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Abstract Recent studies of the high energy‐conversion efficiency of the nanofluidic platform have revealed the enormous potential for efficient exploitation of electrokinetic phenomena in nanoporous membranes for clean‐energy harvesting from salinity gradients. Here, nanofluidic reverse electrodialysis (NF‐RED) consisting of vertically aligned boron‐nitride‐nanopore (VA‐BNNP) membranes is presented, which can efficiently harness osmotic power. The power density of the VA‐BNNP reaches up to 105 W m−2, which is several orders of magnitude higher than in other nanopores with similar pore sizes, leading to 165 mW m−2of net power density (i.e., power per membrane area). Low‐pressure chemical vapor deposition technology is employed to uniformly deposit a thin BN layer within 1D anodized alumina pores to prepare a macroscopic VA‐BNNP membrane with a high nanopore density, ≈108pores cm−2. These membranes can resolve fundamental questions regarding the ion mobility, liquid transport, and power generation in highly charged nanopores. It is shown that the transference number in the VA‐BNNP is almost constant over the entire salt concentration range, which is different from other nanopore systems. Moreover, it is also demonstrated that the BN deposition on the nanopore channels can significantly enhance the diffusio‐osmosis velocity by two orders of magnitude at a high salinity gradient, resulting in a huge increase in power density.
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Abstract 2D layered nanomaterials have attracted considerable attention for their potential for highly efficient separations, among other applications. Here, a 2D lamellar membrane synthesized using hexagonal boron nitride nanoflakes (h‐BNF) for highly efficient ion separation is reported. The ion‐rejection performance and the water permeance of the membrane as a function of the ionic radius, ion valance, and solution pH are investigated. The nonfunctionalized h‐BNF membranes show excellent ion rejection for small sized salt ions as well as for anionic dyes (>97%) while maintaining a high water permeability, ≈1.0 × 10−3L m m−2h−1bar−1). Experiments show that the ion‐rejection performance of the membrane can be tuned by changing the solution pH. The results also suggest that the rejection is influenced by the ionic size and the electrostatic repulsion between fixed negative charges on the BN surface and the mobile ions, and is consistent with the Donnan equilibrium model. These simple‐to‐fabricate h‐BNF membranes show a unique combination of excellent ion selectivity and high permeability compared to other 2D membranes.