Precise solid-phase synthesis of CoFe@FeO_x nanoparticles for efficient polysulfide regulation in lithium/sodium-sulfur batteries.

Abstract

Complex metal nanoparticles distributed uniformly on supports demonstrate distinctive physicochemical properties and thus attract a wide attention for applications. The commonly used wet chemistry methods display limitations to achieve the nanoparticle structure design and uniform dispersion simultaneously. Solid-phase synthesis serves as an interesting strategy which can achieve the fabrication of complex metal nanoparticles on supports. Herein, the solid-phase synthesis strategy is developed to precisely synthesize uniformly distributed CoFe@FeO_x core@shell nanoparticles. Fe atoms are preferentially exsolved from CoFe alloy bulk to the surface and then be carburized into a Fe_xC shell under thermal syngas atmosphere, subsequently the formed Fe_xC shell is passivated by air, obtaining CoFe@FeO_x with a CoFe alloy core and a FeO_x shell. This strategy is universal for the synthesis of MFe@FeO_x (M = Co, Ni, Mn). The CoFe@FeO_x exhibits bifunctional effect on regulating polysulfides as the separator coating layer for Li-S and Na-S batteries. This method could be developed into solid-phase synthetic systems to construct well distributed complex metal nanoparticles.