A Scalable Nickel-Cellulose Hybrid Metamaterial with Broadband Light Absorption for Efficient Solar Distillation

Sophisticated metastructures are usually required to broaden the inherently narrowband plasmonic absorption of light for applications such as solar desalination, photodetection, and thermoelectrics. Here, nonresonant nickel nanoparticles (diameters < 20 nm) are embedded into cellulose microfibers via a nanoconfinement effect, producing an intrinsically broadband metamaterial with 97.1% solar-weighted absorption. Interband transitions rather than plasmonic resonance dominate the optical absorption throughout the solar spectrum due to a high density of electronic states near the Fermi level of nickel. Field solar purification of sewage and seawater based on the metamaterial demonstrates high solar-to-water efficiencies of 47.9-65.8%. More importantly, the solution-processed metamaterial is mass-producible (1.8 × 0.3 m² ), low-cost, flexible, and durable (even effective after 7 h boiling in water), which are critical to the commercialization of portable solar-desalination and domestic-water-purification devices. This work also broadens material choices beyond plasmonic metals for the light absorption in photothermal and photocatalytic applications.