Static disc electrode

Static-disc electrode with perpendicular flow T 3.27 nfc Df Be Sc ... 

Unfortunately, the to-electrode precipitation required for conventional (photo)electrochemical measurements on colloidal semiconductors necessarily perturbs the (assumed) spherical diffusion fields and surface adsorption equilibria that obtain at particles in the free solution state, phenomena which are instrumental in determining the dynamic and static charge transfer characteristics of the semiconductor. Consequently, there is a requirement for photoelectrochemical techniques capable of in situ, non-per-turbative investigations of the mechanistic details and catalytic properties of colloidal semiconductors in solution conditions typical of their intended ultimate application. Two such techniques are photoelectrophoresis and the Optical Rotating Disc Electrode (ORDE, developed by Albery et al.). As mentioned above, the former technique has already been reviewed by this author elsewhere [47]. Thus, the remainder of this review will concentrate on measurements that can be made with the latter... 

The effect of convection on the DPV response can be predicted by a theoretical comparison between the limit of a Nerns-tian diffusion layer in which the solution is fully stagnant and a rotating disc electrode [73, 74]. The general trend is as the speed of rotation increases (which corresponds to a reduction in diffusion layer thickness in the static simulation), the peak... 

Fig. 2. Influence of the radial diffusion on the current-time response under diffusion-limited conditions. (A) at the static spherical electrode of the radius ro = 0.5mm (B) at the disc microelectrode of the radius a = 5 m. Simulated currents in dimensionless scales ipi = 1/ (nFTrrocXD ) and I/(nF7racXD ), respectively 1, currents according to the Cottrell equation 2, currents corrected for the radial diffusion 3, steady state currents. (A) = 2000, (B)...

Cyclic voltammetry (CV) and linear sweep voltammetry (LSV) are the most popular techniques in present electrochemical and bioelectrochem-ical research work. CV at static electrodes (Pt discs, mercury hanging electrodes, Pt microelectrodes and carbon fiber electrodes) is now routinely used to characterize the redox properties of compounds, to identify active intermediates and products and to qualitatively estimate their stability. In appropriate cases quantitative treatment is also possible [79]. 

The time resolution for the detection of a product at the disk by the ring current is in the range of 0.1 s, which is required for the transport due to the laminar flow of the electrolyte in front of the electrode. Therefore, this method is suited for measurements of potentio-static dissolution transients in this time frame. One example for corrosion is the separation of currents measured during passivation transients at the disc into a part for metal dissolution and another for oxide formation. The ring current allows calculating the dissolution rate i at the disc according to Equation 1.130, whereas the difference to the total disc current foi - ic = K yields the current density of layer formation These investigations may be done with the time resolution of the method of ca. 0.1 s, i.e., x c and may be followed as a function of time. 

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