Reversed charge transfer induced by nickel in Fe-Ni/Mo2C@nitrogen-doped carbon nanobox for promoted reversible oxygen electrocatalysis

The interaction between metal and support is critical in oxygen catalysis as it governs the charge transfer between these two entities, influences the electronic structures of the supported metal, affects the adsorption energies of reaction intermediates, and ultimately impacts the catalytic performance. In this study, we discovered a unique charge transfer reversal phenomenon in a metal/carbon nanohybrid system. Specifically, electrons were transferred from the metal-based species to N-doped carbon, while the carbon support reciprocally donated electrons to the metal domain upon the introduction of nickel. This led to the exceptional electrocatalytic performances of the resulting Ni-Fe/Mo₂C@nitrogen-doped carbon catalyst, with a half-wave potential of 0.91 V towards oxygen reduction reaction (ORR) and a low overpotential of 290 mV at 10 mA cm⁻² towards oxygen evolution reaction (OER) under alkaline conditions. Additionally, the Fe-Ni/Mo₂C@carbon heterojunction catalyst demonstrated high specific capacity (794 mA h g_Zn⁻¹) and excellent cycling stability (200 h) in a Zn-air battery. Theoretical calculations revealed that Mo₂C effectively inhibited charge transfer from Fe to the support, while secondary doping of Ni induced a charge transfer reversal, resulting in electron accumulation in the Fe-Ni alloy region. This local electronic structure modulation significantly reduced energy barriers in the oxygen catalysis process, enhancing the catalytic efficiency of both ORR and OER. Consequently, our findings underscore the potential of manipulating charge transfer reversal between the metal and support as a promising strategy for developing highly-active and durable bi-functional oxygen electrodes.