Preparation and properties of coke powder activate

Authors: Heming Luo Fengbo Zhang Xia Zhao Deyi Zhang Yanxia Sun Peng Yang

Publish Date: 2013/02/09

Volume: 24, Issue: 7, Pages: 2473-2478

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Abstract

Coke powder activated carbon CPAC was prepared by dippingcalcined KOH activation method Using CPAC as the raw material a series of composite electrode materials of CPAC/αCoOH2 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 Xray diffraction The results show that composite materials CPAC/αCoOH2 have a flowerlike structure The results of electrochemical performances show that the composite material has a good electrochemical capacity of 4723 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/αCoOH2 has a lower electrochemical impedance than that of CPACRecently 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 2 3 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 6 7 The electrode materials have an extremely high influence on the property of the ECs and an appropriate electrode material plays an important role in enhancing the energy density and the range of working potential windows 8 9 10 So far several kinds of porous carbon materials 11 12 13 14 15 have been widely applied in the electrochemical doublelayer 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 But the specific capacitance of the porous carbon materials is lower so it is necessary to improve the specific capacitance by depositing the metal oxides and metal hydroxides on their surface Therefore 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 And as we know αCoOH2 and βCoOH2 are two different crystal structures of CoOH2 compounds and the former has attracted much attention for its outstanding electrochemical performance 18 20 21Coke powder is generally known as the coke particles with an average diameter of less than 5 mm produced in the breaking process of coke and treated as a waste because of its small particle size Nowadays the reuse of coke powder is mainly focused on the treatment of waster water after being activated by alkaline compounds 22 However the coke powder has been rarely employed as electrode material In this study coke powder activated carbons CPAC were prepared by dippingcalcined activation method with the modifier of KOH using coke powder as the raw material 23 and the composite electrode materials CPAC/αCoOH2 were synthesized by the Sol–gel method Moreover the physics and electrochemical performances of the composite electrode materials were systematically investigatedCPAC were prepared according to our previous study 23 Dissolved certain quality of CoCl2·6H2O into 50 mL distilled water and stirred for 30 min at room temperature Then CPAC were added with a little of alcohol and made sure the mass ratio of cobalt respectively was 5 10 20 30 50 wt  After subsequent stirring for 30 min aqueous ammonia 10 wt  was added into each of samples and the pH value was adjusted to between 9 and 10 And after stirring for 6 h and standing for 4 h each of the precipitates was collected by filtration under reduced pressure Finally each of the samples was washed to pH value is 7 with distilled water and dried for 24 h at 80 °C Cooling in the normal temperature samples were fully grinded in the agate mortar respectivelyCPAC/αCoOH2 electrode was composed of composite materials acetylene black and polytetrafluoroethylene PTFE emulsion with a mass ratio of 811 and drops of anhydrous ethanol were added to get paste sample Then the paste sample was filled into a foam nickel with an apparent area of 10 × 10 mm2 dried at 80 °C for 2 h under vacuum and pressed to a sheet at the pressure of 10 MPa for 1–2 min to assure a good electronic contact and to form an effective quadrate coating next drying at 80 °C for 4 hMorphology observation of the composite materials was performed on a FESEM JSM6701F Japan and a XRD D/Max2400 Rigaku Japan technique The electrochemical measurement of electrodes were carried out using an electrochemical working station CHI660B Shanghai China in a three electrode cell at room temperature In the normal three electrode system CPAC/αCoOH2 composite electrode was used as working electrode Furthermore 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

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