Abstract.Recently there has been substantial interest in optimising perovskite type ceramics as mixed ionic-electronic conductors (MIECs) for use in ceramic oxygen generators and solid oxide fuel cells. However these materials suffer from thermomechanical deficiencies and therefore there is a need to develop alternative materials.Using the IEDP/SIMS technique the La2_xSrxNil-yFeyO4+8 series of compounds has been investigated and the oxygen tracer diffusion and surface exchange coefficients determined. It has been found that the oxide ion diffusivity of the x and y = 0 material is very close to that of the fast oxide ion conducting perovskites such as Lal_xSrxCoO3 (LSC) but on acceptor doping with Sr a considerable decrease in the oxygen tracer diffusion coefficient was observed. Further studies on the effects of B site doping, where y > 0, indicate that this has very little effect on the transport properties.

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Inorganic perovskites exhibit many important physical properties such as ferroelectricity, magnetoresistance and superconductivity as well their importance as energy materials. Many of the most important energy materials are inorganic perovskites and find application in batteries, fuel cells, photocatalysts, catalysis, thermoelectrics and solar thermal. In all these applications, perovskite oxides, or their derivatives offer highly competitive performance, often state of the art and so tend to dominate research into energy material. In the following sections, we review these functionalities in turn seeking to facilitate the interchange of ideas between domains. The potential for improvement is explored and we highlight the importance of both detailed modelling and in situ and operando studies in taking these materials forward.

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Mixed ionic and electronic conducting (MIEC) perovskite oxides (ABO 3 ) have a substantial role in carbon-neutral clean energy conversion and storage technologies. Owing to their favorable catalytic properties, high ionic and electronic conductivity, and chemical and redox stability, MIEC perovskite oxides are promising electrode materials in multiple applications, such as solid oxide fuel/ electrolysis cells, oxygen transport membranes, metal−air batteries, electrochemical sensors, and electrocatalysts for water splitting. Here, taking (La 0.8 Sr 0.2 ) 0.95 Cr 0.5 Fe 0.5 O 3−δ (LSCrF8255) as a model MIEC perovskite oxide, we demonstrate that the oxygen mass transport properties are significantly enhanced under a humid reducing water vapor environment (pO 2 < 1 mbar, pH 2 O = 30 mbar) by up to 4 orders of magnitude compared to those measured under dry (pO 2 = 200 mbar) and wet (pO 2 = 200 mbar, pH 2 O = 30 mbar) oxygen atmospheres. A 0.8 eV decrease in the activation energy for oxygen bulk diffusion was also found under water vapor, and a decrease in activation energy of 0.7 eV for water surface exchange compared to oxygen surface exchange was found. The mechanisms underpinning these enhancements were explored. Furthermore, LSCrF8255 has also exhibited a consistent surface composition evolution regarding Sr segregation and phase separation and an excellent bulk stability under both oxidizing and reducing environments at elevated temperatures.