Phase-Change Microcapsules Boosting Clean Water Production and Electricity Output through Janus Bilayer Poly(vinyl alcohol)/Chitosan Composite Aerogels.

To address two critical global challenges─clean water scarcity and energy poverty─an innovative Janus bilayer composite aerogel is designed as a single solar-driven platform for sustainable clean water production and electricity generation. This type of Janus bilayer aerogel was successfully fabricated with a hydrophobic upper layer comprising a poly(vinyl alcohol) (PVA)/chitosan (CS)/carbon black (CB) composite aerogel and a hydrophilic lower layer based on a PVA/CS/phase-change microcapsule composite aerogel. With such a Janus bilayer structure, the composite aerogel demonstrates efficient light absorption and superior salt-resistant performance by its upper layer and prominent latent heat-storage and water-transport abilities by its lower layer. More importantly, the introduction of phase-change microcapsules enables the lower layer of the developed bilayer aerogel to store photothermal energy absorbed by its upper layer, continually driving interfacial evaporation under insufficient solar irradiation conditions. Benefiting from these advantages, the developed composite aerogel-based evaporator shows a high evaporation rate of 2.23 kg m h under one-sun irradiation alone with good resistance to salt accumulation. Compared to a control evaporator without any phase-change microcapsules, the developed evaporator obtained an increase in the total mass change of 150% under dark conditions. Meanwhile, a thermoelectrical generator equipped with the composite aerogel exhibits an open-circuit voltage of 143.89 mV under one-sun irradiation alone with an elongated power output period of 30 min. With an innovative Janus bilayer structural design by combining a biodegradable PVA/CS aerogel with phase-change microcapsules and CB nanoparticles, this study represents a significant advancement in renewable energy utilization, particularly in sustainable water purification and hybrid energy systems. The developed Janus bilayer composite aerogel exhibits great application potential in highly efficient freshwater production and electricity generation under intermittent sunlight irradiation.