White Graphene Meets Graphene: A Hybrid 2D Nanofluidic Membrane with High Cation Selectivity for Photothermal‐Enhanced Osmotic Energy Conversion

Hexagonal boron nitride (h-BN, referred to as white graphene) nanosheets are attractive for building nanofluidic membranes due to their extraordinary chemical and oxidation resistance. However, the membranes stacked from BN nanosheets exhibit low ionic selectivity and unresponsiveness to external stimuli. Herein, graphene oxide (GO) nanosheets with large lateral dimensions are used to induce a more ordered and parallel stacking of BN nanosheets, resulting in a BN/GO hybrid membrane with significantly enhanced cation selectivity. Under 0.5/0.01 m KCl, the hybrid membrane containing 25 wt.% GO with 16 µm thickness achieves near-ideal cation selectivity, producing an output power density of 6.21 W/m²-a 72% improvement over a pure BN membrane. Leveraging the photothermal effect of GO, the power density is further increased by 10.6% to 6.74 W/m² under 400 mW/cm² simulated sunlight. After thickness optimization, the photothermal-enhanced power density reaches 9.11 W/m². The power density of the BN/GO hybrid 2D membrane is superior to that of the reported BN-nanosheet-based membranes under artificial seawater and river water (0.5/0.01 m NaCl). This work provides an effective strategy to enhance osmotic energy conversion, especially in sunlight-rich environments.