Clay-based anion-selective 2D nanofluidics boost natural osmotic power generation

Abstract

Two-dimensional (2D) nanofluidics technology has shown great potential in efficient osmotic energy harvesting, but the lack of anion-selective 2D nanofluidic membranes limits the development of full concentration cells towards real-world applications. Herein, an anion-selective 2D nanofluidic membrane (2D-NFM) was constructed based on hydrotalcite-like layered double-hydroxides (LDHs), whose naturally positively charged surface and nanoconfined interlamellar channels endowed the membrane with excellent anion selectivity in a wide range of electrolyte concentration. The selective anion transport was further confirmed by the lower calculated transmission barrier of anions compared with the cations based on the strong electrostatic interaction within the positively charged nanochannels. Benefiting from good hydrophilicity and narrow nanochannels, the output power density of the 2D-NFM in an NaCl solution with a 50-fold concentration gradient could reach 3.06 W m⁻², while the value could reach 3.92 W m⁻² when natural seawater and river water were used as electrolytes. This work is expected to provide an effective strategy for constructing high-performance anion-selective 2D nanofluidic devices for osmotic energy harvesting.