Graphene oxide/silica nanoparticle composite membrane for enhanced ion migration and osmotic energy conversion

Nanochannel-based osmotic energy conversion is an emerging technique and is regarded as a promising candidate for salinity-gradient energy utilization. The power density of the ion-selective membrane is greatly affected by the trade-off between ion selectivity and permeability. To address this issue, this work adopts a top-down self-assembly method to embed silica nanoparticles in graphene oxide nanochannels, thereby expanding the nanochannel spacing and charge density of graphene oxide membrane. The negative charges of nanoparticles increase the space charge density and supplement the ion selectivity in nanochannels, which can mitigate the weakening effect of enlarged channel spacing on ion selectivity. Consequently, the obtained graphene oxide/silica nanoparticle composite membrane achieved a 24.2 % enhancement in output power of the NOEC device under 0.5 M/0.01 M NaCl solution. Moreover, the net power density of graphene oxide/silica nanoparticle composite membrane excluding the contribution of electrode potential reached 2.0 W·m⁻². A numerical model based on the finite element method is established to reveal the enhanced mechanism of silica nanoparticles on space charge density and ion selectivity. Finally, the adaptability of the fabricated composite membrane was also proved by regulating the pH and concentration gradients, and the osmotic power density was improved up to 5.6 W·m⁻² under 5 M/0.01 M concentration difference and pH of 11. This work provides a simple strategy to enhance ion migration in 2D nanochannels and break through the ion selectivity-permeability trade-off to promote osmotic energy conversion.