Activated cathodes

Data, for a 32% caustic concentration at 90°C and a current efficiency of 96.0%, obtained in laboratory cells using a DSA anode and an activated cathode, where the membrane is against the anode at a 3-mm gap. 

Fig. 16. Performance data obtained ia laboratory cells using Nafion NX-961, DSA anode, activated cathode, narrow gap, at 90°C. Energy consumption is...

Reserve batteries have been developed for appHcations that require a long inactive shelf period foUowed by intense discharge during which high energy and power, and sometimes operation at low ambient temperature, are required. These batteries are usually classified by the mechanism of activation which is employed. There are water-activated batteries that utilize fresh or seawater electrolyte-activated batteries, some using the complete electrolyte, some only the solvent gas-activated batteries where the gas is used as either an active cathode material or part of the electrolyte and heat-activated or thermal batteries which use a soHd salt electrolyte activated by melting on appHcation of heat. 

Mild steel cathodes are used extensively in chlor-alkah and chlorate cells. Newer activated cathode materials have been developed that decrease cell voltages about 0.2 V below that for cells having mild steel cathodes. Some activated cathodes have operated in production membrane cells for three years with only minor increases in voltage (17). Activated cathodes can decrease the energy consumption for chlorine—caustic production by 5 to 6.5%. 

The reaction mixture is filtered. The soHds containing K MnO are leached, filtered, and the filtrate composition adjusted for electrolysis. The soHds are gangue. The Cams Chemical Co. electrolyzes a solution containing 120—150 g/L KOH and 50—60 g/L K MnO. The cells are bipolar (68). The anode side is monel and the cathode mild steel. The cathode consists of small protmsions from the bipolar unit. The base of the cathode is coated with a corrosion-resistant plastic such that the ratio of active cathode area to anode area is about 1 to 140. Cells operate at 1.2—1.4 kA. Anode and cathode current densities are about 85—100 A/m and 13—15 kA/m, respectively. The small cathode areas and large anode areas are used to minimize the reduction of permanganate at the cathode (69). Potassium permanganate is continuously crystallized from cell Hquors. The caustic mother Hquors are evaporated and returned to the cell feed preparation system. 

Cyclic voltammetry (adsorption, monolayers) Potentiodynamic polarisation (passivation, activation) Cathodic reduction (thickness) Frequency response analysis (electrical properties, heterogeneity) Chronopotentiometry (kinetics)... 

Introduction of electrOcheiiiicaUy active cathodes that facilitate passivation Raise potential by external e.m.f Additions of Pt. Pd and other noble metals to Ti, Cr and stainless steels Anodic protection of steel, stainless steel and Ti... 

Nevertheless, water is decomposed with evolution of hydrogen but under controlled conditions and with a reasonable reaction rate. With water as the active cathode material, the battery system—used in military underwater applications—can be designed as (-) Li / KOH / H20 (+) [19]. The... 

Electrons appear as starting materials, so this half-reaction is the reduction, which takes place at the cathode. Lead(IV) oxide is an active cathode in a lead storage battery. 

The electrochemical behavior of thin-film oxide-hydroxide electrodes containing chromium, nickel and cobalt compounds was investigated. Experimental results have shown that such compounds can be successfully used as active cathodic materials in a number of emerging primary and secondary battery applications. 

Organometallic compounds can be generated at the electrode in three ways. An alkyl halide is reduced at an active cathode, for example, Pb, Sn, which reacts with the intermediate radical [163, 164]. A Grignard reagent or an at-complex is oxidized at an active anode and the intermediate radical reacts with the anode... 

In comparison with the surface layer chemistry on active cathode materials where both salt anions and solvents are involved, a general perception extracted from various studies is that the salt species has the determining influence on the stabilization of the A1 substrate while the role of solvents does not seem to be pronounced, although individual reports have mentioned that EC/DMC seems to be more corrosive than PC/DEC. Considering the fact that pitting corrosion occurs on A1 in the polymer electrolytes Lilm/PEO or LiTf/PEO, where the reactivity of these macromolecular solvents is negligible at the potentials where the pitting appears, the salt appears to play the dominant role in A1 corrosion. 

Meyers, J. P. Villwock, R. D. Darling, R. M. Newman, J. In Advances In Mathematical Modeling and Simulation of Electrochemical Processes and Oxygen Depolarized Cathodes and Activated Cathodes for Chlor-Alkall Processes, Van Zee, J. W., Puller, T. P., Poller, P. C., Hine, P., Eds. The Electrcohemical Society Proceedings Series Pennington, NJ, 1998 Vol. PV 98-10. 

Eor the purpose of modeling, consider a planar SOEC divided into anode gas channel, anode gas diffusion electrode, anode interlayer (active electrode), electrolyte, cathode interlayer (active electrode), cathode gas diffusion electrode, and cathode gas channel. The electrochemical reactions occur in the active regions of the porous electrodes (i.e., interlayers). In an SOFC, oxidant reduction occurs in the active cathode. The oxygen ions are then transported through the electrolyte, after which oxidation of the fuel occurs in the active anode by the following reactions. 

Raney-nickel catalysts are barely sensitive to catalyst poisoning (as are Pt-activated cathodes), e.g., by iron deposition, but they deteriorate due to loss of active inner surface because of slow recrystallization—which unavoidably leads to surface losses of 50% and more over a period of 2 years. A further loss mechanism is oxidation of the highly dispersed, reactive Raney nickel by reaction with water (Ni + 2H20 — Ni(OH)2 + 02) under depolarized condition, that is, during off times in contact with the hot electrolyte after complete release of the hydrogen stored in the pores by diffusion of the dissolved gas into the electrolyte. 

This type of N-doped soot catalyst is of particular interest for the development of advanced fuel cells. As this type of catalyst is not poisoned by carbon monoxide, it is a promising candidate for O2 cathodes in methanolconsuming fuel cells (132). In methanol-combusting cells, diffusive transport of methanol from the anode to the cathode cannot be avoided, with the consequence that the activity of Pt-activated cathodes becomes severely impaired by CO poisoning of the Pt catalyst therefore, a CO-insensitive cathodic electrocatalyst seems to be indispensible. Yet the longevity of this type of catalyst is still in dispute (133). 

Active cathode material Product Electrons involved Ah/g Ah/cnr... 

Ni can be taken as the reference material against which all other materials should be evaluated. On the average, the operating overpotential of untreated Ni electrodes is about 0.4 V at 0.2 A cm-2 [5], Beyond Ni, we deal with activated cathodes , which in fact derive from the idea of activated anodes such as the DSA . By activated electrodes we mean that the surface has been subjected to some treatments aimed at increasing its catalytic activity. This can be a treatment which modifies the surface structure and the morphology of the base metal, but more often the treatment is aimed at coating the base metal with a more active material [31]. 

In other cases, thermal decomposition is used to prepare the active layer which is then activated either by a high temperature treatment in H2 atmosphere, or by in situ reduction under cathodic load. It has been reported that for molybdate-activated cathodes the latter procedure is less satisfactory than the former [153]. Thus, temperature, procedure of preparation and activation are all crucial parameters which can dramatically influence the final activity. 

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