Cathodic condition

Research and development efforts have been directed toward improved ceU designs, theoretical electrochemical studies of magnesium ceUs, and improved cathode conditions. A stacked-type bipolar electrode ceU has been operated on a lab scale (112). Electrochemical studies of the mechanism of magnesium ion reduction have determined that it is a two-electron reversible process that is mass-transfer controUed (113). A review of magnesium production is found ia Reference 114. 

In practice, the defect structure of the materials LiJCo, M)02 and Lix(Ni, M)02 under oxidizing conditions found at cathodes, is complex. For example, oxidation of Fe3+ substituted lithium nickelate, LL(Ni, Fe)02, under cathodic conditions leads to the formation of Fe4+ and Ni4+. Conductivity can then take place by means of rapid charge hopping between Fe3+, Ni3+, Fe4+, and Ni4+, giving average charges of Fe3+S and Ni3+S. These solids are the subject of ongoing research. 

If the same experiment is performed with an n-type Si electrode under identical illumination intensity the anodic photocurrent is found to be larger than for the p-type electrode under cathodic conditions. This increase is small (about 10%) for current densities in excess of JPS. Figure 3.2 shows that in this anodic regime injected electrons are also detected at p-type electrodes. This allows us to interpret the 10% increase in photocurrent observed at n-type electrodes as electron injection during anodic oxide formation and dissolution. 

A sufficiently anodic bias and the availability of holes are the two necessary conditions for the dissolution of silicon aqueous HF. In this case the Si dissolution rate is proportional to the current density divided by the dissolution valence. In all other cases silicon is passivated in HF this is the case under OCP, or under cathodic conditions, or under anodic conditions if the sample is moderately n-type doped and kept in the dark. If an oxidizing agent like HN03 is added silicon will already dissolve at OCP, but the dissolution rate remains bias dependent. If an anodic bias is applied the dissolution rate will be enhanced, whereas a cathodic bias effectively decreases the rate of dissolution. 

In alkaline electrolytes, in contrast, silicon is readily dissolved at OCP. Under cathodic conditions the dissolution becomes reduced, while under low anodic potentials the dissolution rate is enhanced compared to the OCP rate. If, however, the anodic potential becomes larger than the PP, the silicon electrode is passivated due to a thin anodic oxide film and the dissolution rate becomes negligible. The current density needed to keep the electrode in the passive state corresponds to the dissolution rate of the anodic oxide in the alkaline electrolyte used and is usually very low. 

While the external quantum efficiency of PS reported for solid-state contacts is usually low, wet contacts are found to give high EL efficiencies at low applied bias under anodic [Vi2, Itl, Ge2, Ha7] as well as cathodic conditions [Bsl]. An example of bright EL from a micro PS sample in acetic acid under anodic bias is shown... 

Figure 35. Comparison between simulated and measured current distributions in a PEFC with 15 jum membrane (EW < 1000) and under anode and cathode conditions of 3/3 bar, 1.2/2 stoichiometry, and 75%/0% relative humidity. The cell temperature is 80...

However, as discussed more fully in section 5, it is not entirely clear how significant the bulk path is in the case of LSM, which is almost a pure electronic conductor under typical cathode conditions. In the Mizusaki study cited above, the authors went on to show that following anodic polarization (or strong cathodic polarization), the LSM film becomes severely damaged and cracked and reverts to behavior more... 

One expected consequence of these properties is that LSM will not be a mixed conductor at low polarization under normal cathode conditions. Likewise, at cathode polarizations thermodynamically corresponding to Pq < atm (--"—500 mV) we... 

PAGE was carried out according to the modified method of Reisfield et al. (10), using Fuchsin Red as a marker. Gels were run under cathodic conditions and then stained with Coomassie Blue. 

The C.P.D. is obtained directly by the magnetron and the capacitor (or Kelvin) methods. Other methods which have proved successful rely on the variation of anode potential in a diode with constant cathode conditions. In this case, since adsorption changes the effective anode potential, the applied potential necessary to restore the anode current to its original value is equal to the C.P.D. between the two surfaces. As considered in Sec. II, a true average work function is measured in the C.P.D. method when the two conductors are separated by a distance which is much greater than the size of the patches on the surface. These conditions are invariably fulfilled in the capacitor and the space-charge-limited diode methods. 

A measurement of/H can be achieved electrochemically (32). Under galva-nostatic (constant current) cathodic conditions, the fractional efficiency of hydrogen absorption is the ratio of the amount of hydrogen produced electrochemically to the amount absorbed by the metal, as is illustrated in Fig. 25. While this appears to be a very simple direct measurement, it has the normal problems associated with an accelerated electrochemical measurement, including the need to demonstrate that the parameter measured electrochemically will retain the same value under the much slower natural corrosion conditions. 

Antoine, O. and Durand, R., RRDE study of oxygen reduction on Pt nanoparticles inside Nation H2O2 production in PEMEC cathode conditions, J. Appl. Electrochem., 30, 839, 2000. 

The corrosion rates of the titanium casing under cathodical conditions were smaller than that of stainless steel in nitric acid ( 0,05 mm Ti/y). This value as well as the corrosion rate of the platinized tantalum anode is within the expected order of magnitude (< 0,005 mm/y). 

In a subsequent attempt to mimic more closely the composition and structure within the fuel-cell cathode ([87]), a recast Nation film was applied to a Pt microelectrode in order to study the rate of the ORR as function of temperature and humidification conditions and the cell employed was as described in Fig. 37. This configuration comes closest to PEFC cathode conditions, in that the Pt surface is in contact with the recast ionomer, rather... 

Gourba, E. Cassir, M. Tessier, C. Chemical and electrochemical behaviour of Ni-Ti in the cathodic conditions used in molten carbonate fuel cells. J. Electroanal. Chem. 2001,505 (1-2), 69-77. 

Although originally AISI347 stainless steel seemed a reasonable choice, it was soon shown that it is not suited for long term operation over several years. The best corrosion protection would be provided by materials that can passivate. AISI 316 or AISI 310 stainless steel would in principle provide such a relatively stable and protective oxide scale in the presence of molten carbonate at least under cathodic conditions. 

CORROSION, CATHODIC - Corrosion resulting resulting from a cathodic condition of a structure usually caused by the reaction of an amphoteric metal with the alkaline products of electrolysis. 

Another consideration is the magnitude of the charging current or potential. Charging under highly cathodic conditions by any technique can cause undesirable effects in the metal under study. As... 

The choice of organic solvents permits the occurrence of certain reduction reactions of alkyl halides which, if attempted in aqueous solutions, would rapidly be inhibited by the precipitation of insoluble products on the electrode. Under mildly cathodic conditions, the formation of metal alkyls occurs in high yields when alkyl halides are reduced at cathodes of low boiling metals in acetonitrile, DMF or propylene carbonate containing quaternary ammonium supporting electrolytes. " Whilst the formation of lead tetraethyl from ethyl bromide in DMF proceeds irrespective of the substitution of a sodium salt for the quaternary ammonium salt, the same change of electrolyte in propylene carbonate no longer leads to metal alkyl products. ... 

There is also discussion of the E LogI criterion where a graph of potential versus the logarithm of the applied current is plotted. The transition of the steel from anodic to cathodic condition is indicated by a break in the curve. However, the existence of a break and its location can be subjective and the shape of the curve changes with the scan rate. The RP suggests that... 

---