Disk electrodes electrode potentials

Cu9ln4 and Cu2Se. They performed electrodeposition potentiostatically at room temperature on Ti or Ni rotating disk electrodes from acidic, citrate-buffered solutions. It was shown that the formation of crystalline definite compounds is correlated with a slow surface process, which induced a plateau on the polarization curves. The use of citrate ions was found to shift the copper deposition potential in the negative direction, lower the plateau current, and slow down the interfacial reactions. 

Figure 6.10 Galvanostatic scans of a Pt(l 10) rotating disk electrode in a CO-satuiated 0.1 M HCIO4 solution at two different current scan rates (disk rotation rate 400rev/min). The insert shows the potential fluctuations observed at an apphed current density of 0.74 mA/cm (disk rotation rate 900 rev/min).

A standard rotating disk electrode (RDE) setup with a gas-tight Pyrex cell was used for the experiment on CO adsorption and the HOR. A Pt wire was used as counterelectrode. A reversible hydrogen electrode, RHE(t), kept at the same temperature as that of the cell (t, in °C), was used as the reference. All the electrode potentials in this chapter will be referenced to RHE(f). The electrolyte solution of 0.1 M HCIO4... 

Fig. 2. Curve A Eleotropolymerization of ImH H2(o-NH2)TPP in 0.1M Et NClO /CH CN by sweeping potential at 200mV/s on Pt electrode. Numbers represent scan number. Curve B Cyclic voltammogram of an electropolymerized film of poly-[H2(o-NH2)TPP] on a Pt electrode, in 0.1M Et NClO /CH CN at 200 mV/s. Integration of the charge under the wave shows that coverage is 3.5X10 9 mol/cm of the porphyrin sites. Curve C Rotated disk electrode voltammetry of the Os(lII,Il) reaction for 0.2 mM...

The position of a reference electrode for the RHSE is not as crucial as for the rotating disk electrode because of the uniform potential distribution near the surface. To minimize the flow disturbances which might be introduced by a reference capillary, it is advisable to place the reference tip near the equator rather than near the pole of rotation. For a reference electrode located at a large distance from the RHSE, the ohmic potential drop may be estimated from Eq. (57) as (47) ... 

Experimental results obtained at a rotating-disk electrode by Selman and Tobias (S10) indicate that this order-of-magnitude difference in the time of approach to the limiting current, between linear current increases, on the one hand, and the concentration-step method, on the other, is a general feature of forced-convection mass transfer. In these experiments the limiting current of ferricyanide reduction was generated by current ramps, as well as by potential scans. The apparent limiting current was taken to be the current value at the inflection point in the current-potential curve. 

Fig. 10. Logarithmic plot of apparent limiting current density as a function of potential scan rate at a rotating-disk electrode i = apparent limiting current (or peak current) density iL = true steady-state limiting current density d/dt = potential scan rate expressed in units RT/nF oj = rotation rate (rad sec"l). [From Selman and Tobias (S10).]... 

Fig. 35. Disk and ring voltammograms recorded during the oxidation of thin-layer Co-Al electrodeposits from a Pt-RRDE in pure 60.0 m/o AlCl3-EtMeImCl melt. These deposits were produced with a charge density of 425 mC cm 2 in melt containing 5.00 mmol L-1 M Co(II) at the following deposition potentials (—) 0.200, (—) 0.100, and ( ) 0 V. During stripping, the disk electrode was scanned at 0.002 V s 1, and Er was held at 0.500 V. The angular velocity of the RRDE was 104.7 rad s 1. Adapted from Mitchell et al. [44] by permission of The Electrochemical Society.

We consider the investigation of two consecutive electron-transfer reactions with a ring-disc electrode under stationary conditions. A species A reacts in two steps on the disk electrode first to an intermediate B which reacts further to the product C. The intermediate is transported to the ring, where the potential has been chosen such that it reants bank to A. The overall scheme is ... 

Fe 2S], a [4Fe-4S] and a [3Fe-4S] center. The enzyme catalyzes the reversible redox conversion of succinate to fumarate. Voltammetry of the enzyme on PGE electrodes in the presence of fumarate shows a catalytic wave for the reduction of fumarate to succinate (much more current than could be accounted for by the stoichiometric reduction of the protein active sites). Typical catalytic waves have a sigmoidal shape at a rotating disk electrode, but in the case of succinate dehydrogenase the catalytic wave shows a definite peak. This window of optimal potential for electrocatalysis seems to be a consequence of having multiple redox sites within the enzyme. Similar results were obtained with DMSO reductase, which contains a Mo-bis(pterin) active site and four [4Fe 4S] centers. 

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