Single-Atom Doped Fullerene (MN₄–C₅₄) as Bifunctional Catalysts for the Oxygen Reduction and Oxygen Evolution Reactions

Development of high-performance oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) catalysts is crucial to realizing the electrolytic water cycle. C₆₀ is an ideal substrate material for single atom catalysts (SACs) due to its unique electron-withdrawing properties and spherical structure. In this work, we screened for a novel single-atom catalyst based on C₆₀, which anchored transition metal atoms in the C₆₀ molecule by coordination with N atoms. Through first-principles calculations, we evaluated the stability and activity of MN₄-C₅₄ (M = Fe, Co, Ni, Cu, Rh, Ru, Pd, Ag, Pt, Ir, Au). The results indicate that CuN₄-C₅₄, which is based only on earth-abundant elements, exhibited low overpotentials of 0.46 and 0.47 V for the OER and ORR, respectively, and was considered a promising bifunctional catalyst, showing better performance than the noble-metal ones. In addition, according to the linear relationship of intermediates, we established volcano plots to describe the activity trends of the OER and ORR on MN₄-C₅₄. Finally, d-band center and crystal orbital Hamiltonian populations methods were used to explain the catalytic origin. Suitable d-band centers lead to moderate adsorption strength, further leading to good catalytic performances.