MXenes as Effective Sulfur Hosts and Electrocatalysts to Suppress Lithium Polysulfide Shuttling: A Computational Study

Exploring electrocatalysts for the sulfur reduction reaction (SRR) has emerged as a promising strategy to suppress the shuttle effect and enhance the kinetics in lithium–sulfur (Li–S) batteries. A comprehensive understanding of the electrocatalytic mechanism within Li–S batteries remains elusive, which hinders the rational design of advanced electrocatalysts for these systems. In this study, two-dimensional (2D) transition metal carbides and nitrides (MXenes) have been investigated for the catalytic conversion of lithium polysulfides (LiPSs) using density functional theory (DFT). Our findings reveal that MXenes show a moderate binding affinity for LiPSs, suggesting favorable thermodynamics for their role as electrocatalysts for the SRR. This thermodynamic favorability promotes the suppression of the LiPSs’ shuttle effect and the enhancement of the SRR kinetics. The SRR process in Li–S batteries consists of multiple steps with varying activation energies. Our analysis by constructing the energy diagram for the multistep SRR indicates that the initial reduction of S8 to Li2S8 is facile with a lower activation energy, while the last step where Li2S2 converts to Li2S appears to be a rate-limiting step. To predict the catalytic abilities of MXene structures, we built a volcano-shaped relationship between the adsorption of LiPSs and catalytic activity. We show three MXenes─Ta2CO2, Zr2NO2, and Mo2NO2 as potential electrocatalysts that exhibit lower thermodynamic overpotentials for the SRR. These findings represent a significant step toward developing advanced electrocatalysts that may unlock the full potential of Li–S batteries, paving the way for improved energy storage systems with enhanced efficiency and performance.