Sustainable upcycling of waste polyethylene terephthalate into hierarchically porous carbon nanosheet for interfacial solar steam and hydroelectricity generation

Solar-driven interfacial evaporation coupled with hydroelectricity technology is regarded as a hopeful tactic to co-generate freshwater and electricity. However, constructing low-cost evaporators/generators remain a grand challenge. Herein, we report a salt-assisted carbonization method to convert waste polyethylene terephthalate to be hierarchically porous carbon nanosheet (HPCN) and build a flexible HPCN-based evaporator for freshwater and hydroelectricity co-generation. HPCN exhibits a wrinkled structure with the thickness of ca. 3.4 nm. The HPCN-based evaporator displays good hydrophilicity, high sunlight absorption (98%), high solar-to-thermal conversion, reduced water evaporation enthalpy, and low thermal conductivity. It exhibits high evaporation rate (2.65 kg m⁻² h⁻¹) and conversion efficiency (98.0%) through 1 kW m⁻² irradiation, exceeding many advanced solar evaporators. Importantly, the HPCN evaporator-based hydroelectricity generator realizes high voltage (255 mV) and current (310 nA) with good stability. The combination of large specific surface area with wealthy oxygen-containing groups of HPCN plays important roles in hydroelectricity generation. In outdoor experiment, the freshwater production amount from per meter square achieves 6.32 kg. This work provides a green approach to upcycle waste plastics to be functional carbon materials and offers a new platform to construct advanced evaporators for solar evaporation and hydroelectricity generation.