Space charge-enhanced ion permselectivity of nanofluidic membranes for ionic power harvesting

Abstract

Nanofluidic membranes with efficient ion permselectivity hold great promise for ionic power harvesting and storage. However, overcoming the intrinsic permeability-selectivity trade-off by regulating the energy barriers that govern ion transport remains a significant challenge. This study addresses this limitation by introducing a novel strategy that precisely tailors the space charges within graphene oxide (GO) nanofluidic membranes. Through a combination of experimental and simulation approaches, we demonstrate that the engineered space charges at the membrane surface effectively break the permeability-selectivity trade-off. Specifically, the membranes achieve an impressive K+ permeation rate of approximately 0.19 mol m-2 h-1 while maintaining a high K+/Mg2+ selectivity ratio of around 34, outperforming most existing nanofluidic membranes. The underlying mechanism is attributed to an enhanced difference in the energy barriers for the transport of K+ and Mg2+ ions through the nanofluidic channels. This outstanding performance enables the direct harvesting of ionic power from equimolar solutions of KCl and MgCl2. These findings offer valuable insights into the design and optimization of next-generation high-performance nanofluidic membranes for advanced ion transport applications.