Ultra-High Freshwater Production Via Coupling Photo-/Electro-Thermal Self-Heating and Self-Insulating Janus Membrane

Thermally driven membrane distillation (TDMD) has emerged as a promising seawater desalination technology to address the freshwater shortage and energy crisis. However, the conventional “bulk-heating” technologies results in serious temperature polarization phenomenon, hindering efficient utilization of the energy. Here, an innovative hydroxylated CNTs-engineered polyvinylidene fluoride (H-CNT@PVDF) membrane is proposed which imparts an efficient, localized photo-/electro-thermal self-heating effect. To prevent the heat loss from the self-heating layer to bulk water, a transparent silica aerogel microspheres (SAM) layer is deposited on the H-CNT layer, achieving excellent self-insulating effect. The innovative SAM@H-CNT@PVDF Janus membrane achieves a 486% increase in MD flux compared with the conventional membrane. Although SAM layer only account for 3.8% of the membrane, the thermal resistance increases, unexpectedly, by more than 600%, which allows most of the heat to be concentrated at the H-CNT layer and used for seawater evaporation. The overall energy-to-water efficiency reach 94.5%, outperforming state-of-the-art MD devices. Additionally, the SAM layer demonstrates excellent anti-electrooxidation effect with the current degradation decreasing from 75.6% to 21.1%, ensuring long-term working for the membrane. The membrane represents a significant advancement in MD technology and holds substantial promise for ultra-low energy seawater desalination, offering a promising solution to water-energy nexus.