Disk electrodes current-potential curves

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. 

FIGURE 1.10. Rotating disk electrode voltammetry. A + e B, with a concentration of A equal to C° and no B in the solution a Linearized concentration profiles —, at the plateau (vertical arrow in b), , at a less negative potential (horizontal arrow in b). b Current potential curve, c Concentrations of A and B at the electrode surface, d Logarithmic analysis of the current potential curve. 

Assume that the reaction ox + c <=> red at the planar electrode is diffusion controlled. Sketch and correlate the concentration profiles Cox =f(x), where x is the distance from the electrode surface to the bulk of the solution, with the shape of the current-potential curve for electrolysis carried out at (a) a stationary disk electrode and (b) a rotating disk electrode. Support your explanation by the equations. (Skompska)... 

Voltammetry is a term used to include all the methods that measure current-potential curves (voltammograms) at small indicator electrodes other than the DME [6], There are various types of voltammetric indicator electrodes, but disk electrodes, as in Fig. 5.17, are popular. The materials used for disk electrodes are platinum, gold, graphite, glassy carbon (GC), boron-doped diamond8, carbon paste, etc. and they can be modified in various ways. For electrode materials other than mercury, the potential windows are much wider on the positive side than for mercury. However, electrodes of stationary mercury-drop, mercury-film, and mercury-pool are also... 

A rotating disk electrode (RDE) [7] is used to study electrode reactions, because the mass transfer to and from the electrode can be treated theoretically by hydrodynamics. At the RDE, the solution flows toward the electrode surface as shown in Fig. 5.22, bringing the substances dissolved in it. The current-potential curve at the RDE is S-shaped and has a potential-independent limiting current region, as in Fig. 5.6. The limiting current (A) is expressed by Eq. (5.33), if it is controlled by mass transfer ... 

A third approach is to use microelectrodes for low-temperature studies. The iR drop is intrinsically lower with microelectrodes, and it is often possible to obtain accurate current-potential curves at low temperatures even at rather large scan rates. The reason for this is that the current (when diffusion from the periphery of a disk electrode is negligible) is proportional to the area of the electrode that is, it is proportional to r2. Thus (considering Eq. 16.13), iR is proportional to r and the iR error decreases smoothly as smaller and smaller disk... 

Fig. 24. Current-potential curves for a Teflon-bonded Ru02 layer on a GC disk electrode in...

Fig. 18. Current-potential curve for a rotating (1000 rpm) n-GaAs-electrode in the dark in 6 M HCl with 0.76 mM Cu ". Dashed curves are the partial currents of anodic decomposition (] ) and of Cu -reduction (jrea), as determined by a rotating ring-disk electrode [93]...

As mentioned in Sec. 2.1, simple superposition of the respective current-potential curves for the two partial reactions does not always yield the curve obtained with a complete electroless bath. This is illustrated in Fig. 21 [126], in which the current-potential curve obtained with a complete electroless copper bath containing EDTA (curve 1) is compared with the curve obtained in solution in the absence of formaldehyde (curve 2) and with that obtained in solution in the absence of Cu(II) (curve 3). All three curves were recorded at room temperature with a copper disk electrode rotating at 2100 rpm, while scanning the potential in the positive direction... 

The cause of this effect of nickel ions was investigated voltammetrically with a gold-plated rotating platinum disk electrode [158]. The current-potential curves shown in Fig. 33 demonstrate that the anodic oxidation of the reducing agent... 

Fig. 7. Galvanodynamic cathodic current-potential curves at different rotation speeds of the disk electrode. These curves were used to study the Influence of mass transfer on aluminum deposition. (EL II/A 100°C scan rate 2.3 A/dm s).

Fig. 9 gives an example of how to determine the charge transfer current density. The plotted lines were evaluated according to the least squares method. The data were taken from the stationary potentiostatic current-potential curves at five different rotating electrode disk speeds. 

Figure 2. (top) Current-potential curve for a rotating disk electrode (1600 rpm) under 1 bar H2 in... 

Fig. 2 Current-potential curves for a mixture of pyrocatachol (1 mM) and o-benzoquinone (1 mM) on Pt and Bi/Pt rotating disk electrodes in 0.5 M HCIO4 with 1 mM Bi(CI04)j. Sweep rate 10 mV s . Rotation frequency (1) 12.5, (2) 25, (3) 50 and (4) 75 Hz. (Reproduced with permission from Ref [2].)...

Fig. n Current-potential curves for reduction of PhCH(N02)2 0 mM) on a Pt rotating disk electrode in 0.5 M HCIO4 curve (1) and Pt with adlayers of Bi,... 

Figure 8.4 shows the importance of the coordination mode around the metal ion for the electrochemical properties of the layer. In Fig. 8.4 the mediation of the Fe(II)/(III) oxidation is studied by using a rotating disk electrode. Initially a thin film of [Ru(bipy)2(PVP)5Cl] is used and with this coating the current potential curve I is obtained (see Fig. 8.4b). On photolysis of the coating and formation of the aquocomplex (according to Reaction 5) curve II is obtained. Rotating disk behavior very clearly shows that the redox potential of the modifying layer is of prime importance to the electrochemical properties of the modified electrode.

