Coupling Ultrafine Transition Metal and Rare Earth Oxide Nanocrystals toward Highly Active and Stable Catalysts for Lithium–Sulfur Batteries

Electrocatalysts are extremely important for accelerating the redox reaction kinetics in lithium-sulfur (Li-S) batteries. As two kinds of competitive electrocatalysts, however, transition metals (TMs) usually react with sulfur species resulting in passivated surfaces, while stable rare earth oxides (REOs) exhibit low catalytic activity. Therefore, developing promising catalysts with long-term activity and stability is a crucial task. Herein, a TMs-REOs heterojunction catalyst consisting of N-doped carbon shell containing embedded ultrafine Gd₂O₃ and Co nanocrystals (named as Gd₂O₃/Co@NC) is elaborately designed and fabricated. Experimental and theoretical results reveal that the strong coupling between Co and Gd₂O₃ in a large number of heterojunctions endows the catalyst with moderate adsorption and satisfactory durability. Consequently, the cells assembled with a Gd₂O₃/Co@NC modified separator exhibit high rate capacity (628.0 mAh g^-1 at 4C), cycling stability (504.2 mAh g^-1 after 500 cycles at 2C), and sulfur utilization (4.8 mAh cm^-2 under sulfur loading of 5.1 mg cm^-2). This study highlights the invalidation mechanism of TMs in Li-S batteries and will inspire the design of advanced heterojunction catalysts through the coupling of TMs and REOs.