Bio-inspired Double Angstrom-Scale Confinement in Ti-deficient Ti_0.87O₂ Nanosheet Membranes for Ultrahigh-performance Osmotic Power Generation

Osmotic power, a clean energy source, can be harvested from the salinity difference between seawater and river water. However, the output power densities are hampered by the trade-off between ion selectivity and ion permeability. Here we propose an effective strategy of double angstrom-scale confinement (DAC) to design ion-permselective channels with enhanced ion selectivity and permeability simultaneously. The fabricated DAC-Ti_0.87O₂ membranes possess both Ti atomic vacancies and an interlayer free spacing of ≈2.2 Å, which not only generates a profitable confinement effect for Na⁺ ions to enable high ion selectivity but also induces a strong interaction with Na⁺ ions to benefit high ion permeability. Consequently, when applied to osmotic power generation, the DAC-Ti_0.87O₂ membranes achieved an ultrahigh power density of 17.8 W m⁻² by mixing 0.5/0.01 M NaCl solution and up to 114.2 W m⁻² with a 500-fold salinity gradient, far exceeding all the reported macroscopic-scale membranes. This work highlights the potential of the construction of DAC ion-permselective channels for two-dimensional materials in high-performance nanofluidic energy systems.