Recent advances in the design of a high performance metal–nitrogen–carbon catalyst for the oxygen reduction reaction

Abstract

Developing highly active, stable, and cost-effective cathode oxygen reduction reaction (ORR) catalysts is of great practical significance to promote the widespread applicability of fuel cells (FCs). Recent studies have witnessed remarkable progress in exploring the synthesis of high-performance ORR catalysts. Platinum group metal (PGM)-free catalysts with metal–nitrogen–carbon (M–N–C) sites are considered to be promising candidates for ORR catalysts due to their low cost and good applicability to multiple ORR steps. Here, we provide a focused discussion on the design strategies of high-efficiency M–N–C catalyst synthesis from the aspects of increasing active site density, improving intrinsic activity, facilitating mass transfer and avoiding the linear scaling relationship (LSR). The synthesis of M–N–C single-atom catalysts opens up a new way to increase active site density. The selection of an appropriate central metal and coordination atom as well as the adjustment of the local coordination environment are very crucial to enhance catalyst intrinsic activity. The reasonable design of a porous structure is an important prerequisite to promote mass transfer and build the largest three-phase interface. The development of new active sites makes it possible to avoid the LSR and prepare catalysts with ultra-low overpotential. Furthermore, the main mechanisms causing the rapid degradation of M–N–C catalyst activity, such as active site demetallization, H₂O₂ hazards and flooding problems, are discussed, and effective mitigation strategies are proposed to improve the M–N–C catalyst stability. Ultimately, the designs of high performance M–N–C catalysts for the ORR are summarized and prospected.