Identifying the Evolution of Selenium-Vacancy-Modulated MoSe₂ Precatalyst in Lithium-Sulfur Chemistry

Witnessing compositional evolution and identifying the catalytically active moiety of electrocatalysts is of paramount importance in Li-S chemistry. Nevertheless, this field remains elusive. We report the scalable salt-templated synthesis of Se-vacancy-incorporated MoSe₂ architecture (SeVs-MoSe₂ ) and reveal the phase evolution of the defective precatalyst in working Li-S batteries. The interaction between lithium polysulfides and SeVs-MoSe₂ is probed to induce the transformation from SeVs-MoSe₂ to MoSeS. Furthermore, operando Raman spectroscopy and ex situ X-ray diffraction measurements in combination with theoretical simulations verify that the effectual MoSeS catalyst could help promote conversion of Li₂ S₂ to Li₂ S, thereby boosting the capacity performance. The Li-S battery accordingly exhibits a satisfactory rate and cycling capability even with and elevated sulfur loading and lean electrolyte conditions (7.67 mg cm^-2 ; 4.0 μL mg^-1 _S ). This work elucidates the design strategies and catalytic mechanisms of efficient electrocatalysts bearing defects.