Working electrode, cyclic voltammetry

For PPV-imine and PPV-ether the oxidation potential, measured by cyclic voltammetry using Ag/AgCl as a reference are ,M.=0.8 eV and 0.92 eV, respectively. By adopting the values 4.6 eV and 4.8 eV for the work functions of a Ag/AgCl and an 1TO electrode, respectively, one arrives at zero field injection barriers of 0.4 and 0.55 eV. These values represent lower bounds because cyclic voltammetry is carried out in polar solvents in which the stabilization cncigy of radical ions exceeds that in a polymer film, where only electronic polarization takes place. E x values for LPPP and PPPV are not available but in theory they should exceed those of PPV-imine and PPV-ether. 

Figure 2.15 Schematic representation of the equipment necessary to perform linear sweep voltammetry LSV) or cyclic voltammetry CV). WFG waveform generator, P potentiostat, CR chart recorder, EC electrochemical cell, WE working electrode, CE counter electrode, RE...

Electron transfer of the glucose oxidase/polypyrrole on the electrode surface was confirmed by differential pulse voltammetiy and cyclic voltammetry. The glucose oxidase clearly exhibited both reductive and oxidative current peaks in the absence of dissolved oxygen in these voltammograms. These results indicate that electron transfer takes place from the electrode to the oxidized form of glucose oxidase and the reduced form is oxidized by electron transfer to the electrode through polypyrrole. It may be concluded that polypyrrole works as a molecular wire between the adsorbed glucose oxidase and the platinum electrode. 

The ohmic drop effect we are discussing deals only with the Ru portion ofthe cell resistance (Figure 1.5c). Indeed, the action of the potentiostat makes the working electrode potential independent not only of the possible shift of the counter electrode potential as the current varies, but also independent of the ohmic drop in the Rc portion of the cell resistance. In the case of cyclic voltammetry, the equation above becomes... 

Whereas the work function of the electrodes is measured by photoelectron spectroscopy, the organic materials are usually characterized by cyclic voltammetry [226]. The values can be extrapolated to the gas phase by choosing an... 

Figure 3.27. Energy level scheme of the device in Figure 3.26, consisting of the electrode work functions and the molecular HOMOs and LUMOs. The relative energy level of HOMOs and LUMOs can he determined hy cyclic voltammetry and optical spectroscopy. Note the hole blocking character of the electron-transport layer. This feature is important since holes that proceed via the HOMO levels have much higher mobilities than electrons proceeding via the LUMO levels.

The ability of varying the rate of the mass transport by agitating the solution (or the working electrode) constitutes the basis of hydrodynamic methods (hydrodynamics = liquids in motion), which are a further support to the study of electrode kinetics. Nevertheless we wish to cite them here simply to cover a drawback of cyclic voltammetry. In fact, cyclic voltammetry is unable to discriminate between oxidation and reduction processes, and vice-versa. 

Nanocarbons can also be deposited onto surfaces via electrochemistry, such as electrophoretic deposition described earlier. A method for one-step electrochemical layer-by-layer deposition of GO and PANI has been reported by Chen et al. [199]. A solution of GO and aniline was prepared and deposited onto a working electrode via cyclic voltammetry. GO was reduced on the surface when a potential of approx. -1 V (vs. SCE) was applied compared to the polymerization of aniline which occurred at approx. 0.7 V (vs. SCE). Repeated continuous scans between -1.4 to 9 V (vs. SCE) resulted in layer by layer deposition [199]. A slightly modified method has been reported by Li et al. who demonstrated a general method for electrochemical RGO hybridization by first reducing GO onto glassy carbon, copper, Ni foam, or graphene paper to form a porous RGO coating [223]. The porous RGO coated electrode could then be transferred to another electrolyte solution for electrochemical deposition, PANI hybridization was shown as an example [223]. 

Cyclic voltammetry was conducted using a Powerlab ADI Potentiostat interfaced to a computer. A typical three electrode system was used for the analysis Ag/AgCl electrode (2.0 mm) as reference electrode Pt disc (2.0 mm) as working electrode and Pt rod (2.0 mm) as auxiliary electrode. The supporting electrolyte used was a TBAHP/acetonitrile electrolyte-solvent system. The instrument was preset using a Metrohm 693 VA Processor. Potential sweep rate was 200 mV/s using a scan range of-1,800 to 1,800 mV. 

Cyclic voltammetry experiments were controlled using a Powerlab 4/20 interface and PAR model 362 scanning potentiostat with EChem software (v 1.5.2, ADlnstruments) and were carried out using a 1 mm diameter vitreous carbon working electrode, platinum counter electrode, and 2 mm silver wire reference electrode. The potential of the reference electrode was determined using the ferrocenium/ ferrocene (Fc+/Fc) couple, and all potentials are quoted relative to the SCE reference electrode. Against this reference, the Fc /Fc couple occrus at 0.38 V in acetonitrile and 0.53 V in THF [30, 31]. 

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