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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 Fe₃O₄reduction (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 (ZrO₂and BaZr_0.4Ce_0.4Y_0.1Yb_0.1O₃). With in situ created Fe₃O₄, the degree of reduction is measured by the change of H₂O and H₂concentrations in the effluent using a mass spectrometer, from which the kinetic rate constant is extracted as a function of inlet H₂concentration 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.