%0 Journal Article 
%A Carrillo, Alfonso J.
%A Chinchilla Reyes, Lidia Esther
%A Iglesias Juez, Ana
%A Gutiérrez Rubio, Santiago
%A Sastre, Daniel
%A Pizarro, Patricia
%A Hungría Hernández, Ana Belén
%A Coronado, Juan M.
%T Determining the Role of Fe-Doping on Promoting the Thermochemical Energy Storage Performance of (Mn1-xFex)(3)O-4 Spinels
%D 2021
%@ 2366-9608
%U http://hdl.handle.net/10498/25801
%X Mn oxides are promising materials for thermochemical heat store, but slow reoxidation of Mn3O4 to Mn2O3 limits efficiency. In contrast, (Mn1-xFex)(3)O-4 oxides show an enhanced transformation rate, but fundamental understanding of the role played by Fe cations is lacking. Here, nanoscale characterization of Fe-doped Mn oxides is performed to elucidate how Fe incorporation influences solid-state transformations. X-ray diffraction reveals the presence of two distinct spinel phases, cubic jacobsite and tetragonal hausmannite for samples with more than 10% of Fe. Chemical mapping exposes wide variation of Fe content between grains, but an even distribution within crystallites. Due to the similarities of spinels structures, high-resolution scanning transmission electron microscopy cannot discriminate unambiguously between them, but Fe-enriched crystallites likely correspond to jacobsite. In situ X-ray absorption spectroscopy confirms that increasing Fe content up to 20% boosts the reoxidation rate, leading to the transformation of Mn2+ in the spinel phase to Mn3+ in bixbyite. Extended X-ray absorption fine structure shows that Fe-O length is larger than Mn-O, but both electron energy loss spectroscopy and X-ray absorption near edge structure indicate that iron is always present as Fe3+ in octahedral sites. These structural modifications may facilitate ionic diffusion during bixbyite formation.
%K high-resolution STE
%K Min situ XAS
%K manganese oxides
%K redox
%K thermochemical heat storage
%~ Universidad de Cádiz