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The Cathodic Reaction

The reduction of oxygen is itself a complex electrochemical process. As described in Section 9.2, O2 reduction is considered to proceed along two parallel pathways, the direct four-electron pathway and the peroxide pathway (Eq. 9-9). Both pathways [Pg.312]

If the O2 molecule is adsorbed so that its axis is parallel to the catalyst surface, it divides into adsorbed oxygen atoms these can be reduced and protonated to give water (Fig. 9-9, left side). The right-hand side shows the oxygen molecule adsorbed [Pg.312]

In alkaline solution the peroxide pathway is dominant and relatively fast. Organic or inorganic impurities at the surface favor this pathway. Generally, Pt is the most active catalyst. The reduction kinetics are faster in concentrated KOH or NaOH than in concentrated H3PO4 or H2SO4. At highly dispersed Pt on carbon support, the reduction occurs predominantly via the four-electron pathway. [Pg.313]

In alkaline and neutral solutions silver and carbon are also used as catalysts. In acid electrolytes carbon is not effective for O2 reduction. New ways for oxygen reduction catalysis have been offered via the interaction of O2 with transition metal complexes, as demonstrated for the face-to-face Co-Co-4 porphyrin and a number of transition metal macrocycles on earbon, graphite, or metal substrates. Heat treatment at 700-1200 K of macroeyeles such as cobalt tetramethoxyphenyl porphyrin (Co-TMPP) and Fe-(TMPP) improve the activity in alkaline and acid media, respectively. [Pg.313]


If two redox electrodes both use an inert electrode material such as platinum, tlie cell EMF can be written down iimnediately. Thus, for the hydrogen/chlorine fiiel cell, which we represent by the cell Fl2(g) Pt FICl(m) Pt Cl2(g) and for which it is clear that the cathodic reaction is the reduction of CI2 as considered in section... [Pg.602]

It should be pointed out that external polarization differs from the unbiased (open circuit) case in that after application of, say, an anodic voltage only the oxidation reaction takes place on the metal, whereas the cathodic reaction (H — H2) occurs at the external counter-electrode. [Pg.2720]

The cathodic reaction (the right-hand cell) is the reduction of Fe + to Fe +... [Pg.468]

Chloiine is pioduced at the anode in each of the three types of electrolytic cells. The cathodic reaction in diaphragm and membrane cells is the electrolysis of water to generate as indicated, whereas the cathodic reaction in mercury cells is the discharge of sodium ion, Na, to form dilute sodium amalgam. [Pg.482]

Most of the voltage savings in the air cathode electrolyzer results from the change in the cathode reaction and a reduction in the solution ohmic drop as a result of the absence of the hydrogen bubble gas void fraction in the catholyte. The air cathode electrolyzer operates at 2.1 V at 3 kA/m or approximately 1450 d-c kW-h per ton of NaOH. The air cathode technology has been demonstrated in commercial sized equipment at Occidental Chemical s Muscle Shoals, Alabama plant. However, it is not presentiy being practiced because the technology is too expensive to commercialize at power costs of 20 to 30 mils (1 mil = 0.1 /kW). [Pg.500]

The mechanism of the cathode reaction for all three types of Mn02 can best be described by two approximately one-electron steps. [Pg.521]

In a battery, the anode and cathode reactions occur ia different compartments, kept apart by a separator that allows only ionic, not electronic conduction. The only way for the cell reactions to occur is to mn the electrons through an external circuit so that electrons travel from the anode to the cathode. But ia the corrosion reaction the anode and cathode reactions, equations 8 and 12 respectively, occur at different locations within the anode. Because the anode is a single, electrically conductive mass, the electrons produced ia the anode reaction travel easily to the site of the cathode reaction and the 2iac acts like a battery where the positive and negative terminals are shorted together. [Pg.524]

Zinc—Silver Oxide Batteries. Miniature 2inc—silver oxide batteries have a 2inc anode, and a cathode containing silver oxide [20667-12-3] Ag20. The cathode reaction... [Pg.530]

The cathode reaction involves reduction of silver oxide to metallic silver [7440-22-4J. The reaction is a two-phase, heterogeneous reaction producing a substantially constant voltage during discharge. Some manganese dioxide may be added to the cathode, as in the case of mercury oxide cells. [Pg.530]

