Copper/ceria anode

Poor activity for direct oxidation of hydrocarbons and propensity for carbon formation when exposed to hydrocarbons. To improve the activity for direct oxidation and reduce the anode s propensity for carbon formation, copper - ceria anodes are being developed. 

Figure 17. Fuel cell performance obtained from the SSC (anode) GDC (electrolyte) I copper-ceria (anode) cell, shown in Fig. 15.

Combination of foam stracture with functional materials is another intriguing topic. Combination of porous metal with active materials used for sensors, fuel cells, and batteries are particularly promising. Exemplary composites include copper-ceria (for the anode in solid oxide fuel cells as suggested in Section a... 

FIGURE 6.11 Diagram of the processing technique used to prepare Cu-Ce02-YSZ anodes for direct oxidation of hydrocarbon fuels by preparing a porous preform of YSZ and then infiltrating it with cerium nitrates to form ceria and then with copper nitrates to form metallic copper [84]. Reprinted from [84] with permission from Elsevier. 

Alloying the nickel of the anode to improve tolerance for fuel contaminants has been explored. Gold and copper alloying decreases the catalytic activity for carbon deposition, while dispersing the anode with a heavy transition metal catalyst like tungsten improves sulfur resistance. Furthermore, ceria cermets seem to have a higher sulfur tolerance than Ni-YSZ cermets [75],... 

The selective oxidation or preferential oxidation of CO in hydrogen-rich stream is another important object for ceria based catalysts. The gas mixture from steam reforming/partial oxidation of alcohols or hydrocarbons, followed by the WGS reaction contains mainly FI2, CO2 and a small portion of CO, H2O, and N2. When such gaseous stream would be taken as input for hydrogen fuel cells, the CO has to be removed to avoid poisoning of the anode electrocatalysts. Ceria based nanomaterials, such as ceria/gold, ceria/copper oxide catalysts exhibit suitable catalytic activities and selectivities for CO PROX process. 

The present work was focused on the synthesis of nanocrystalline components for electrochemical cells via the cellulose-precursor technique. This method was used to prepare nanostructured intermediate-temperature (IT) SOFC anodes made of a series of cermets comprising gadolinia-doped ceria (CGO), yttria-stabilized zirconia (YSZ), Gdi.86Cao.i4Ti207.5 (GCTO) pyrochlore, metallic nickel and copper. Perovskite-type SrFcojAlo.sOs.s (SFA) powder, also obtained via the cellulose precursor, was applied onto membranes of the same composition to enhance specific surface area and electrocatalytic activity in the reactors for methane conversion [3]. 

Direct oxidation (or direct utilization) The fuel is oxidized directly in the SOFC without external reformation. The SOFC has been shown to have the capabihty for direct oxidation of different types of fuels [4, 36-38]. To address the carbon deposition issue associated with nickel commonly used in the anode composition, other metals such as copper have been tested. The abihty of copper to resist carbon formation leads to the development of a composite anode composed of a ceria support and a copper phase [38]. The key technical challenges in the development of direct-oxidation SOFCs relate to the anode, especially the electrode s performance, stability, and direct-oxidation capabihty. 

Recent studies have also identified some alternative anodes, one being copper-based and incorporating significant quantities of ceria in addition to YSZ [68,114] and the other adding yttria-doped ceria to nickel and YSZ [69], both of which have been reported to show considerable promise for the direct electrocatalytic oxidation of the hydrocarbon fuels, without the need for any co-fed oxidant. However, the conditions under which such anodes can be used for direct hydrocarbon oxidation may be a problem for their widespread application, whilst their long-term performance in terms of deactivation resulting from carbon deposition remains to be investigated. 

Replacement of most or all of the Ni is also investigated using an anode catalyst, such as doped ceria, that is stable in contact with YSZ in SOFC fuel conditions [10]. Ceria offers improved stability, though its electronic conductivity is much less than that of Ni. As the electronic current passing from the metal support to the active electrode area is carried by the ceria catalyst coating, cell performance may be limited by ceria electronic conductivity. This situation can be improved by addition of a conductive component to the anode backbone, such as copper or stainless steel particles. Ris0 has demonstrated the latter choice and promising durability of the cell is reported. 

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