Impedance characteristics and electrical double-layer capacitance of composite polystyrene–cobalt–arsenate membrane

In continuation of our previous work with composite polystyrene–cobalt–arsenate (PS–Co–As), we further extended impedance measurements. All calculations reported were extracted from experiments carried out in the frequency range of 1–5 kHz and different concentrations (0.0001 ≤ c(M) ≤ 1) of KCl and NaCl at isothermal temperature (25 ± 0.1 °C). The membrane capacitance and resistance measurements were observed to depend on the concentration and the applied frequency of the electrolyte. The observed capacitances and resistances were used to calculate the membrane resistances (RM), capacitance (CM), reactance (XX), and also derive the impedance (Z). At higher frequencies, the capacitances became low and the impedance decreased with increasing frequency with a corresponding increase in the measured phase angle. On the other hand at the highest frequencies attainable, the phase angle became low. At low frequencies, the phase angle was become independent of the cation, while the impedance showed a clear dependence. The diffused double-layer polarization charge on the geometric capacitor played important role by affecting the overall membrane capacitance. The applied frequencies affected the double-layer capacitance due to the movement of ions across the membrane. At the membrane–electrolyte interface, the electrical double-layer was influenced in addition to being controlled by the transport of ions.