Key Takeaways & Executive Findings
- •• • The porous carbon derived from waste polyester via MOF-assisted carbonization achieves a high specific surface area of 904 m² g⁻¹, enabling efficient ion transport and photothermal conversion, which is critical for high-rate water evaporation and electricity generation. • • The bifunctional evaporator delivers an open-circuit voltage of 250 mV and a short-circuit current of 14 μA under 1 sun, demonstrating a practical pathway for simultaneous freshwater and electricity production from solar energy. • • The evaporation rate reaches 2.34 kg m⁻² h⁻¹ with a reduced water evaporation enthalpy of 1.7 kJ g⁻¹, indicating that the material's hierarchical pore structure and oxygen groups weaken hydrogen bonding, thereby lowering energy input for desalination. • • Mechanistic insights from molecular dynamics simulations confirm that selective Na⁺ interaction induces differential ion migration, generating a streaming potential; this understanding is essential for optimizing hydrovoltaic efficiency in real-world brine applications.
Abstract
The integration of interfacial photothermal conversion and hydrovoltaic effects into bifunctional evaporators offers a promising route to simultaneously address freshwater scarcity and energy demands. However, the development of low-cost bifunctional evaporators and elucidation of the underlying co-generation mechanism remain challenging. Here, we report a porous carbon derived from waste polyester via a metal-organic framework (MOF)-assisted carbonization strategy, which is subsequently fabricated into a bifunctional evaporator for freshwater and hydroelectricity co-generation. The porous carbon exhibits a high specific surface area of 904 m² g⁻¹, hierarchical micro- and mesopores, and abundant oxygen-containing groups. The resulting evaporator demonstrates broadband light absorption, localized thermal management, good hydrophilicity, and high flexibility. Under 1 sun illumination, it achieves an open-circuit voltage of 250 mV, a short-circuit current of 14 μA, and an evaporation rate of 2.34 kg m⁻² h⁻¹, ranking among the most efficient freshwater-hydroelectricity co-generators. The weakened hydrogen-bonding network reduces the water evaporation enthalpy to 1.7 kJ g⁻¹. Mechanistic studies, including molecular dynamics simulations, reveal that selective Na⁺ interaction induces differential ion migration rates, generating a streaming potential. Additionally, the photothermal effect enhances voltage output by promoting interfacial ion concentration gradients. Outdoor tests confirm stable voltage output of 250 mV and freshwater production of 2.34 kg m⁻². This work provides a scalable platform for fabricating advanced evaporators from waste plastics and unravels the co-generation mechanism, offering a sustainable strategy to mitigate freshwater and energy crises.
1. Introduction
Conventional desalination technologies, such as reverse osmosis and thermal distillation, are energy-intensive and geographically constrained to coastal regions, limiting their scalability for inland freshwater supply. Solar-driven interfacial evaporation has emerged as a sustainable alternative, but its energy efficiency is often compromised by heat losses and the need for high-cost photothermal materials. Similarly, hydrovoltaic electricity generation, which harvests energy from water evaporation, remains inefficient due to poor ion selectivity and insufficient understanding of the underlying charge transport mechanisms. The integration of these two functions into a single evaporator could maximize resource utilization, yet existing bifunctional systems suffer from complex fabrication, high material costs, and suboptimal performance.
This work addresses these bottlenecks by introducing a low-cost, scalable porous carbon derived from waste polyester through a metal-organic framework (MOF)-assisted carbonization. The resulting material exhibits a high specific surface area (904 m² g⁻¹) and hierarchical porosity, which are critical for enhancing both photothermal conversion and ion transport. The evaporator achieves a high evaporation rate (2.34 kg m⁻² h⁻¹) and a notable open-circuit voltage (250 mV), while mechanistic studies reveal that selective Na⁺ interaction drives streaming potential generation. By converting waste plastics into high-value functional materials, this approach not only mitigates plastic pollution but also provides a cost-effective route to co-generate freshwater and electricity, offering a practical solution to global water and energy challenges.
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Yan She, Guixin Hu, Xueying Wen, Huiyue Wang, Ming Yang, Lingling Feng, Zhikun Dai, Qianyu Wei, Ran Niu, Jiang Gong (2026). High-Performance Freshwater-Hydroelectricity Co-Generation by Porous Carbon through Waste Polyester-Derived MOF-Assisted Carbonization. SCIENCE CHINA Materials. https://doi.org/10.1007/s40843-025-3762-9
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Frequently Asked Questions
What is the long-term stability of the porous carbon-based evaporator under continuous solar illumination and saline conditions?
The study does not explicitly report long-term stability data, but the material's high chemical stability and flexibility suggest potential for sustained operation. The porous carbon is derived from waste polyester and exhibits robust structural integrity, which likely contributes to durability. However, further testing under prolonged exposure to brine and cyclic wetting-drying conditions is necessary to confirm operational lifetime.
How does the performance of this evaporator compare with state-of-the-art bifunctional systems in terms of cost and scalability?
The use of waste polyester as a precursor significantly reduces material costs compared to pristine carbon sources. The MOF-assisted carbonization process is scalable, and the resulting porous carbon achieves an evaporation rate of 2.34 kg m⁻² h⁻¹ and an open-circuit voltage of 250 mV, which are competitive with or superior to many reported systems. For instance, Ge et al. reported 2.38 kg m⁻² h⁻¹ and 0.73 V, but with a more complex carbon black/polypyrrole composite. The cost advantage of waste-derived carbon makes this approach more viable for large-scale deployment.
What is the mechanism behind the enhanced voltage output under photothermal conditions?
The photothermal effect increases the local temperature at the evaporation interface, which enhances ion mobility and promotes a larger concentration gradient between the hot and cold regions. This gradient amplifies the streaming potential generated by the selective interaction of Na⁺ ions with the negatively charged oxygen-containing groups on the porous carbon surface, as confirmed by molecular dynamics simulations. The result is a higher open-circuit voltage under illumination.
Can this technology be adapted for seawater desalination with high salinity (e.g., 3.5 wt% NaCl) without significant performance degradation?
The study demonstrates performance in pure water or low-salinity conditions, but the mechanism relies on ion-selective transport, which may be affected by high salt concentrations. In 3.5 wt% brine, the streaming potential could be reduced due to screening effects, but the photothermal evaporation rate is likely to remain high. Further experiments are needed to quantify performance in real seawater, but the material's hydrophilicity and pore structure are promising for salt rejection.
What is the energy payback period or overall efficiency of the freshwater-electricity co-generation system?
The paper does not provide a full energy balance or payback analysis. However, the evaporation enthalpy is reduced to 1.7 kJ g⁻¹, which is significantly lower than the latent heat of pure water (2.26 kJ g⁻¹), indicating high energy efficiency for water production. The electrical output (250 mV, 14 μA) is modest, but the system's dual function and low-cost materials could offset initial investment. A comprehensive life-cycle assessment would be required to determine the payback period.
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