Structure-activity relationship of doped-nitrogen (N)-based metal-free active sites on carbon for oxygen reduction reaction

Abstract

Resolving the structure-activity relationship of doped-nitrogen (N)-based active sites on carbon and their variation mechanism during oxygen reduction reaction (ORR) process have been very desirable for the deep understanding of doped-N-based carbon materials. Here, by correlating the ORR catalytic performance with chemical compositions of N-doped carbon samples and performing systematic quantum chemical calculations, we partially resolved the structure-activity relationship of different N-containing active sites on N-doped carbon, including the ORR-induced transformation of both pyridinic and graphitic N to pyrrolic N, the revealing of the catalytic activity order of different N-containing sites for ORR from both experimental and theoretical points of view systematically: pyridinic N > pyrrolic N > graphitic N > oxidized N > C (carbon). The tiny structure difference-induced huge ORR activity difference of N-containing sites was also revealed. All these new understandings to the doped-N-based ORR carbon catalysts can guide the rational design of N-doped metal-free catalysts.