Frequency Response of Electrode Materials in EIS Measurement

Frequency reply of Electrode Materials in EIS MeasurementFurthermore, complementary in influenceation about the frequency resolution of electrode textiles is provided by EIS measurements and one can estimate the electrical capacity changes with the operating frequency.64-65 It is salubrious know that the complex form of content is dependent on frequency, which is specify as follow66-67 (6)where C() is the real part of the complex capacitance and C() is the ideational part of the complex capacitance C() and they ar expressed as formulas (7) and (8)66-67 (7) (8)where Z() and Z() are the respective real and imaginary part of the complex impedance Z(). is the angulate frequency and it is given by =2f. At low frequency, C() corresponds to the capacitance of the electrode material and C() is ascribed to the energy dissipation by an irreversible process that leads to a hysteresis.66-67 Fig. 15 surfaces the real and imaginary part capacitance as a function of frequency for Li-POA P/ERG/GC, POAP/ERG/GC and ERG/GC electrodes. It can be clearly observed that C() gradually decrease with the increase of scan range for each electrode as shown in Fig. 12F, however, the Li-POAP/ERG/GC electrode exhibits slow up deterioration of capacitance referable to fast ion diffusion and transport (Fig. 15A). In addition, the C() of the Li-POAP/ERG/GC electrode approaches saturation at a frequency below 0.01 Hz whereas the C() of POAP/ERG/GC electrode does not show any sign of saturation as low as 0.01 Hz, indicating slow diffusion of electrolyte ions (Figs. 15A and B). Importantly, the repose time constant (0), which is also known as the dielectric relaxation time of the supercapacitor,66, 68 is a figure of deserve of a supercapacitor. This parameter represents one of its discharge char workeristics. It has been analyze for each electrode found on the analysis of complex capacitance. The relaxation time constant, 0 (=1/2f0) can be calculated from the plots of C() and C( ) vs. frequency. From the frequency match to the fractional of the upper limit survey of C(), the relaxation time constant (0) can be determined. The change in the imaginary part of the complex capacitance C() with frequency goes through a maximum at a frequency, f0, from which the value of 0 can be calculated. From Figs. 15A and B, it can be noted that the Li-POAP/ERG/GC electrode shows a clear peak formation while the POAP/ERG/GC electrode has not telescopeed the maximum even at the lowest frequency used in this study. The f0 value of Li-POAP/ERG nanobuilding complex is 3.9810-2 Hz, corresponding to the characteristic relaxation time constant 0 = 3998 ms, which is frequently lower than that of POAP/ERG nanocomposite, revealing fast accessibility of the electrolyte ions for the former nanocomposite. The smaller 0 of the nanocomposite correlates with the discover capacitance retention at high scan rates in the CV measurements. Therefore, lithium intercalated POAP/ERG nanocompo site is a potential promising electrode material for delivering high power and energy. In addition, investigation of the complex capacitance form of the ERG/GC electrode reveals that the C() of this electrode approaches saturation at a frequency below 15.8 Hz, which federal agency that equilibrium ion adsorption can be achieved in 63.3 ms, suggesting most of the electrolyte ions reach the adsorption sites (Fig. 15C). In comparison to Li-POAP/ERG/GC electrode, the smaller value of relaxation time constant (0 = 2.5 ms) correlates with very ultra-fast accessibility of the electrolyte ions for the ERG/GC electrode and the better capacitance retention at high scan rates in the CV measurements which is in good agreement with results obtained from cyclic voltammetric measurements (Fig. 12F, green line).In order to investigate the effects of disparate types of anions on the specific capacitance of POAP/ERG nanocomposite, the modification of the ERG/GC electrodes has been carried out in di fferent acidic solutions containing HNO3, HClO4 and HCl and corresponding lithium salts as supporting electrolyte and subsequently, have been evaluated in the corresponding monomer cede solutions. The cyclic voltammograms of the modified electrodes in presence of different anions are shown in Fig. 16A. Qualitative analysis of total charges associated with the voltammograms recorded in the presence of different anions reveals that the specific capacitance for anions decreases in the direction of K+. In addition, the determine of specific capacitance derived from the cyclic voltammetric (Fig. 16D) and impedance spectroscopic measurements (Figs. 16E and F) do thusly coincide as tabulated in Table 3. Although one can comport the smaller size of Li+ ion to provide facile insertion/ ejection to/from the electroactive film, the greater specific capacitance has been obtained in the presence of Na+. As for studied anions, it has been noted that the trends in direction of ionic mobility and ionic roentgen are going the same way.69-70 Possessing the greatest mobility and the smallest radius have guide to estimation of the greater specific capacitance would be obtained as a consequence of more being intercalated into the POAP/ERG nanocomposite, which is in good agreement with observational results. On the contrary, the trends in ionic mobility 69 and ionic radius 71 contrast with those in hydration enthalpy 70 and hydration number 71 for the studied cations. These inconsistencies have hindered prediction of which cation would be incorporated into the POAP/ERG nanocomposite easily. The obtained specific capacitance value (Table 3) decrease in the order of Na+ Li+ K+ which confirms the facile incorporation of Na+ into the POAP/ERG is more than likely.Along the lines of evaluating of effects of different types of cations and anions on the POAP/ERG nanocomposite, we have examined the extent to which the incorporation of different cations and anions has affected eac h of components of the POAP/ERG nanocomposite. In this case, ERG/GC electrodes have been investigated in different solutions containing different cations and anions. The capacitive air of ERG/GC electrodes in the presence of different cations and anions have been evaluated at 50 mV s-1 as shown in Figs. 17A and B, respectively. The electrodes have presented negligible difference in their current response while have shown typical rectangular make out indicating an excellent capacitive behavior. Therefore, it can be concluded that graphene sheets in the POAP/ERG nanocomposite act as numerous ion-buffering reservoirs and provide for ions shortened diffusion path into the composite which results in the superior electrochemical performance of the nanocomposite.