According to Equation 1, the calculated C s values of ZnO nanorods, pristine Gr sheets, and the graphene-ZnO hybrid electrode are 36, 112, and 156 F g−1, respectively, at a scan rate of 5 mV s−1. The specific capacitance of the graphene-ZnO hybrid electrode was much higher than that of the ZnO nanorods and pristine Gr sheets. Moreover, this value

is higher than that of previously reported. To obtain a more detailed information on the capacitance performance of the as-prepared graphene-ZnO hybrid nanostructure, the CV curves with various scan rates were studied. Figure 4b summed the C s of ZnO, pristine Gr, and graphene-ZnO hybrid electrodes at various scan rates. It can be seen that the Pifithrin-�� mw specific capacitance decreased with an increase in the scan rate from 5 to 500 mV s−1. The reason may be that insufficient time available for ion diffusion and adsorption inside the smallest pores within a large particle at high scan rates

[37]. Moreover, the C s of the graphene-ZnO hybrid electrode was much higher than that of a ZnO and pristine Gr electrodes for all the scan rates tested. Figure 4c shows galvanostatic charge–discharge measurements of the graphene-ZnO hybrid electrode at a constant current density of 2.0 mA cm−2. It can be seen that the curves were linear and exhibited a typical triangular shape even charging/discharging 3-mercaptopyruvate sulfurtransferase for 12,000 s, which indicated good electrochemical capacitive characteristics. The enhanced electrochemical performance find more of the graphene-ZnO hybrid

can be attributed to the sandwiched structure. Here, the Bioactive Compound Library price graphene in the hybrid electrode provides better electronic conductivity and excellent interfacial contact between ZnO and graphene, which results in the fast transportation of electrons throughout the entire electrode matrix [38]. Moreover, it is evident that when the ZnO size is reduced to nanometer dimensions, the surface area and electroactive sites increase, which effectively reduces the diffusion length of the Na+ ion in the electrode matrix [39, 40]. Figure 4 CV curves, specific capacitance, galvanostatic charge–discharge curve, and Nyquist plots of electrodes. (a) CV curves of the as-prepared ZnO, graphene and the graphene-ZnO hybrid electrode at a scan rate of 5 mV s−1 in 0.5 M Na2SO4 electrolyte solution. (b) Specific capacitance of ZnO, pristine graphene, and the graphene-ZnO hybrid electrode at different scan rates calculated from CV curves. (c) Galvanostatic charge–discharge curve of the graphene-ZnO hybrid electrode at a constant current density of 2.0 mA cm−2. (d) Nyquist plots for ZnO, pristine graphene, and the graphene-ZnO hybrid electrode.