Current density / potential curves, platinum electrodes

In order to determine the kinetic parameters of the reaction corrected from diffusion phenomenon, a voltammetric investigation was pursued with a rotating platinum ring disk electrode. Figure 21.10 represents current density-potential curves obtained for different rotation speeds and for the positive variations of potential. It appears that the current density of the rotating disk increases with the rotation rate. 

Turning now to the acidic situation, a report on the electrochemical behaviour of platinum exposed to 0-1m sodium bicarbonate containing oxygen up to 3970 kPa and at temperatures of 162 and 238°C is available. Anodic and cathodic polarisation curves and Tafel slopes are presented whilst limiting current densities, exchange current densities and reversible electrode potentials are tabulated. In weak acid and neutral solutions containing chloride ions, the passivity of platinum is always associated with the presence of adsorbed oxygen or oxide layer on the surface In concentrated hydrochloric acid solutions, the possible retardation of dissolution is more likely because of an adsorbed layer of atomic chlorine ... 

A cell with a capacity of 1 L was made of mild steel. An amorphous carbon rod (diameter 25 mm length 15 cm) was used as anode, the inside wall of the cell as cathode and a platinum wire was used as reference electrode. The anode compartment of the cell was separated from the cathode compartment by a skirt of steel welded to the cell cover. The anode gas was passed through a tube filled with tablets of NaF to absorb anhyd HF gas and then led to a gas sampler. Fluorine was detected with K.I soln. After the starting material was added into the molten KIIF2/HF salt, the electrolyte was pre-electrolyzed at a low current density until NF2 was detected, and then current efficiency of each product and polarization curves by galvanostatic or potential sweep method were determined (Table 1). At optimum conditions the current efficiency of NF3 was 55%. 

The electrochemical activity of the counter electrode can be checked by cychc voltammetry (CV) with respect to the triiodide/iodide redox couple in a sample electrolyte. Comparison of the peak potentials of reduction and oxidation and current densities thereof with those of various platinum electrodes gives preliminary assessment of the cathode material for use in DSSCs. PPDOT-Et2 conter electrodes, as well as the above-described PEDOT-PSS counter electrodes, demonstrated peak potentials and redox current densities close to those of the platinum electrode. In Figure 3.8, the redox behavior of PPDOT-Et2 in a triiodide/iodide-based electrolyte (ImM D, lOmM Lil, 0.1 M LiC104 in AN) is compared with that of the sputtered platinum electrode, where a PPDOT-Et2 film was deposited by a charge capacity of 40mCcm for polymerization. The two anodic and cathodic peaks in the CV curves represent the following two reactions [31] ... 

In the Rotating Disk Electrode (RDE) technique, the current-potential curves on smooth platinum exhibit an anodic limiting current density, which depends on rotation rate in both acidic and alkaline media [46]. These plots are well described by equation (19), which holds for a diffusion overpotential alone. Similar relationships have been observed in acidic solutions for Ir, Rh, and Pd, and well-characterized Pt-Ru, Pt-Rh, Pt-Sn [53], and Pt-Au [51] alloys, and also for Ni in alkaline solutions. In the case of platinum, a evolution of the limiting diffusion current density to a limiting reaction current density ( x) independent of rotation rate, is observed as a consequence of the rate-determining H2 adsorption. 

Rates of corrosion can also be measured using an electrochemical technique known as potentiodynamic polarization. The potential of the test metal electrode relative to a reference electrode (commonly the saturated calomel electrode SCE) is varied at a controlled rate using a potentiostat. The resultant current density which flows in the cell via an auxiliary electrode, typically platinum, is recorded as a function of potential. The schematic curve in fig. 2 is typical of data obtained from such a test. These data can provide various parameters in addition to corrosion rate, all of which are suitable for describing corrosion resistance. The corrosion potential F corr is nominally the open circuit or rest potential of the metal in solution. At this potential, the anodic and cathodic processes occurring on the surface are in equilibrium. When the sample is polarized to potentials more positive than Scon the anodic processes, such as metal dissolution, dominate (Anodic Polarization Curve). With polarization to potentials more negative than Scorr the cathodic processes involved in the corrosion reaction such as oxygen reduction and hydrogen evolution dominate (Cathodic Polarization Curve). These separate halves of the total polarization curve may provide information about the rates of anodic and cathodic processes. The current density at any particular potential is a measure of the... 

The iodine-iodide electrode has been investigated and reported by many authors. Brunner [162] and Vetter [163] have given comprehensive and detailed descriptions of the chemical reactions, the equilibrium potential, polarization phenomena, and current density vs. potential curves of the iodine-iodide redox system, obtained with platinum as the noble metal electrode. 

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