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

Abstract 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 Cu 99 Au 1 precursor and controlling the dealloying process. In situ and ex situ characterizations reveal the dealloying mechanism of Cu 99 Au 1 in a 1 m HNO 3 solution as that involving the phase transformation of Cu(Au) → Au(Cu) → Au, giant volume shrinkage (≈87%), structural evolution/coarsening…