Ion-selective graphene nanomesh membrane for sustainable osmotic power generation

ABSTRACT Atomically thin 2D membranes with minimum ion transport pathways and low ion transport resistance are ideally suited for constructing ion-selective membranes for electric power generation, and have attracted considerable recent interest. However, the practical applications of such 2D membranes for electric power generation have been severely limited due to the lack of nanoporous 2D membranes with narrow distributed nanopore arrays and sufficient charge density. Here, we report a centimeter-scale ultrathin graphene nanomesh (GNM) membrane with narrow pore size distribution (∼1.5 nm) and rich in carboxylic groups (GNM–COO−) for efficient osmotic power generation. The high-density nanometer pores anchored by negatively charged carboxylic groups allow efficient transport of K+ while selectively blocking Cl−. We show that the GNM–COO− membrane with asymmetric charge structure exhibits a diode-like ionic rectification property and facilitates directional ion transport. When employed as an ion-selective membrane for osmotic power generation, the designed GNM–COO− membrane delivers an exceptionally large output power density (175.1 W m−2) at a 50-fold salinity gradient, and retains stable power generation performance for 2 months. This work provides a strategy to develop high-performance ion-selective membranes for the sustainable harnessing of blue clean energy.