The cathodic reaction is the reduction of iodine to form lithium iodide at the carbon collector sites as lithium ions diffuse to the reaction site. The anode reaction is lithium ion formation and diffusion through the thin lithium iodide electrolyte layer. If the anode is cormgated and coated with PVP prior to adding the cathode fluid, the impedance of the cell is lower and remains at a low level until late in the discharge. The cell eventually fails because of high resistance, even though the drain rate is low. [Pg.535]

In electro winning, the cathode reaction is the same as for electrorefining (see eq. 31). However, because of the use of insoluble anodes, oxygen is released at the anode. [Pg.207]

The ions, M , formed by this reaction at a rate, may be carried into a bulk solution in contact with the metal, or may form insoluble salts or oxides. In order for this anodic reaction to proceed, a second reaction which uses the electrons produced, ie, a reduction reaction, must take place. This second reaction, the cathodic reaction, occurs at the same rate, ie, = 7, where and are the cathodic and anodic currents, respectively. The cathodic reaction, in most cases, is hydrogen evolution or oxygen reduction. [Pg.274]

P is a symmetry factor equal to the fraction of the potential that promotes the cathodic reaction. The reaction rate and current are related through Faraday s law... [Pg.64]

The cathode reaction is the reduction of water to produce hydrogen (eq. 8). The mechanism of the anodic deposition of Mn02 has been investigated (44,47). [Pg.77]

Thus, hydrogen gas is generated in most acid solutions. If dissolved oxygen is present, the cathodic Reaction 7.2 can be accelerated by depolarization as in Reaction 7.3 ... [Pg.160]

Iron atoms pass into solution in the water as Fe leaving behind two electrons each (the anodic reaction). These are conducted through the metal to a place where the oxygen reduction reaction can take place to consume the electrons (the cathodic reaction). This reaction generates OH ions which then combine with the Fe ions to form a hydrated iron oxide Fe(OH)2 (really FeO, H2O) but instead of forming on the surface where it might give some protection, it often forms as a precipitate in the water itself. The reaction can be summarised by... [Pg.226]

Because of the high oxidizing potential of Cr +, the cathodic reaction becomes reduction of the hexavalent chrome to the corresponding trivalent state, instead of reduction of water to form hydroxide ions and hydrogen [30-32]. [Pg.440]

In the systems illustrated in Figure 53.1, the anodic reaction has to be electrically balanced by the cathodic reaction, since electrical charge cannot build up at any location. A continuous electrical circuit is required through the metal (for electron conduction) and the environment (for ionic conduction). [Pg.890]

It must be emphasised that although, the rate of anodic dissolution of iron increases with,increase in. pH this will not necessarily apply to the corrosion rate which will be dependent On a number of other. factors, e.g. the thermodynamics and kinetics of the cathodic reaction, film formation, etc. [Pg.105]

Fig. 1.41 Schematic anodic polarisation curves for a passivatable metal showing the effect of a passivating agent that has no specific cathodic action, but forms a sparingly soluble salt with the metal cation, a without the passivating agent, b with the passivating agent. The passive current density, the active/passive transition and the critical current density are all lowered in b. The effect of the cathodic reaction c, is to render the metal active in case a, and passive... Fig. 1.41 Schematic anodic polarisation curves for a passivatable metal showing the effect of a passivating agent that has no specific cathodic action, but forms a sparingly soluble salt with the metal cation, a without the passivating agent, b with the passivating agent. The passive current density, the active/passive transition and the critical current density are all lowered in b. The effect of the cathodic reaction c, is to render the metal active in case a, and passive...
In Section 1.4 it was pointed out that a fundamental principle of corrosion is that the sum of the rates of the cathodic reactions must equal the sum of the rates of the anodic reactions, irrespective of whether the attack is uniform or localised ... [Pg.154]


See other pages where The Cathodic Reaction is mentioned: [Pg.2731]    [Pg.488]    [Pg.500]    [Pg.521]    [Pg.522]    [Pg.528]    [Pg.528]    [Pg.531]    [Pg.531]    [Pg.532]    [Pg.533]    [Pg.534]    [Pg.536]    [Pg.275]    [Pg.277]    [Pg.282]    [Pg.283]    [Pg.2032]    [Pg.31]    [Pg.51]    [Pg.1328]    [Pg.891]    [Pg.891]    [Pg.85]    [Pg.97]    [Pg.120]    [Pg.120]    [Pg.138]    [Pg.140]    [Pg.160]   


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