Sunflower-Stalk-Based Solar-Driven Evaporator with a Confined 2D Water Channel and an Enclosed Thermal-Insulating Cellular Structure for Stable and Efficient Steam Generation

Given the worsening freshwater scarcity around the world, the interfacial solar-driven steam generation for seawater desalination and wastewater treatment has attracted wide attention due to its rich energy resources, convenience, and environmental friendliness. However, challenges still remain for developing high-efficiency interfacial solar-driven steam generation devices from low-cost, readily available, and green material resources. Herein, taking advantage of the delicate composite structure of the sunflower stalk, a sunflower-stalk-based solar-driven evaporator with a confined two-dimensional (2D) water supply pathway and an enclosed thermal-insulating structure is reported. The pith of sunflower stalks is composed of well-arranged honeycomb-like parenchyma cells that endow sunflower stalks with low thermal conductivity comparable to that of synthetic plastic foam. The low-tortuosity vascular bundles in the skin can serve as a natural 2D water pathway for rapid water transportation. The benefit of these functions is that an evaporator based on a carbon-nanotube-coated sunflower stalk (C-Ss) achieves a high evaporation rate of 1.76 kg m-2 h-1 under 1 sun irradiation (1 kW m-2). The C-Ss also shows a highly stable evaporation performance, high ion rejection efficiency, and a self-cleaning ability during the actual seawater desalination process. With advantages of abundant resources, easy fabrication, and sustainability, this C-Ss-based evaporator provides a promising choice for freshwater production in developing regions.