C–O−–K+ (Na+) groups in non-doped carbon as active sites for the oxygen reduction reaction

Abstract

Carbon-based materials exhibit high electrocatalytic activity for the oxygen reduction reaction (ORR), which is an essential step for several renewable and clean energy systems. To make them alternatives to Pt-based catalysts for the ORR, a deep understanding on the ORR active sites on the carbon surface is needed but remains a major challenge. In nitrogen (N)-doped carbons, the carbon atoms next to pyridinic N are suggested to be the active sites for the ORR. Here we show that non-doped carbon materials (from carbon dots by annealing treatment at 1000 °C) create surface defects by removing the carbonate groups from the carbon surface under alkaline conditions (KOH/NaOH). Subsequently, the K⁺ (Na⁺) attached to the defects (e.g., hydroxyl group) to form the adjacent C–O⁻–K⁺ (Na⁺) groups (C–O⁻–K⁺ (Na⁺) pairs), which are suggested to be the real catalytic active sites for the ORR, similar to those of Pt catalysts.