Dynamic polarization curves

This parameter specifies the potential upon which the AC signal is imposed. Oftentimes, to maintain the steady state of the system, the DC potential is selected as 0 mV vs. open circuit. However, the response of a system can be evaluated over a potential range by running successive experiments with different DC potentials. Thus the impedance response of a system could be mapped to a potentio-dynamic polarization curve by specifying various DC potentials defined by the polarization curve. In all experiments performed in this laboratory, the DC potential was set to 0 mV versus open circuit. 

Figure3.3 Dynamic polarization curves (scan ratev = lOmVs-1) forOj reduction on an OPC disk (area = 0.196 cm2) of an Au OPG RRDE (N = 0.38) in 02 saturated 0.1 M NaOH recorded at rotation rates of co = 900, 1600 and 2500rpm (upper panel).

The reduction of dioxygen in aqueous 02 saturated alkaline solutions on Au single crystal electrodes exhibits a pronounced dependence on the surface microstructure. This behavior is clearly evidenced by the RDE dynamic polarization curves in 0.1 M NaOH shown in Figure 3.4, from which the electrocatalytic activity is found to follow the sequence Au(l 0 0) > Au(l 1 0) > Au(l 11). Rather startlingly, the activity of Au (111) for small T, even surpasses that of Pt(l 11) at the same pH (see dotted curve in this figure) under otherwise virtually the same experimental conditions [18, 19]. 

Figure 3.9 (A) Dynamic polarization curves obtained using the pyrolytic graphite (PC) disk (A = 0.46 cm2) of a Pt PG RRDE recorded in 1.5 mM Co (111) (cyclam) in 0.5 M HCIO4 aqueous solutions,forw= 100,400,900 and 1600 rpm, where SSCE stands for a sodium chloride saturated calomel electrode. The corresponding ring currents obtained for Ering = 0.6 V are shown in the lower panel. (B) Plots of fJjTjc and /ring versus CO1 2.

Figure 3.15 (A) Dynamic polarization curves obtained with a carbon disk (A = 0.46cm2, top) of a Pt carbon RRDE (N = 0.175) and corresponding Pt ring (bottom) currents recorded in 1.5 mM Co(lll)(cyclam) in 0.5 M HCI04aqueoussolutionsintheabsence (curve 1) and in the presence of 02 at 900 rpm (curve 2), that is, Jc0(cyclam)/o2 small, for Ering = 0.6 (curve 3) and 1.0V versus SSCE (curve 4) both in the presence of 02. (B) Corresponding dynamic polarization curves recorded with the same...

Figure 3.44 (A) Dynamic polarization curves (v = 2 mVs 1, C0= 1000 rpm) recorded in 02-saturated 0.1 M NaOH, with a Pt OPG RRDE (AdiSk = 0.5cm2, N = 0.146) with the OPG disk modified by a spontaneously adsorbed layer of FeTsPc (solid squares), MnTsPc (empty triangles), CoTsPc (empty circles) and NiTsPc (solid triangles). (B) Pt ring currents, lr ng, recorded simultaneously with the ring polarized...

Figure 3.48 Upper panels dynamic polarization curves...

Figure 3.53 (A) Dynamic polarization curves Koutecky-Levich (right ordinate, upper abscissa, (v = 8.3 mVs-1) for a CoPI OPG RDE in 1 M open circles) plots based on i im values from...

Kinetic data extracted from the foot of RDE dynamic polarization curves for 02 reduction yielded for pH < 11 linear log[i/(ilim — i)] versus E, or Tafel plots, with a slope of around 120 mV per decade, and thus consistent with the first electron transfer as being rate determining for the reduction of the CoPI-02 adduct. As expected for a reversible (Nerstian) two-electron redox couple, the Tafel slope at pH = 14, decreased to 30 mV per decade. It is interesting to note that an oxidized form of the closely related CoOEP displays extraordinary reversibility for the 02—H202 couple in solutions of pH < 1 [63]. 

Figure 3.58 Dynamic polarization curves co = 250rpm (upper curves). The corresponding...

Figure 3.62 Dynamic polarization curves (v = 10 mVs-1) for dioxygen reduction at a Pt PG RRDE with the disk coated with 1.2 x 10-9 nmol cm-2 of the dicobalt 1,8-anthryldiporphyrin (A) and its corresponding monocobalt analogue (B) collected at 100 rpm in...

Figure 3.65 Dynamic polarization curves for 02 reduction at a PC disk of a Pt PC RRDE coated with DPX and DPXM (solid and dashed lines, respectively, A), and DPD and DPDM (solid and dashed lines, respectively, B) collected at 100 rpm in air-saturated solutions of 0.5 M HCI04-1.5 M CF3COOH for DPX and DPD, and 2 M HCIO4 for DPXM and DPDM. Ering= 1.0V.

Experimentally, these conditions axe satisfied when static or dynamic polarization curves axe performed at small scanning rates of the voltage. 

The use of Fourier Transform instruments eliminates much of the limitations of the EMIRS, since no more potential modulation is needed. The signal-to-noise ratio is far less than the dispersive instrument and can be improved statistically by adding more scans, since the spectral acquisition time is much lower. With the Fourier Transform equipment, also the irreversible processes can be studied, since it is no longer required to return to the same potentials as for modulation (see Sect. 3.4.4). This not only allows the acquisition of derivative or bipolar bands but also the acquisition of integral bands, as in the case of the adsorbed CO on platinum electrodes [20-25], which was impossible with EMIRS. The speed of spectral acquisition of Fourier Transform Infrared (FTIR) instruments allows also the follow-up of a reaction during a dynamic polarization curve [26, 27]. 

As this is a highly aggressive, accelerating test, tests with less concentrated solutions (0.1 M, 0.5 M) or solutions with additions (2-5 ppm HF, 2 ppm F ) can be found in the literature (Han, 2009 Yang, 2010). As dynamic polarization curves and thereof obtained corrosion potentials and corrosion current... 

Later in this chapter, the reader will be provided with experimental potentio-dynamic polarization curves obtained using the 273A potentiostat/galvanostat device and the experimental set up shown in Figure 6.1. 

Investigation of the anodic dissolution below the critical potential is likely to provide more relevant information on the mechanism of selective dissolution [178]. The emphasis is generally put on the current-time relationships, which are supposed to reflect the mechanism of transport within the surface layer. Dynamic polarization curves and current-time decays have been investigated for Cu-Au and Ag-Pd in LiCl... 

Sluijter, W. L., and Kreijger, P. C., "Potentio Dynamic Polarization Curves and Steel Corrosion," Heron (Delft), 1977, 22,1,13-27. 

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