The synergistic effect of space and surface charge on nanoconfined ion transport and nanofluidic energy harvesting

Abstract Diverse nanoconfined ion transport behaviors have attracted increasing attention in constructing ion-channel-inspired nanoconfined systems for high nanofluidic energy conversion performance. Conventional nanofluidic systems cannot simultaneously obtain high ion-selectivity and high ion-flux in a large region due to the decreasing effect of the electrical double layer (EDL) formed on the charged surface. Here, space charge is introduced in the nanoconfined system to effectively solve this problem by employing the synergistic effect of surface and space charges. The charge effect contribution on controlled-ion-transport is further decoupled into surface charge, space charge and synergistic effects for the first time. The surface charge induces charge separation within the EDL in a smaller diameter channel while the space charge dominates the ion-selectivity by the ion-exchange mechanism in a larger diameter channel. The synergistic effect, contributed by EDL and ion-exchange effects, is extremely important in large (around 100 nm), short nanochannel (around 100 nm), and high concentration fold (around 1000-fold) conditions to achieve high ion-selectivity, ion-flux, and nanofluidic energy conversion performances, which is systematically analyzed by theoretical simulation results. These results reveal the mechanism for enhanced ion transport behaviors and provide a solid foundation for designing high-performance nanofluidic devices in fields of desalination, sensor, energy conversion and storage.