Tetrazole-functionalized benzoquinoline-linked covalent organic frameworks with efficient performance for electrocatalytic H2O2 production and Li-S batteries

It is of pressing necessity in clean energy conversion and storage to develop electrochemical materials with high activity and stability toward electrocatalytic hydrogen peroxide (H2O2) production and lithium-sulfur (Li-S) batteries. As a star material, covalent organic frameworks (COFs) have been rationally applied in electrochemistry due to their controllable design, regular channels, and post-synthesis modifications. Herein, we present a new tetrazole-functionalized covalent organic framework (COF-TZ) via successive cycloaddition, which has stable linkages through benzoquinoline ring formation. COF-TZ was applied to the electrocatalytic 2e(-) oxygen reduction reaction (ORR) process and selective H2O2 production was successfully achieved due to the enhancement of pi-conjugated networks and the introduction of heteroatoms. Notably, the H2O2 yield of COF-TZ was 85.1% to 93.4% at 0.2-0.5 V vs. RHE, which is the highest among metal-free COF-based ORR catalysts. Moreover, COF-TZ can effectively coordinate and uniformly disperse cobalt to obtain Co@COF-TZ, which could be ascribed to the existence of nitrogen active coordination sites. S-Co@COF-TZ was further acquired via a sulfur melting and diffusion technique. According to Li-S battery performance tests, S-Co@COF-TZ exhibits small-impedance, high-capacity, and long-term cycle capabilities, which could be attributed to the regular microporous structure limiting lithium polysulfides (LiPSs), the coordination of cobalt accelerating the catalytic transformation of LiPSs, and the stable benzoquinoline ring structures. Therefore, this study may not only provide a logical design of functional COFs but also promote the development of electrocatalytic H2O2 production and Li-S batteries.