A Hydrogenated Metal Oxide with Full Solar Spectrum Absorption for Highly Efficient Photothermal Water Evaporation

Searching for cost-effective photothermal material that can harvest the full solar spectrum is critically important for solar-driven water evaporation. Metal oxides are cheap materials but cannot cover the full solar spectrum. Here we prepared a hydrogenated metal oxide (H_1.68MoO₃) material, in which H-doping causes the insulator-to-metal phase transition of the originally semiconductive MoO₃. It offers a blackbody-like solar absorption of ≥95% over the entire visible-to-near-infrared solar spectrum, owing to its unusual quasi-metallic energy band, and high solar-to-heat conversion rate due to quick relaxation of excited electrons. Using a self-floating H_1.68MoO₃/airlaid paper photothermal film, we achieved a stable and high water vapor generation rate of 1.37 kg m^–2 h^–1, a superb solar-to-vapor efficiency of 84.8% under 1 sun illumination, and daily production of 12.4 L of sanitary water/m² from seawater under natural sunlight. This thus opens a new avenue of designing cost-effective photothermal materials based on metal oxides.