Synthesis of a Co-Nx type catalyst derived from the pyrolysis of a covalent triazine-based framework for oxygen reduction reaction

Abstract

• A Co N C catalyst had been developed using an inexpensive and N -rich precursor. • The covalent triazine-based framework provided high density and evenly distributed M N C sites. • The HAT-CN-Co/C-800 catalyst showed the highest ORR activity close to Pt/C. The preparation of non-noble metal catalysts with performance in the oxygen reduction reaction (ORR) comparable or superior to platinum-based catalysts remains challenging. In the present study, hexaazatriphenylenehexacarbonitrile (HAT-CN), which is rich in both cyano groups and pyrazine units, was used as the precursor and then cyclotrimerized into a covalent triazine-based framework with a macrocyclic structure containing abundant complexation sites for transitional metal ions. Subsequently, a series of non-platinum Co N C type catalysts (HAT-CN-Co/C) were prepared, and then pyrolyzed at different temperatures (700 °C, 800 °C, and 900 °C). The pyrolysis treatment endowed the catalysts with activated Co-N x sites, large pore sizes and high specific surface areas, which can promote oxygen transfer and accelerate the ORR catalytic process. It is found that the catalyst (HAT-CN-Co/C-800) obtained from pyrolysis at 800 °C possessed the best ORR activity and followed the four- electrons transfer pathway; the onset potential of ORR was determined as 0.972 V vs reversible hydrogen electrode (RHE), very close to that of Pt/C (0.993 V vs RHE), and the half-wave potential (0.895 V vs RHE) was significantly higher than that of Pt/C (0.859 V vs RHE). Furthermore, the HAT-CN-Co/C-800 catalyst showed good durability (83.2 % current retention after 28000 s) and significant methanol tolerance with good application potential as a substitute for the platinum-based ORR catalyst in fuel cell.