Figure 1.16. Cyclic voltammograms under N2 (A,C) and rotating ring-disk current-potential curves in aqueous air-saturated pH 7 buffers (B,D) of 2FeCu and 2Fe-only directly adsorbed on a graphite electrode (A,B) and as a 0.7% (mol) suspension in a 1-/rm-thick phosphadytilcholine film on the electrode surface (C.D). The rapid charge transfer within the films of adsorbed catalysts is supported by the linear dependence of the peak currents on the scan rate. The non-ideal shape of the peaks is due to cooperative behavior of the catalytic films as a whole. The Fe / and Cu / potentials are the same in the adsorbed catalysts (A) but separate when the catalysts are in the lipid film (C). Autooxidation of the catalyst-02 complex is the major source of ring-detectable byproducts (see below) and accounts for the potential-dependent selectivity of electrode-adsorbed catalysts (B). The measured collection efficiency of the ring electrode toward H2O2 in these experiments was 15%.

Silicon. The snrface of silicon immersed in fluoride media is of interest for semiconductor processing and production of porous silicon (Section 5.7) [541, 542, 549, 550]. A typical current-potential curve of p-Si in a flnoride electrolyte (0.975 MNH4CI + 0.025 MNH4F + 0.025 MHF, pH 2.8) measured at a rotating disk electrode at rotation rate of 3000 rpm and potential scanning speed of 5 mV s is shown in Fig. 7.29. The steep rise of the current density near... 

Figure 7.29. Typical current-potential curve of p-Si [(100) orientation, doping 10 cm" ] in dilute fluoride electrolyte (here 0.975 M NH4CI + 0.025 M NH4F + 0.025 M HF, i.e., fluoride concentration 0.05 M, pFI 2.8). Rotating disk electrode rotation rate 3000 rpm, potential scanning speed 5 mV s". Reprinted, by permission, from F. Ozanam, C. da Fonseca, A. V. Rao, and J.-N Chazalviel, Appl. Spectrosc. 51,519 (1997), p. 521, Fig. 1. Copyright 1997 Society for Applied Spectroscopy.

Figure 3.3 Current—potential curve recorded on a rotating disk glassy carbon electrode coated with 20wt %Pt/C catalyst, measured in O2-saturated 0.1 M HCIO4 at 30 °C. Potential scan rate 5 mV electrode rotating rate 1600 rpm. Catalyst loading 0.048 mgp, cm Ryan Baker, Jiujun Zhang, Unpublished data.

Figure 4.6 (A) Current-potential curves for 02-saturated 1.0 M NaOH solution at a polished glassy carbon disk electrode, T= 298 K potential scan rate,...

Figure 5.5 (A) Current-potential curves at different electrode rotating rates, recorded on a Pt disk electrode (0.196 cm ) using a potential scan rate of 5 mV s in Oa-saturated 0.5 M H2SO4 aqueous solution (B) the Levich plot (C) the Koutecky—Levich plots at different electrode potentials and (D) plot of E vs ln(/i<,o). The measurement was...

Figure 5.15 Koutecky-Levich plots at different electrode potentials. The current-potential curves recorded on the Co-N-S/C catalyst-coated GC disk electrode (0.28 cm ) at different electrode rotation rates in 02-saturated 3.0 M KOH solution. Potential scan rate 25 mV s and catalyst loading 7.06 x 10 g cm ...

Figure 6.5 Current—potential curves recorded on an RRDE electrode in 02-free 1.0 M KNO3-1-0.01 M [Fe(lll)(CN)6] aqueous solution with a disk potential scan rate of 50 mV s where f is 0.361 vs SHE. (For color version of this figure, the reader is referred to the online version of this book.)...

As an example. Figure 6.10 shows the ORR current—potential curves at the disk electrode and their corresponding currents at the ring electrode, recorded at different electrode rotating rates, where the horizontal abscissa is the disk potential, and the upper vertical ordinate is the ring current and the lower vertical ordinate is the disk current. 

Figure 6.10 Current—potential curves at the disk electrode (below the x-axis in each figure) and the current at the ring electrode (Pt) (above the x-axis in each figure), recorded in Oa-saturated 1.0 mol dm KOH aqueous solution at different electrode-rotating rates. Disk electrode surface coated with a layer of (A) W2C/C, (B) Ag/C, (C) Ag-W2C/C, or (D) Pt/C. Potential scan rate 5 mV s ring potential fixed at 0.474 V vs Hg/HgO, and ring collection efficiency 20%. The insets present the Koutecky—Levich p ols of the disk electrode at different potentials. (For color version of this figure, the reader is referred to the online version of this book.)...

Figure 7.14 (A) Current—potential curves for Co"HFPC adsorbed on a rotating graphite disk electrode at different rates of rotation as (marked on each curve), recorded in an air-saturated 0.1 M Na2S04 solution buffered to a pH 6. Temperature 20 °C. Potential scan rate 10 mV s (B) Koutecky—Levich plot, data from (B). The thinner solid line is calculated according to Levich theory for a 2-electron O2 reduction process. The thicker solid line and data points are the experimental data. Reprinted with permission from Ref. 47.

Figure 7.15 Current—potential curves on (A) glassy carbon disk for O2 reduction and (B) Pt ring electrode for H2O2 oxidation obtained in an RRDE study. The disk electrode was coated by PtA/ulcan with a Pt loading of 0.014 mg cm T = 60 °C 02-saturated 0.5 M H2SO4 scan rate = 5 mV s Ring potential = 1.2 V. Reprinted with permission from Ref. 48.

Figure 7.16 Current—potential curves (bottom) of the carbon-supported nanosized Pt and PtNi alloy catalysts coated on a glassy carbon disk electrode in Oa-satu-rated 0.5 M HCIO4 solution (scan rate of 5 mV s and rotating speed of 2000 rpm) and the corresponding ring currents (Pt at 1.2 V vs RHE) data for the hydrogen peroxide production (upper) on Pt/C, Pt Ni(2 1)/C and Pt Ni(1 1)/C systems. Reprinted with permission from Ref. 55.

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