Rotating disk electrode half-wave potential

The voltammetric oxidation of HOOH at a rotated-disk electrode yields a peaked anodic wave with a half-wave potential (Em) of + 2.1 V versus SCE. The maximum current (ilim) for HOOH oxidation at the rotated-disk electrode is directly proportional to the concentration of HOOH, and is consistent with a first-order diffusion-controlled process. 

Figure 9.1 illustrates the electrochemical reduction of 02 at platinum electrodes in aqueous media (1.0 M NaC104). The top curve represents the cyclic voltammogram (0.1 V s-1) for 02 at 1 atm ( 1 mM), and the lower curve is the voltammogram with a rotated-disk electrode (900 rpm, 0.5 V min-1). Both processes are totally irreversible with two-electron stoichiometries and half-wave potentials (EU2) that are independent of pH. The mean of the Em values for the forward and reverse scans of the rotated-disk voltammograms for 02 is 0.0 V versus NHE. If the experiment is repeated in media at pH 12, the mean Em value also occurs at 0.0 V. 

The slope of this straight line is 16.91 x n V-1 at 25 °C. However, it is more common to use the inverse function E = Ei/2 + 2.303 x (RT/nF) log [(fi, - I) /I], with the slope 0.059/nV. Both functions are called the logarithmic analysis of DC polarogram. They both cross the potential axis at the half-wave potential, which corresponds to I = Ii/2. The main characteristic of fast and reversible electrode reactions is that the half-wave potential is independent of the drop life-time in DC polarography, or the rotation rate of the rotating disk electrode, or the radius of microelectrode. If this condition is satisfied, the slope of the logarithmic analysis indicates the number of electrons in the electrode reaction. 

The electron affinity of 3-(iV-methylpiperazino)-5-nitroindazole, 3,5-dinitroindazole, and molecular complex of the last with water is discussed on the basis of their half-wave potentials and in connection with their eventual radiosensitizing properties [667], The mechanism of EC behavior of 2-substituted 5(6)-nitrobenzimidazoles in acetonitrile has been investigated by classical polarography, cyclic voltammetry, and platinum rotating disk electrode with a ring (RDER) [888,991], It is shown that... 

Abbreviations are CV — cyclic voltammetry DMF — N,N-Dimethylformamide E swp — potential sweep E° — standard potential — peak potential E — half-peak potential E — half wave potential M — mol/L i eCN — acetonitrile pol — polarography rot Pt dsk — rotated Pt disk SCE — saturated calomel electrode TBABF — tetrabutylammonium tetrafluoroborate TBAl — tetrabutylammonium iodide TBAP — tetrabutylammonium perchlorate TEABr — tetraethylammonium bromide TEAP — tetraethylammonium perchlorate THF — tetrahydrofu-ran TPACF SO — tetrapropylammonium trifluoromethanesul-fite TPAP — tetrapropylammonium perchlorate and wr — wire. 

The half-wave potential of the catalytic wave for O2 reduction by rotating disk voltammetry. This value depends on the electrode rotation rate, bulk O2 concentration, pH, and in many cases on the scan rate, the amount of the adsorbed catalyst, and the nature of the supporting electrol5h e n.m. - not meaningful (no defined wave). 

For non-noble metal ORR catalysts, the definition of catalytic activity is different from that of Pt-based catalysts. For a nonnoble metal catalyst, the similar preparation procedure for CL and ORR measurement steps using rotating disk electrode technique to that for Pt-based catalyst have been widely used in literature. However, due to both the ORR onset and half-wave potentials catalyzed by non-noble metal catalysts are much lower than those of Pt-based catalysts, it is difficult or impossible to observed ORR current density at 0.9 V vs RHE. A current density at other lower potentials may be used to define the catalyst activity for the purpose of comparison. In this case, Eqn (3.7) may still usable except the electrode potential is not 0.9 V, instead of... 

---