Oxygen Transfer on Substituted ZrO2, Bi2 O 3, and CeO2 Electrolytes with Platinum Electrodes: I . Electrode Resistance by D‐C Polarization

Abstract

The electrode behavior of Ptosputtered and PT-gauze electrodes on ZrO2-Y203, Bi20~-Er20.~, and CeO~-Gd203 solid electrolytes was investigated by means of d-c measurements in the temperature region of 770-1050 K and in the oxygen partial pressure region of 10 -~ -1 atm O2 using N2-O2 mixtures. On these different materials the same electrode morphology was realized and was preserved during the subsequent experiments. The electrode process is strongly influenced by the nature of the electrolyte. The electrode resistance for Pt electrodes on Bi203-Er203 was found to be many times lower than on ZrO2-Y20~ and CeO2-Gd20~. On zirconia-and ceria-based materials-diffusion of atomic oxygen on the Pt electrode is the rate-determining step in the electrode process, whereas for bismuth sesquioxide-based materials diffusion on the oxide surfaces is rate determining.There is a considerable interest in solid electrolytes for use in oxygen sensors, oxygen pumps, and high temperature fuel cells. In these applications the electrode polarization and the electrolyte resistance both play an important role. These effects influence the response of an oxygen sensor and give rise to energy losses and therefore to a decreased efficiency, of oxygen pumps and fuel cells. Many studies are performed on electrode processes. However, the dominant elementary steps of the overall process are still unknown in most cases.The kinetics of the electrode process is strongly influenced by the electrode structure (1-6), electrode material (4, 5, 7-9), and the electrolyte (4, 5, 7). Information about the role of the electrolyte in the electrode process is very scarce and is limited to the role of the dopant. Schouler (4) found that the oxygen partial pressure dependence of the electrode resistance of a sputtered platinum electrode depends on the Y203 content of the ThO2 electrolyte. Fabry and Kleitz (7) found that the activation energy of the electrode resistance of a point electrode on calcia-stabilized zirconia is higher than that on yttria-stabilized zirconia. Wang anal Nowick (5) reported that the exchange current of a Pt-paste electrode is not influenced by the nature and the. concentration of the dopant of the CeO2 electrolyte.Even less attention is paid to the influence of the nature of the electrolyte on the overall electrode proi Present address:

Surface oxygen exchange properties of bismuth oxide-based solid electrolytes and electrode materials

“…The useful pressure range in the current exchange The same, inverse, pressure dependence was observed by Verkerk et al [6] for the electrode resistance (which is inversely proportional to the exchange current) measured at 970 K in BE20 and BE40 (Bi203 with respectively 20 and 40 mol% ErnO3) samples provided with porous platinum electrodes. They concluded that the mass transport (diffusion) of adsorbed surface oxygen to be the rate determining step.…”

“…The remarkable results of these studies, summarized by Steele and coworkers [ 5 ], were (i) that for scandia-stabilised zirconia the exchange rate increased by a factor of 5 after bismuth implantation [4] and (ii) that the exchange rates for zirconiabased materials were a factor of 103 smaller than deducted from electrochemical measurements using porous platinum electrodes [6], while (iii) for bismuth erbium oxides high and identical values were obtained for both methods, indicating a possible enhancement of the exchange kinetics by the bismuth ion.…”

Effect of Ionic Conductivity of Zirconia Electrolytes on the Polarization Behavior of Various Cathodes in Solid Fuel Cells

“…Referring to many styles [19][20][21][23][24][25][26][27][28][29] it is reasonable to consider the following cathodic charge-transfer reaction at Pt/zirconia interface…”

Model for Solid Electrolyte Gas Electrode Reaction Kinetics; Key Concepts, Basic Model Construction, Extension of Models, New Experimental Techniques for Model Confirmation, and Future Prospects

“…These works are listed in the references. [90][91][92][93][94][95][96] Recently, there are many review papers published on the SOFC electrode materials and reactions. Here, the reviews by Adler 97 and by Tsipis, Vladislav and Kharton 98 are listed in the reference as the representative examples.…”