Operando electrochemical Raman and IR spectroscopic studies of covalent organic frameworks for energy storage and conversion systems

I present designs of covalent organic frameworks (COFs) and underpin their significant applications in organic Li-ion batteries and electrochemical CO₂ reduction. Our COF designs encompass various tunable characteristics such as pore sizes, functional groups, and film thickness, ranging from nanometers to micrometers. These COFs serve as versatile platforms for Li⁺storage electrodes, electrolytes, and CO₂/CO gas adsorption, which have been explored using <i>operando </i>electrochemical Raman and IR spectroscopy.<br/>As a representative example, we have successfully incorporated redox-active azo groups into COFs to facilitate two-electron transfer, examining their potential as organic electrodes. Ensuring reversibility and stability proved crucial, with results highly contingent on neighboring functional groups. We explored three distinct linkages: beta-ketoenamine, imine, and thiazole-fused rings, each exhibiting varying cycling stabilities under identical operational conditions. It underscores the significance of fully conjugated organic systems. Furthermore, the overlap of vertical pi orbitals stemming from the azo moiety enhanced rate capability. <i>Operando</i> electrochemical Raman spectroscopy for the surface of cross-sectional COF electrode demonstrated reversible azo reaction with Li⁺ during the charging and discharging process.