Identifying the Evolution of Selenium‐Vacancy‐Modulated MoSe₂Precatalyst in Lithium–Sulfur Chemistry

Abstract

Witnessingc ompositional evolution and identifying the catalytically active moiety of electrocatalysts is of paramount importance in Li-S chemistry.N evertheless,t his field remains elusive.Wereport the scalable salt-templated synthesis of Se-vacancy-incorporated MoSe 2 architecture (SeVs-MoSe 2 ) and reveal the phase evolution of the defective precatalyst in working Li-S batteries.T he interaction between lithium polysulfides and SeVs-MoSe 2 is probed to induce the transformation from SeVs-MoSe 2 to MoSeS.F urthermore,o perando Raman spectroscopya nd ex situ X-rayd iffraction measurements in combination with theoretical simulations verify that the effectual MoSeS catalyst could help promote conversion of Li 2 S 2 to Li 2 S, thereby boosting the capacity performance.The Li-S battery accordingly exhibits asatisfactory rate and cycling capability even with and elevated sulfur loading and lean electrolyte conditions (7.67 mg cm À2 ; 4.0 mLmg À1 S ). This work elucidates the design strategies and catalytic mechanisms of efficient electrocatalysts bearing defects.

Manipulating Electrocatalytic Polysulfide Redox Kinetics by 1D Core–Shell Like Composite for Lithium–Sulfur Batteries

“…The lithium‐ion diffusion rate could be established using the classic Randles–Sevcik equation: where D Li+ is the lithium ion diffusion coefficient, I p is the peak current, n is the electrons transferred number during the reaction, A is the electrode area, v is the sweep rate, and C Li+ represents the Li‐ion molar concentration. [ 40,41,50 ] As shown in Figure 3e,f, the slopes derived from the peaks I and II of the MoSe 2 @C/rGO/S electrodes are both higher than that of rGO/S electrode, implying the faster Li ion diffusion rate and better redox kinetics. The enhanced lithium ion diffusion could be further understood by the DFT calculations.…”

“…As presented in Figure S7 in the Supporting Information, after adsorption of Li 2 S 6 , the Mo and Se peaks of original MoSe 2 are well manifested, while two additional peaks of MoS and SeLi bond are presented. [ 40 ] Therefore, the strong chemical interaction is given birth between MoSe 2 and Li 2 S 6 . Moreover, the formation of bonds at atomic level could be investigated by DFT calculations, which would be discussed later.…”

“…Recently, transition metal selenides have attracted much attention as emerging catalysts in the immature lithiumsulfur battery investigation since they possess moderate electronegativity differences between transition metals and selenium, favorable electronic properties and moderate affinity towards polysulfides. [37][38][39][40][41][42][43] For example, Zhang et al proposed that a triple-phase interface among electrolyte/CoSe 2 /reduced graphene oxide nanosheets could regulate the uniform nucleation and growth of insoluble Li 2 S. [37] Wang's group synthesized ultrathin MoSe 2 nanosheets grown on hollow carbon as a novel functional reservoir for polysulfides. They also find MoSe 2 have high chemical affinity toward polysulfides and could effectively mediated their fast redox conversion.…”

Synergetic Anion Vacancies and Dense Heterointerfaces into Bimetal Chalcogenide Nanosheet Arrays for Boosting Electrocatalysis Sulfur Conversion

“…The introduction of anion vacancies provides another effective strategy to enhance the electrocatalytic activity of TMCs toward boosted Li−S battery upon discharging/charging process. [ 25–27 ] Electrons in the Se‐defect can be excited into the conduction band, producing a low bandgap in the conduction band which is favorable to the sulfur conversion reaction. [ 28 ] Moreover, sulfur‐vacancies (S‐vacancies) can regulate the electronic structure of adjacent atoms, thus reducing the decomposition energy barrier of the reaction intermediate.…”

“…Although promising progress has been made, electrocatalytic activity is still unsatisfactory for a wellfunctioning Li−S battery in terms of boosting the entire sulfur conversion reaction.The introduction of anion vacancies provides another effective strategy to enhance the electrocatalytic activity of TMCs toward boosted Li−S battery upon discharging/charging process. [25][26][27] Electrons in the Se-defect can be excited into the conduction band, producing a low bandgap in the conduction band which is favorable to the sulfur conversion reaction. [28] Moreover, sulfurvacancies (S-vacancies) can regulate the electronic structure of adjacent atoms, thus reducing the decomposition energy barrier Vacancy and interface engineering are regarded as effective strategies to modulate the electronic structure and enhance the activity of metal chalcogenides.…”