Electrode potential, effect anodic oxide formation

The pH of the electrolyte is effective on the reaction kinetics at the individual electrodes and the electrode potential at which oxidation or reduction takes place [26]. Electrolyte is typically a strong acid or a strong base, such as sulfuric acid or potassium hydroxide, which include highly mobile hydronium or hydroxide ions, respectively [20]. Typically, operation of fuel cell in alkaline media can develop the electrooxidation of the catalyst-poisoning carbon monoxide species on the anode and the kinetics of ORR is improved at the cathode [26]. However, in membrane-based fuel cells, due to the potential of carbonate formation resulting in clogging the membrane, the long-term stability is restricted and limits the use of these alkali-compatible membranes for liquid fuel cell operations [26]. 

A special problem can be the passivation of the electrode surface by insulating layers, for example, formation of oxides on metals at a too high anodic potential or precipitation of polymers in aprotic solvents from olefinic or aromatic compounds by anodic oxidation. As a result, the effective surface and the activity of the... 

In a recent publication, Schafer and coworkers point out the utility of the electrode as a reagent which is effective in promoting bond formation between functional groups of the same reactivity or polarity [1]. They accurately note that reduction at a cathode, or oxidation at an anode, renders electron-poor sites rich, and electron-rich sites poor. For example, reduction of an a, -un-saturated ketone leads to a radical anion where the )g-carbon possesses nucleophilic rather than electrophilic character. Similarly, oxidation of an enol ether affords a radical cation wherein the jS-carbon displays electrophilic, rather than its usual nucleophilic behavior [2]. This reactivity-profile reversal clearly provides many opportunities for the formation of new bonds between sites formally possessing the same polarity, provided only one of the two groups is reduced or oxidized. Electrochemistry provides an ideal solution to the issue of selectivity, given that a controlled potential reduction or oxidation is readily achieved using an inexpensive potentiostat. 

On the basis of oxidation potentials, current-potential relationships, and isotope effects, an electron-transfer mechanism is suggested for the anodic oxidation of methyl N,N-dialkyl substituted carbamates, which can reasonably explain the formation of all three types of products. Also, N-acylazacycloalkanes are converted anodically at a platinum electrode in R0H-Et4NBF4 into a-monoalkoxy or a,a -dialkoxy derivatives depending on the electrolysis conditions employed.198... 

In the equation 25 n is the number of electrons and F, k and C(02) are Faraday constant, rate constant and bulk O2 concentration, respectively. In addition, P and y are symmetry factors, while E is the electrode potential. The term 0ad relates to total surface coverage by OHads and adsorbed anions. The effect of surface oxides on the metal electrode surface was clearly demonstrated for series of Pt-based electrocatalysts [53, 54], leading to a general recipe for design of electrocatalysts with improved ORR activity. In specific, if oxide formation is hindered onset potential for ORR is shifted to higher anodic potentials. Underlying principles of this route have been set by combining electrochemical measurement... 

While in the previous two examples we have discussed the initial stages of oxidation, we now shall focus our attention on the optical properties of thicker oxide layers. Anodically formed iridium oxide films have attracted particular attention because of their pronounced electrochromic effect. When an Ir electrode is scanned anodically in 0.5 M H2SO4, oxidation starts at +0.6 V versus SCE. On the cathodic scan, however, the oxide layer is not reduced to the metallic state but to a low-conductivity hydroxide film facilitating further oxide formation with each anodic potential cycle. Continuous cycling of the iridium electrode between -0.25 and +1.3 V (SCE), at a frequency of 1 cps, therefore has been used as a standard treatment for the formation of thick anodic iridium oxide films. ... 

---