Solar Evaporator with Dual Gradient Heating Effect for Sustained and Efficient Desalination

Solar desalination shows promise in tackling freshwater shortages, but challenges arise from the trade-off between water transportation and heat supply, affecting evaporators' efficiency and salt resistance. Additionally, intermittent nature of solar radiation significantly diminishes overall evaporative performance. This study presents dual-gradient heating solar evaporator for efficient desalination. Dual-gradient heating is enabled through wettability difference (hydrophilicity aerogel and hydrophobicity film) and difference in phase transition temperature of phase change material, thus, effective heat supply can be provided to evaporation layer consisting of vertically oriented phase-change aerogel by surrounding heating layer consisting of phase-change film, with and without solar radiation. Employing this design, evaporator demonstrates industry-leading comprehensive performance in practical use. Under one sun illumination, evaporation rate achieves 6.84 kgm-2h-1 in 5.0 wt% salinity, with efficiency of 90.9%. In darkness, evaporation rate remains high at 2.61 kgm-2h-1 (30 minutes). Moreover, evaporator exhibits outstanding solar energy storage capacity and long-term stabe evaporative performance and salt resistance for 7-day testing. Furthermore, evaporator successfully produces freshwater from real Bohai Sea water under weak outdoor lighting, addressing recommended daily intake of water for 2.5 households. This work introduces new perspective for maximizing utilization of solar energy for seawater desalination and overcoming intermittent solar radiation.