Wie wird Sauerstoff in Oxide eingebaut? Kinetische Studie einer “simplen” Feststoffreaktion am Modellmaterial SrTiO₃

Abstract

Die Kinetik der Stöchiometrieänderung eines Oxids – zugleich Beispiel einer (nominell) einfachen Festkörperreaktion und Grundlage vieler technisch relevanter Vorgänge – wird untersucht und im Detail analysiert. Als Modellreaktion wurde der Sauerstoffeinbau in Strontiumtitanat gewählt. Der gesamte Prozess kann von der Oberflächenreaktion bis hin zum Volumentransport phänomenologisch und mechanistisch verstanden werden. Schlüssel hierzu sind ein genaues Verständnis der Defektchemie des Perowskits wie auch die Anwendung einer Vielzahl experimenteller und theoretischer Methoden, die zum Teil eigens im Rahmen dieser Untersuchung entwickelt wurden. Die Bedeutung von Reaktions‐ und Transportschritten für (elektro)chemische Anwendungen wird herausgestellt.

Thermodynamics of Electrochemical Lithium Storage

“…This change can vary the storage capacity significantly, yet a few remarks must suffice. It is well established from high-temperature chemistry that heavy Fe doping of SrTiO 3 [47] or heavy Pr doping of CeO 2 [48] leads to significant variations in both the integral as well as the differential storage capacity. Yet, it is also clear that heavy doping of a binary finally is equivalent to forming a ternary compound.…”

“…Unlike the previous case, it is advantageous and common here to relate the cell voltage to chemical phase potentials [Eq. (47)]…”

Relating Microstructure to Surface Exchange Kinetics Usingin SituOptical Absorption Relaxation

“…An in situ Optical Transmission Relaxation (OTR) approach was applied to quantify the oxygen surface exchange coefficient (k chem ). In relatively oxidizing conditions, Fe present in SrTi 1-x Fe x O 3-δ consists of Fe 4+ and Fe 3+ valence states (13,17), and the reduction/oxidation reaction in STF35 can be described in the following defect reaction:…”

“…SrTi 1-x Fe x O 3-δ (STF) is a mixed ionic and electronic conductor with rapid surface exchange kinetics (9,10) of significant interest for solid oxide cell oxygen electrodes (11) and automotive oxygen sensors (12). As such, many works have reported the defect chemistry (5,13), ionic or electronic transport properties (14), structural properties (11), and oxygen reduction kinetics (3). The impact of bulk defect chemistry and electronic structure on k were also reported (9,15).…”

Influence of Electrode Potential on Oxygen Mobility Probed by Polarized Isotopic Exchange in Solid Oxide Electrolyser Cells: Insights for Electro‐Assisted Oxidation Reactions

“…Kinetics of oxygen exchange are assumed to be first or pseudo-first order reactions, implying that molecular oxygen is involved in the rate determining step (rds). [34] Two distinct kinetic models are proposed. In the case of LSM and LNO (where the one atom heteroexchange prevails), a simple first order decay of g as a function of time is observed and can be described with Equation 20:…”