Anchoring Mn-N coordination sites on a hybrid sp2–sp3 carbon surface for efficient oxygen reduction

The design of durable and efficient non-precious metal catalysts for the oxygen reduction reaction (ORR) is crucial for advancing fuel cell and metal–air battery technologies. Single-atom catalysts (SACs) have attracted significant attention owing to their high activity and atom utilization efficiency. However, conventional Fe–N–C SACs suffer from Fenton-related side reactions, while traditional carbon supports are susceptible to oxidative degradation under high potentials. Herein, we report a Mn single-atom catalyst (Mn–N–D) anchored on a partially graphitized sp 2 /sp 3 carbon support derived from low-cost industrial diamond. The partial transformation of the sp³ carbon surface into sp² carbon generates conductive domains that stabilize atomically dispersed Mn–N 4 moieties. The optimized Mn–N–D catalyst exhibits enhanced alkaline ORR performance, delivering a half-wave potential of 0.831   V vs. RHE. Experimental and density functional theory (DFT) analyses reveal the pyridinic-N-coordinated Mn–N 4 configuration serves as the primary active site, facilitating O–O bond cleavage and promoting the four-electron reaction pathway. This work provides a cost-effective strategy for constructing high-performance SACs through the synergistic integration of robust sp 3 carbon with conductive sp 2 carbon domains.