3D star-like atypical hybrid MOF derived single-atom catalyst boosts oxygen reduction catalysis

Abstract Developing high-efficiency, stable and non-precious electrocatalysts for oxygen reduction reaction (ORR) is highly important for energy conversion and storage. Single atom catalysts (SACs) show good potential in enhancing ORR, however, the specifical control over the coordination surroundings around single metal center to intrinsically modify the electron structure is still a great challenge. Herein, we demonstrate that a 3D hybrid MOF composed of cobalt doped ZIF-L and ZIF-8, featuring star morphology with six equal branches, can be used as an advanced precursor for making the Co SACs for greatly boosted ORR. The as-synthesized CoSA-N-C exhibits excellent ORR activity with E1/2 of 0.891 V in alkaline medium, outperforming the commercial Pt/C by 39 mV. Moreover, the E1/2 of CoSA-N-C (0.790 V) is merely 15 mV, less than that of Pt/C (0.805 V) in acid medium, which is among the best in the reported state-of-the-art SACs. DFT calculations demonstrate that the enhanced ORR performance is assigned to the formation of atomically isolated cobalt atom coordinated three N atoms and one C atom, which is easier to decrease the free energy of rate determining step and accelerate the ORR process than that of traditional cobalt atom coordinated four N atoms. In addition, a primary Zn-air battery with CoSA-N-C cathode reveals a maximum power density of 92.2 mW cm−2 at 120.0 mA cm−2, far higher than that of commercial catalysts (74.2 mW cm−2 at 110.0 mA cm−2).