Platinum depolarization potential

The Kad Fischer jack on the back of most pH meters, used to monitor Kad Fischer titrations, suppHes a constant regulated current to the cell, which can consist of two identical (platinum) working electrodes. The voltammograms shown in Figure 9 illustrate the essential features of this technique. The initial potential difference, AH, is small because both redox forms of the sample coexist to depolarize the electrodes. The sample corresponds to the wave on the right-hand (cathodic) side of each figure and is therefore easily oxidized. The titrant is represented by the wave on the left-hand (anodic) side and is therefore easily reduced. Halfway to the end point the potential difference,, remains small, but at the end point the potential difference,... 

Therefore, one main drawback of the PEMFC configuration with a standard proton exchange membrane (such as Nafion) and a standard platinum gas diffusion cathode is the cathode depolarization caused by a mixed potential resulting from the methanol crossover through the mem-... 

The polymerization of anions is a special type of irreversible anodic processes. Of these the oxidation of sulphate to persulphate ions has been studied in the deepest detail. In the production of pcrsulphuric acid the yield is increased to a certain limit by a higher concentration of the initial sulphuric acid and an increased current density at the anode of smooth platinum. In too concentrated sulphuric acid the pcrsulphuric acid is already hydrolysed to a considerable extent to monopersulphuric acid (Caro s acid), which then acts as a depolarizer and lowers the required high potential at the anode. Electrolysis of sulphate solutions also gives persulphates and in this reaction the current efficiency will depend on the nature of the cation the efficiency increasing in the order of Na+, K+ and NHj. 

Electrolytic Oxidation I. Electrode Potential.—A series of stable potentials is difficult to obtain at an anode in the presence of a depolarizer the potential generally rises rapidly from the low value, at which the anode dissolves, to the high value for passivity and oxygen evolution. Since a platinum electrode is nearly always passive, however, it is possible to obtain graded potentials to a limited extent the data quoted in Table LXXXVI were recorded for the oxidation of an acid solution of... 

Suitable working electrodes for voltammetry are those that can be driven to take up a new potential in response to an applied external voltage, a process known as electrode polarization. Reduction or oxidation of an electrochemically active species at a working electrode results in depolarization of the electrode. The word depolarizer is therefore sometimes used to describe an electrochemically active species. In voltammetry, the working electrode may be fabricated from metals such as gold or platinum, various forms of carbon, or metallic mercury. 

Hence, the equation of -function type (2.10) describes the polarographic current-potential wave of a many-electron electrochemical process with depolarization. For example, it was established [2] that this kind of equation provides good approximation for the electrochemical wave of reduction of Si(IV) on a platinum electrode in KCl-KF-K2SiF6 melt (Fig. 2.6). 

The 21 formed in the second reaction is determined either by visual chemical titration with a reagent such as sodium thiosulfate in the presence of a suitable endpoint indicator or by amperometric, coulometric, or photometric titration methods. The most sensitive KF methods for the measurement of iodine are coulometric. For both the volumetric-amperometric and coulometric methods the endpoint is detected by a pair of platinum electrodes called the indicator electrodes. An electrical potential (100-400 mV) is applied across the electrodes to balance the circuit and the endpoint is reached when the concentration of I2 ( 50pmoll ) depolarizes the cathode deflecting a galvanometer. The volumetric method measures the amount of standardized reagent necessary to depolarize the platinum electrodes. The coulometric method utilizes, in addition to the indicator electrodes, a second pair of platinum electrodes (generator electrodes) that electrolytically convert the 1 to I2. The current consumed in this process is used to calculate the amount of water using the equation that describes Faraday s laws of electrolysis. 

Differences in the reduction potentials for copper, bismuth, lead and cadmium with a dropping mercury electrode has been seen In Figure 12.. Similar differences exist If a platinum electrode Is used providing a suitable depolarizing agent Is employed to prevent excess polarization at the anode. Hydrazine hydrochloride or hydroxylamlne hydrochloride are the usual depolarizers (l4). 

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