Oxygen Ion‐Conducting Materials

Abstract

Oxygen ionic and mixed ionic-electronic conductors find important applications in solid-state electrochemical devices, including sensors, solid oxide fuel cells, hightemperature electrolyzers, and oxygen separation membranes. This chapter presents a brief overview of oxide phases with high diffusivity of O 2À anions, providing an introduction to this fascinating topic. Particular emphasis is centered on the comparative analysis of ionic and electronic conductivity variations in the major groups of solid oxide electrolytes and mixed conductors, such as perovskite-and fluorite-related compounds, apatite-type silicates, and derivatives of g-Bi 4 V 2 O 11 and b-La 2 Mo 2 O 9 . The defect chemistry mechanisms relevant to the oxygen ion migration processes are briefly discussed. IntroductionTechnologies based on the use of high-temperature electrochemical cells with oxygen anion-or mixed-conducting ceramics provide important advantages with respect to the conventional industrial processes [1][2][3][4][5][6][7][8]. In particular, solid oxide fuel cells (SOFCs) are considered as alternative electric power generation systems due to high energy-conversion efficiency, fuel flexibility, and environmental safety [1][2][3]. Dense ceramic membranes with mixed oxygen-ionic and electronic conductivity have an infinite theoretical separation factor with respect to oxygen, and can be used for gas separation and the partial oxidation of light hydrocarbons [4,5,7,8] (these and other applications are reviewed in Chapters 12 and 13). For all types of electrochemical cells, the key properties which determine the use of a material are the partial ionic and electronic conductivities. As an example, solid electrolytes for SOFCs, oxygen pumps and electrochemical sensors should exhibit a maximum oxygen ionic conductivity, while the electronic transport should be minimal. In contrast, for SOFC electrodes Solid State Electrochemistry I: Fundamentals, Materials and their Applications. Edited by Vladislav V. Kharton

Oxygen ion transport numbers: assessment of combined measurement methods

“…Although the measurement methods are well known, their use is rather complex. In fact, experimental errors are often comparable with the measured quantities [6][7][8][9][10]. One important source of uncertainty is the influence of interfacial processes on the measured bulk ionic and/or electronic transference parameters, which is observed in many cases.…”

“…Several modifications of the EMF and faradaic efficiency techniques, taking electrode polarisation into account, were suggested in previous work [10,18]. For both EMF and faradaic efficiency measurements, the modified techniques in combination with electrodes having a high polarisation resistance considerably enhance the accuracy of the determination of even minor electronic contributions to the total conductivity of solid electrolytes.…”

“…For both EMF and faradaic efficiency measurements, the modified techniques in combination with electrodes having a high polarisation resistance considerably enhance the accuracy of the determination of even minor electronic contributions to the total conductivity of solid electrolytes. Such an improvement is possible due to enhanced measurable effects, namely the deviation of the cell EMF from the theoretical Nernst voltage or the difference between the total and ionic currents through a cell in the case of faradaic efficiency measurement [10,18].…”

“…One important source of uncertainty is the influence of interfacial processes on the measured bulk ionic and/or electronic transference parameters, which is observed in many cases. In particular, significant electrode polarisation and/or slow surface exchange are known to affect the electromotive force (EMF) of electrochemical concentration cells [10][11][12], conductivity relaxation kinetics [13], oxygen and hydrogen permeation [14][15][16][17] and faradaic efficiency [17,18].…”

Влияние природы галогена на локальную структуру и интеркалацию воды в оксигалогенидах Ba-=SUB=-2-=/SUB=-InO-=SUB=-3-=/SUB=-X (X = F, Cl, Br)

“…Соединения со структурой перовскита или производной от нее являются наиболее изученными кислородно-ионными и протонными проводниками [3][4][5][6][7]. Поиск материалов среди других структурных классов и накопление знаний в этой области может привести к со-зданию нового поколения электрохимических устройств.…”