Salt-Assisted Pyrolysis of Covalent Organic Framework for Controlled Active Nitrogen Functionalities for Oxygen Reduction Reaction

The development of defect-containing metal-free carbon materials is an exciting challenge, as it could contribute greatly to the emergence of more sustainable fuel cells and metal–air batteries. Here we report the combination of a covalent organic framework (COF) as a host material and potassium carbonate as an activator to synthesize, from relatively low temperature and with good control, hierarchical mesoporous/microporous structures, high-porosity (up to 2053 m2 g−1) and nitrogen-doped carbon materials with oxygen reduction reaction (ORR) activity. Indeed, the formation of large sp2 domains and the nature of heteroatom catalytic active sites, ranging from a large content of pyridinic (N-6) to quaternary (N-Q) functionalities, could be simply controlled within a range of pyrolysis temperatures from 625 °C to 775 °C. The resulting ORR properties of carbon material exhibit systematic behaviour regarding the pyrolysis temperature, testifying good control upon carbon material nature. Thus, this work opens new ways to explore COF capabilities to efficiently synthesize metal-free carbon materials for electrochemical energy storage and conversion systems.