Bimetallic Sulfide with Controllable Mg Substitution Anchored on CNTs as Hierarchical Bifunctional Catalyst toward Oxygen Catalytic Reactions for Rechargeable Zinc–Air Batteries

The exploitation of high-efficiency and cheap bifunctional cathode electrocatalyst is of significant importance to rechargeable zinc-air batteries. In this paper, a bimetallic sulfide coupled with a CNT ((Co, Mg)S2@CNTs) hybrid catalyst is developed via a proposed vulcanization process. The (Co, Mg)S2@CNTs) with controllable Mg substitution has a tailored crystal structure (amorphous and crystalline), which catalyzes the oxygen reduction/evolution reaction (ORR/OER). The active sites of CoS2@CNTs are activated by doping Mg ions, which accelerates the kinetics of the oxygen adsorption for ORR and oxygen desorption for OER. Meanwhile, the hybrid catalyst exhibits a unique hierarchal morphology and a "catalytic buffer", which further accelerate the mass transfer of catalytic processes. In addition, the outer wall of CNTs as substrate effectively avoid the agglomeration of (Co, Mg)S2 particles by reasonably providing adsorption sites. The inner and outer walls of CNTs form a high-speed conduction pathway, quickly transferring the electrons produced by oxygen catalytic reactions. As a result, the (Co, Mg)S2@CNTs exhibit an ORR performance comparable with commercial catalyst Pt/C-RuO2 and remarkable OER performance (Ej=10 = 1.59 V). The high power density of 268 mW cm-2 and long-term charge/discharge stability of the zinc-air battery proves the feasibility of (Co, Mg)S2@CNTs application in high-power devices.