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Solar-driven photothermal conversion devices are currently highly investigated in seawater evaporation and desalination applications. However, considering cases in small portable household outfits, it remains a considerable challenge to develop a scalable low-cost system with practically stable evaporation and salt-resistant performance. Herein, we demonstrate an inexpensive bilayered evaporation system, utilizing CuS/bacterial cellulose (BC) hybrid gel membranes as a photothermal conversion layer via an in situ synthetic route and BC-wrapped polyethylene foam as a water transport and heat insulation layer. The optimized evaporation rate reached 1.79 kg m −2 h −1 under 1 kW m −2 and the efficiency reached 98.5%, which is comparable to the best performance for BC-based composites that have been reported so far. The evaporation rate remained stable after 40 cycles, which suggests excellent cyclability of prepared gel membranes. More significantly, the bilayered evaporator also reveals excellent salt-resistant performance of more than 12 h and a stable evaporation rate. The excellent property was attributed to the effective heat localization from the upper CuS/ BC layer, while the bottom BC layer secured adequate water supply and transport. We also examined the flexibility and portability of these membranes, showing their practical value for a variety of portable household water technologies.

The large osmotic energy between river water and seawater is an inexhaustible blue energy source; however, the complicated manufacturing methods used for ion-exchange devices hinder the development of reverse electrodialysis (RED). Here, we use a wet-spinning method to continuously spin meter-scale 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-oxidized bacterial cellulose (TOBC) nanofiber filaments, which are then used to construct nanochannels for osmotic energy conversion. These are then used to build a nacre-like structure by adding graphene oxide (GO), which provides narrow nanochannels in one-dimensional and two-dimensional nanofluid systems for rapid ion transport. With a 50-fold concentration gradient, the nanochannels in the fibers generate electricity of 0.35 W m −2 , with an ionic mobility of 0.94 and an energy conversion efficiency of 38%. The assembly of GO and TOBC results in a high power density of 0.53 W m −2 using artificial seawater and river water. The RED device fabricated from TOBC/GO fibers maintains a stable power density for 15 days. This research proposes a simple method to reduce the size of nanochannels to improve the ionic conductivity, ionic selectivity, and power density of cellulose-based nanofibers to increase the possibility of their application for the conversion of osmotic energy to electrical energy.

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