Electrochemical double layer capacitors electric equivalent circuit

The first step in developing an equivalent electrical circuit for an electrochemical system is to analyze the nature of the overall current and potential. For example, in the simple case of the uniformly accessible electrode shovm in Figure 9.1(a), the overall potential is the sum of the interfacial potential V plus the Ohmic drop Rgi. Accordingly, the overall impedance is the sum of the interfacial impedance Zo plus the electrolyte resistance Re- At the interface itself, shown in Figure 9.1(b), the overall current is the sum of the Faradaic current if plus the charging current I c through the double layer capacitor C. Thus, the interfacial impedance results from the double-layer capacity in parallel with the Faradaic impedance Zf. 

EIS data are analysed by fitting them to an equivalent electrical circuit model consisting of resistors, capacitors, and inductors. The working electrode interface undergoing an electrochemical reaction is analogous to an electronic circuit and can be characterised as an electrochemical system in terms of equivalent circuit. Typical circuits are shown in Figs. 1.10, 1.11, 1.12 and 1.13 where is admittance (ohm-cm ),Cf is double-layer capacitance and a is the exponents [114]. (/ .E Reference Electrode and W Working Electrode)... 

To a first approximation, the BLM can be considered to behave like a parallel plate capacitor immersed in a conducting electrolyte solution. In reality, even such a thin insulator as the modified BLM (designated by and R, in Fig. 108) could block the specific adsorption of some species from solution and/or modify the electrochemical behavior of the system. Similarly, System C may turn out to be a semiconductor(l)-insulator-semiconductor(2) (SIS ) rather than a semiconductor(l)-semiconductor(2) (SS ) junction. The obtained data, however, did not allow for an unambiguous distinction between these two alternative junctions we have chosen the simpler of the two [652], The equivalent circuit describing the working (Ew), the reference (Eg), and the counter (Ec) electrodes the resistance (Rm) and the capacitance (C of the BLM the resistance (R ) and capacitance (Ch) of the Helmholtz electrical double layer surrounding the BLM as well as the resistance of the electrolyte solution (RSO ) is shown in Fig. 108a [652],... 

The second meaning of the word circuit is related to electrochemical impedance spectroscopy. A key point in this spectroscopy is the fact that any -> electrochemical cell can be represented by an equivalent electrical circuit that consists of electronic (resistances, capacitances, and inductances) and mathematical components. The equivalent circuit is a model that more or less correctly reflects the reality of the cell examined. At minimum, the equivalent circuit should contain a capacitor of - capacity Ca representing the -> double layer, the - impedance of the faradaic process Zf, and the uncompensated - resistance Ru (see -> IRU potential drop). The electronic components in the equivalent circuit can be arranged in series (series circuit) and parallel (parallel circuit). An equivalent circuit representing an electrochemical - half-cell or an -> electrode and an uncomplicated electrode process (-> Randles circuit) is shown below. Ic and If in the figure are the -> capacitive current and the -+ faradaic current, respectively. 

Immittance — In alternating current (AC) measurements, the term immittance denotes the electric -> impedance and/or the electric admittance of any network of passive and active elements such as the resistors, capacitors, inductors, constant phase elements, transistors, etc. In electrochemical impedance spectroscopy, which utilizes equivalent electrical circuits to simulate the frequency dependence of a given elec-trodic process or electrical double-layer charging, the immittance analysis is applied. 

Although simple impedance measurement can tell the existence of an anodic film, electrochemical impedance spectroscopy (EIS) can obtain more information about the electrochemical processes. In general, the anode/electrolyte interface consists of an anodic film (under mass transport limited conditions) and a diffuse mobile layer (anion concentrated), as illustrated in Fig. 10.13a. The anodic film can be a salt film or a cation (e.g., Cu ) concentrated layer. The two layers double layer) behave like a capacitor under AC electric field. The diffuse mobile layer can move toward or away from anode depending on the characteristics of the anode potential. The electrical behavior of the anode/electrolyte interface structure can be characterized by an equivalent circuit as shown in Fig. 10.13. Impedance of the circuit may be expressed as... 

---