Green conversion of waste polyester into few-layer graphene for interfacial solar-driven evaporation and hydroelectric electricity generation

Abstract

The coupling of solar-driven interfacial evaporation with hydrovoltaic technology is emerged as a hopeful approach to alleviate energy crisis and freshwater shortage. However, constructing low-cost evaporators with high-performance freshwater and electricity co-generation and unveiling the co-generation mechanism remain a grand challenge. Herein, we report the green transformation of waste poly(ε-caprolactone) into graphene through a salt-assisted carbonization strategy and build a flexible bi-functional graphene-based evaporator for freshwater and electricity co-generation. The graphene exhibits a typical wrinkled structure with curved edges and is composed of 7-8 discontinuous layers with rich oxygen-containing groups. The graphene-based evaporator exhibits excellent sunlight absorption (98%), photo-to-thermal conversion property, good water transport ability, low water evaporation enthalpy, and low thermal conductivity of 0.06 W m^-1 K^-1. The evaporator not only exhibits a notable water evaporation rate (2.92 kg m^-2 h^-1), but also achieves the maximum output voltage of 310 mV, surpassing many previously reported evaporators/generators. The result of molecular dynamics simulation proves the diffusion difference between H⁺ and OH^- in water and graphene, which eventually leads to the voltage generation. Not only will this work help to improve the upcycling of waste plastics and achieve carbon neutrality, but it will also open an avenue for co-generation of freshwater and electricity.