Light-driven cation pumping in atomic-level van der Waals heterostructures towards efficient osmotic energy harvesting.

Efficient light-driven ion pumping under nanoconfinement offers a promising strategy for enhancing solar-assisted salinity-gradient energy conversion. Here, we report a cascaded graphene oxide-covalent organic framework (GO-COF) van der Waals (vdW) heterostructure membrane that functions as a light-driven cation pump, enabling enhanced osmotic energy conversion under illumination through the cascaded interfacial design. The membrane integrates highly ordered nanochannels with coupled GO-COF heterointerfaces and sulfonated cation-active sites, establishing molecularly defined pathways for directional ion transport. Upon illumination, the vdW heterostructure generates a spatially asymmetric transmembrane potential, which serves as an internal driving force for active cation pumping. This optically induced ion-pumping process enables directional cation transport against concentration gradients of up to 500-fold without external electrical input. When coupled to an osmotic energy conversion system, the enhanced cation pumping directly translates into boosted power generation, delivering an output power density of 9.23 W m-2 (44.5% enhancement) with a total energy conversion efficiency of 29% and stable long-term operation. Robust pumping and power output are further maintained across diverse electrolyte systems and natural seawater. This work establishes cascaded vdW heterostructure membranes as an effective materials platform for optically regulated ion pumps, providing new opportunities for solar-assisted osmotic energy harvesting.