Regulation of bioinspired ion diodes: From fundamental study to blue energy harvesting

Ionic current rectification (ICR) phenomenon occurs in potassium channels embedded in the biological cell membranes, which is that ions can be translocated predominately only in one direction (inwards or outwards across the membrane), underlying the electric power generation in electric eels. Inspired by this, artificial ion diodes with ICR behaviors based on asymmetric nanochannels have been developed for both fundamental study and practical applications. In this review, we focus on the underlying mechanism and main influencing factors of the ICR behavior, which lay the foundation of ion diodes, and reviewed the corresponding regulation strategies in diverse bioinspired artificial nanochannels with various dimensions and structures. We systematically classified the regulation methods into five categories according to the fundamental parameters affecting the rectification, including: geometry, electrolyte, surface charge, wettability and working mode. Based on this fundamental research, ICR properties have been recently introduced into blue energy harvester systems, enabling high power generation performance. Furthermore, we put up some ideas on how to face the changing salinity environment for ion diodes, especially in hypersaline environment, which plays a vital role in water-nexus energy science. We prospect sub-nano channels or salinity adaptive nanoporous membranes could expand the application scope.