Plasma Surface Engineering of NiCo 2 S 4 @rGO Electrocatalysts Enables High-Performance Li-O 2 Batteries.

The sluggish redox reaction kinetics for aprotic Li-O 2 batteries (LOBs) caused by the insulating discharge product of Li 2 O 2 could result in the poor round-trip efficiency, low rate capability, and cyclic stability. To address these challenges, we herein fabricated NiCo 2 S 4 supported on reduced graphene oxide (NiCo 2 S 4 @rGO), the surface of which is further modified via a unique low-pressure capacitive-coupled nitrogen plasma (CCPN-NiCo 2 S 4 @rGO). The high ionization environment of the plasma could etch the surface of NiCo 2 S 4 @rGO, introducing effective nitrogen doping. The as-prepared CCPN-NiCo 2 S 4 @rGO has been employed as an efficient catalyst for advanced LOBs. The electrochemical analysis, combined with theoretical calculations, reveals that the N-doping can effectively improve the thermodynamics and kinetics for LiO 2 adsorption, giving rise to a well-knit Li 2 O 2 formation on CCPN-NiCo 2 S 4 @rGO. The LOBs based on the CCPN-NiCo 2 S 4 @rGO oxygen electrode deliver a low overpotential of 0.75 V, a high discharge capacity of 10,490 mA h g -1 , and an improved cyclic stability (more than 110 cycles). This contribution may pave a promising avenue for facile surface engineering of the electrocatalyst in LOBs and other energy storage systems.