Understanding the Enhanced Osmotic Energy Conversion in Heterogeneous Membranes Using Engineered Branched Alumina...

Heterogeneous membranes with two composite layers of distinct pore sizes have emerged as promising candidates for efficient osmotic energy extraction from salinity gradients. Previous studies about heterogeneous membranes report a strong link between the induced diode-like rectification property and improved osmotic energy conversion performance. Nevertheless, the inherently large interfacial resistance of heterogeneous membranes may offset such enhancement. To further understand the osmotic energy conversion behavior in heterogeneous membranes, a series of the branched alumina nanochannel (BAN) membranes consisting of large stem channels interconnected with small branched channels are designed. The interconnected and orderly aligned structure of the stem and branched channels ensures high effective driving force and ion selectivity while reducing interfacial resistance at the same time. Experimental and simulation results confirm the rectification effect induced by the asymmetric pores of BAN, which can achieve an osmotic power ≈130% higher than that of the conventional cylindrical nanochannel membranes. Additionally, a power density as high as 5.42 W m^-2 is obtained by mixing seawater and river water, surpassing most of the existing heterogeneous membranes and the commercial benchmark. The BAN membrane proposed in this work provides a promising platform for the development of highly efficient osmotic energy harvesting devices.