Computational screening on azafullerene-supported bifunctional single-atom catalysts for oxygen evolution and reduction reactions.

Developing efficient bifunctional catalysts toward both the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) remains challenging. Herein, we systematically explored the catalytic activity of single-atom catalysts (SACs) for the OER and ORR with 27 transition metal atoms supported on pyrrolic/pyridinic azafullerenes CN and CN using first-principles calculations. The catalytic performance of these single-atom catalysts TM@azafullerenes is highly dependent on the number of electrons in the TM d-orbitals. Azafullerene-supported Rh, Ir, and Co catalysts show overpotentials comparable or even superior to those of TM-N-graphene, emerging as promising candidates for bifunctional ORR and OER catalysts. Further bonding analysis shows that the TM-N bonds (TM = Rh, Co, and Ir) exhibit ionic characteristics, and molecular dynamics simulations (AIMD) demonstrate that these catalysts remain stable at 300 K. Descriptors, including the integrated crystal orbital Hamilton population and incorporating the d-orbital electron count and the electronegativity effectively elucidate the origins of the high catalytic activity for the ORR/OER. Our findings not only enrich the understanding of single-atom catalysts but also stimulate further development of novel fullerene-based SACs.