The urgency of climate issues requires an urgent transition to sustainable energy production methods, requiring safe and stable energy storage technology over time. Recently, metal powders, and in particular iron powder, have been considered as very promising candidates thanks to their high energy density compared with other conventional energy storage systems. The stored energy is released during the exothermic oxidation of the metal powder, which is then regenerated by hydrogen-based solid-state direct reduction with hydrogen produced from renewable energy sources. Direct reduction of sintered iron ore pellets is generally studied in the context of sustainable steel production, but the particle size, morphology, composition and microstructure are strongly different from the powder obtained after combustion, while these parameters have a large influence on solid-state direct reduction mechanisms and kinetics. A positive influence of pre-oxidizing fine magnetite ores was observed on the direct reduction kinetics, associated to an increase of the nucleation sites. In this study, we investigate the influence of pre-oxidation on the direct reduction of combusted powder. The microstructural evolution, phase evolution and reduction kinetics of both combusted and pre-oxidized powder is studied at 500°C in 100% hydrogen using thermogravimetry and in-situ high-energy X-ray diffraction in addition to microscopy characterization. With this study, we aim at highlighting the preferred microstructure to obtain after iron combustion for the subsequent reduction process.