Rational design of Fe-M-N-C based dual-atom catalysts for oxygen reduction electrocatalysis

Fe-N-C based single-atom catalysts (SACs) with isolated Fe atoms dispersed on nitrogen-doped carbon matrix have achieved sustained attention for oxygen reduction reaction due to their great potential in replacing the Pt based noble catalysts in terms of catalytic activity. To further trigger the intrinsic activity of Fe-N-C, Fe based dual-atom catalysts (DACs, i.e., Fe-M-N-C) have been intensively studied, which confer the catalysts with readily tunable geometric configurations, electronic structures, thereby tailored catalytic properties. In this review, current progress on the rational design of Fe-M-N-C based DACs for enhanced oxygen reduction catalysis is summarized. Firstly, the ORR mechanisms on DACs are discussed where the second metal atoms can function through synergistic effect and/or modulation effect to promote the intrinsic catalytic activity. Moreover, the currently available synthetic approaches, characterization techniques and computational methods are systematically reviewed to aid the investigation of DACs. Then, DACs are classified into marriage-type and conjunct-type based on the interaction between metal atoms, whose properties are discussed at length with the atomic configuration. At last, the main challenges of Fe-M-N-C based DACs are summarized and some appealing directions towards highly efficient and stable energy applications are provided for their further enhancement.