Determining the Role of Fe-Doping on Promoting the Thermochemical Energy Storage Performance of (Mn1- x Fex )3 O4 Spinels

Mn oxides are promising materials for thermochemical heat store, but slow reoxidation of Mn₃ O₄ to Mn₂ O₃ limits efficiency. In contrast, (Mn_{1- x} Fe_x )₃ O₄ 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.

Nanosized silver bromide: an efficient catalyst for alcohol oxidation in the presence of a multinuclear silver complex

We detected AgBr as a true catalyst for alcohol oxidation in the presence of a silver complex.

Water oxidation by a soluble iron(iii)–cyclen complex: new findings

Herein, the role of iron oxide in the electrochemical water oxidation of an iron cyclen (cyclen = 1,4,7,10-tetraazacyclododecane) is considered.

New findings and the current controversies for water oxidation by a copper(ii)-azo complex: homogeneous or heterogeneous?

In this paper, new findings for the water-oxidizing activity of [(L)Cu(II)(NO3)], (L = (E)-3-(pyridin-2-yldiazenyl)naphthalen-2-ol (HL)) under both electro-water oxidation conditions and in the presence of cerium(iv) ammonium nitrate are reported.