Enhanced performance of atomically dispersed dual-site Fe-Mn electrocatalysts through cascade reaction mechanism

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-N_x-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 (E_1/2) of 0.88 V (vs. RHE) as well as a superior stability. Besides, the Fe/Mn-N_x-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 (E_ads) of *OH on Fe-N_x site, followed by transfer of the *OH to adjacent Mn-N_x sites. As a result, the first three steps during ORR more favored occur on the Fe-N_x 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-N_x site.