Cathode materials chromium oxides

Tin Free Steel—Electrolytic Chromium-Coated. A less expensive substitute for tinplate, electrolytic chromium coated-steel, has been developed and is designated TFS-CT (tin free steel-chromium type) or TFS-CCO (tin free steel-chromium-chromium oxide) (19). This material can be used for many products where the cathodic protection usually supplied by tin is not needed. A schematic cross section is shown in Figure 2. Electrolytic, chromium-coated steel is made by electro-lytically depositing a thin layer of metallic chromium on the basic tin mill steel, which is in turn covered by a thin passive coherent layer of chromium oxide. 

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. 

Newly developed alloys have improved properties in many aspects over traditional compositions for interconnect applications. The remaining issues that were discussed in the previous sections, however, require further materials modification and optimization for satisfactory durability and lifetime performance. One approach that has proven to be effective is surface modification of metallic interconnects by application of a protection layer to improve surface and electrical stability, to modify compatibility with adjacent components, and also to mitigate or prevent Cr volatility. It is particularly important on the cathode side due to the oxidizing environment and the susceptibility of SOFC cathodes to chromium poisoning. 

Molten Carbonate Fuel Cell The electrolyte in the MCFC is a mixture of lithium/potassium or lithium/sodium carbonates, retained in a ceramic matrix of lithium aluminate. The carbonate salts melt at about 773 K (932°F), allowing the cell to be operated in the 873 to 973 K (1112 to 1292°F) range. Platinum is no longer needed as an electrocatalyst because the reactions are fast at these temperatures. The anode in MCFCs is porous nickel metal with a few percent of chromium or aluminum to improve the mechanical properties. The cathode material is hthium-doped nickel oxide. 

One of the most important problems found during stack operation using metallic interconnect materials is the formation of volatile chromium oxides and/or oxy-hydroxides [6, 7] at the cathode side of the cell leading to serious deterioration of the cell performance [7]. Several authors proposed various protective coating types to prevent the deleterious effect of volatile Cr-species [8]. 

In the anodic atmosphere, metallic nickel is stable, and so nickel coating improves the durability of the stainless steel. On the cathode side, chromium easily dissolves from the stainless steel. Therefore, the outer layer and inner layer are porous LiFe02 and dens chromium-rich oxide layer as the corrosion protection layer, respectively. The corrosion of the current collectors increases the electronic resistance and decreases the amount of electrolyte. Therefore, the material is selected with a lower electronic resistance of the corrosion layer and lower crmsumption of electrolyte. Based on these requirements, SUS316L is better than SUS310 even it has higher Ni and Cr crmtents [2, 4, 5]. 

Metallic chromium is also produced by an electrolytic method. Ferrochromium is crushed and dissolved at a temperature near the boiling point in a mixture of sulfuric acid and used anolyte. In a crystallizer the iron is separated as iron ammonium sulfate at a temperature of 5°C. The temperature in the electrolytic cells is 53°C. In the process sulfuric add and hexavalent chromium are formed in the anolyte. Because of that it must be prevented from mixing with the catholyte. Otherwise the divalent chromium there wiU be oxidized and the chromium predpitation disturbed. The cathode material is 316-type molybdenum-alloyed stainless steel, the anode material silver-alloyed lead or titanium covered with iridium. For environmental reasons dichromate plants are dosed and the aluminothermic part of the chromium metal production increases. About 1990 it was 60 % and in the begiiming of the 2000s 90 %. 

A serious challenge in the use of LSM as a cathode material in intermediate temperature SOFC stems from the use of metallic interconnects. Many of these metals contain chromium, which forms a stable protective oxide (chromia) layer with reasonable conductivity (see Section 7.1.4 on interconnects for more details). However, chromia vapors can lead to serious poisoning of the cathode (21, 22). Although one might attribute this problem more to the interconnect material than to the cathode, the poisoning effect was found to depend strongly on the electrolyte/cathode material combination. 

We took advantage of the dispersibility of Pd Ce02 core-shell structures to deposit them into the porous scaffold of SOFC materials as anode catalysts in order to enhance the thermal stability of these materials. The porous scaffolds were composed of yttrium-stabilized zirconia (YSZ) covered with a film of the conductive oxide lanthanum strontium chromium manganite (LSCM). For comparison of the activity and thermal stability, we prepared other electrodes that were identical except that the catalyst was simply Pd (from Pd(II) nitrate) in one case and a mixture of Pd and CeOg (from Pd(II) and Ce(III) nitrate salts) in the other. All the samples were first calcined at 700 °G to remove any by-products and to stabilize the materials. Then, accelerated aging tests were performed by calcining the samples at 900 °C for 2 hours. Initially we tested all the formulations in symmetric cells, e.g. cells where the anode and cathode materials are the same. The corresponding Nyquist plots are shown in Fig. 7.12(a). 

Molten Carbonate Fuel Cell. The electrolyte ia the MCFC is usually a combiaation of alkah (Li, Na, K) carbonates retaiaed ia a ceramic matrix of LiA102 particles. The fuel cell operates at 600 to 700°C where the alkah carbonates form a highly conductive molten salt and carbonate ions provide ionic conduction. At the operating temperatures ia MCFCs, Ni-based materials containing chromium (anode) and nickel oxide (cathode) can function as electrode materials, and noble metals are not required. 

The nickel-chromium plating process includes the steps in which a ferrous base material is electroplated with nickel and chromium. The electroplating operations for plating the two metals are basically oxidation-reduction reactions. Typically, the part to be plated is the cathode, and the plating metal is the anode. 

The perovskite oxides used for SOFC cathodes can react with other fuel cell components especially with yttria-zirconia electrolyte and chromium-containing interconnect materials at high temperatures. However, the relative reactivity of the cathodes at a particular temperature and the formation of different phases in the fuel cell atmosphere... 

Since ionic radii and valences of iron and chromium ions are similar to gallium ion, substitution of these cations with gallium ion may result in powders with similar crystal structure and properties to LSGM. Moreover, LaFe03- and LaCr03-based oxides are candidate cathode and anode materials for SOFC, respectively. 

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