Unraveling microenvironment modification in an atomically dispersed bimetallic FeCu catalyst in the oxygen reduction reaction

The important effect of microstructure in Fe-Cu bimetallic catalysts on the mechanism of the oxygen reduction reaction (ORR) was theoretically and experimentally investigated. Three types of Fe sites regulated by Cu were constructed: Fe clusters modified with Cu-N₄, Fe-Cu dimers, and isolated Fe/Cu single atoms. A theoretical study revealed that although copper could reduce the d-band center of Fe, the Fe-Cu dimer displayed unique attributes. Notably, the dimer increased the energy of *π antibonding orbitals combined with Fe²⁺/Fe³⁺-3d and *OH-2p, accelerated *OH removal and produced the lowest predicted overpotential (0.48 V). Three catalysts featuring the above models were experimentally embedded on porous nitrogen-doped carbon. FeCu-NC-2 with Fe-Cu dimers exhibited the most positive half-wave potentials of 0.904 V in alkaline and 0.720 V in neutral solutions. A Zn-air battery and a microbial fuel cell equipped with FeCu-NC-2 as the cathodic catalyst produced stable and high power densities of 568.6 mW cm^-2 and 2467 mW m^-2, respectively.