Hierarchically Structured Black Gold Film with Ultrahigh Porosity for Solar Steam Generation

Plasmonic metals demonstrate significant potential for solar steam generation (SSG) because of their localized surface plasmon resonance effect. However, the inherently narrow absorption spectra of plasmonic metals significantly limit their applications. The fabrication of nanostructures is essential to achieve broadband solar absorption for high-efficiency vapor generation. Herein, a self-supporting black gold (Au) film with an ultrahigh porosity and a hierarchically porous structure is fabricated by formulating an extremely dilute Cu99Au1 precursor and controlling the dealloying process. In situ and ex situ characterizations reveal the dealloying mechanism of Cu99Au1 in a 1 m HNO3 solution as that involving the phase transformation of Cu(Au) -> Au(Cu) -> Au, giant volume shrinkage (approximate to 87%), structural evolution/coarsening of ligaments, and development of ultrahigh porosity (86.2%). The multiscale structure, consisting of ultrafine nanoporous nanowires, aligned nanogaps, and various microgaps, provide efficient broadband absorption over 300-2500 nm, excellent hydrophilicity, and continuous water transport. In particular, the nanoporous black Au film shows high SSG performance with an evaporation rate of 1.51 kg m(-2) h(-1) and a photothermal conversion efficiency of 94.5% under a light intensity of 1 kW m(-2). These findings demonstrate that the nanoporous Au film has great potential for clean water production and seawater desalination.

Automated summary

This study investigates the fabrication and performance of nanoporous gold film, revealing its broadband absorption, efficient photothermal conversion, and steam generation capabilities, making it suitable for clean water production and seawater desalination.