Sparse multi-nanopore osmotic power generators

Ultrathin nanopore membrane is an emerging energy harvesting system capable of generating electricity from salinity gradients. Here, we report on the evaluation of its practical feasibility by exploring the energy conversion efficiency of single to densely packed multi-pores in a thin silicon nitride. The ionic current characteristics of single pores reveal a quasi-perfect cation selectivity when shrinking the diameter to 20 nm. The perm-selective nanopore is shown to yield osmotic power of 160 pW under a 1,000-fold transmembrane salt concentration difference. Meanwhile, whereas larger energy is gained by parallelly integrating multiple pores, excessive porosity also led to degraded energy conversion efficiency, thereby demonstrating an optimal power density of 100 W per square meter for 100 nm-sized multi-nanopores with a grid spacing of 1 μm. The present findings offer a guide to design highly efficient nanopore membrane osmotic power generators.