Cyclic peak current density

Cyclic voltammetry provides a simple method for investigating the reversibility of an electrode reaction (table Bl.28.1). The reversibility of a reaction closely depends upon the rate of electron transfer being sufficiently high to maintain the surface concentrations close to those demanded by the electrode potential through the Nemst equation. Therefore, when the scan rate is increased, a reversible reaction may be transfomied to an irreversible one if the rate of electron transfer is slow. For a reversible reaction at a planar electrode, the peak current density, fp, is given by... 

In an ideal case the electroactive mediator is attached in a monolayer coverage to a flat surface. The immobilized redox couple shows a significantly different electrochemical behaviour in comparison with that transported to the electrode by diffusion from the electrolyte. For instance, the reversible charge transfer reaction of an immobilized mediator is characterized by a symmetrical cyclic voltammogram ( pc - Epa = 0 jpa = —jpc= /p ) depicted in Fig. 5.31. The peak current density, p, is directly proportional to the potential sweep rate, v ... 

ECL detection of Ru(bpy)2+ (or TBR) was conducted on a Si-glass chip with an ITO anode [727]. Through the transparent ITO anode, orange light (620 nm) was observed and recorded by a detector. It was found by cyclic voltammetry that the oxidation potential was more positive, and the peak current density was less on an ITO anode, as compared to the use of a Pt anode. In this work, Au cannot be used as an anode, presumably because of polymerization of TPA at the gold surface [727]. 

Determining the peak current density in cyclic voltammetry can sometimes be problematic, particularly for the reverse sweep, or when there are several peaks, which are not totally separated on the axis of potential. The usual way to determine the peak currents is shown in Fig. 7L. For the forward peak, the correction for the baseline is small and does not substantially affect the result. For the two reverse peaks, however, the baseline correction is quite large and may introduce a substantial uncertainty in the value of the peak current density. In fact, there is no llieory behind the linear extrapolation of the baselines shown in F/g. 7L, and this leaves room for some degree of "imaginative extrapolation." This is one of the weaknesses of cyclic voltammetry, when used as a niumtitative tool, in the determination of rate constants and reaction mechanisms. 

Fig. 7L Commonly used graphical method of extrapolating the baseline, to measure the peak current densities in cyclic voltammetry.

Plots of the peak current densities observed during the scan toward negative potentials, t p versus v l/2, extracted from the cyclic voltammetric data (see insert, Figure 3.7) were found to be linear with a zero intercept. This behavior is characteristic of a strictly diffusion controlled process for which... 

Electrochemical Measurements Under conditions in which the interactions among adsorbates can be neglected, and assuming that all adsorption sites are strictly identical (Langmuir isotherm), and that the electron transfer rates are very fast, the peak potential, Ep, and peak current density, ip, observed in cyclic voltammetry are given, respectively, by ... 

UV-vis spectra and cyclic voltammetry confirmed the stepwise quantitative film formation. In the UV-vis spectrum of the bis(tpy)iron complex film, absorbance of the peak at 592 nm attributed to the MLCT transition increased linearly with the number of stepwise complexa-tions, n, and the peak current density, /p, of the reversible peak of the Fem/Fen couple... 

Figure 7. Plot of cyclic voltanmetry anodic peak current density vs. time for the oxidation 0.58 mM eugenol, pH 7 phosphate buffer at nonmodified graphite and o PNVP-modified graphite (19.5 mrad).

Cyclic voltammetry — diagnostic criteria for four illustrative mechanisms. = peak potential, E j2 = half peak potential, AEp = E - JFp, /p = peak current density superscripts f, b = forward and back reactions... 

Fig. 4.6 Maximum anodic peak potential ( p) vs. SCE (0.244 V vs. RHE) and peak current density (Ip) acquired during a cyclic voltammogram at 50 mV s for atomic fractions,...

In one of the most relevant papers in this field, Dima et al. [13] studied the electrocatalytic behavior of different polycrystalline metals such as Ru, Rh, Ir, Pd, Pt, Cu, Ag and Au for nitrate (100 mM) reduction in 0.5 M H2SO4. On the basis of the peak current density related to nitrate reduction on cyclic voltammograms, the activities of each electrode were compared. It was determined that rhodium is the most active catalyst among the noble metals for the reduction of nitrate, with the activity decreasing in the order Rh, Ru, Ir, Pt, Pd and Cu, Ag, Au for transition metals. The high electrocatalytic performance of Rh for nitrate reduction was also observed by Brylev et al. [19]. By using Differential Electrochemical Mass Spectrometry (DEMS), a reduction mechanism for nitrate reduction has been determined for transition metals (Fig. 2). 

