Abundant Active-sites Engineering Enables Porous Co-N-C Electrocatalyst with Superior Oxygen Reduction Reaction Activity

Abstract

The insufficiency of effective active sites and the poor stability are identified as primary factors for the performance limitations of non-precious metal carbon-based catalysts towards 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 the 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 heteroatoms N 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 carbon framework, thereby boosting electron transfer rates and enlarging the electrochemical active area. The transmission resistance of components can be effectively reduced in the carbon framework with a hierarchical pore structure, which can enhance the rate of oxygen electrocatalytic reduction. Consequently, the obtained Co-N-C catalyst exhibits outstanding oxygen reduction reaction catalytic activity comparable to that of commercial Pt/C, along with superior stability and alcohol tolerance.