Spray-Applied MXene Coatings on Metal–Organic Framework Monoliths for Adaptive All-Day Atmospheric Water Harvesting at Mitigated Energy Cost

All-day atmospheric water harvesting (AWH) using metal–organic frameworks (MOFs) presents an appealing approach for achieving high-yield water production in arid regions. However, current all-day MOF-based AWH strategies often involve intricate material preparation procedures and high energy input for water desorption, raising concerns about the water production cost. Leveraging the naturally abundant solar energy available in arid areas, herein, sprayable Ti3C2 MXene/silane-decorated hyperbranched polymer solutions (Ti3C2/sHBP) are presented. These solutions enable easy formation of robust, spray-applied coatings on monolithic MOFs upon exposure to sunlight, resulting in monolithic Ti3C2/sHBP-coated MOFs (TCM). The presence of Ti3C2/sHBP coatings equips TCMs with dual solar and electrical heating capabilities, enabling adaptive all-day AWH based on sunlight availability: solar heating-driven AWH when sufficient sunlight is present, combined solar/electrical heating-driven AWH when sunlight is insufficient, and electrical heating-driven AWH during periods without sunlight. Compared to traditional electrical heating-driven AWH, this adaptive all-day AWH delivers a similar water production performance with a 28.8% reduction in energy consumption for water desorption. Imparting MOF monoliths with dual heating functionality through a straightforward spray-applied coating demonstrates a novel, facile, and cost-effective strategy for enabling adaptive all-day AWH with excellent water productivity at a significantly mitigated energy cost.