Determining the Role of Fe-Doping on Promoting the Thermochemical Energy Storage Performance of (Mn1−xFex)3O4 Spinels,Small Methods

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Determining the Role of Fe-Doping on Promoting the Thermochemical Energy Storage Performance of (Mn1−xFex)3O4 Spinels
Small Methods ( IF 10.7 ) Pub Date : 2021-09-09 , DOI: 10.1002/smtd.202100550
Alfonso J Carrillo ₁ , Lidia E Chinchilla ₂ , Ana Iglesias-Juez ₃ , Santiago Gutiérrez-Rubio ₄ , Daniel Sastre ₄ , Patricia Pizarro _{4,

5} , Ana B Hungría ₂ , Juan M Coronado ₃

Affiliation

Mn oxides are promising materials for thermochemical heat store, but slow reoxidation of Mn₃O₄ to Mn₂O₃ limits efficiency. In contrast, (Mn₁₋_xFe_x)₃O₄ 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.

中文翻译：

确定 Fe 掺杂对提高 (Mn1−xFex)3O4 尖晶石热化学储能性能的作用

Mn 氧化物是用于热化学蓄热的有前途的材料，但 Mn ₃ O ₄缓慢再氧化为 Mn ₂ O ₃限制了效率。相反，(Mn ₁₋_x Fe _x ) ₃ O ₄氧化物显示出更高的转化率，但缺乏对 Fe 阳离子所起作用的基本了解。在这里，对 Fe 掺杂的 Mn 氧化物进行纳米级表征，以阐明 Fe 掺入如何影响固态转变。X 射线衍射表明，对于铁含量超过 10% 的样品，存在两种不同的尖晶石相，即立方方锰矿和四方锰铝石相。化学绘图揭示了晶粒之间 Fe 含量的广泛变化，但在晶粒内分布均匀。由于尖晶石结构的相似性，高分辨率扫描透射电子显微镜无法明确地区分它们，但富含 Fe 的微晶可能对应于雅科布石。原位 X 射线吸收光谱证实，将 Fe 含量提高至 20% 可提高再氧化率，尖晶石相中的²⁺到方铁锰矿中的Mn ³⁺。扩展的 X 射线吸收精细结构表明 Fe  O 长度大于 Mn  O，但电子能量损失光谱和近边缘结构的 X 射线吸收表明铁总是以 Fe ^{3+ 的形式}存在于八面体位置。这些结构改性可以促进方铁锰矿形成过程中的离子扩散。

更新日期：2021-10-28

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