Continuous hydrogel architecture inside and outside nanochannels: Bridging internal-external ion transport for low-resistance osmotic energy harvesting

Osmotic energy from salinity gradients is a promising sustainable and clean energy source. Traditional nanofluidic membranes used for salinity gradient energy conversion face an intrinsic compromise between structural stability (achieved by intra-channel confinement) and low resistance (requiring extra-channel ion acceleration). Here, we propose a hybrid (FEH@AAO) membrane with fully encapsulated hydrogel (FEH) onto porous anodic aluminum oxide (AAO) nanochannels that integrates rigid nanochannel confinement with an external hydrogel ion diffusion network. The hydrogel grows continuously inside and outside AAO nanochannels, while inhibiting swelling deformation (enhancing mechanical robustness) and reducing mass transfer resistance (acting as an “ion accelerator”). Under a 50-fold NaCl gradient, FEH@AAO membrane achieves a power density of 8.84 W/m 2 , which is 28 % higher than traditional designs. The internal resistance has decreased by 35 %. In a natural seawater/river water mixture, it maintains ∼90 % power output over 7 days, outperforming most reported membranes. This work presents a structural optimization strategy that, by optimizing mass transfer outside nanochannels, achieves low ion transport resistance and exceptional long-term structural integrity for osmotic energy conversion.