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