A sequential process to synthesize Fe3O4@MnO2 hollow nanospheres for high performance supercapacitors

Abstract

Designing efficient, durable, and affordable electrodes for supercapacitors is indispensable for utilizing clean and renewable energy resources. Herein, a three-step sequential process, including two hydrothermal procedures followed by an etching treatment, was developed to synthesize Fe₃O₄@MnO₂ hollow nanospheres (Fe₃O₄@MnO₂-HNS) using solid silica as a hard template. Fe₃O₄@MnO₂-HNS has the largest specific surface area (121.99 m² g⁻¹) due to a double hollow structure compared to other samples. The as-prepared Fe₃O₄@MnO₂-HNS exhibited superior electrochemical performance as compared to pristine hollow nanospheres of either Fe₃O₄ or MnO₂. When applied to practical asymmetric supercapacitor devices (Fe₃O₄@MnO₂-HNS as a positive electrode and activated carbon (AC) as a negative electrode), Fe₃O₄@MnO₂-HNS//AC exhibited prominent performance, such as a high capacity of 168.81 C g⁻¹ (375.14 F g⁻¹) at 0.5 A g⁻¹, a large energy density of 15.84 W h kg⁻¹ at a power density of 803 W kg⁻¹, and an excellent stable charge–discharge durability of 70.6% over 5000 cycles at 2 A g⁻¹. We envision that Fe₃O₄@MnO₂-HNS may be a promising alternative for applications in energy storage and electrocatalysis where discrete electrochemical performances are desired.