Shape-controlled fabrication of MnO/C hybrid nanoparticle from waste polyester for solar evaporation and thermoelectricity generation

The integration of freshwater and electricity cogeneration through photothermal effect is regarded as a new and promising strategy for high-efficiency solar energy utilization. However, the central issue is the design of low-cost, flexible photothermal materials to efficiently utilize solar energy. Herein, flexible MnO/C nanoparticle-based solar evaporators are constructed to realize simultaneously interfacial solar evaporation and thermoelectricity generation. The MnO/C nanoparticle is facilely fabricated by pyrolysis of Mn-MOF, which is synthesized from discarded poly(ethylene terephthalate) bottles in one-pot solvothermal method. By altering pyrolysis temperature of Mn-MOF from 400 °C to 700 °C, the morphology of MnO/C nanoparticle is readily tailored from cube to sphere, octahedron and polyhedron. Owing to the fast water transport, strong sunlight absorptivity, high solar-to-heat conversion efficiency, and low evaporation enthalpy, the hybrid solar evaporator presents the high evaporation rate of 2.38 kg m−2 h−1 and solar-to-vapor conversion efficiency of 98.4% under 1 Sun irradiation, surpassing many advanced photothermal materials. More importantly, integrated with a thermoelectric module, the bifunctional solar evaporator recovers low-grade heat from water evaporation to perform thermoelectric conversion, achieving the maximum output voltage of 330 mV under 3 Sun irradiation. This work highlights the potential of flexible and durable solar evaporators for freshwater and power cogeneration, not merely contributing to achieving carbon neutrality and upcycling of waste plastics, but also opening opportunities for giant electricity supply from sustainable solar energy.