Flexible thin-film black gold membranes with ultrabroadband plasmonic nanofocusing for efficient solar vapour generation

Abstract

Solar steam generation has been achieved by surface plasmon heating with metallic nanoshells or nanoparticles, which have inherently narrow absorption bandwidth. For efficient light-to-heat conversion from a wider solar spectrum, we employ adiabatic plasmonic nanofocusing to attain both polarization-independent ultrabroadband light absorption and high plasmon dissipation loss. Here we demonstrate large area, flexible thin-film black gold membranes, which have multiscale structures of varying metallic nanoscale gaps (0–200 nm) as well as microscale funnel structures. The adiabatic nanofocusing of self-aggregated metallic nanowire bundle arrays produces average absorption of 91% at 400–2,500 nm and the microscale funnel structures lead to average reflection of 7% at 2.5–17 μm. This membrane allows heat localization within the few micrometre-thick layer and continuous water provision through micropores. We efficiently generate water vapour with solar thermal conversion efficiency up to 57% at 20 kW m−2. This new structure has a variety of applications in solar energy harvesting, thermoplasmonics and related technologies.

Cold Vapor Generation beyond the Input Solar Energy Limit

“…However, conventional techniques for generating solar vapor typically rely on costly and cumbersome optical concentration systems to enable bulk heating of a liquid, resulting in relatively low efficiencies (e.g., 30–40%) due to heat absorption throughout the entire liquid volume that is not directly translated into vapor production. Recently, various advanced and expensive metallic plasmonic5, 6, 7, 8, 9, 10, 11, 12, 13 and carbon‐based nanomaterials14, 15, 16, 17, 18, 19, 20, 21, 22, 23 have been explored for use in solar vapor/steam generation. However, the vaporization efficiencies of these reported structures are still relatively low under 1 sun illumination (e.g., from 48%10 to 83%21).…”

“…Recently, various advanced and expensive metallic plasmonic5, 6, 7, 8, 9, 10, 11, 12, 13 and carbon‐based nanomaterials14, 15, 16, 17, 18, 19, 20, 21, 22, 23 have been explored for use in solar vapor/steam generation. However, the vaporization efficiencies of these reported structures are still relatively low under 1 sun illumination (e.g., from 48%10 to 83%21). Very recently, we demonstrated a cost‐effective strategy using thermally isolated carbon‐coated paper (CP) on polystyrene foam with a record high efficiency of ≈88% in the laboratory environment 24.…”

“…However, the widely used definition of the solar energy conversion efficiency (e.g., refs. 9, 10, 11, 12, 13, 16, 18, 19, 20, 21, 26, 30) is obviously not applicable in this transient process since there is no solar input. Therefore, the physical picture of the solar‐driven evaporation should be revisited.…”

Tuning Transpiration by Interfacial Solar Absorber‐Leaf Engineering

“…In recent years, interfacial solar steam/vapor generation is attracting a lot of attention for achieving high energy transfer efficiency. And various optical and thermal designs at the solar absorber–water interface for potential applications in water purification,10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23 seawater desalination,24, 25, 26, 27 and power generation28, 29 appear.…”

“…On the basis of global water cycle, moderate global temperature, humidity, and precipitation may be attainable through the tunable plant transpiration. Moreover, photothermal conversion shows the potential as the regulator of the nature, besides the emerging applications, such as radiative cooling,42, 43, 44, 45 thermophotovoltaics,46, 47, 48, 49 water purification,10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23 seawater desalination,24, 25, 26, 27 and power generation 28, 29…”