3D-structured carbonized sunflower heads for improved energy efficiency in solar steam generation.

Solar steam generation is regarded as a perspective technology, due to its potentials in solar light absorption and photothermal conversion for seawater desalination and water purification. Although, lots of steam generation systems have been reported to possess high conversion efficiencies recently. Researches of simple, cost-effective and sustainable materials still need to be done. Here, inspired by natural young sunflower heads' property-increasing the temperature of dish-shaped flowers by tracking the sun, we used 3D-structured carbonized sunflower heads as an effective solar steam generator. The evaporation rate and efficiency of these materials under 1 sun (1 kW m-2) is 1.51 kg m-2 h-1 and 100.4%, respectively, beyond the theoretical limit of 2D materials. This high solar efficiency surpasses all other biomass-based materials ever reported. It is demonstrated that such a high capability is mainly attributed to the 3D-structured top surface, which could reabsorb lost energy of diffuse reflection and thermal radiation, as well as provide enlarged water/ air interface for steam escape. 3D-structured carbonized sunflower heads provide a new method for future design and fabrication of high-performance photothermal devices.