Anodes potential range

The limited anodic potential range of mercury electrodes has precluded their utility for monitoring oxidizable compounds. Accordingly, solid electrodes with extended anodic potential windows have attracted considerable analytical interest. Of the many different solid materials that can be used as working electrodes, the most often used are carbon, platinum, and gold. Silver, nickel, and copper can also be used for specific applications. A monograph by Adams (17) is highly recommended for a detailed description of solid-electrode electrochemistry. 

TABLE 5.6 Anodic Potential Range of Electrode and Peak Potential for Oxidation of Fen(CN>6... 

Electrode Material Anodic Potential Range in Aqueous Solution (V vs. SCE) Peak Potential for Oxidation of 10 3 M Fen(CN)4- ... 

Deposition of Pb in 5mM Pb(C104)2 and lOmM HCIO4 solution at large overpotentials occurs via a 3D island growth. It follows a progressive nucleation process at low overpotentials and is mainly initiated at the surface inhomogeneities. The number of atoms in the critical nucleus is estimated to be very small, about 11. The small Pb clusters are stable within a certain anodic potential range. 

Easy to prepare and maintain Good anodic potential range with small background (residual) currents Generally cannot be used with nonaqueous solvents Periodic repacking is needed 0.1 m KC1 (-1 to +1.25)... 

In earlier voltammetric experiments [17] it has been found that Tl underpotential deposition occurs in two distinctly separated potential intervals that have been associated with the successive formation of two monolayers prior to Tl bulk deposition, whereby the voltammogram in the more anodic potential range (assigned to the formation of a first monolayer) exhibits a very similar splitting into three distinct peaks Al/Dl, A2/D2, A3/D3 as observed in the system Pb/Ag(l 11) (see Fig. 2). 

Lindquist, J- (1973) Carbon paste electrode with a wide anodic potential range. Anal Chem., 45, 1006—1008. 

Among the various tungsten carbide phases, WC has been known for the most stable phase. Chen and co-workers reported that WC was more stable than W2C under anodic potential range (6). In this report, W2C led to the anodic current peak at lower anodic potential (between 0.4 and 0.6 V vs Normal Hydrogen Electrode (NHE)) than WC (above 0.6 V vs NHE) in 0.5 M H2SO4 electrol3dn. This anodic current at lower potential means that W2C is more easily oxidized than WC and could be more easily lost in electrochemical applications. In addition, W2C showed higher corrosion currents than WC at the same potential (147). 

The previous sections indicated that at present PtRu remains the most effective binary catalyst for methanol oxidation. A significant amount of work has been carried out and various theoretical and experimental techniques have been brought to bear in order to reveal the details of the Pt-Ru catalytic/co-catalytic effect. For DMFC performance enhancement, which is the prevalent point of view adopted in this review, the situation is further complicated since in addition to intrinsic kinetic effects, the anode performance depends in a synergistic and often poorly understood manner on the PtRu catalyst preparation method, PtRu atomic ratio, surface morphology (e.g., roughness), presence and type of support, operating anode potential range, methanol concentration, and temperature. 

An anodic potential range where there is a slight decrease in the rate of self-assembly with increasingly anodic potentials. 

In general platinum and gold are the most widely used metallic electrodes. These electrodes present favorable electron transfer kinetics and a large anodic potential range. However, their use on cathodic potential (-0.2 V imtil -0.5 V) is limited by the low hydrogen overvoltage and the formation of oxide on the surface of the electrode. The oxide film can be eliminated with a cleaning-reactivation cycle [27]. The problem is less severe in nonaqueous electrolyte, but in nonaqueous media platinum can present catalytic characteristics [16, 21]. 

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