Three Birds with One Stone: Decoration of Carbon Fiber Fabric with MnO2 Nanoplates for Efficient Photo/Electro-thermal Evaporation of Seawater

Photo/electro-thermal evaporation is a promising tactic for alleviating the scarcity of fresh water, but its practical application still faces many challenges such as weak photoabsorption, high vaporization enthalpy and serious water-electrolysis during photo-thermal/electrothermal evaporation. To solve these problems, inspired by black rose petal and electric heater, we report a biomimetic design of fabric for achieving efficient photothermal/electrothermal desalination. The photo/electrothermal fabric is fabricated by decorating super-hydrophilic MnO₂ nanoplates as shell on hydrophobic carbon fiber (CF) as core via an electro-deposition method. MnO₂ nanoplate decoration as a stone confers three fascinating features (birds): (I) the hydrophilic nature of MnO₂ contributes to the fabric’s superhydrophilicity and decreased evaporation enthalpy (2032 kJ kg⁻¹) in comparison with that (2410 kJ kg⁻¹) of pure water; (II) nanoplate structure confers the light-trapping effect and thus the improved photoabsorption efficiency of 95.1%; (III) CF-core/MnO₂-shell structure can effectively suppress electrolysis of water and lead to good electrothermal conversion property. As a result, CF/MnO₂ fabric-based hanging evaporator shows the high photo-thermal evaporation rate of 2.3 kg m⁻² h⁻¹ at 1 sun (1 kW m⁻²) and electrothermal evaporation rate of 5.3 kg m⁻² h⁻¹ at 3 V. Importantly, by the combined effects of 1 sun and 3 V, CF/MnO₂ fabric achieves a striking synergetic evaporation rate of 8.5 kg m⁻² h⁻¹, exceeding the sum (7.5 kg m⁻² h⁻¹) of the individual photo-thermal and electro-thermal evaporation rates. The present high synergetic evaporation performance benefits from efficient photo/electrothermal conversion of the fabric and sufficient water-supplementation at the fiber-water interface resulting from thermosiphon effect. Thus, this study offers a novel possibility in the rational design of photo-electrothermal materials for efficient evaporation of seawater.

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