Oxidative degradation technology development

In this chapter the technological development in cathode materials, particularly the advances being made in the material s composition, fabrication, microstructure optimization, electrocatalytic activity, and stability of perovskite-based cathodes will be reviewed. The emphasis will be on the defect structure, conductivity, thermal expansion coefficient, and electrocatalytic activity of the extensively studied man-ganite-, cobaltite-, and ferrite-based perovskites. Alterative mixed ionic and electronic conducting perovskite-related oxides are discussed in relation to their potential application as cathodes for ITSOFCs. The interfacial reaction and compatibility of the perovskite-based cathode materials with electrolyte and metallic interconnect is also examined. Finally the degradation and performance stability of cathodes under SOFC operating conditions are described. 

The U.S. Department of Energy s Office of Technology Development has sponsored full-scale environmental restoration technology demonstrations since 1990. The Savannah River Site Integrated Demonstration focuses on the bioremediation of groundwater contaminated by chlorinated solvents. Several laboratories, including the Savannah River site, have demonstrated the ability of methanotrophic bacteria (i.e., those that oxidize methane) found in soil, sediment, and aqueous material, to completely degrade or mineralize chlorinated solvents. 

Development of chlorine electrode materials has benefited from the experience of chlor-alkali electrolysis cell technology. The main problem is to find the best compromise between cycle life and cost. Porous graphite, subjected to certain proprietary treatments, has been considered a preferable alternative to ruthenium-treated titanium substrates. The graphite electrode may undergo slow oxidative degradation, but this does not seem to be a significant process. 

Table 9.1 summarizes catalyst compositions and corresponding performances. The oxidation of ethane to acetic acid is now commercial an industrial plant is installed, with the technology developed by Saudi Basic. Elements that have contributed to the successful development of the process are (1) the discovery of a catalytically active compound, the multifunctional properties of which can be modified and tuned to be adapted to reaction conditions through incorporation of various elements (2) the stability of the main products, ethylene and acetic acid, which do not undergo extensive consecutive degradation reactions (3) the possibility of recycling the unconverted reactant and the major by-product, ethylene (4) the use of reaction conditions that minimize the formation of CO and (5) an acceptable overall process yield. 

Most current technology development is focused on the use of platinum (or platinum and ruthenium) supported on carbon particles, in order to reduce the amount of platinum required on the anode down to 0.05-0.45 mg cm", as described in [10]. These types of anodes are prone to degradation during fuel starvation due to the reaction in Equation 17.6, the oxidation of carbon, which is catalyzed by the presence of platinum [11]. This reaction proceeds at an appreciable rate at the electrode potentials required to electrolyze water in the presence of platinum (greater than approximately 1.4 V [24). This is shown schematically in Figure 17.4. The catalyst support is converted to CO2, and Pt and/or Ru particles may be lost from the electrode, resulting in loss of performance. 

Degradable plastics can be manufactured by a variety of processes [10]. An early approach to the problem was to add oxidation accelerators such as ben-zophenone to make unstable plastics. As the technology developed, more sophisticated systems were devised since packaging materials must not only degrade, but must do so at a controlled and predictable rate. A number of these systems have also been described. 

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