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, comprising of phosphate-functionalised poly-vinyl alcohol (pPVA) and carboxy-methyl 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 water-mediated proton concentration gradients 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 an efficient desalination and purification of contaminated wastewater by up to 99%. Concurrently, the SCPC evaporator produces consistent, high evaporation-driven electrical output VOC and ISC 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.