High-performance osmotic energy harvesting enabled by the synergism of space and surface charge in two-dimensional nanofluidic membranes.

[Display omitted] • Two kinds of natural and renewable materials are combined to fabricate novel 2D membranes for osmotic energy conversion. • The heterogeneous membranes help to the balance of the trade-off between ion selectivity and ion flux. • A record power density of ∼16.57 W/m2 is achieved with the synergism of space and surface charge. • The ion transport mechanism is theoretically investigated by numerical simulations based on Poisson and Nernst–Planck models. As promising prospects for renewable power harvesting, two-dimensional (2D) nanochannels for osmotic energy capture in a reverse electrodialysis arrangement have garnered significant attention. However, existing 2D nanochannel membranes have shown limited power generation capabilities due to challenges in balancing ion flux and selectivity. Here, we construct montmorillonite (MMT)/TEMPO-mediated oxidation cellulose nanofibers (TOCNFs) nanocomposite membranes for enhanced ion transmembrane transport. The intercalation of TOCNFs not only enlarges the interlayer distance, but also provides abundant space charge inside the nanochannels. Benefiting from the strong ion selectivity and high ion flux, the composite membrane achieves a remarkable power output of ∼16.57 W/m2 in the gradient of artificial seawater and river water, exceeding that of the state-of-the-art heterogeneous membrane-based osmotic energy conversion systems. Both experimental and theoretical findings confirm that the synergism of space and surface charge plays a crucial role in promoting osmotic energy conversion. This research contributes valuable insights into the optimization of 2D membranes for efficient clean energy harvesting purposes. [ABSTRACT FROM AUTHOR]