Designing Thiophene‐Enriched Fully Conjugated 3D Covalent Organic Framework as Metal‐Free Oxygen Reduction Catalyst for Hydrogen Fuel Cells

The application of three‐dimensional (3D) covalent organic frameworks (COFs) in renewable energy fields is greatly limited due to their non‐conjugated skeletons. Here, we design and successfully synthesize a thiophene‐enriched fully conjugated 3D COF (BUCT‐COF‐11) through an all‐thiophene‐linked saddle‐shaped building block (COThTh‐CHO). The BUCT‐COF‐11 exhibits excellent semiconducting property with intrinsic metal‐free oxygen reduction reaction (ORR) activity. Using the COF as cathode catalyst, the assembled anion‐exchange membrane fuel cells (AEMFCs) exhibited a high peak power density up to 493 mW cm−2. DFT calculations reveal that thiophene introduction in the COF not only improves the conductivity but also optimizes the electronic structure of the sample, which therefore boosts the ORR performance. This is the first report on the application of COFs as metal‐free catalysts in fuel cells, demonstrating the great potential of fully conjugated 3D COFs as promising semiconductors in energy fields. A thiophene‐enriched fully conjugated 3D covalent organic framework was designed and synthesized. Attributed to its conjugated and thiophene‐enriched skeletons, the material exhibited intrinsic metal‐free oxygen‐reduction catalytic activity. It was for the first time integrated into the hydrogen fuel cells as cathode catalyst, and the devices displayed a peak power density up to 493 mW cm−2.