Elucidating the oxygen reduction reaction kinetics on defect engineered nanocarbon electrocatalyst: interplay between the N-dopant and defect sites

The active sites of electrocatalysts play a crucial role in the material design and mechanistic exploration of an electrocatalytic reaction. Defect-tailored heteroatom-doped carbon-based electrocatalysts for oxygen reduction reaction (ORR) have been much explored, but there is ambiguity in the prediction of active sites responsible for the performance of the material. To find the origin of the activity of this class of catalysts towards ORR, in this work, we use the quantum mechanics/machine learning (QM/ML) approach to derive energy-optimized models with both N-atoms and 5-8-5 defect sites which manifest exemplary ORR activity. Following this approach, we synthesized defect-engineered graphene (DG) using the zinc template method at 1050 degrees C to achieve optimum N-dopants and intrinsic (5-8-5) defects. The obtained electrocatalyst exhibits hierarchical porosity, high surface area, low nitrogen content, good stability and a satisfying ORR performance with a half-wave potential (E-1/2) of 0.82 V, comparable to that of commercial Pt/C (E-1/2 = 0.82 V). Further, the full energy profile was deduced using density functional theory and the charge redistribution in the material cross-verified a reduced overpotential for ORR. This work provides a strategy for the synthesis of noble-metal-free high-performance electrocatalysts for energy conversion.