Abstract
An aqueous metal ion capacitor comprising of a zinc anode, an oxidized carbon nanotubes (oCNTs) cathode and a zinc sulfate electrolyte is reported. Since the shuttling cation is Zn2+, this typical metal ion capacitor is named as zinc-ion capacitor (ZIC). The ZIC integrates the divalent zinc stripping/plating chemistry with the surface-enabled pseudocapacitive cation adsorption/desorption on oCNTs. The surface chemistry and crystallographic structure of oCNTs were extensively characterized by combining X-ray photoelectron spectroscopy, Fourier-transformed infrared spectroscopy, Raman spectroscopy and X-ray powder diffraction. The function of the surface oxygen groups in surface cation storage was elucidated by a series of electrochemical measurement and the surface-enabled ZIC showed better performance than the ZIC with an un-oxidized CNT cathode. The reaction mechanism at the oCNT cathode involves the additional reversible Faradaic process, while the CNTs merely show electric double layer capacitive behavior involving a non-Faradaic process. The aqueous hybrid ZIC comprising the oCNT cathode exhibited a specific capacitance of 20 mF cm-2 (corresponding to 53 F g-1) in the range of 0-1.8 V at 10 mV s-1 and a stable cycling performance up to 5000 cycles.
Highlights
Supercapacitors, called electrochemical capacitors (ECs), are such high-performance energy storage devices with excellent power capability, short charge-discharge time, long cyclic life, and outstanding reversibility (Yan et al, 2014)
We found that the oxidized carbon nanotubes can increase the pseudocapacitance due to the interaction between the oxygen-containing functional groups and the Zn2+, thereby enhancing the capacitance of the zinc-ion capacitor (ZIC)
Since cyclic voltammetry is a suitable technique to characterize the capacitive behavior of electrode materials, the electrochemical performances of oxidized carbon nanotubes (oCNTs) and CNTs were studied in a threeelectrode cell by using cyclic voltammetry
Summary
Supercapacitors, called electrochemical capacitors (ECs), are such high-performance energy storage devices with excellent power capability, short charge-discharge time, long cyclic life, and outstanding reversibility (Yan et al, 2014). The galvanostatic charge/discharge studies of the ZICs based on the oCNT and CNT cathodes were carried out at 2, 5, and 10 mA cm–2 within 0–1.8 V in the 1M ZnSO4 liquid electrolyte.
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