Oxidation-reduction electrode potential cycling

Optical properties of gold nanorod arrays have been studied and were found to be dominated by surface plasmon modes superimposed on interference effects [99]. The formation of a surface complex composed of molecules (e.g. pyridine or pyr-azine) strongly bound to silver formed during oxidation-reduction electrode potential cycles is evident in ER spectra shown in Fig. 5.18. They show pronounced absorptions not found with the respective molecules in solution. 

The pc-Au/propylene carbonate (PC) + NaC104 interface has been studied by Nguyen Van Huong.481 A flame-annealed (02 + H2) pc-Au sphere was used. Before each experiment the pc-Au electrode was cleaned in an NaC104 aqueous solution by a few potential cycles involving oxidation-reduction of the surface until the i,E and C,E curves exhibited stable character. The C,E curves were recorded in the interval 15 150... 

The oxidation-reduction cycles (ORCs) necessary to roughen the electrode surface are generally performed as potential steps, linear sweeps with a... 

If [BMIMJPFg ionic liquid is saturated with GeCLj (Figure 6.2), two main reduction processes (Pi and P2) are observed in the cathodic regime [42], The first reduction peak, with a minimum at +500 mV vs. Ge (Pi) is attributed to the reduction of Ge(IV) to Ge(II). At potentials below 0 mV (P2) the bulk deposition of Ge from Ge(II) sets in, as can be seen with the naked eye. The rising cathodic current at about —1000 mV vs. Ge is attributed to the irreversible reduction of the organic cation. If only Pi is passed, an oxidation process is not observed. If Ge deposition is performed an oxidation peak at 1000 mV is observed, which means that this peak must be correlated to Ge electrooxidation. A series of oxidation peaks above +1500 mV is also observed if the electrode potential is cycled between +1000 and... 

The chemical reaction mechanism of electropolymerization can be described as follows. The first step in course of the oxidative electropolymerization is the formation of cation radicals. The further fate of this highly reactive species depends on the experimental conditions (composition of the solution, temperature, potential or the rate of the potential change, galvanostatic current density, material of the electrode, state of the electrode surface, etc.). In favorable case the next step is a dimerization reaction, and then stepwise chain growth proceeds via association of radical ions (RR-route) or that of cation radical with a neutral monomer (RS-route). There might even be parallel dimerization reactions leading to different products or to the polymer of a disordered structure. The inactive ions present in the solution may play a pivotal role in the stabilization of the radical ions. Potential cycling is usually more efficient than the potentiostatic method, i.e., at least a partial reduction... 

Fig. 18.8. Doping and undoping of a poly(pyrrole) film during oxidation and reduction cycles. When a poly(pyrrole) coated electrode is cycled between the reduction and oxidation potentials, the current observed at the oxidation potential is related to the ability of anions to enter the polymer film and dope the polypyrrole.

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