Enhanced Performance of Atomically Dispersed Dual-site Fe-Mn Electrocatalysts Through Cascade Reaction Mechanism

Abstract Constructing and excavating single atom catalysts with high-density active sites and long-life durability for energy storage and conversion devices still remain bestially challenges. In this paper, a novel dual-site electrocatalyst with atomically dispersed Fe/Mn-Nx-C dual metal sites embedded in N-doped carbon matrix is successfully designed and synthesized, which exhibits a state-of-the-art oxygen reduction reaction (ORR) activity with a half-wave potential (E1/2) of 0.88 V (vs. RHE) as well as a superior stability. Besides, the Fe/Mn-Nx-C catalyst reaches a high power density of 208.6 mW cm-2 and a specific energy density of 825.5 W h kg-1 when this catalyst is employed in Zn-air battery, which is superior to most of the reported non-precious catalysts. Furthermore, theoretical DFT calculations reveal the excellent performance is induced through a synergic dual-site cascade mechanism, which overcomes the issue of low adsorption energy (Eads) of *OH on Fe-Nx site, followed by transfer of the *OH to adjacent Mn-Nx sites. As a result, the first three steps during ORR more favored occur on the Fe-Nx sites instead of the Mn sites to generate *OOH and *O intermediates due to the lower energy barriers. This mechanism is further approved by addition of methanol to verify the preferred adsorption of *OH on the Mn-Nx site.