Design Principles of Permselective Nanochannels for Iontronic Applications in the Energy‐Water Nexus: Taking Covalent Organic Frameworks as an Example

Abstract Inspired by biological ion channels, artificial nanochannels with high ionic selectivity have emerged as powerful platforms for nanofluidic iontronics, linking advances in energy and water technologies. This perspective outlines the fundamental design principles for constructing permselective nanochannels and examines their implications for osmotic energy harvesting and related applications. It is highlighted how pore size, surface charge density, channel density, and length collectively govern transport behavior, often in non‐monotonic ways that challenge conventional assumptions. Special attention is given to concentration polarization, an omnipresent yet frequently overlooked bottleneck, and to strategies for mitigating it through asymmetric architectures, Janus charge distributions, and external stimuli such as thermal or photonic fields. Beyond long‐range Coulombic interactions, the growing recognition of short‐range mechanisms that sustain robust ionic selectivity under high salinity is also discussed. Finally, applications ranging from renewable power generation and lithium extraction are surveyed to integrate hydrogen production and biomimetic sensing, underscoring the broad potential of permselective nanochannels to drive sustainable solutions across the energy‐water nexus.