Understanding synergistic catalysis on Pt-Cu diatomic sites via operando X-ray absorption spectroscopy in sulfur redox reactions

Abstract

Sulfur redox reactions render lithium−sulfur (Li−S) batteries with an energy density of > 500 Wh kg−1 but suffer a low practical capacity and fast capacity fade due to sluggish SRR kinetics, which lies in the complex reaction process that involves a series of reaction intermediates and proceeds via a cascade reaction. Here, we present a Pt-Cu dual-atom catalyst (Pt/Cu-NG) as an electrocatalyst for sulfur redox reactions. Pt/Cu-NG enabled the rapid conversion of soluble polysulfide intermediates into insoluble Li2S2/Li2S, and consequently, it prevented the accumulation and shuttling of lithium polysulfides, thus outperforming the corresponding single-atom catalysts (SACs) with individual Pt or Cu sites. Operando X-ray absorption spectroscopy and density functional theory calculations revealed that a synergistic effect between the paired Pt and Cu atoms modifies the electronic structure of the Pt site through d-orbital interactions, resulting in an optimal moderate interaction of the metal atom with the different sulfide species. This optimal interaction enhanced charge transfer kinetics and promoted sulfur redox reactions. Our work thus provides important insights on the atomic scale into the synergistic effects operative in dual-atom catalysts and will thus pave the way to electrocatalysts with enhanced efficiency for high-performance Li−S batteries.