Noble metals anodes

The ideal performance of a fuel cell depends on the electrochemical reactions that occur with different fuels and oxygen as summarized in Table 2-1. Low-temperature fuel cells (PEFC, AFC, and PAFC) require noble metal electrocatalysts to achieve practical reaction rates at the anode and cathode, and H2 is the only acceptable fuel. With high-temperature fuel cells (MCFC, ITSOFC, and SOFC), the requirements for catalysis are relaxed, and the number of potential fuels expands. Carbon monoxide "poisons" a noble metal anode catalyst such as platinum (Pt) in low-temperature... 

The ceramic properties of EU2O3 were investigated by Curtis and Tharp [305]. The electric conductivities of rare earth oxides including EU2O3 between 600—1300° C were reported [675]. The selective oxidation of Ci to C5 olefins and Ci to C5 alcohols by direct fuel cells employing noble metal anodes and aqueous H2SO4 electrolytes was found to be enhanced [676] by small additions of soluble salts of Ce, Eu and Yb. 

In some anodic reactions, especially in aprotic media, the products obtained form a layer of tarry material on the electrode surface that (by covering it) insulates it electrically from the solution. The removal of this layer and the attainment and maintenance of a clean, reproducible surface are often a major problem in the use of noble metal anodes. Sometimes it is possible to avoid fouling of the electrode by using pulse electrolysis. 

Cathodically protect, ideally to the potential of corroding active metal at the crevice. Approaching such a potential reduces the corrosion rate, but not to zero. In seawater, use of sacrificial iron and similar less-noble-metal anodes have proved useful [45]. 

The overall reaction is characterized by product analyses and coulombic efficiency determinations. Carbon dioxide, which is the primary product in most organic reactions at noble-metal anodes, can be removed from acidic solutions in the anode compartment of the electrolytic cell by passing an inert gas through the cell, and then reacting quantitatively, e.g., with Ba(OH)2 or Ascarite. Carbon dioxide is not as easily determined in alkaline electrolyte, which must be analyzed, e.g., by volumetric methods or chromatography. Nonvolatile products from the oxidation are determined by analysis of the electrolyte, e.g., by gas chromatography, preferably with a flame ionization detector, or mass spectroscopy. Organic products can be extracted from the electrolyte... 

Burke, L.D., O Dwyer, K.J. (1989) Mediation of oxidation reactions at noble metal anodes by low levels of in situ generated hydroxy species. Electrochimica Acta, 34,1659-1664. 

Mussy JPG, Macpherson JV, Delplancke JL (2003) Characterisation and behaviour of Ti/Ti02/noble metal anodes. Electrochim Acta 2003(48) 1131-1141... 

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