Facet Strain Strategy of Atomically Dispersed Fe-N-C Catalyst for Efficient Oxygen Electrocatalysis

Increasing the portion of highly active metal centers in atomically dispersed M-N-C catalysts is significant for the overall oxygen reduction reaction (ORR) performance. A "facet strain strategy" is designed by using a trans-layer compressive strain of the {110} facet of FeCo nanoparticles encapsulated in graphitic Fe-N-C layers to further activate the primitive FeN4 catalytic centers on the graphitic sub-layer that are omitted in commonly direct access activation strategies. Using X-ray absorption near-edge spectroscopy and extended X-ray absorption fine structure, the highly active FeN4 type is detected with compressed Fe-N bonds. Density functional theory calculation discloses that, in virtue of lattice mismatch, FeCo {110} facets transmit a trans-layer compressive strain to reconstruct the FeN4 sites on surrounding graphitic sub-layers to optimize the Fe-OH* adsorption energy in the rate-determining step. The redesigned catalyst exhibits enhanced ORR activity, outperforming the primitive Fe-N-C and commercial Pt/C benchmarks. This study will enrich insights toward developing MN4 and nanoparticle composite electrocatalysts.