Clean energy storage in microcapacitor with β-FeSi2 nanoparticles

Fangfei Li, University of Duisburg-Essen, Duisburg, Germany
Hans Orthner, University of Duisburg-Essen, Duisburg, Germany
Martin Paul Geller, University of Duisburg-Essen , Duisburg, Germany
Hartmut Wiggers, University of Duisburg-Essen , Duisburg, Germany
Axel Lorke, Unversity of Duisburg-Essen, Duisburg, Germany

The demand for high performance electric power storage and increasing concern over environment issues require not only high energy density but also clean energy sources. Among all the novel energy sources, batteries and supercapacitors develop dramatically in recent years, along with the fast growing industry of portable electronic devices and electronic vehicles, providing a promising solution to clean energy storage.

Normally, electrochemical energy storage such as batteries and supercapacitors work with liquid electrolyte, either organic or inorganic, which is usually toxic and harmful to the environment. However, we present a non-toxic, environmentally friendly and cost-effective capacitor coated with β-FeSi2 nanoparticles that works in saturated water vapor. To that goal, the effect of water vapor and β-FeSi2 nanoparticles during charging and discharging is studied. The active material β-FeSi2 nanoparticles are produced via direct gas phase synthesis, and enables mass production at low price. For testing the capacitor performance, a dispersion of β-FeSi2 nanoparticles is spincoated onto an interdigitated structure, which is printed on a SiO2 substrate (4×4 mm²) using lithography. The interdigitated structure is employed to enable an easier access for water vapor to β-FeSi2 nanoparticles that locate beneath the surface, compared to conventional double plate capacitor.

The β-FeSi2 nanoparticles-coated microcapacitor tested under saturated water vapor shows a specific capacitance of approximately 10 mF/g, which is three orders of magnitude higher than the capacitance of the β-FeSi2 capacitor tested under dry air. Also the capacitor without β-FeSi2 thin film exhibits negligible capacitance, compared to the capacitor with nanoparticles.

At low charging voltage (0.1 V -1.5 V), the stored charge increases linearly with applied voltage. While for higher voltage (1.6 V -3 V), the stored charge shows a complex behavior, indicating electrochemical reactions taking place. The device is electrically robust, can be reused many times, even after applying high voltage.

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