Cathodes oxygen electrode

These main objectives can be reached only by modifying the structures and compositions of primarily the anode (methanol electrode) and secondarily the cathode (oxygen electrode) as discussed in Sections 111 and IV, respectively. In addition. Section IV discusses the conception of new proton exchange membranes with lower methanol permeability in order to improve the cathode characteristics. Section V deals with the progress in the development of DMFCs, while in Section VI the authors attempt to make a prognosis on the status of DMFC R D and its potential applications. 

Pandard P, Rawson DM. An amperometric a al biosensor for herbicide detection employing a carbon cathode oxygen electrode. Environ Toxicol and Water Quality 1993 8 323-333. 

The cathode (oxygen electrode) must provide a common interface for the oxygen and the electrolyte, catiyze the oxygen reduction reaction, and conduct electrons from the external circuit to the oxygen electrode reaction site. 

Cathode—the electrode of an electrolytic cell where reduction takes place. During corrosion, this is the area at wliich metal ions do not enter the solution. During cathodic reactions, cations take up electrons and discharge them, hence reducing oxygen. That is, there is a reduction from a higlier to a lower state of valency. 

It is so universally applied that it may be found in combination with metal oxide cathodes (e.g., HgO, AgO, NiOOH, Mn02), with catalytically active oxygen electrodes, and with inert cathodes using aqueous halide or ferricyanide solutions as active materials ("zinc-flow" or "redox" batteries). The cell (battery) sizes vary from small button cells for hearing aids or watches up to kilowatt-hour modules for electric vehicles (electrotraction). Primary and storage batteries exist in all categories except that of flow-batteries, where only storage types are found. Acidic, neutral, and alkaline electrolytes are used as well. The (simplified) half-cell reaction for the zinc electrode is the same in all electrolytes ... 

Cells of cylindrical geometry are produced mainly in four sizes D (LR-20), C (LR-14), AA (LR-6), and AAA (LR-03). The two other alkaline cells in this section (using HgO or an oxygen electrode as cathode) are almost exclusively produced as small button cells. 

Oxygen anions are thus now attracted to the electrode with the positive charge or the electrode which has been made positive by anodic polarization. Backspillover will continue untill the charge is neutralized. Similarly oxygen anions will be repelled from the negatively charged or cathodically polarized electrode to enter into the YSZ structure. The charges q+ and q. thus disappear and thus TV and TV vanish. 

Figure 13. Comparison of oxygen electrode performance in H2-02 PEMFC and DMFC ( ) potential of the H2-O2 PEMFC cathode, (o) potential of the DMFC cathode, (A) DMFC cell potential.

Similar size effects have been observed in some other electrochemical systems, but by far not in all of them. At platinized platinum, the rate of hydrogen ionization and evolution is approximately an order of magnitude lower than at smooth platinum. Yet in the literature, examples can be found where such a size effect is absent or where it is in the opposite direction. In cathodic oxygen reduction at platinum and at silver, there is little difference in the reaction rates between smooth and disperse electrodes. In methanol oxidation at nickel electrodes in alkaline solution, the reaction rate increases markedly with increasing degree of dispersion of the nickel powders. Such size effects have been reported in many papers and were the subject of reviews (Kinoshita, 1982 Mukerjee, 1990). 

An example for a compound of the perovskite type is LaNiOj. In other com-ponnds of the perovskite type, nickel may be replaced by cobalt or iron, and lan-thannm in part by alkaline-earth metals, an example being Lag 8Sro2Co03. The activity of perovskites toward cathodic oxygen reduction is low at room temperature but rises drastically with increasing temperature (particularly so above 150°C). In certain cases the activity rises so much that the equilibrium potential of the oxygen electrode is established. 

The laboratory unit was based on a ElectroCell MP cell with an elec-trode/membrane area of 0.01 m2. A DSA (Dimensionally Stable Anode) anode served as oxygen electrode, Ni as cathode. Anion exchange membranes = Neosepta ACM (Tokuyama Soda) AMH cation ex-change membranes = Nafion 324 Nation 902. 

Electrode A is called the anode because the anodic reaction is favored over the cathodic reaction. In a fuel cell, the anodic oxidation of H2 is favored. The corresponding reaction at the cathode, electrode B, is the cathodic oxygen reduction reaction,... 

In addition, in a DAFC, the proton exchange membrane is not completely alcohol tight, so that some alcohol leakage to the cathodic compartment will lead to a mixed potential with the oxygen electrode. This mixed potential will decrease further the cell voltage by about 0.1-0.2 V. It turns out that new electrocatalysts insensitive to the presence of alcohols are needed for the DAFC. 

Wendt, H. and Plzak, V. (1990) Electrode kinetics and electrocatalysis of hydrogen and oxygen electrode reactions. 2. Electrocatalysis and electrocatalysts for cathodic evolution and anodic oxidation of hydrogen, in Electrochemical Hydrogen Technologies (ed. H. Wendt), Elsevier, Amsterdam, Chapter 1. 2. 

An approach similar to this avoids the use of a comparative nohle metal electrode and neglects overpotential losses at the electrodes. In this method, the potential applied at the hydrogen (or oxygen) electrode (in a three electrode configuration) is compared with the potential generated at an ideal fuel cell anode (or cathode). In the case of a n-type semiconductor photoanode ... 

M Ag, in order to calculate the self-dissociation constants. Since alkali oxides are extremely difficult to prepare in the pure state and to handle, it was decided to produce the oxide ion coulometrically. Consequently, a known current of approximately 8 microamp. was run through the cell, the oxygen electrode acting as the cathode. The current was drawn from an electronically controlled constant current device and timed so that the number of equivalents of charge passing could be calculated. This was assumed to be the number of oxide ions produced. The variation in potential with oxide ion followed the Nernst expression very precisely. 

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