A(CoFe)(S2)2/CoFe heterostructure constructed in S, N co-doped carbon nanotubes as an efficient oxygen electrocatalyst for zinc-air battery

Transition metal alloys can exhibit synergistic intermetallic effects to obtain high activities for oxygen reduction/evolution reactions (ORR/OER). However, due to the insufficient stability of active sites in alkaline electrolytes, conventional alloy catalysts still do not meet practical needs. Herein, by using polypyrrole tubes and cobalt-iron (CoFe) Prussian blue analogs as precursors, CoFe sulfides is in-situ formed on CoFe alloys to construct (CoFe)(S-2)(2)/CoFe heterostructure in sulfur (S) and nitrogen (N) co-doped carbon nanotubes (CoFe@NCNTs-nS) via a low-temperature sulfidation strategy. The as-marked CoFe@NCNTs-12.5S exhibits a comparable ORR activity (half-wave potential of 0.901 V) to Pt/C (0.903 V) and a superior OER activity (overpotential of 272 mV at 10 mA cm(-2)) to RuO2 (299 mV). CoFe@NCNTs-12.5S also exhibits ultralow charge transfer resistances (ORR-6.36 Omega and OER-0.21 Omega) and an excellent potential difference of 0.617 V. The sulfidation-induced (CoFe)(S-2)(2)/CoFe heterojunctions can accelerate interfacial charge transfer process. Tubular structure not only disperses the (CoFe)(S-2)(2)/CoFe heterostructure, but also reduces the corrosion of active-sites to enhance catalysis stability. Zinc-air battery with CoFe@NCNTs-12.5S achieves a high specific capacity (718.1 mAh g(-1)), maintaining a voltage gap of 0.957 V after 400 h. This work reveals the potential of interface engineering for boosting ORR/OER activities of alloys via in-situ heterogenization.