High‐Yield and Low‐Cost Solar Water Purification via Hydrogel‐Based Membrane Distillation

Abstract As an eco‐friendly means, solar water purification has attracted substantial research interest regarding material design, system engineering, and energy management. However, the low water yield and relatively high cost essentially restrict its practical potential. Here, a hydrogel‐based ultrathin membrane (HUM) is developed to synergistically coordinate facilitated vapor transfer and environmental energy harvesting for solar‐driven membrane distillation. The evaporation front is directly exposed to an airflow, which fundamentally eliminates the temperature polarization induced energy consumption. As such, the humidity of the output flow is significantly increased, and thus the vapor collection ratio rises to over 80% to achieve a high water yield of 2.4 kg m –2 h –1 under one sun without any energy recycling and cooling accessories. The HUM with a raw material cost of $0.36 m –2 offers a competitive potential cost of freshwater production of about $0.3–1.0 m –3 . This work demonstrates a promising membrane distillation strategy based on sustainable energy toward both decentralized water purification and large‐scale water treatment.