sponge as a water supplier. The efficiencies of the solar steam generation platforms using black Ni and Au films under an illumination of 5 kW m⁻² were 83.8% and 78.3%, respectively.