Crafting Hierarchical Nanochannels Within Boron Nitride 2D Nanofluidic Membranes for Enhanced Osmotic Energy Harvesting

2D nanofluidic membranes stacked from boron nitride (BN) nanosheets represent a highly promising candidate for osmotic energy harvesting. However, achieving a high ion flux through BN membranes while maintaining their inherent ion selectivity still remains a challenge. Herein, a layer-by-layer (LBL) assembly strategy was employed to fabricate BN-nanosheet/Cu(OH)₂-nanowire alternately stacked membranes. After etching the sacrificial Cu(OH)₂ nanowire templates, a hierarchical nanochannel architecture composed of nanowire-templated and BN-interlayer-formed nanochannels was crafted within BN membranes. These hierarchical nanochannels increased the short-circuit current of the BN membrane by 44% without obviously compromising its inherent selectivity. Consequently, the BN membrane with hierarchical nanochannels achieved an output power density of 6.95 W/m² under a 0.01/0.5 m KCl, which was approximately 37% higher than that of the pristine BN membranes. The crafted hierarchical nanochannels surpass the majority of BN-based 2D nanofluidic membranes reported to date, while also demonstrating excellent long-term stability. A tandem stack consisting of 20 membranes with hierarchical nanochannels produces an output voltage of 1.6 V, demonstrated the capability to power electronic devices directly.