Integrated Janus Evaporator with an Enhanced Donnan Effect and Thermal Localization for Salt-Tolerant Solar Desalination and Thermal-to-Electricity Generation

Solar-driven interfacial evaporation (SIE) technology has great advantages in seawater desalination. However, during the long-term operation of a solar evaporator, salts can be deposited on the solar absorbing surface, which, in turn, hinders the evaporation process. Therefore, there is an urgent need to propose new antisalt strategies to solve this problem. Here, we present a novel cogeneration system leveraging a salt-tolerant, heterogeneous Janus-structured evaporator (FHJE) for simultaneous solar desalination and thermoelectric generation. The top evaporation layer is composed of a graphene-based photothermal membrane pre-embedded with Fe³⁺ cations, which enhanced solar absorption and energy conversion abilities. Meanwhile, the Fe³⁺ cations further contribute to the Donnan effect, effectively repelling salt ions in saltwater. The bottom layer comprises a hydrogel composed of hydrophilic phytic acid (PA) and poly(vinyl alcohol) (PVA), fostering facilitation of water transport. The FHJE was demonstrated to exhibit evaporation rate and efficiency as high as 3.655 kg m^-2 h^-1 and 94.7% in 10 wt% saltwater, respectively, and superior salt resistance ability without salt accumulation after 8 h of continuous evaporation (15 wt%). Furthermore, a hydropower cogeneration evaporator device was constructed, and it possesses an open-circuit voltage (V_OC) and a maximum output power density of up to 143 mV and 1.33 W m^-2 under 1 sun, respectively. This study is expected to provide new ideas for comprehensive utilization of solar energy.