Floatable ionic photothermal aerogels for water and energy harvesting under solar light

Abstract

The integration of sunlight-driven seawater desalination and the hydrovoltaic effect furnishes a promising strategy to address the growing global challenges of energy and drinking water scarcity. However, it's still a challenge to produce fresh drinking water while generating electricity with high yield. Here, a compact evaporation-driven freshwater-electricity generation device was designed by incorporating calcined loofah sponge (CLS) and sulfonated graphene oxide (sGO) into a hydrogel matrix (SCPC). The top layer containing CLS@sGO serves as a light-trapping photothermal material to convert sunlight into heat, while the bottom hydrogel layer, consisting of phosphate-functionalised polyvinyl alcohol (p-PVA) and carboxymethyl cellulose (CMC), functions as a hydrophilic vertically aligned porous network for the easy transfer of water for evaporation. Molecular dynamics simulations have further revealed that proton concentration gradient mediated by water transport can induce an additional ionic electric field within the solute-containing intermediate water region, thereby contributing to the overall electrical output. Interestingly, the designed SCPC evaporator demonstrated a very high evaporation rate of 2.8 kg m⁻² h⁻¹ and an exceptional UV-vis-NIR sunlight absorbance of 96% under 1 sun. Through this sunlight-driven interfacial evaporation process, the system achieved efficient desalination and purification of contaminated wastewater by up to 99%. Concurrently, the SCPC evaporator produces consistent, high evaporation-driven electrical output V_oc and I_sc of 0.64 V and 0.48 mA, respectively, placing its performance at a competitive level among state-of-the-art systems. The outdoor interfacial evaporation experiments conducted under natural sunlight further validated the durability and operational reliability of the SCPC evaporator, demonstrating great potential in on-field applications.