Author Description

This PhD thesis presents an in-depth characterization of the magnesium manganese oxide redox system for energy storage applications. The study is divided into three main parts. Each one of them explores the features of the energy storage material at increasing length scales: starting from the pellet-scale (on the order of millimeters), then moving to the packed-bed scale (on the order of centimeters), and finally reaching the reactor-scale (on the order of meters), in which the energy storage concept is demonstrated in an experimental reactor. The first part of the study deals with the experimental characterization and modeling of the magnesium manganese oxide redox system thermodynamics. The test sample is an individual cylindrical pellet in the 1:1 magnesium-to-manganese molar ratio composition. Its extent of oxidation is measured via a series of thermogravimetric experiments conducted at temperatures between 1000 and 1500 °C and oxygen partial pressures between 0.01 and 0.9 bar(a). The experimental results are used to develop two thermodynamic models that accurately predict the behavior of the redox system within these temperature and oxygen partial pressure ranges. Furthermore, these models allow to improve the material characterization by providing estimates on the average enthalpy and entropy of reaction. This study provides the minimum theoretical knowledge needed to develop computational models to predict and optimize the operation of such energy storage material when integrated in a large-scale reactor.The second part of the study deals with the measurement of the effective electrical conductivity of a packed bed of magnesium manganese oxide pellets. During this experimental campaign, different pellet form factors (cylindrical and spherical) and compositions (1:1 and 3:2 magnesium-to-manganese molar ratios) have been examined. These measurements are performed using a four-wire technique at temperatures ranging between 1000 and 1500 °C under atmospheric p