Interfacial Mesochannels as Cation Pump for Enhanced Osmotic Energy Harvesting

Membranes integrating 1D materials are rapidly emerging as highly promising platforms for osmotic energy harvesting. However, their power output is often constrained by insufficient ion selectivity. Herein, we demonstrate a cation pumping strategy by designing mesoporous silica coated multiwalled carbon nanotubes/aramid nanofiber (MCNTs@mSiO₂/ANF) composite membranes as osmotic power generators. Cations can be initially enriched in the negatively charged and small-pore-sized (∼ 3 nm) interfacial mesopore channels, establishing a strong cation concentration gradient toward the interfiber nanochannels. The gradient continuously drives cations into the interfiber pores, facilitating charge separation, and improving ion selectivity. Additionally, the hydrophilic nature of the mesoporous silica shells promotes ion transport and contributes to high ion flux. Consequently, the fabricated MCNTs@mSiO₂/ANF composite nanochannel membranes can deliver a notable power density of 8.24 W m^-2 with an excellent ion selectivity of 0.91 under a 50-fold NaCl salinity gradient. Importantly, the membranes demonstrate long-term stability for osmotic energy capturing. When placed between natural seawater and river water, the composite membranes yield an impressive power density of 9.93 W m^-2, surpassing that of the state-of-the-art 1D material-based membranes. This work paves the way for the practical applications of nanofiber-based membranes in sustainable osmotic energy conversion.