No abstract

The ionic and n-type conductivities of ceria-based electrolytes doped with gadolinium (10 and 20 cation %) or gadolinium and praseodymium (2% Pr and 18% Gd) were studied by impedance spectroscopy in air, between 573 and 1273 K, and by constant frequency (10 kllz) conductivity measurements as a function of the oxygen partial pressure (p02) between about 1020 atm and air in the temperature range 1073 to 1273 K. Ion blocking measurements were also performed between 1073 and 1273 K with air at the reversible electrode. From data obtained with different experimental techniques it was concluded that estimates for the electronic conductivity of all compositions were consistent and that all materials behaved in a rather similar manner. Estimated n-type conductivities suggest that Pr-doped materials have a slightly lower electronic conductivity and a larger electrolytic (and ionic) domain, but overall differences are quite small. The model behavior used in analyzing experimental results is discussed based on the existing knowledge of the defect chemistry of ceria-based electrolytes, and a range of working conditions is identified where the ionic conductivity can be assumed constant and the electronic conductivity proportional to p'4.

2001 inorganic chemistry, review inorganic chemistry, review Z 0100 40 -260 Ceria-Based Materials for Solid Oxide Fuel Cells --(KHARTON, V. V.; FIGUEIREDO, F. M.; NAVARRO, L.; NAUMOVICH, E. N.; KO-VALEVSKY, A. V.; YAREMCHENKO, A. A.; VISKUP, A. P.; CARNEIRO, A.; MARQUES, F. M. B.; FRADE, J. R.; J.

No abstract

In this paper we studied the performance of bioanodes under different experimental conditions using polarization curves and impedance spectroscopy. We have identified that the large capacitances of up to 1 mF·cm −2 for graphite anodes have their origin in the nature of the carbonaceous electrode, rather than the microbial culture. In some cases, the separate contributions of charge transfer and diffusion resistance were clearly visible, while in other cases their contribution was masked by the high capacitance of 1 mF·cm −2 . The impedance data were analyzed using the basic Randles model to analyze ohmic, charge transfer and diffusion resistances. Increasing buffer concentration from 0 to 50 mM and increasing pH from 6 to 8 resulted in decreased charge transfer and diffusion resistances; lowest values being 144 Ω·cm 2 and 34 Ω·cm 2 , respectively. At acetate concentrations below 1 mM, current generation was limited by acetate. We show a linear relationship between inverse charge transfer resistance at potentials close to open circuit and saturation (maximum) current, associated to the ButlerVolmer relationship that needs further exploration.