Theoretical insights into Cu-mediated electronic modulation in FeCoNi-based multimetallic catalysts for polysulfide...

FeCoNi is a widely used multimetallic framework for lithium-sulfur electrocatalysis, yet the mechanistic contribution of Cu remains incompletely resolved. Here, calculations on representative FeCoNi and dilute single-CuFe₈Co₁₀Ni₁₃Cu₁ models are employed to elucidate how local Cu incorporation regulates polysulfide adsorption, sulfur-reduction thermodynamics and interfacial charge redistribution. The calculations reveal that Cu incorporation selectively strengthens soluble long-chain Li₂S₆ adsorption, decreases the limiting to Li₂S* free-energy change from 1.07 to 1.01 eV and induces pronounced local charge redistribution within the cooperative Fe/Co/Ni/Cu environment. A batch-matched FeCoNi@CP control further validates the catalytic modulation effect of Cu. Modulus-weighted Li₂S₆ symmetric-cell fitting yields R _ct values of 10.74, 38.23 and 144.89 Ω for FeCoNiCu@CP, FeCoNi@CP and pristine CP, respectively, while matched variable-scan-rate CV measurements demonstrate enhanced low-potential cathodic kinetics for FeCoNiCu@CP. At 2C, FeCoNiCu@CP delivers higher and more stable early-stage electrochemical performance than FeCoNi@CP, achieving 739.0 versus 608.0 mA h g^-1 at cycle 10 and 663.9 versus 621.8 mA h g^-1 at cycle 100. Element-resolved Bader charge analysis further suggests that Fe and Ni act as the main charge-transfer reservoirs, Co participates in cooperative charge donation, and Cu serves as a highly responsive local electronic regulator during Li₂S₄/Li₂S₆ adsorption. These findings indicate that Cu does not function as an isolated dominant active center, but electronically modulates the FeCoNi-based multimetallic surface to balance polysulfide anchoring and conversion. These results demonstrate that Cu incorporation promotes interfacial electron regulation and accelerates polysulfide conversion through a local electronic modulation effect rather than acting as an isolated dominant active site.