Toward highly efficient bifunctional electrocatalysts for zinc–air batteries: from theoretical prediction to a ternary FeCoNi design

3d Transition-metal nitrogen-carbon nanocomposites (T-N-C, T = Fe, Co, Ni, etc.) with highly active M-N_x sites have received much attention in the field of rechargeable zinc-air battery research. However, how to rationally dope metallic elements to decorate T-N-C catalysts and enhance their electrocatalytic performances remains unclear. Herein, we demonstrated that cobalt-doped Fe-rich catalysts are effective in improving ORR performances by density functional theory (DFT) calculations. On this basis, we reported a kind of novel bifunctional electrocatalyst of hollow nitrogen-doped carbon tubes with coexisting M-N-C single atoms and alloy nanoparticles (denoted Fe_xCo_yNi_z@hNCTs). Benefiting from the synergistic effect between different components, the as-prepared Fe₄Co₁Ni₂@hNCT catalyst exhibited a small overpotential difference of 0.75 V between an OER potential at 10 mA cm^-2 and an ORR half-wave potential, as well as an excellent zinc-air battery performance, when serving as the air cathode. This work provided a scalable design concept for multi-metal doping toward high-performance T-N-C electrocatalysts.