Single-phase bimetal sulfide or metal sulfide heterojunction: Which one is better for reversible oxygen electrocatalyst?

Bimetallic sulfides, integrating the merits of individual components, are ideal structures for efficient electrocatalysis. However, for bimetallic sulfides including metal sulfide heterojunctions (MSH) and single-phase bimetallic sulfides (SBS), it is still unclear about which one has better catalytic activity toward reversible oxygen catalysis and its difference on catalytic mechanism. In this work, we demonstrate a bimetallic sulfide electrocatalyst that could transform from metal sulfide heterojunction (CoS/FeS) to single-phase bimetallic sulfide (CoFeS 2 ) through a facile temperature control strategy. The single-phase bimetallic sulfide (CoFeS 2 ) affords high intrinsic activity, fast reaction kinetics and superior durability toward oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). Density functional theory (DFT) simulations reveal that the (CoFeS 2 ) has homogeneous electron distribution of the CoFeS 2 structure, improves the central energy level of d band, and optimizes the O* and OOH* intermediate and efficiently reduces the energy barrier of the reaction rate-determining step (RDS). The assembled rechargeable zinc-air battery is more stable than the Pt/C and IrO 2 assemblies due to the excellent electrocatalytic activity and stability of CoFeS 2 /NC, suggesting that it has potential for use in practical applications.