Abstract

Coke powder activated carbon (CPAC) was prepared by dipping-calcined KOH activation method. Using CPAC as the raw material a series of composite electrode materials of CPAC/α-Co(OH)2 with different mass fractions of cobalt were synthesized by the Sol–gel method. The physical properties of the resulting samples were characterized by the field emission scanning electron microscopy and the X-ray diffraction. The results show that composite materials, CPAC/α-Co(OH)2, have a flower-like structure. The results of electrochemical performances show that the composite material has a good electrochemical capacity of 472.3 F g−1 with a cobalt doping amount of 30 wt %. By the cyclic voltammetry testing, we found that the anodic peak potential of the redox peaks in composite electrode materials shifted positively when the scan rate increased, while the cathodic peak potential shifted negatively, and that would cause a gradual increase of the peak potential difference of redox peaks. In contrast, the lower of the scan rate, the smaller of the peak potential difference and the better of the reversibility of composite material. The results of impedance testing show that CPAC/α-Co(OH)2 has a lower electrochemical impedance than that of CPAC.

Highlights

  • As a kind of new energy store and conversion equipment, electrochemical supercapacitors (ECs) have generated great interests due to their large capacitance, long cycle life and quick charge/discharge performance, etc. [1–4]

  • By the cyclic voltammetry testing, we found that the anodic peak potential of the redox peaks in composite electrode materials shifted positively when the scan rate increased, while the cathodic peak potential shifted negatively, and that would cause a gradual increase of the peak potential difference of redox peaks

  • Based on the energy store mechanism, electrochemical supercapacitors can be separated into two different categories: electric double layer capacitors (EDLCs) and redox pseudocapacitors [5–7]

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Summary

Introduction

As a kind of new energy store and conversion equipment, electrochemical supercapacitors (ECs) have generated great interests due to their large capacitance, long cycle life and quick charge/discharge performance, etc. [1–4]. Based on the energy store mechanism, electrochemical supercapacitors can be separated into two different categories: electric double layer capacitors (EDLCs) and redox pseudocapacitors [5–7]. Several kinds of porous carbon materials [11–15] have been widely applied in the electrochemical double-layer capacitors (EDLCs), owing to characteristics of abundant raw materials, low production cost, high special surface area, higher electrochemical stability, better electrical conductivity, and so on. One can build the electrochemical supercapacitors, which have the advantages of both of electric double layer capacitors (EDLCs) and redox pseudocapacitors [16, 17]. Considering the low cost and excellent capacitance, the cobalt compounds have been widely used as electrode materials [18, 19]. The physics and electrochemical performances of the composite electrode materials were systematically investigated. A platinum gauze electrode and a saturated calomel electrode (SCE) were served as the counter electrode and the reference electrode, respectively, and KOH solution (2 mol L-1) was used as the electrolyte

Experimental
Characterization and electrochemical measurement
XRD analysis
Chronopotentiometry
Cyclic voltammetry
AC impedance
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