Porphyrin polymer-derived single-atom Fe assisted by Fe2O3 with oxygen vacancy for efficient oxygen reduction reaction

Single-atom catalysts (SACs) have been deemed as one of the most prospective substitutes for high-efficiency oxygen reduction reaction (ORR) catalysts due to its theoretical maximum atomic utilization. However, the convenient preparation and the further improvement in activity of SACs are laborious. Herein, the N-doped porous carbon (NC) material with in site produced Fe-N-4 single-atom catalytic sites (FeSA) accompanied by Fe2O3 species with abundant oxygen vacancies (Ov-Fe2O3) as co-catalytic sites (Ov-Fe2O3@FeSA@NC) is successfully obtained by using a well-designed porphyrin conjugated mesoporous polymer (CMP) consisting of iron porphyrin and metal free porphyrin units as a precursor, and followed by pyrolysis. A series of controllable experiments reveal that FeSA assisted by Ov-rich Fe2O3 render Ov-Fe2O3@FeSA@NC outstanding ORR activity in the alkaline medium with the onset and half-wave potentials (E-onset and E-1/2) of 0.987 V and 0.901 V vs RHE, which significantly outperformed the electrochemical activity of FeSA@NC (E-onset = 0.962 V, E1/2 = 0.850 V) and Ov-Fe2O3@NC (E-onset = 0.913 V, E1/2 = 0.821 V) with individual FeSA and Ov-Fe2O3 active sites, respectively. This work innovatively demonstrates the importance of oxygen vacancy-assisted single-atom catalysts for oxygen reduction catalysis, and also provides guidance for the design of high-performance SACs.