correct and refolmulate:“The areal capacitance the three simples micro-supercapacitors with different scan rates 0.1, 0.5, and 3 mV/s have been calculated using equation (1). Fig. 6C shows areal capacitances as a function of scan rates (5-200 mV/s ) for all samples. In all the samples areal capacitance decreases with increasing scan rate from 10 mVs-1 to 200 mVs-1. The areal capacitance of micro-supercapacitor increases with decrease in scan rate because as scan rate decreases the electrolyte ions has longer time to enter in the bulk of electrode surface, but at higher scan rate electrolyte ion movement limited to solely surface of electrode (ref). The areal capacitances of 0.1; 0.5, and 3 mV/s are 38 mF cm-2 , 16 mF cm-2, and 17 mF cm-2, obtained at scan rate of 50 mVs-1. These value for the areal capacitance is much higher than bulk CuO supercapacitor (0.12 - 25 mF cm-2) (ref) and several carbon based microsupercapacitors such as porous carbon (1.5-3.5 mF cm-2 ) ref, onion like carbon (1.7 mF cm-2) ref, copper oxide nanosheet (0.12 mF cm−2) ref. reduced graphene (0.08 mFcm-2), laser scribed graphene (2.32 mF cm-2) and laser written reduced graphene (0.51 mF cm-2 ). The obtained specific capacitance values are comparable with or better than several oxide based micro-supercapacitor such as VN-NiO (1.85 mFcm-2), hydrous RuO2 (40.7 mF cm-2) , MnO2 (56.3 mF cm-2) and NPG/ MnO2 ( 7.1 mF cm-2).
Galvanostatic charge-discharge (GCD) procedure was used to evaluate the electrochemical performance of the three simple micro-supercapacitor. Fig.7A shows GCD curves of micro-supercapacitors at 1 mAcm-2 in potential range of 0.3V to 0.8V. The nonlinear shape of GCD curves (Fig. 7A) reveals the features of pseudocapacitance, which are in conformity with the result of the CV curves (Fig 6A). The capacitance obtained from GCD at 2 mA cm−2 are 31 mF cm−2, 10 mF cm−2, and 8 mF cm−2 for nanostructures grown at 0.1 mVs−1, 0.5 mV s−1, and 3 mVs−1, respectively, in good agreement with the CV results. The specific capacitance calculated by GCD at different current densities, 2 to 20 mA cm−2, is shown in Fig. 11.(f). The maximum specific capacitance of 31 mF cm−2 is obtained at 2 mA cm−2 in the case of the sample obtained at 0.1 mV s−1, which is in agreement with the specific capacitance calculated from the cyclic voltammetry. The higher specific capacitance values at lower current densities are attributed to the longer time available to the electrolyte ions to access the bulk of the active electrode materials and lower potential drop compared to higher current density [ref]. This significant difference in the specific capacitance can be attributed to the difference in the morphology of surface of the three simple. The morphology may affect the specific capacitance of copper oxide in three aspects: the electrical resistance, the electrolyte diffusion within CuO nanostructures and the specific surface area of CuO [29]. The bundle-like Cu(OH)2 is longer and thus have larger electrical resistance than nanocube/bandle-like Cu2O/Cu(OH)2. The increasing order of the specific capacitance (nanocub/bundle-like Cu2O/Cu(OH)2 < bundl-like Cu(OH)2) was consistent with increasing sequence of Cu(OH)2 specific surface area, indicating that the highly mesoporous structure and high specific surface area of the electrode facilitates the ions to transfer into the porous structure more easily which would lead to more redox faradic reactions and surface adsorption of electrolyte cations.”