Potassium-Ion Conduction in Covalent Organic Frameworks

Covalent organic frameworks could be explored as unique materials for mass transport, as they possess built-in pathways originating from their well-defined one-dimensional channels. Potassium-ion conduction holds significant scientific interest and technological relevance. However, the study on potassium-ion-conducting materials is still in its infancy, and how potassium ions move through artificial pores remains unclear. Here, we report a strategy for enabling potassium-ion conduction in stable crystalline porous frameworks by designing polyelectrolyte interfaces and revealing key structural parameters that control potassium-ion motion. Systematic engineering of pore walls with different numbers of oligo(ethylene oxide) chains creates covalently linked yet discrete polyelectrolyte interfaces at predesigned density in the pores. We found that polyelectrolyte interfaces offer a scaffold to anchor counteranions on pore walls through single-file nitrogen chains via electrostatic interactions and release potassium ions to the "pool" of electrolyte chains, constituting well-defined lanes for potassium-ion transport. Remarkably, we observed that the effect of the polyelectrolyte interface on conductivity is not a simple linear summation of individual chains but rather a nonlinear exponential increment, achieving exceptional conductivities and allowing low-energy-barrier transport via ion hopping in the electrolyte network. These results and insights revealed the essence of polyelectrolyte frameworks in developing potassium-ion-conducting materials and pave the way to all-solid potassium-ion batteries and devices.