In dilute solutions of PbCl2 in molten KCl-LiCl at 400 °C the cathodic deposition of lead was found to be diffusion controlled with the influence of nucleation on substrates of glassy carbon, tungsten and molybdenum. Figure 4.6.2 shows typical cyclic voltammograms obtained at a glassy carbon electrode. A linear relationship was obtained between the peak current density and the square root of the scan rate. The diffusion coefficient was calculated to be 2-10 cm /s. 

Figure 7.8.1 Cyclic voltammogram of LIF-KF-K2SIF (1 mass%). Working electrode Ag (surface area = 0.3l cm ) auxiliary electrode vitreous carbon reference electrode Pt. Scan rate =100mVs T=800°C. Inset linear relationship of SI(IV) reduction peak current density versus the square root of the scanning potential rate...

Figure 9. Cyclic voltammogram of NaF-KF-Na2SiFg (Cq = 0.24 mol kg ) at 850 °C working electrode Ag auxiliary electrode Si reference electrode Si Scan rate = 100 mV s /Inset Linear relationship of Si(lV) reduction peak current density versus the square root of the scanning potential rate. Reproduced with permissions Copyright 2012, Elsevier [84].

Pt-Rh/carbon fibre Galvanostatic electrodeposition Continuous Pt-Rh layer on carbon fibres 5.2 mg cm Cyclic voltammetry at 25 °C in 1.03 mM NHj-1-0.1 MKOH Peak current density 15 mA cm (scan rate n = 10 mV s 37... 

Pt deposited on Rh/RANEY Ni Galvanostatic electrodeposition Amorphous, boulder-like Pt deposits 10 mg cm Pt -1-1 mg cm Ru Cyclic voltammetry at 25 CinlMNHj-rlM KOH Peak current density ca. 200 mA cm (i/=10mV s ) 38... 

Pt/graphite Pulsed potentiostatic electrodeposition Pt layer consisting of aggregates Cyclic voltammetry at room temperature in 0.1 MNH3-t0.2 M NaOH Peak current density varied from ca. 15 mA to ca. 32 mA (y = 20 mV s ), depending on the deposition potential 43 D. 2, 0... 

Pt black Potentiostatic electrodeposition Pt film with rough surface Cyclic voltammetry at room temperature in 0.1 MNH3-tl MKOH Peak current density 22.5 mA cm (y = 5mV s ) 44... 

Pt/ITO Galvanostatic electrodeposition Dispersed Pt particles, particle size 700-800 nm 0.12mgcm Cyclic voltammetry at 25 Cin0.2MNH3-l-lM KOH Peak current density 0.7 mA cm (v = 5 mV s ) 46... 

Pt/ITO Galvanostatic electrodeposition 3D porous flower-like Pt particles assembled by nanosheets 0.065 mg cm Cyclic voltammetry at 25°Cin0.1MNH3+lM KOH Peak current density 3.5 mA cm v= 10 mV s ) 47... 

Pt/ITO Cyclic voltammetric electrodeposition Hierarchical Pt nanoparticles with various morphologies including sheet-, flower-, prickly sphere- and cauliflowerlike shapes 0.055- 0.095 mg cm Cyclic voltammetry at 25°Cin0.1MNH3-tlM KOH Peak current density increased fiom 2.5 to 4.3 mA cm (v = 10 mV s ) with the increasing Pt loading bom 0.055 to 0.095 mg cm 4S... 

Pt/glassy carbon Galvanostatic electrodeposition Pt nanoparticles with size of several nm to tens of nm within a short deposition time, or Pt nanosheets at a longer deposition time 0.007- 0.055 mg cm Cyclic voltammetry at 25 °Cin0.1MNH3-tlM KOH Peak current density increased from 0.8 to 4.6 mA cm (i/= 10 mV s ) with increasing Pt loading from 0.007 to 0.055 mg cm 49... 

Unsupported Pt Microemulsion method with N2H4 as the reducing agent Pt nanoparticles with size 4.5 0.8 nm Cyclic voltammetry at room temperature in 0.1 MNH3 + O.2M NaOH Peak current density ca. 0.2 mA cm (v=10mVs ) 51... 

Figure 1 shows cyclic voltammograms in these two solutions. A reduction current is observed with two reduction peaks in the oxygen-saturated electrolyte. In the argon-saturated electrolyte, a single reduction peak at lower current density is observed. From the difference between the reduction currents in the two solutions, the reduction current in the... 

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