Metal ceramic composite electrodes

Metal Ceramic Composite Electrodes (Metal CCEs)... 

Carbon-ceramic composite electrodes (CCEs) and the closely related metal-sihcate electrodes are comprised of carbon or metal dispersion in sol-gel derived silicates or Or-mocers. In this construction the silicate serves as a porous binder for the conductive dispersion. The conductive component is added as powders, nanoparticles, or nanotubes whose particle size ranges between sub-millimeter and a few nanometers. The initial intention was to provide improved conductivity by the interconnected conductive powder, but soon, other favorable attributes of the metal-sihcate hybrids were discovered, including improved catalytic reactivity, biological compatibility, and control of the thickness of the wetted section of the electrodes in aqueous electrolyte. Since the metal silicate and graphite silicate call for different preparation protocols they are addressed separately. 

Four different classes of composite ceramic electrodes were reported (1) ceramic carbon electrodes, (2) metal powder-ceramic composite electrodes, (3) carbon nanotube-silicate composites, and (4) coated aluminosilicate-ceramic electrodes. The first two fillers are basically three dimensional, whereas the third and fourth classes represent 1-D and 2-D anisotropic fillers. 

Domenech A, Domenech-Carbo MT, Osete L, Gimeno JV, Bosch F, Mateo R (2002) Electrochemical identification of metal ions in archaeological ceramic glazes by stripping voltammetry at graphite/polyester composite electrodes. Talanta 56 161-174. 

The usual anode is a cermet (composite material made of a ceramic and a metal). Porous Ni-YSZ (yttria-stabilised zirconia) is the state-of-the-art electrode, presenting electronic and ionic conductivities in order to increase the number of reaction sites, called triple phase boundaries. It corresponds to the area where 0 , e and H2 are all present for the time required for the oxidation reaction to occur. No single phase has been found to completely fit all the requirements for an anode thermal and chemical compatibilities with the electrolyte, mixed ionic and electronic conductivity, high electro-catalytic activity and stability in reductive atmosphere. 

There are, however, a number of important systems where this situation does not hold, for example ceramic-metal composites, and ceramic composites of electronic and ionic conductors, used as electrodes in sohd oxide fuel cells. Composite electrodes are important in a solid oxide fuel cell (SOFC), as they provide the contact area necessary for the electrode processes to occur. This is usually visualized as the three-phase boundary (TPB), the boundary line where electronic conductor, ionic conductor, and pores meet. A composite cathode is shown schematically in Figure 4.1.14, after Costamagna et al. [1998]. The processes occurring in a composite electrode are briefly as follows ... 

Yoon el al. [112] reported an all-solid-state sensor for blood analysis. The sensor consists of a set of ion-selective membranes for the measurement of H+, K+, Na+, Ca2+, and Cl. The metal electrodes were patterned on a ceramic substrate and covered with a layer of solvent-processible polyurethane (PU) membrane. However, the pH measurement was reported to suffer severe unstable drift due to the permeation of water vapor and carbon dioxide through the membrane to the membrane-electrode interface. For conducting polymer-modified electrodes, the adhesion of conducting polymer to the membrane has been improved by introducing an adhesion layer. For example, polypyrrole (PPy) to membrane adhesion is improved by using an adhesion layer, such as Nafion [60] or a composite of PPy and Nafion [117],... 

A polymer electrolyte with acceptable conductivity, mechanical properties and electrochemical stability has yet to be developed and commercialized on a large scale. The main issues which are still to be resolved for a completely successful operation of these materials are the reactivity of their interface with the lithium metal electrode and the decay of their conductivity at temperatures below 70 °C. Croce et al. found an effective approach for reaching both of these goals by dispersing low particle size ceramic powders in the polymer electrolyte bulk. They claimed that this new nanocomposite polymer electrolytes had a very stable lithium electrode interface and an enhanced ionic conductivity at low temperature. combined with good mechanical properties. Fan et al. has also developed a new type of composite electrolyte by dispersing fumed silica into low to moderate molecular weight PEO. 

In addition to being able to catalyze the dissociation of O2. the material used for the cathode must be electronically conductive in the presence of air at high temperature, a property found primarily in noble metals and electronically conductive oxides. Ionic conductivity is also desirable for extending the reaction zone well into the electrode since the ions must ultimately be transferred to the electrolyte. Since precious metals are prohibitively expensive when used in quantities sufficient for providing electronic conductivity, essentially all SOFC prototypes use perovskite-based cathodes, with the most common material being a Sr-doped LaMnOs (LSM). In most cases, the cathode is a composite of the electronically conductive ceramic and an ionically conductive oxide, often the same material used in the electrolyte. 

The bipolar plate design is illustrated in Fig. 47. It consists of a cross-flow arrangement where the gas-tight separation is achieved by dense ceramic or metallic plates with grooves for air and fuel supply to the appropriate electrodes. A porous cathode, a dense and thin electrolyte and a porous anode form a composite flat layer placed at the top of the interconnected grooves. The deposition of the porous electrodes can be achieved by mass production methods. Moreover, the bipolar plate configuration technology makes it possible to check for defaults, independently and prior to assembly of the interconnection plate and the anode-electrolyte-cathode structure. 

The basic requirement in biosensor development is ascribed to the successful attachment of the recognition material, a process governed by various interactions between the biological component and the sensor interface. Advanced immobilization technologies capable of depositing biologically active material onto or in close proximity of the transducer surface have been reported. In this context, the choice of a biocompatible electrode material is essential. The material surfaces (support) include almost all material tjrpes metals, ceramics, polymers, composites and carbon materials [8]. In most cases, when a native material does not meet all the requirements for... 

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