resumo
Electrode polarization in potentiometric oxygen sensors may lead to significant errors in the oxygen activity measurements, due to minor electronic conduction in solid electrolytes. These errors increase with increasing electronic contribution to total conductivity and electrode polarization resistance, and with decreasing electrolyte thickness. Similar effects have been observed when using oxygen concentration cells for the determination of ion transference numbers of solid electrolytes and mixed conductors. In this work a revised equivalent circuit was used to analyze the e.m.f. reading of potentiometric oxygen sensors under the conditions when electrode polarization cannot be neglected. It is shown that the cell response can be approximately described as E approximate to E(0)t(1)[1 + (L-c/L)], where E-0 is the Nernst potential, t(1) is the ionic transport number, L is the electrolyte thickness, and L, is a critical electrolyte thickness determined by the transport properties of the cell material and interfacial resistance of the electrodes. The errors associated with electrode polarization may be nearly corrected by using impedance spectroscopy to estimate the polarization resistance, and combining these data with the concentration cell e.m.f. However, severe current density limitations are expected for very diluted atmospheres, i.e., under moderately reducing atmospheres; this gives very inaccurate sensor response, and no corrections have been found for this type of deviations.
palavras-chave
OXIDE FUEL-CELLS; NONFLOWING ATMOSPHERES; SURFACE EXCHANGE; EMF-MEASUREMENTS; FUGACITY CONTROL; DOPED CERIA; CONDUCTION; KINETICS; MICROSTRUCTURE; RESISTANCE
categoria
Chemistry; Electrochemistry; Instruments & Instrumentation; Physics
autores
Frade, JR; Kharton, VV; Shaula, AL; Marques, FMB
nossos autores
Fernando Manuel Bico Marques
Professor Catedrático
Jorge Ribeiro Frade
Professor(a) Jubilado(a)