A bilayer solar evaporator with all-in-one design for efficient seawater desalination

Bilayer solar evaporator combines high photothermal conversion capacity and low heat loss, has become the new darling in interfacial solar steam generation (ISSG). However, the bilayer structure generally achieved by introducing a photothermal coating on the substrate is not conducive to long-term use due to the poor stability of coating. Herein, a fully biomass-based bilayer evaporator is all-in-one designed, using chitosan (CS) as building blocks and CS derived N, S - doped porous carbon (NSPC) as fillers via pre-freezing and freeze-drying. This facile method could realise the quantitative addition of photothermal materials and controllably regulate the structure of the bilayer evaporator, making the structural optimisation readily available. The optimised evaporator exhibits a remarkable evaporation rate of 2.51 kg m^-2h^-1. After 1000 times of pressing, it still maintains at 2.42 kg m^-2h^-1. Additionally, the evaporator displays outstanding long-lasting stability, excellent salt-resistant and degradability. More importantly, a solar desalination device is fabricated for harvesting freshwater outdoor. The daily water production per unit area (4.55 kg) meets the consumption of two adults. This work provides a controllable synthesis strategy of bilayer evaporators for handling global freshwater shortages.