A Kinetic Study on H2 Reduction of Fe3O4 for Long-Duration Energy-Storage-Compatible Solid Oxide Iron Air Batteries

Abstract

Long duration energy storage (LDES) is economically attractive to accelerate widespread renewable energy deployment. But none of the existing energy storage technologies can meet LDES cost requirements. The newly emerged solid oxide iron air battery (SOIAB) with energy-dense solid Fe as an energy storage material is a competitive LDES-suitable technology compared to conventional counterparts. However, the performance of SOIAB is critically limited by the kinetics of Fe3O4 reduction (equivalent to charging process) and the understanding of this kinetic bottleneck is significantly lacking in the literature. Here, we report a systematic kinetic study of Fe3O4-to-Fe reduction in H2/H2O environment, particularly the effect of catalyst (iridium) and supporting oxides (ZrO2 and BaZr0.4Ce0.4Y0.1Yb0.1O3). With in situ created Fe3O4, the degree of reduction is measured by the change of H2O and H2 concentrations in the effluent using a mass spectrometer, from which the kinetic rate constant is extracted as a function of inlet H2 concentration and temperature. We find that kinetics can be nicely described by Johson-Mehl-Avrami (JMA) model. We also discuss the stepwise reduction mechanisms and activation energy for the reduction process.