Distance effect of carbon defects as design principles for metal-free oxygen reduction electrocatalysts

The experimental design of defective carbon-based catalysts currently mainly focuses on the arrangement and combination of various types of defects. The distance effect of defects and defect-defect interaction on the oxygen reduction reaction (ORR) catalytic activity remains fully unexplored. Herein, we first investigated the potential effect of inter-defect distance on ORR activity along zigzag and armchair directions through density functional theory (DFT) calculations, and pronounced catalytic activity anisotropy was observed. The shortest inter-defect distance along the zigzag distance results in the highest ORR activity with an ORR overpotential of 0.50 V on the Stone-Wales defect. While the shortest inter-defect distance along the armchair direction cannot influence or even impede the ORR process. Meanwhile, restricting the expansion of intra-defect distance caused by variations in the inter-defect distance could further enhance the ORR activity with an ultralow overpotential of 0.43 V on the C585 defect. Furthermore, the p_z band centers of carbon active sites exhibit a linear relationship with the binding strength of O intermediates, which can be a good catalytic descriptor to describe the ORR activity of carbon defects. Our findings highlight interesting avenues for controllable design and synthesis of catalysts in the field of high-density defect catalysis.