Abundant active-site engineering enables porous Co–N–C electrocatalysts towards superior oxygen reduction reaction activity

Abstract

The insufficiency of effective active sites and poor stability are identified as primary factors responsible for the performance limitations of non-precious metal carbon-based catalysts towards the oxygen reduction reaction (ORR). Increasing the number of non-precious metal and N–C active sites while achieving their uniform distribution continues to be a major challenge in the advancement of oxygen reduction catalysts. In this work, riboflavin was employed to modify the precursors ZIF-8 and ZIF-67, leveraging the high electronegativity of nitrogen atoms in the isoalloxazine ring to enhance the anchoring effect on metal ions, thereby reducing the agglomeration of Co ions during pyrolysis. Furthermore, during the high-temperature pyrolysis process, the cleavage and integration of nitrogen-containing functional groups in riboflavin not only led to an increase in the doping density of N heteroatoms within the carbon framework but also enriched the pore structure of the catalyst. Co–N active sites and plentiful N–C active sites can be uniformly dispersed within the micro–mesoporous Co–N–C framework, thereby boosting electron transfer rates and enlarging the electrochemically active surface area. The transmission resistance of components can be effectively reduced in the carbon framework with a hierarchical pore structure, which could enhance the rate of oxygen electrocatalytic reduction. Consequently, the obtained Co–N–C catalyst exhibits outstanding catalytic activity in the oxygen reduction reaction comparable to that of commercial Pt/C, along with superior stability and alcohol tolerance.