Multifunctional Fully Biomass-Derived Bilayer Aerogel for Efficient Solar-Driven Desalination and Thermoelectricity Generation

Solar-powered interfacial evaporation is an emerging solar energy harvesting technology developed to address the global energy crisis and freshwater shortage. However, non-directionally flowing water inevitably acts as a medium for top-down heat transfer via thermal convection, resulting in a poor evaporation performance. Herein, a fully biomass-based bilayer multifunctional solar evaporator consists of an upper lignin-derived porous carbon (LPC)-embedded chitosan/lignin (CSL) composite aerogel layer featuring vertically small channels and an underlying hydrophilic CS aerogel. The photothermal and evaporation capabilities of the top layer, combined with enhanced capillary forces, drive efficient evaporation. The presence of lignin not only increases the hydrophilicity and saturated water content of the composite aerogel but also serves as a precursor for light-absorbing materials. The bottom large-sized CS aerogel channels inhibit excess water transfer to the upper layer and also reduce water vaporization enthalpy. This unique design allows it to maximize heat from sunlight and localize the generated heat while providing an adequate water supply. Thus, the optimized self-floatable LPC@CSL-5:5@CS bilayered aerogel evaporator achieved a desirable water evaporation rate of 1.717 kg m^-2 h^-1 and energy efficiency of 90.63% under one solar (1 kW m^-2) irradiation. Furthermore, the designed evaporator also presented durable salt tolerance, excellent stability, and recyclability. Notably, the LPC-50 mg@CSL-5:5 aerogel generated a voltage output of 279 mV under 3 sun, which could power an electronic fan. The overall system is both all-biomass and cost-effective, and this multifunctional aerogel evaporator shows great potential for large-scale applications, including solar desalination, wastewater purification, and thermoelectric generation.