High efficiency nitrogen doping and single atom cobalt anchoring via supermolecules for oxygen reduction electrocatalysis

Abstract

Single atom catalysts (SACs) stabilized by nitrogen in a carbon support and having maximized atom utilization efficiency and an unsaturated environment exhibit high catalytic activity and selectivity. Incorporating nitrogen into the carbon lattice efficiently and uniformly is a critical step in preparing such catalysts but is challenging. The synthesis of Co and N co-doped porous carbon nanospheres (CoN-PCNS) in which Co is dispersed on the atomic scale is described herein, based on the facile pyrolysis of a mixture of cyclodextrin-based supermolecules with CoCl₂. Non-covalent host–guest interactions between cyclodextrin and p-phenylenediamine in the supramolecular complex give optimal nitrogen species mobility and retention. These factors enable a thorough reaction between nitrogen and carbon during crosslinking to give ultrahigh nitrogen doping efficiency, with approximately 57% nitrogen retention upon pyrolysis and consequently a homogeneous dispersion of coordinated CoN₄ sites throughout the carbon matrix. The CoN-PCNS exhibits impressive electrocatalytic activity during oxygen reduction, with an onset potential of 0.93 V, limiting current density of 5.74 mA cm⁻², good methanol tolerance and negligible activity decay under alkaline conditions after 10 000 voltage cycles. Density functional theory calculations suggest that CoN₄ is the most active among the various sites.