Coated anodes impurity effects

In chlor-alkali production, EMOS should be able to determine problems with both anode coatings and membranes. The literature is replete with examples of the effect of different impurities on membranes [2] and of the analysis of different problems using polarisation curves to determine their cause [3, 4]. These analysis techniques have been incorporated into the expert system in the form of approximations of the polarisation curves. Use is made of the familiar k-factor (see Equation 8.2) or the more accurate logarithmic form of this factor (Equation 8.3) ... 

Fig. 1 shows one of the first electrolytically deposited alumimun coatings to be obtained from this type of electrolyte. Since electrolytic aluminum deposition from this system has no true smoothening effect, thick layers become even rougher, as illustrated by the thickly coated cathode plate shown in Fig. 1. The cathodic deposition and the anodic dissolution of aluminum corresponded to almost 100 <7o of the amount expected according to the Faraday rule, which is an important prerequisite for even considering using this electrolysis technique for technical applications. Independently of the layer thickness, the deposited aluminum layers are found to be ectraordinarily pure. Spectroscopic investigations have revealed purities of up to 99.999%. Even when relatively impure raw aluminum with purities of 99.7% functions as the anode, very pure aluminum can be deposited. Therefore, obviously not only a technique of electroplating aluminum was discovered, but also a method of...

Devianto et al. [21] investigated the poisoning effect of H2S on Ni-based anodes in MCFC at low H2S concentrations, simulating biogas impurity. A conventional Ni-Cr anode was coated with ceria using dip coating to form a rare earth metal oxide thin layer on the surface of the anode. Electrochemical studies of the Ni-based samples were performed in symmetric cells under anode atmosphere (H2, CO2, H2O, and N2 as balance) with 2, 6, 12, and 24 ppm of H2S by means of electrochemical impedance spectroscopy. 

Membrane and electrode damage effect cell performance, i.e., cause lower current efficiency, increased cell voltage, and, as a result, increased power consumption [143]. Some impurities affect the anode or cathode coating and cause an increase in overvoltage or simply deposit in the membrane, increasing its resistance and thus the cell voltage. The increase in voltage may in some cases be partially reversible when the impurity concentration drops to the recommended limits. 

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