Integrated thermal energy storage in graphene-based composite evaporator for high-efficiency water generation

Abstract

Solar-driven water evaporation is a promising approach to ease the problem of global water shortages using sustainable energy. Numerous research works have been focused on the development and optimization of solar absorbers to achieve highly efficient interfacial solar vapor generation. However, it remains a great challenge to achieve high-performance water generation due to the intermittent solar irradiation. Herein, an integrated structure consisting of graphene microlattice (GML) filled with carbon nanotubes (CNT) reinforced phase change material (PCM) for thermal energy storage and graphene oxide (GO)-based hydrogel for water evaporation was developed to extend the duration of water generation. The CNT-GML/PCM composite not only acts as an additional heat source under solar irradiation, achieving a high evaporation rate of 3.55 kg/m2 h under one sun, but also releases latent heat to the hydrogel evaporator when the solar illumination was turned off, maintaining a high evaporation rate of 2.67 kg/m2 h for 30 minutes. This value is even higher than the evaporation rate of GO-based hydrogel evaporator, which is 2.08 kg/m2 h under one sun. During three 60-minute on and 30-minute off cycles, the total water generation of the integrated structure reached to 14.64 kg/m2, which is almost a double of the hydrogel evaporator only (7.39 kg/m2), thanks to the additional heat supply from CNTGML/PCM composites. This work demonstrates an effective strategy to prolong the duration of water generation under practical intermittent sunlight conditions by integrating thermal energy storage capability into solar evaporators.