Rotating disk electrode scan rate

Figure 6.9 Cyclic voltammetry of a Pt(llO) rotating disk electrode in a CO-saturated 0.1 M HCIO4 solution, (a) Influence of the voltage scan rate, (b) Influence of the disk rotation rate.

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).

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).]... 

Shuman and Michael [326,327] introduced a technique that has sufficient sensitivity for kinetic measurement at very dilute solutions. It combines anodic scanning voltammetry with the rotating-disk electrode and provides a method for measuring kinetic dissociation rates in situ, along with a method for distinguishing labile and non-labile complexes kinetically, consistent with the way they are defined. 

The homogeneous catalysis method is suitable to measure rate constants over a very wide range, up to the diffusion limit. The lower limit is determined by interferences, such as convection, which occur at very slow scan rates. It is our experience that, unless special precautions are taken, scan rates below lOOmV/s result in significant deviations from a purely diffusion-controlled voltammetric wave. For small values of rate constants (down to 10 s ), other potentiostatic techniques are best suited, such as chronoamperometry at a rotating disk electrode UV dip probe and stopped-flow UV-vis techniques. ... 

The first voltammetric methods met are stationary voltammetries performed on a dropping mercury electrode (polarography) or on a solid rotating disk electrode. The limiting current measured is directly proportional to the concentration of the electroactive species in the solution. Experimental potential scan rate is lower than lOrnVs-1. 

Figure 3.13 Electrochemical oxidation of HOOH and reduction of its products at GC electrodes in MeCN (0.1 M TEAP) (a) linear-sweep anodic voltammograms for (A) 0, (B) 0.3, (C) 1.7, and (D) 3.3 mM HOOH (scan rate 2 V min-1 electrode area, 0.46 cm2) (b) rotated-ring electrode cathodic voltammogram (scan rate 10 mV s-1) of the product from the oxidation of 4 mM HOOH at the rotated-disk electrode (rotation rate 1600 rpm) for (A) ED disconnected, and (B) En = +2.6 V versus SCE (c) rotated-ring electrode cathodic voltammogram (scan rate 10 mV s-1) of the products from the oxidation of 1 mM HOOH at the rotated-disk electrode (rotation rate 4900 rpm) for (A) disconnected and (B) ED = +2.6 V versus SCE.

Curve (b) of Figure 4 shows the same silent system as curve (a) but now upon a contracted current scale, while curve (c) shows the effect of ultrasonic irradiation upon curve (b), scanned at the same rate and in the oxidation direction only. Note that curves (b) and (c) are on the same current scale, both taken from ref. 31. Ultrasound has produced a 10-fold increase in maximum current. The plateau shape shows a limiting current at the extreme of oxidation potential reflecting hydrodynamic control independent of the voltammetric sweep rate. (This shape is also seen in other voltammetric procedures, e.g. when using rotating disk electrodes or microelectrodes.) In Figure 4 curve (c) this limiting current is found to be inde-... 

Investigation was made into the transport characteristics of ascorbic acid (AA). Cyclic voltammo-grams of 10 mM A A at different scan rates were recorded at platinum (Figure 21.8) without stirring the solution with the rotating disk electrode (RDE). 

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 9 (Upper curves) cyclic (scan rate = 1.0 V s and (lower curves) rotated disk electrode (rotation rate = 200 rad s scan rate = 5 mVs kinematic viscosity = 1 x 10 cm s ) voltammograms at 25 °C for...

Figure 11 (Upper curves) cyclic (scan rate =1.0Vs and (lower curves) rotated disk electrode (rotation...

Figure 31. O2 reduction on adsorbed layers of various transition metal tetrasulfonated phthalocyanines on the basal plane of stress-annealed pyrolytic graphite in O.lAfNaOH. Macrocyclic preadsorbed from aqueous 10 M MeTSPc solution. Rotating disk electrode. Rotation rate 4500 rpm. Disk area 0.20 cm. Potential scan rate (cathodic) 10 mV/sec. T =...

Figure 7.70 Cathodic photocurrent-potential c-e) p-GaAs covered with 6,40, and 100 nm curves at p-GaAs in aqueous solutions (pH large Au particles, respectively (curve f) p-3) under illumination (curve a) bare p-GaAs GaAs covered with platinized Au particles rotating disk electrode (curve b) gold-plated (40 nm) rotation velocity, 200 rpm scan rate, p-GaAs covered with 0.7 monolayers (curves 10 mV s" (after [105]).

The rotating disk electrode is becoming one of the most powerful methods for studying both diffusion in electrolytic solutions and the kinetics of moderately fast electrode reaction because the hydrodynamics and the mass-transfer characteristics are well understood and the current density on the disk electrode is supposed to be uniform. Levich [179] solved the family of equations and provided an empirical relationship between diffusion limiting current (id) and rotation rate ( >) as shown in Eq. (9.42). In particular applications in fuel cells, the empirical relationship which is given by Levich was also used in linear scan voltammetry (LSV) experiment performed on a RDE to study the intrinsic kinetics of the catalyst [151,159,180-190]. However, it is more appropriate to continue the discussion later in detail in the LSV section. 

Fig. 8 Catalysis of O2 reduction at a ring-disk electrode in contact with an aqueous 0.5 M H2SO4 solution, the graphite disk (EPGE) being modified by adsorption of a biscobalt diporphyrin, C02ETE4. (a) Disk current, solution saturated with oxygen, p02 = 1 atm rotation rate 100 r min scan rate ...

Figure 9.1 Electrochemical behavior of dioxygen (1 atm) in aqueous solutions (1 M NaC104) at a platinum electrode (area 0.458 cm2) A) the cyclic voltammogram was initiated at the rest potential with a scan rate of 0.1 V s-1 (B) the rotated-disk (400-rpm) voltammogram was obtained with a scan rate of 0.5 V min-1. 

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).

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