Inert electron-conducting electrodes

Inert electron-conducting electrodes (Pt, Au, graphite, etc., in certain solutions), for example ... 

This kind of source has the advantages of the fixed chemical potential of sodium, good contact between liquid sodium and the solid electrolyte, and no additional electronic conducting electrode is needed as the counter electrode (C) to connect with the external electric circuit. In practice, elemental sodium is too active, and a very tight seal is required to prevent sodium vapor from migrating and reacting chemically with CO and in the sink vapor phase. Consequently, the system setup becomes more complex. The choice of the source in the current study is a combination of Na COj, CO and O2 gas phase, and an inert Pt counter... 

Crystalline powders agglomerated under pressure or with a suitable inert binder (measurements of CP, Br , P, Pb, Ag+ and CN ) provide other mineral membranes. The internal electrolyte can be eliminated (by dry contact). However it is preferable to insert a polymer layer with a mixed-type conductivity to ensure the passage of electrons from the ionic conductivity membrane towards the electronic conductivity electrode (Figure 19.3). 

While in the experiments described so far both ionic and electronic species are transferred, it is also possible to determine the partial electronic conductivity by using ionically blocking electrodes to suppress the ionic transport so that only electrons and holes can pass. This technique is known as the asymmetric polarization or Hebb-Wagner technique. By using a chemically inert electronic conducting material, no ions will be delivered to the electrolyte when a voltage is applied with such a polarization that the mobile ions tend to be depleted at the inert electrode. An electrode used on the other side fixes the chemical potential of the mobile component of the electrolyte by the applied voltage at that phase boundary. 

Since model compounds reveal well-defined cyclic voltammograms for the Cr(CNR)g and Ni(CNR)g complexes (21) the origin of the electroinactivity of the polymers is not obvious. A possible explanation (12) is that the ohmic resistance across the interface between the electrode and polymer, due to the absence of ions within the polymer, renders the potentially electroactive groups electrochemically inert, assuming the absence of an electronic conduction path. It is also important to consider that the nature of the electrode surface may influence the type of polymer film obtained. A recent observation which bears on these points is that when one starts with the chromium polymer in the [Cr(CN-[P])6] + state, an electroactive polymer film may be obtained on a glassy carbon electrode. This will constitute the subject of a future paper. 

The ideal battery separator would be infinitesimally thin, offer no resistance to ionic transport in electrolytes, provide infinite resistance to electronic conductivity for isolation of electrodes, be highly tortuous to prevent dendritic growths, and be inert to chemical reactions. Unfortunately, in the real world the ideal case does not exist. Real world separators are electronically insulating membranes whose ionic resistivity is brought to the desired range by manipulating the membranes thickness and porosity. 

The O2/H2O system is very slow so that the exchange current a I equilibrium is extremely low (10 /10 A cm 2) as a consequence, any other reaction at the electrode will hamper its study and that could be the reaction of impurities or other redox reactions involving the electrode itself. The so-called noble metals are not really inert and do interact with oxygen a platinum surface in contact with an O saturated solution adsorbs oxygeti as an electronically conducting monolayer but can be further oxidized to PIO, PtO . A detailed analysis of these phenomena, which falls outside the scope of the present review, can be found elsewhere [311. A platinum electrode, when a complete electronically conducting monolayer of I l—O is formed at the surface of the metal, behaves as an ideally inert electrode in such conditions, rest potentials dependent on pO2 and pH can be measured during a few hours, close to... 

The anode and cathode should be stable in the electrolysis medium, allow the desired oxida-tion/reduction reactions at the highest possible rates with miiumal by-product formation, and be of reasonable cost. In actuality, the electrodes may corrode or undergo physical wear during reactor operation, which may limit their lifetime. Often, if an expensive electrode material is needed for a given reaction, it can be plated or physically coated on a less costly, inert, and electronically conducting substrate. Common anode and cathode materials are listed in Table 26.8. 

This is a reduction reaction because the positively charged metal ions have gained electrons, lost their charge, and become neutral atoms. The neutral atoms deposit on the electrode, a process called electrodeposition. This electrode is termed a cathode. At the cathode, reduction of an electroactive species takes place. An electroactive species is one that is oxidized or reduced during reaction. Electrochemical cells also contain nonelectroactive (or inert) species such as counterions to balance the charge, or electrically conductive electrodes that do not take part in the reaction. Often these inert electrodes are made of Pt or graphite, and serve only to conduct electrons into or out of the half-cell. 

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