Identification of linear scaling relationships in polysulfide conversion on α-In2Se3-supported single-atom catalysts.

ABSTRACT

Developing highly active single-atom catalysts (SACs) for suppressing the shuttle effect and enhancing the kinetics of polysulfide conversion is regarded as an important approach to improve the performance of Li-S batteries. However, the adsorption behaviors of polysulfides and the catalytic properties of host materials remain obscure due to the lack of mechanistic understanding of the structure-performance relationship. Here, we identify that the adsorption energies of polysulfides on 3d transition-metal atoms supported by two-dimensional α-In2Se3 with downward polarization (TM@In2Se3) are highly correlated with the d-band centers of the TM atoms. Introduction of the TM atoms on the α-In2Se3 surface improves the electrical conductivity and meanwhile, significantly enhances the adsorption strength of polysulfides and suppresses the shuttle effect. A mechanistic study of polysulfide conversion on TM@In2Se3 shows that the Li2S2 dissociation is the potential-determining step with low activation energies, indicating that TM@In2Se3 can accelerate the kinetics of polysulfide conversion. Electronic structure analysis shows that the kinetics of the potential-determining step on TM@In2Se3 is related to the TM-S interaction in Li2S2-adsorbed TM@In2Se3. A linear scaling relationship between activation energy and the integrated crystal orbital Hamilton population of TM-S in the potential-determining step on TM@In2Se3 is identified. Based on the evaluation of stability, conductivity and activity, we concluded that Ti@In2Se3, V@In2Se3, and Fe@In2Se3 are the promising cathode materials for Li-S batteries. Our findings provide a fundamental understanding of the intrinsic link between the electronic structure and catalytic activity for polysulfide conversion and pave a way for the rational design of SAC-based cathodes for Li-S batteries.