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 the 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 the area of 0.78 mm2, exceeding other reported macroscopic-scale membranes. The electrochemical device delivered the power density of 73 and 233 W m-2 at ambient temperature and 343 K, respectively, in a 50-fold concentration gradient, outperforming previously reported 2D nanofluidic membranes by a factor 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.