Iron as Energy Carrier─Mechanistics of Iron Oxidation and Iron Oxide Reduction Deduced from In Situ Techniques

Iron is a very promising candidate for the use as a chemical energy carrier. Recent evidence shows that the oxidation behavior of iron powders differs from the well understood iron slab oxidation. Hence, for application it is crucial to understand the reaction behavior of iron and iron oxide powders in the micrometer range. As the reactions are fast, approaches using quantitative in situ analytical methods are desired. Herein, we follow iron powder oxidation and iron oxide powder reduction using in situ 57Fe Mössbauer spectroscopy and in situ X-ray diffraction. A time resolution of 30 min is achieved with Mössbauer spectroscopy even for iron powder with natural isotopic abundance (2.1% 57Fe isotope). We show that both methods are suitable and complementary, motivating future coherent approaches. By combining compositional results from Mössbauer spectroscopy and X-ray diffraction with morphological characterization as Electron Backscattering Diffraction, advanced mechanistic models for the processes during oxidation and reduction are proposed.