Metalloporphyrin-immobilization MOFs derived metal-nitrogen-carbon catalysts for effective electrochemical oxygen reduction

The development of noble metal-free and activity-stable catalysts for oxygen reduction reaction (ORR) is critical to renewable energy technologies. ZIF-67, a kind of metal-organic frameworks (MOFs), are used to immobilize two different metalloporphyrins (Co/Mn [5,10,15,20-tetrakis (4-carboxyphenyl)porphyrin], Co-TCPP and Mn-TCPP) as precursors and to synthesize a series of metal-nitrogen-carbon catalysis materials (M@NC) via pyrolysis at different temperatures. The pyrolysis products Co@NC-800 and Mn/Co@NC-800 under an inert atmosphere at 800 degrees C displayed excellent electrocatalytic oxygen reduction performance in alkaline medium. Among them, Co@NC-800 has the best electrocatalytic oxygen reduction performance and its onset potential (E-onset), half-wave-potential and limiting current density are very similar to the corresponding values of commercial 20% PVC. Furthermore, the resulting Co@NC-800 shows the best long-term durability and methanol tolerance than commercial PVC, indicative of its potential applications in fuel cells. The introduction of metalloporphyrin on ZIF-67 not only increases the metal content and N content in the pyrolysis products but also makes it easier to start decomposition at a lower temperature, and also easy to generate more Co-N-x species, which makes them have a high electrocatalytic activity.