Upcycling waste polypropylene separators into carbon nanotubes for efficient interfacial solar-driven evaporation and hydroelectric power generation

Abstract

The solar interfacial steam and power co-generation technology is a promising way of dealing with freshwater shortage and the energy crisis. Nevertheless, there is still significant struggle to build efficient evaporators for concurrent freshwater and power generation. In this contribution, we design Ni–Mo–Al hybrid catalysts for the controlled carbonization of waste polypropylene (PP) separators to prepare carbon nanotubes (CNTs) and subsequently construct CNT-based evaporators for interfacial evaporation and energy harvesting. The Ni–Mo–Al catalyst with an optimized molar ratio of 5–0.1–1 shows the best catalytic effect. The resultant CNTs possess high yield and purity, favorable crystallinity and a high graphitization degree. The CNT-based evaporator possesses good water absorption and low heat conductivity and achieves a high evaporation rate (2.79 kg m⁻² h⁻¹) with high efficiency (98.3%). Furthermore, the evaporation system attains an output voltage of 350 mV, as well as a good sustainable output capacity. The result of density functional theory (DFT) simulation explains that H⁺ diffuses faster than OH⁻ and then accumulates at the top, thus leading to a potential difference between the top and bottom of the material, which in turn creates voltage. This work not only realizes the green upcycling of waste PP separators, but also builds low-cost, high-performance freshwater and power generation integrated devices.