Different hydrophilic bilayer membranes for efficient osmotic energy harvesting with high-concentration exfoliation

Sustainable, clean, seawater-river interface osmotic energy shows great potential in replacing traditional fossil fuel sources. Two-dimensional (2D) nanofluidic channels, known for their high throughput, high integration density, and excellent scalability, render practical applications feasible for osmotic energy harvesting. However, 2D nanofluidic channels face challenges such as high internal resistance and high costs, which keep the ultimate goal of large-scale osmotic energy harvesting distant. Herein, a novel method to regulate ion transport resistance by constructing different hydrophilic asymmetric nanofluidic channels using bilayer membrane of vermiculite and MXene is proposed. Vermiculite nanosheets are prepared via polymer-assisted exfoliation method utilizing polyethyl-phosphate glycol ester. After simple stirring and maturation process, the exfoliation concentration can reach 20 phr within 8 h, which is 20 times higher than the previously reported maximum. The internal resistance of the bilayer membrane decreased from 24.1 kΩ to 15.0 kΩ as the direction of ions transport changes. Oxygen plasma assistance enabled the bilayer membrane to reach a maximum power density of 4.66 W m⁻². The high-efficiency preparation method of vermiculite nanosheets and the emphasis on membrane surface properties offer new insights into practical osmotic energy harvesting.