Praseodymium-cerium oxide thin film cathodes: Study of oxygen reduction reaction kinetics

Abstract

Praseodymium-Cerium Oxide (Pr x Ce 1-x O 2−δ ; PCO), a potential three way catalyst oxygen storage material and solid oxide fuel cell (SOFC) cathode, exhibits surprisingly high levels of oxygen nonstoichiometry, even under oxidizing (e.g. air) conditions, resulting in mixed ionic electronic conductivity (MIEC). In this study we examine the redox kinetics of dense PCO thin films using impedance spectroscopy, for x00.01, 0.10 and 0.20, over the temperature range of 550 to 670°C, and the oxygen partial pressure range of 10 −4 to 1 atm O 2 . The electrode impedance was observed to be independent of electrode thickness and inversely proportional to electrode area, pointing to surface exchange rather than bulk diffusion limited kinetics. The large electrode capacitance (10 −2 F) was found to be consistent with an expected large electrochemically induced change in stoichiometry for x00.1 and x00.2 PCO. The PCO films showed surprisingly rapid oxygen exchange kinetics, comparable to other high performance SOFC cathode materials, from which values for the surface exchange coefficient, k q , were calculated. This study confirms the suitability of PCO as a model MIEC cathode material compatible with both zirconia and ceria based solid oxide electrolytes.

Advances in Cathode Materials for Solid Oxide Fuel Cells: Complex Oxides without Alkaline Earth Metal Elements

“…[ 367,368 ] Some elements with variable valence state have been doped into cceria. [369][370][371] The Pr with mixed trivalent and tetravalent state could simultaneously increase the oxygen vacancies and the electronic conductivity of ceria. [ 372 ] Chen et al investigated the surface exchange kinetic of Ce 1-x Pr x O 2-δ ( x = 0.1 and 0.2) fi lms.…”

“…The surface exchange coeffi cients of Ce 0.8 Pr 0.2 O 2-δ between 550 and 670 °C were found to be comparable in magnitude to those from traditional high performance LSCF and LSC materials. [ 370 ] Shown in Figure 14 a is the temperature dependence of the total conductivity of sintered Ce 1-x Pr x O 2-δ ( x = 0.05-0.9). [ 372 ] When the concentration of Pr was very low ( x ≤ 0.1), the temperature dependence of conductivity in the high temperature range was similar to that of Gd doped ceria whose main carriers were oxygen ions.…”

High temperature X-ray diffraction and thermo-gravimetrical analysis of the cubic perovskite Ba0.5Sr0.5Co0.8Fe0.2O3−δ under different atmospheres

“…The low creep resistance questioning the actual use of BSCF in high temperature gas separation membranes and several attempts to stabilize BSCF by chemical substitution have appeared, both to avoid the formation of the hexagonal polymorph and to increase the creep resistance [22][23] . Chemical expansion [24][25] , particularly for ceria and perovskite materials with transition metals (Co, Fe) on the Bsite is another concern with respect to the mechanical stability of oxygen permeation membranes [26][27][28][29][30][31][32] . The chemical and thermal expansion of BSCF has also been reported by several groups [33][34][35][36][37][38] , showing lower chemical expansion than other similar candidate membrane materials due to smaller changes in oxygen stoichiometry and a generally larger unit cell, which is less sensitive to temperature and stoichiometry changes 38 .…”

Chemomechanics of ionically conductive ceramics for electrical energy conversion and storage

“…Specifically, IS can be used to deconvolute resistive and capacitive contributions from the electrolyte and electrodes, bulk and interfacial effects, and equilibrium and kinetic processes, including the ability to study electrode kinetics (exchange or diffusion limited, rate coefficients, etc.) [58,59]. In these systems, reaction or migration steps are coupled, and each step has an associated characteristic frequency.…”