Abstract
Mn oxide and/or Co oxide are deposited on flexible carbon cloth by a cathodic potentiodynamic procedure from their respective sulfates. In KOH electrolyte, the charge stored from reversible redox reactions of the two oxides (battery response) overlaps with the charge stored from the double layer of the carbon cloth (supercapacitor response). These charges or capacities are compared. For the electrodes having one oxide only, either Mn or Co oxide, the highest capacity is obtained for 8 wt% oxide load. To overcome this limitation, both Mn and Co oxide are simultaneously or sequentially electrodeposited on carbon cloth over a broad compositional range. The electrode capacity can reach 71 mA·h·g−1 or 0.9 mA·h· cm−2, which are higher than the values found for the bare carbon cloth. The electrode capacity depends on the relative content of the carbon cloth and the two deposited oxides according to the rule of mixtures. The decrease of the specific surface area of the carbon cloth is discussed in relation to the deposited oxide. The high capacity retention vs current is due to the contribution of the carbon cloth substrate. The electrode cycle life is discussed on the basis of the supercapacitor response and battery one.
Highlights
Co oxide, usually identified as the spinel Co3O4, has been considered as another active electrode material for supercapacitors since the pioneer works[42,43] despite its electrochemical response in KOH electrolyte is dominated by a battery behavior.[44]
The cyclic voltammetries (CVs) of the bare carbon cloth (CC) is included. It shows a nearly rectangular shape from −0.8 to 0.1 V vs. Hg/HgO that can be ascribed to a response of electrochemical double layer capacitor; the low intense and very broad peak at ca. −0.4 V suggests a pseudo capacitance in addition to the double layer capacitance
The CV of the Mn sample shows two oxidation peaks in charge, at ca. −0.25 and 0 V, and two reduction peaks in discharge, at ca. −0.35 and −0.05 V. These peaks, which are ascribed to Mn3+-Mn4+ redox reactions in 1M KOH electrolyte,[26,30] differs from the nearly rectangular CV of the Mn oxide in Na2SO4 electrolyte.[2,3]
Summary
Usually identified as the spinel Co3O4, has been considered as another active electrode material for supercapacitors since the pioneer works[42,43] despite its electrochemical response in KOH electrolyte is dominated by a battery behavior.[44]. The aim of this work is to study the effect of the deposited Mn and/or Co oxide on the charge or capacity of the electrodes. The limitation in capacity of electrodes having one oxide only is overcome by depositing two oxides. They are simultaneously or sequentially electrodeposited on carbon cloth. The material used as scaffold or substrate is an activated carbon cloth (CC) of 0.57 mm thick (Figure 1a) manufactured by Carbongen SA. The specific surface area of 1100 m2 g−1 derives from the presence of micropores with an average size of 1.7 nm and mesopores below 3–4 nm. The porosity of the pristine carbon cloth and the oxide-deposited samples was studied by N2 adsorption at 77 K (Micromeritics ASAP 2010).
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