Sandwich-Structured Carbon Paper/Metal–Organic Framework Monoliths for Flexible Solar-Powered Atmospheric Water Harvesting On Demand

Solar-powered atmospheric water harvesting (AWH) with metal–organic frameworks (MOFs) has been recognized as an attractive way to alleviate water shortage stress in rural arid areas given the naturally abundant solar energy. However, the existing solar-powered AWH technologies only allow a singular water production mode: either solar heating-driven AWH which usually results in rather poor water productivity due to the limited availability of sufficient sunlight or conductive heating-driven all-day AWH with significantly improved water productivity but requiring additional electricity provided with a photovoltaic module. This greatly limits the flexibility in managing AWH based on climate conditions, water productivity, and energy cost. Herein, a sandwich-structured MOF monolith (denoted as CACS) with dual heating capacity, localized solar heating (LSH) and electrical heating (LEH), is presented. Compared with LSH, the use of LEH leads to more rapid and uniform heating of CACS monoliths, thereby driving a significantly enhanced water desorption efficiency with faster kinetics. Using the CACS monolith as an AWH sorbent, a new type of atmospheric water harvester is developed and able to produce water in multiple working modes: LSH-, LEH-, and LSH-/LEH-driven AWH, thereby enabling flexible AWH on demand: direct use of sunlight for LSH-driven AWH during the sunlight-sufficient day and/or LEH-driven all-day AWH powered by a photovoltaic module particularly during the sunlight-absent/-insufficient time (night or cloudy day). When working at the LSH-/LEH-driven AWH mode, the resulting prototype delivers 1.4 LH2O kgMOF–1 day–1 of water productivity with 2.3 kW·h L–1H2O of energy consumption, corresponding to 5.4 times higher water productivity than the LSH-driven AWH working mode alone and 17.9% of energy saving at the cost of 22.2% of water productivity reduction compared with the LEH-driven AWH working mode alone. The current work, therefore, demonstrates a novel solar-powered AWH strategy that enables all-day water production with flexible choices on AWH working modes in terms of climate conditions, desired water productivity, and energy cost.