Corrosion cell components anode

A prerequisite of long-life sodium/sulfur batteries is that the cells contain suitable corrosion-resistant materials which withstand the aggressively corrosive environment of this high—temperature system. Stackpool and Maclachlan have reported on investigations in this field [17], The components in an Na/S cell are required to be corrosion-resistant towards sodium, sulfur and especially sodium polysulphides. Four cell components suffer particularly in the Na/S environment the glass seal, the anode seal, the cathode seal, and the current collector (in central sodium arrangements, the cell case). 

There are corrosion problems of the anode and other cell components in HNO3/HCI. 

We have previously mentioned that all of the components of a galvanic cell must be present for corrosion to occur. Corrosion control functions by eliminating or reducing the effectiveness of one or more of these components. Thus we can control corrosion by eliminating anodes and cathodes, by eliminating or reducing differences in potential between metallic sites, and by breaking internal or external circuits. Some of these objectives are achieved by subtle methods but the secret in corrosion... 

The two types of high temperature fuel cell are quite different from each other (Table 6). The molten carbonate fuel cell, which operates at 650°C, has a metal anode (nickel), a conducting oxide cathode (e.g. lithiated NiO) and a mixed Li2C03/K2C03 fused salt electrolyte. Sulphur attack of the anode, to form liquid nickel sulphide, is a severe problem and it is necessary to remove H2S from the fuel gas to <1 ppm or better. However, CO is not a poison. Other materials science problems include anode sintering and degradation, corrosion of cell components and evaporation of the electrolyte. Work continues on this fuel cell in U.S.A. and there is some optimism that the problem will be solved within 10 years. 

The "corrosion cell , which is shown as a highly schematic, instantaneous snapshot of the metal surface (Fig, 10.2) has five essential components (1) anodic zones (2) cathodic zones (3) electrical contact between anodic and cathodic zones (4) an (ionically) conducting solution and (5) a cathodic reactant. 

The design and assembly of PEM fuel cell components, such as flow fields and manifolds, can have a significant influence on water management and feed flows, which will in mrn affect the durability of fuel ceU components. For example, an improper design of the flow fields can result in water blockage, and improper manifold design can induce poor cell-to-cell flow distribution, both of which may cause localized fuel starvation. This localized fuel starvation can then induce an increased local anode potential to levels at which carbon oxidation or even water electrolysis may occur to provide the required protons and electrons for the oxygen reduction reaction (ORR) at the cathode. These reactions will induce corrosion of the carbon support and will result in a permanent loss of electrochemically active area at the anode. 

Electrowinning in molten salts is the only way to obtain some metals in the elementary state. The process, however is not straightforward and involves many problems. Corrosion of the cell components and electrodes is a persistent very serious problem. If the metal deposits as a solid, separation may be diflScult growth of dendrites may cause short-circuit between the anode and cathode. Solubility of the metal in the melt may be a source of current inefficiency. 

In this section, the relationship of corrosion inhibitors to anodic and cathodic polarization wiU be explained. Of the four components of a corrosion cell (anode, cathode, electrolyte, and electronic conductor), three may be affected by a corrosion inhibitor to retard corrosion. The inhibitor may cause ... 

Besides corrosion issues of metal substrates, the use of alloys as mechanical supports of the cells is subject to interdiflfusion of iron, chromium, and nickel between ferritic steel and nickel-containing anodes during cells fabrication and operation. Diffusion of nickel into FSS substrates may cause austenitization of steels, which would result in TEC mismatch with other cell components. Diffusion of iron and chromium into Ni-based anodes may cause formation of oxide scales on nickel particles. This would result in fast degradation of cell performance during operation, as the electrochemically active surface is passivated. In order to overcome these issues, one possibility investigated by MS-SOFC developers is to use protective coatings [1-6, 13]. 

The electrodes are the typical and most important components of an electrochemical cell - especially the working electrode - which usually decide about the success of an electroorganic synthesis. Electrode materials need a sufficient electronic conductivity and corrosion stability as well as, ideally, a selective electrocat-alytic activity which favors the desired reaction. The overvoltages for undesired reactions should be high, for example, for the decomposition of the solvent water by anodic oxygen or cathodic hydrogen evolution. But, additionally, the behavior of electrodes can show unexpected and incomprehensible effects, which will cause difficulties to attain reproducible results. 

Both batteries and fuei cells utilize controlled chemical reactions in which the desired process occurs electrochemically and all other reactions including corrosion are hopefully absent or severely kinetically suppressed. This desired selectivity demands careful selection of the chemical components including their morphology and structure. Nanosize is not necessarily good, and in present commercial lithium batteries, particle sizes are intentionally large. All batteries and fuel cells contain an electropositive electrode (the anode or fuel) and an electronegative electrode (the cathode or oxidant) between which resides the electrolyte. To ensure that the anode and cathode do not contact each other and short out the cell, a separator is placed between the two electrodes. Most of these critical components are discussed in this thematic issue. 

The most important applications of nickel metal involve its use in numerous alloys. Such alloys are used to construct various equipment, reaction vessels, plumbing parts, missile, and aerospace components. Such nickel-based alloys include Monel, Inconel, HasteUoy, Nichrome, Duranickel, Udinet, Incoloy and many other alloys under various other trade names. The metal itself has some major uses. Nickel anodes are used for nickel plating of many base metals to enhance their resistance to corrosion. Nickel-plated metals are used in various equipment, machine parts, printing plates, and many household items such as scissors, keys, clips, pins, and decorative pieces. Nickel powder is used as porous electrodes in storage batteries and fuel cells. 

---