Carbon Nanofiber Aerogel Converted from Bacterial Cellulose for Kilohertz AC-Supercapacitors
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MRS Advances © 2018 Materials Research Society DOI: 10.1557/adv.2018.139
Carbon Nanofiber Aerogel Converted from Bacterial Cellulose for Kilohertz AC-Supercapacitors Nazifah Islam1, Md Nadim Ferdous Hoque1, Yujiao Zu2, Shu Wang2 and Zhaoyang Fan1 1 Department of Electrical and Computer Engineering and Nano Tech Center, Texas Tech University, Lubbock, TX 79409, U.S.A.
2
Department of Nutritional Sciences, Texas Tech University, Lubbock, TX 79409, U.S.A.
ABSTRACT
Compact-size kilohertz (kHz) AC-supercapacitors are being pursued for ripple current filtering and pulsed energy storage. However, their development is limited by a small areal capacitance density due to very thin electrode used for meeting frequency requirement. In our work, crosslinked carbon nanofiber aerogel (CCNFA) was investigated as freestanding electrode for kHz AC-supercapacitors with an areal capacitance density as large as 4.5 mF cm-2 at 120 Hz, 5-10 times larger than most reports. The CCNFA was obtained in a rapid plasma carbonization process of bacterial cellulose. The fabrication route adopted here is simple and straightforward, and the produced CCNFA electrode was found to be very suitable for high-frequency AC-supercapacitors. The operating voltage range of CCNFA based ACsupercapacitors can be expanded to 3 V by utilizing an organic electrolyte. In addition to ACSupercapacitor performance, the morphology and material properties of bacterial cellulose aerogel and CCNFA were also reported.
INTRODUCTION The conventional supercapacitors have a frequency response limited below 1 Hz, or they only work under DC current and therefore cannot be used for current ripple filtering. In contrast, AC-Supercapacitor should have a frequency response above kHz so that they can be used as a filtering capacitor to replace bulky aluminium electrolytic capacitors in common power electronic applications such as line-frequency AC/DC conversion. Both high capacitance density and kilohertz frequency response are crucial for AC-supercapacitor [1]. Great progresses are being achieved by exploring different carbon nanostructures [2-7], but the reported areal capacitance is still low for practical applications. Although fast pseudocapacitors were also reported with large capacitance [8], they are intrinsically slower than double layer capacitors and cannot work at kHz frequencies. Large capacitance of supercapacitors arises from a large surface area of porous carbon, however, the complex pore structure renders them incapable for fast mass transport in electrolyte. For AC-supercapacitors, the structure of the electrode must be carefully tailored to ensure fast mass transport, high electronic conductivity as well as a
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reasonable surface area. These properties are predominantly controlled by the choice of precursor material and
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