Enhancing electrochemical performance of ultrasmall Fe2O3-embedded carbon nanotubes via combusting-induced high-valence dopants

Abstract

• Ti 4+ , Sn 4+ , and Zr 4+ were successfully incorporated in Fe 2 O 3 by a flame synthesis. • The Fe 2 O 3 /CNTs nanocomposite was directly obtained by a flame synthesis. • Combustion reaction generating oxygen functional groups favor the wettability of electrode. • High-valence metal ions optimize the electron structure and enhance Na + adsorption. • The flexible Ti-FeO-CNT//MnO 2 achieved an exceeding high operating potential of 2.0 V. Doping is a reasonable solution to improve the electronic structure and surface properties of nanomaterials. Herein, we propose a rapid and simple methodology, flame synthesis, as an effective preparation strategy for incorporating high-valence metal ions (Ti 4+ , Sn 4+ , and Zr 4+ ) into ultrasmall Fe 2 O 3 on carbon nanotube support (i.e., M-FeO-CNT). The resulting materials exhibit not only a boosted Na + adsorption as shown by density functional theory (DFT) calculations, but also display an increased oxygen deficiency. The electrochemical activity and charge transfer efficiency of Fe 2 O 3 can be improved by reasonably substituting Fe 3+ with Ti 4+ , Sn 4+ , and Zr 4+ . The electrochemical investigation of Ti-doped Fe 2 O 3 (Ti-FeO-CNT) electrode demonstrates a splendid specific capacitance of 1.25 F cm −2 at 1 mA cm −2 in 1 M Na 2 SO 4 . This is significantly higher as compared to the capacitance of 0.48 F cm −2 . Flexible solid-state asymmetric supercapacitor Ti-FeO-CNT//MnO 2 is verified with operating voltage of 2.0 V and stability over 3000 cycles, and delivers a high energy density of 2.14 mWh cm −3 at power density of 25 mW cm −3 . The flame synthesis is expected to be widely applicable for the preparation of high-valence metal ions doped nanosized Fe 2 O 3 functionalized materials, thus opening up new avenues for energy and catalysis research.