Transition Metal-Doped 2D GaN as Single-Atom Electrocatalysts for Lithium–Sulfur Batteries: Insights from First-Principles Calculations

The commercial adoption of lithium–sulfur (Li–S) batteries is primarily limited by the shuttle effect and slow kinetics of the sulfur reduction reaction (SRR), which involves a complex 16-electron conversion process. Single-atom catalysts (SACs) show great potential as electrocatalysts to improve reaction kinetics in Li–S batteries. Using first-principles methods, we conducted computational screening of a series of transition metal (TM) atoms doped into two-dimensional (2D) GaN to enhance the SRR activity. Our results indicate that the important SRR step which involves liquid–solid transformation of Li2S4 into Li2S is correlated linearly with the SRR overpotential via 2.7ΔGLi2S* – ΔGLi2S4*. Based on the volcano plot, two catalysts, namely Pd@GaN and Cu@GaN, are identified as the most effective electrocatalysts, with an overpotential of 0.43 V. These doped atoms remain stable on the 2D GaN even at high temperatures. In addition, both Pd@GaN and Cu@GaN exhibit strong binding energies for high order Li2Sn (n = 4, 6, 8), ranging from −1.81 to −2.99 eV, effectively mitigating the shuttle effect. This study offers theoretical insights into the SRR mechanism on TM-doped 2D GaN and guides the rational design of single-atom catalysts (SACs) for Li–S batteries.