Engineering Molecular\nHeterostructured Catalyst for\nOxygen Reduction Reaction

Abstract

Introducing a second metal species into atomically dispersed\nmetal–nitrogen–carbon\n(M–N–C) catalysts to construct diatomic sites (DASs)\nis an effective strategy to elevate their activities and stabilities.\nHowever, the common pyrolysis-based method usually leads to substantial\nuncertainty for the formation of DASs, and the precise identification\nof the resulting DASs is also rather difficult. In this regard, we\ndeveloped a two-step specific-adsorption strategy (pyrolysis-free)\nand constructed a DAS catalyst featuring FeCo “molecular heterostructures”\n(FeCo-MHs). In order to rule out the possibility of the two apparently\nneighboring (in the electron microscopy image) Fe/Co atoms being dispersed\nrespectively on the top/bottom surfaces of the carbon support and\nthus forming “false” MHs, we conducted in situ rotation\n(by 8°, far above the critical angle of 5.3°) and directly\nidentified the individual FeCo-MHs. The formation of FeCo-MHs could\nmodulate the magnetic moments of the metal centers and increase the\nratio of low-spin Fe­(II)–N₄ moiety; thus the intrinsic\nactivity could be optimized at the apex of the volcano-plot (a relationship\nas a function of magnetic moments of metal–phthalocyanine complexes\nand catalytic activities). The FeCo-MHs catalyst displays an exceptional\nORR activity (<i>E</i>_1/2 = 0.95 V) and could\nbe used to construct high-performance cathodes for hydroxide exchange\nmembrane fuel cells and zinc–air batteries.