Heterogeneous evaporator with low heat conduction loss for efficient solar desalination

Solar-driven evaporation enables environmentally sustainable production of freshwater. However, evaporators with a homogeneous structure often experience high energy loss due to heat conduction to the underlying bulk water, resulting in a low evaporation rate. Here, a novel evaporator with a heterogeneous structure and vertical channels has been designed and fabricated by integrating a polyvinylidene fluoride/polypyrrole (PVDF/PPy) solar heating porous layer (SHPL) on a neat PVDF layer via controllable solvent diffusion and phase separation in cold NaCl solution. This structural advantage of the as-prepared PVDF-SHPL evaporator directly reduces heat conduction loss to 131.1 W m^-2 (vs. 202.9 W m^-2 for the homogeneous SHPL evaporator) that traps heat within the SHPL layer, resulting in a superior pure water evaporation rate (3.5 kg m^-2 h^-1 vs. 2.7 kg m^-2 h^-1 for SHPL) under a solar flux of 1000 W m^-2. Moreover, the PVDF-SHPL heterogeneous evaporator exhibits outstanding salt resistance, stability, and desalination performance. Remarkably, it can produce 23.7 kg m^-2 day^-1 of freshwater from simulated seawater on sunny days in summer, which is sufficient for the daily drinking water needs of 8∼9 adults. This work represents a significant advancement toward energy-neutral solutions for addressing global water scarcity.