Engineering Molecular Heterostructured Catalyst for Oxygen Reduction Reaction

Introducing a second metal species into atomically dispersed metal-nitrogen-carbon (M-N-C) catalysts to construct diatomic sites (DASs) is an effective strategy to elevate their activities and stabilities. However, the common pyrolysis-based method usually leads to substantial uncertainty for the formation of DASs, and the precise identification of the resulting DASs is also rather difficult. In this regard, we developed a two-step specificadsorption strategy (pyrolysis-free) and constructed a DAS catalyst featuring FeCo molecular heterostructures (FeCo-MHs). In order to rule out the possibility of the two apparently neighboring (in the electron microscopy image) Fe/Co atoms being dispersed respectively on the top/bottom surfaces of the carbon support and thus forming false MHs, we conducted in situ rotation (by 8 degrees, far above the critical angle of 5.3 degrees) and directly identified the individual FeCo-MHs. The formation of FeCo-MHs could modulate the magnetic moments of the metal centers and increase the ratio of low-spin Fe(II)-N-4 moiety; thus the intrinsic activity could be optimized at the apex of the volcano-plot (a relationship as a function of magnetic moments of metal-phthalocyanine complexes and catalytic activities). The FeCo-MHs catalyst displays an exceptional ORR activity (E-1/2 = 0.95 V) and could be used to construct high-performance cathodes for hydroxide exchange membrane fuel cells and zinc-air batteries.

Automated summary

Introducing a second metal species into M-N-C catalysts to construct DASs is an effective strategy. We developed a two-step specific adsorption strategy to construct FeCo-MHs catalyst and directly identified individual FeCo-MHs through in situ rotation. The FeCo-MHs catalyst exhibits exceptional ORR activity and can be used for high-performance cathodes in fuel cells and zinc-air batteries.