Thiazolium-Linked Crystalline Porous Covalent Organic Frameworks for Mixed Electronic-Ionic Transport

Developing efficiently mixed electronic-ionic (MEI) conductive microcosmic pathways within a single functional material is essential yet challenging for electronic devices. Covalent organic frameworks (COFs) feature pre-designed functionalities and uniform pores, making them highly desirable platforms for transporting electrons and ions. However, for MEI conductive COFs, achieving high crystallinity when incorporating high-density ionic groups within the extensively π-electron delocalized skeletons remain a challenge due to intermolecular interactions. Herein, we reported a "pre-polymerization followed by self-ionization" approach to synthesize new thiazolium-linked COFs (MEICOFs, M═Cu, Co, Fe), where the ionic groups synthesized following the connection of building blocks. MEICOFs demonstrated broad ultraviolet-visible-near-infrared absorption bands and narrow bandgaps. As a proof of concept, the mixed electronic and hydroxide ionic conductivity of CuEICOF was determined to be 55.2 and 0.01 S m^-1, respectively. Moreover, MEICOFs film could directly catalyze the oxygen reduction reaction without additional conductive agent and the rotation of the electrode.