Hydrophilic sp2-carbon conjugated co-porphyrin covalent organic frameworks for efficient electrocatalytic oxygen reduction reaction.

Abstract

Covalent organic frameworks (COFs) have demonstrated great potential in electrocatalytic oxygen reduction reaction (ORR). However, the continuous proton-coupled electron transfer (PCET) steps with water as the proton donor and the low electron conductivity of hydrophobic COFs increase the kinetic barriers for device applications. Herein, a hydrophilic custom-designed strong electron/proton extractor on CoT-sp²C-P-COF-COOH was developed by converting the cyano groups of CoT-sp²C-P-COF into carboxyl groups. The electrocatalyst constructed by the CoT-sp²C-P-COF-COOH shows impressive ORR activity (E_1/2 = 0.823 V vs. RHE) and outperforms most COF-based catalysts. Additionally, the fabricated Zn-air battery with the CoT-sp²C-P-COF-COOH catalyst displays a high peak power density of 121.8 mW cm^-2 and excellent stability. Theoretical calculations suggest that CoT-sp²C-P-COF-COOH is also more efficient than CoT-sp²C-P-COF to bind with an O₂ molecule to form Co^III-O₂˙^-, which optimizes the electron transfer efficiency and enhances the stabilization of intermediates, thereby synergistically accelerating the PCET step and ORR kinetics. This work highlights the continuous electron extraction and rapid proton transfer during electrocatalysis, and paves the way for advances in designing hydrophilic ORR electrocatalysts at the molecular level.