Electrochemical equivalents series

Argention.—Silver forms a colourless, univalent ion. Its electrochemical equivalent in milligrams per coulomb is given as 1-1172,10 1-1180,11 1-11827,12 1-11829,18 1-1188,14 and 1-1198.18 In the potential series the metal occupies a position intermediate between mercury and platinum. In correspondence with its low electroaffinity it exhibits a strong tendency to form complex ions. The ionic conductivity of silver at 18° C. is 54-0, and at 25° C. 63-4. 

A further series of five experiments was made to determine the ratio of the electrochemical equivalents of gold and silver, by passing the same quantity of electricity through solutions of potassium aurocyanide,... 

During the period 1831 through 1855 Faraday published a number of series of articles, Experimental Researches in Electricity, in the Philosophical TransaC tions of the Royal Society. Partington notes that the major studies of electrolysis and the galvanic cell appeared between 1833 and 1840. The most important discovery of these was the electrochemical equivalent ... 

As fully discussed in Chapter 2, the electrolyte has complex interactions with the electrode materials (active components) of electrochemical supercapacitors (ESs), which play an important role in the performance of ESs. Besides the active component of ESs, the compatibility or possible interaction between the electrolyte and inactive components such as current collectors, binders, and separators should also be considered. For example, the possible corrosion of current collectors in certain electrolytes could reduce the operative cell voltage and decrease the lifetime of ESs. Besides, the transfer of electrolyte ions across the separator could affect the equivalent series resistance (ESR) and the power performance of the ES. Therefore, the inactive components of ESs should be compatible with the electrolytes and electrode materials. 

In this chapter, both electrochemical and physical instrument characterizations for ES materials, components, and performance are discussed. Conventional three-electrode and two-electrode testing cells and their associated design and fabrication techniques for electrochemical characterization of supercapacitors in terms of equivalent series resistance, capacitance, and pseudocapacitance are presented. 

The electrochemical resistances ESR (equivalent series resistance) and EDR (equivalent diffusion resistance) evaluated using electrochemical impedance spectroscopy (EIS) measurements clearly demonstrate that according to the nature of the anion, the mechanism of ion adsorption can be described by pure double-layer adsorption at the specific surface, or by the insertion of desolvated ions into the... 

The impedance data have been usually interpreted in terms of the Randles-type equivalent circuit, which consists of the parallel combination of the capacitance Zq of the ITIES and the faradaic impedances of the charge transfer reactions, with the solution resistance in series [15], cf. Fig. 6. While this is a convenient model in many cases, its limitations have to be always considered. First, it is necessary to justify the validity of the basic model assumption that the charging and faradaic currents are additive. Second, the conditions have to be analyzed, under which the measured impedance of the electrochemical cell can represent the impedance of the ITIES. 

An important area of application of electrolysis is separation and co-deposition. If several ions exist together in an electrolytic solution in a cell, and the voltage is gradually raised from zero, the first metal to be plated is the lowest in the electrochemical series, provided that the ionic concentrations of the different metals are equivalent. As the voltage is increased, the metals which become plated move progressively towards the top of the series. 

To evaluate the magnitude of capacitive currents in an electrochemical experiment, one can consider the equivalent circuit of an electrochemical cell. As illustrated in Figure 24, in a simple description this is composed by a capacitor of capacitance C, representing the electrode/solution double layer, placed in series with a resistance R, representing the solution resistance. 

Figure 5.10 is EIS of marmatite electrode in O.lmol/L KNO3 solution with different pH modifiers at open circuit potential. This EIS is very complicated. Simple equivalent circuit can be treated as the series of electrochemical reaction resistance R with the capacitance impedance Q == (nFr )/(icR ) resulting fi-om adsorbing action, and then parallel with the capacitance Ca of double electric... 

The rate of dE/dt is always kept constant during a potential scan, although obtaining a series of polarograms as a function of v can be extremely informative. (The variation of the sweep rate can be regarded as being equivalent to a variation of varying the time-scale of observation of an electrochemical experiment, as will become clear later in Section 6.4.3.)... 

The voltammetric reduction of a series of dialkyl and arylalkyl disulfides has recently been studied in detail, in DMF/0.1 M TBAP at the glassy carbon electrode The ET kinetics was analyzed after addition of 1 equivalent of acetic acid to avoid father-son reactions, such as self-protonation or nucleophilic attack on the starting disulfide by the most reactive RS anion. Father-son reactions have the consequence of lowering the electron consumption from the expected two-electron stoichiometry. Addition of a suitable acid results in the protonation of active nucleophiles or bases. The peak potentials for the irreversible voltammetric reduction of disulfides are strongly dependent on the nature of the groups bonded to the sulfur atoms. Table 11 summarizes some relevant electrochemical data. These results indicate that the initial ET controls the electrode kinetics. In addition, the decrease of the normalized peak current and the corresponding increase of the peak width when v increases, point to a potential dependence of a, as discussed thoroughly in Section 2. 

In drawing an appropriate equivalent circuit, it is clear that the resistance of the solution should be placed first in the intended diagram, but how should the capacitative impedance be coupled with that of the interfacial resistance One simple test decides this issue. We know that electrochemical interfaces pass both dc and ac. It was seen in Eq. (7.103) that for a series arrangement of a capacitor and a resistor, the net resistance is infinite for = 0, i.e., for dc. Our circuit must therefore have its capacitance and resistance in parallel for under these circumstances, for = 0, a direct current can indeed pass the impedance has become entirely resistive.51... 

---