A subnano-confinement in robust MoS2-based membranes for high-performance osmotic energy conversion

Abstract

Osmotic energy harvesting from salinity gradients shows great potential for sustainable electricity generation, which can be fulfilled using two-dimensional ion-selective nanofluidic devices. Metal dichalcogenide membranes like MoS₂ exhibit good anti-swelling properties in aqueous solution and can be applied in nanofluidic device development. However, conventional MoS₂-based membranes encounter the major issue of low ion selectivity, reducing the electricity generation efficiency. In this paper, we propose the strategy of subnano-confinement using the environmentally benign hydrophilic bacterial nanocellulose (BNC) with negative charges to create high ion-selectivity channels in robust MoS₂-based membranes. The developed membrane exhibited an interlayer spacing of 9.8 Å with desirable negativity in nanochannels, thus generating a favorable confinement for enhancing Na⁺ transport but blocking Cl⁻. The tested membrane provided an area of 0.78 mm², exceeding those of other reported macroscopic-scale membranes. The electrochemical device delivered the power densities of 73 and 233 W m⁻² at ambient temperature and 343 K, respectively, under a 50-fold concentration gradient, outperforming previously reported 2D nanofluidic membranes by a factor of up to 70. Furthermore, the membrane exhibited exceptional long-term stability up to 40 days without performance decay. The current work makes a breakthrough in developing 2D nanofluidic membranes for harvesting osmotic energy.