Sulfonic acid functionalized covalent organic frameworks for lithium-sulfur battery separator and oxygen evolution electrocatalyst

Covalent organic frameworks (COFs) are considered as a class of potential candidates for energy storage and catalysis. In this work, a COF containing sulfonic groups was prepared to be a modified separator in lithium-sulfur batteries (LSBs). Benefiting from the charged sulfonic groups, the COF-SO3 cell exhibited higher ionic conductivity (1.83 mS⋅cm-1). Moreover, the modified COF-SO3 separator not only inhibited the shuttle of polysulfide but also promoted Li+ diffusion, thanks to the electrostatic interaction. The COF-SO3 cell also showed excellent electrochemical performance that the initial specific capacity of the battery was 890 mA h g-1 at 0.5 C and demonstrated 631 mA h g-1 after 200 cycles. In addition, COF-SO3 with satisfactory electrical conductivity was also used as an electrocatalyst toward oxygen evolution reaction (OER) via cation-exchange strategy. The electrocatalyst COF-SO3@FeNi possessed a low overpotential (350 mV at 10 mA cm-2) in an alkaline aqueous electrolyte. Furthermore, COF-SO3@FeNi exhibited exceptional stability, and the overpotential increased about 11 mV at a current density of 10 mA cm-2 after 1000 cycles. This work facilitates the application of versatile COFs in the electrochemistry field.