Electrocatalytic Activity of C_0.12Fe_1.88@CNTs with Iron Defects and Carbon Vacancies and Their Performance of Room-Temperature Sodium-Sulfur Battery

Gram-scale synthesis of C_0.12Fe_1.88 coating carbon nanotubes (C_0.12Fe_1.88@CNTs) is realized via high-temperature pyrolysis of inexpensive ferrocene as a precursor, combined with rapid heating and cooling rates strategy. The electrochemical performance of the sulfur positive electrode was evaluated with C_0.12Fe_1.88@CNTs electrocatalyst as a multifunctional separator in room-temperature sodium-sulfur battery. Polar carbons of C_0.12Fe_1.88@CNTs electrocatalysts in the vacancies multi-site adsorb and anchor polysulfides via abundant carbon vacancies, and the effect of anchoring polysulfides evidently suppresses the polysulfides shuttling. The d-p hybrid orbitals with larger orbital overlap areas are formed between the iron defects and polysulfides or sodium sulfide, and the d-p orbital hybridization effect reduces the activation energy of the reaction. The iron defect active sites accelerate the reduction of polysulfides to sodium sulfide, reducing the concentration of sodium polysulfide at the interface, which further inhibits the shuttle of polysulfides. Meanwhile, the iron defect active sites forming Na-Fe-S bonds accelerate the oxidation of Na₂S to S and Na. The results show that initial discharge capacity of the cell with the C_0.12Fe_1.88@CNTs separator is 1 396 mAh/g at 0.1C and maintains a reversible capacity of 486 mAh/g after 1 000 cycles at 1 A/g. The research provides strong theoretical reference for the application of multifunctional separators with low cost and high catalytic activity in sulfur cathodes.