Electrodes charge condition

Electrodes. A number of different types of nickel oxide electrodes have been used. The term nickel oxide is common usage for the active materials that are actually hydrated hydroxides at nickel oxidation state 2+, in the discharged condition, and nickel oxide hydroxide [12026-04-9] NiO OH, nickel oxidation state 3+, in the charged condition. Nickelous hydroxide [12034-48-7J, Ni(OH)2, can be precipitated from acidic solutions of bivalent nickel... 

In order to establish safe values for velocity-diameter product, various studies have been made to determine the minimum liquid surface potential that will result in an incendive discharge in the presence of a grounded electrode. Studies reviewed in [8] showed that for credible charging conditions, liquids must be negatively charged to yield incendive bmsh discharges. The consensus has been that to avoid incendive discharges the maximum liquid... 

In acid electrolytes, carbon is a poor electrocatalyst for oxygen evolution at potentials where carbon corrosion occurs. However, in alkaline electrolytes carbon is sufficiently electrocatalytically active for oxygen evolution to occur simultaneously with carbon corrosion at potentials corresponding to charge conditions for a bifunctional air electrode in metal/air batteries. In this situation, oxygen evolution is the dominant anodic reaction, thus complicating the measurement of carbon corrosion. Ross and co-workers [30] developed experimental techniques to overcome this difficulty. Their results with acetylene black in 30 wt% KOH showed that substantial amounts of CO in addition to C02 (carbonate species) and 02, are... 

In the analysis of molecular capacitors, the diffuse layer and elastic capacitors, we have always assumed that the electrode charge density a could be controlled. Under such conditions it is generally possible for C to become negative while the system remains stable. For example, contraction of the gap z in an elastic capacitor proceeds smoothly with cr growing until the plates come in contact, while C becomes negative for z < 2/3. At the same time, as shown in Section II for an EC connected to a battery, the EC collapses after z 0.6 is reached. How can these seemingly contradictory results be reconciled And how can cr-control be related to reality Is C < 0 observable These questions are addressed in this section. 

The question of the allowed sign of C was and remains a topic of discussion with significant contradictions. We suggest here that a major reason for these contradictions is that theoretical calculations for electrified interfaces are more easily carried out assuming a uniform electrode charge. Most studies have used this condition and, on some occasions, the restriction of cr-control took its toll. And those were exactly the situations where negative capacitance was predicted. 

Under real conditions it is very difficult to fulfil the condition of constant electrode charge after disconnecting the external source. For example, a negatively charged electrode is discharged by the reduction of traces of impurities such as metal ions or oxygen. 

Thin-film ideal or Nemstian behavior is the starting point to explain the voltammetric behavior of polyelectrolyte-modified electrodes. This condition is fulfilled when (i) the timescale of the experiment is slower than the characteristic timescale for charge transport (fjD pp, with Ithe film thickness) in the film, that is all redox within the film are in electrochemical equibbrium at any time, (ii) the activity of redox sites is equal to their concentration and (iii) all couples have the same redox potential. For these conditions, anodic and cathodic current-potential waves are mirror images (zero peak splitting) and current is proportional to the scan rate [121]. Under this regime, there exists an analytical expression for the current-potential curve ... 

As described in the theoretical section of this book, an electrochemical reaction consists of different steps, and each of these steps (transport and/or charge-transfer steps) can be rate determining. In this section, it is explained why it is not possible to obtain a purely transport-controlled oxidation reaction for sulphite as outlined in the previous section. This is caused by the platinum electrode surface condition that has a large influence on the electron-transfer rate. Therefore, the electrochemical behaviour of the electrode surface itself is described first and limited to observations made during oxidation of dithionite and sulphite. 

Under closed-circuit conditions, the electrochemical reactions involve a number of sequential steps, including adsorption/desorption, surface diffusion of reactants or products, and the charge transfer to or from the electrode. Charge transfer is restricted to a narrow (almost one-dimensional) three-phase boundary (tpb) among the gaseous reactants, the electrolyte, and the electrode-catalyst. 

In 1970, Lambla et al. published the first report on this type of polymerisation and specified that with a potential difference of about 5 kv between the submerged electrodes, separated by a distance of 5 mm, the cationic polymerisation of liquid styrene took place both with the tipped electrode charged positively or negatively. They also underlined the necessity of purifying the monomer as thorou y as possible in order to obtain good and reproducible yields. In 1971, Brendl also described the polymer-isaticHi of liquid styrene under similar conditions and diseased the effect of such param-... 

Another indicator of specific adsorption of charged species is the Esin-Markov effect, which is manifested by a shift in the PZC with a change in electrolyte concentration (33). Table 13.3.2 provides data compiled by Grahame (2). The magnitude of the shift is usually linear with the logarithm of electrolyte activity, and the slope of the linear plot is the Esin-Markov coefficient for the condition of = 0. Similar results are obtained at nonzero, but constant, electrode charge densities hence the Esin-Markov coefficient can be written generally as... 

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