当前位置: X-MOL 学术J. Mater. Chem. A › 论文详情
Our official English website, www.x-mol.net, welcomes your feedback! (Note: you will need to create a separate account there.)
Developing intercalation based anode materials for fluoride-ion batteries: topochemical reduction of Sr2TiO3F2via a hydride based defluorination process†
Journal of Materials Chemistry A ( IF 11.9 ) Pub Date : 2018-05-04 00:00:00 , DOI: 10.1039/c8ta01012a
Kerstin Wissel 1, 2, 3, 4, 5 , Supratik Dasgupta 1, 2, 4, 5, 6 , Alexander Benes 2, 4, 5, 7, 8 , Roland Schoch 5, 9, 10, 11 , Matthias Bauer 5, 9, 10, 11 , Ralf Witte 5, 12, 13 , Andrew Dominic Fortes 14, 15, 16, 17 , Emre Erdem 5, 18, 19, 20 , Jochen Rohrer 1, 2, 4, 5, 21 , Oliver Clemens 1, 2, 3, 4, 5
Affiliation  

Within this study, we demonstrate a newly developed reductive topochemical defluorination method which allows for a selective extraction/substitution of fluoride ions out of transition metal oxyfluorides using NaH as the reducing agent at temperatures as low as 300 °C, enabling the preparation and investigation of anode materials for fluoride-ion batteries in the charged state. A sequence of topochemical reactions, first substitutive fluorination of the K2NiF4 type precursor oxide Sr2TiO4 to Sr2TiO3F2 followed by the reductive defluorination/hydride-fluoride-substitution of Sr2TiO3F2, leads to the formation of compounds with approximate compositions of Sr2TiO3FH0.48 and Sr2TiO3H1.48. The evolution of the unit cell volumes upon extraction/substitution of fluoride ions has been monitored by an X-ray diffraction study. Strong structural changes were observed during the reaction, expressed by a decrease of the c-axis from ∼15.5 Å in Sr2TiO3F2 to ∼13.0 Å in Sr2TiO3FH0.48 and ∼12.7 Å in Sr2TiO3H1.48, with additional symmetry lowering for Sr2TiO3FH0.48, and confirmed by neutron powder diffraction. Changes of the Ti oxidation states and coordination environment were examined and confirmed by means of X-ray absorption spectroscopy, electron paramagnetic resonance and magnetic measurements. Furthermore, we found that the surface chemistry of such compounds differs significantly from the bulk properties by means of an X-ray photoelectron spectroscopy study, showing that surface compositions of Sr2TiO3F and Sr2TiO3 with Ti3+ and Ti2+ species can be obtained on the reaction, respectively. We further highlight that a ‘direct’ reduction of the oxide precursor Sr2TiO4 to Sr2TiO3 is not possible using the same method. Therefore, the two-step modification of Sr2TiO4 allows for the preparation of compounds with low oxidation states at the lowest temperatures used so far for hydride based reductions of titanium containing oxides (300 °C compared to ∼600 °C used previously). The observed differences in the reactivity of oxyfluorides compared to oxides are well supported by DFT based calculations of formation energies. They show that the formation of NaF is a strong driving force, resulting in exergonic reductions/hydride-fluoride substitution reactions as compared to the endergonic formation of Na2O for pure oxide compounds.

中文翻译:

开发用于氟离子电池的基于插层的负极材料:通过基于氢化物的脱氟工艺对Sr 2 TiO 3 F 2进行拓扑化学还原

在这项研究中,我们展示了一种新开发的还原性拓扑化学脱氟方法,该方法可在低至300°C的温度下使用NaH作为还原剂从过渡金属氟氧化物中选择性萃取/取代氟离子,从而能够制备和研究处于充电状态的氟离子电池负极材料。局部化学反应的序列,K个第一替代氟化2 NIF 4型前体氧化物的Sr 2的TiO 4到的Sr 2的TiO 3 ˚F 2随后的还原脱氟/锶的氢化氟取代2的TiO 3 ˚F 2,导致形成具有Sr 2 TiO 3 FH 0.48和Sr 2 TiO 3 H 1.48的近似组成的化合物。通过X射线衍射研究已经监测了在提取/取代氟离子后晶胞体积的变化。反应期间观察到强烈的结构变化,其c轴从Sr 2 TiO 3 F 2中的〜15.5Å降低到Sr 2 TiO 3 FH 0.48中的〜13.0Å和Sr 2 TiO 3 H中的〜12.7Å减小1.48,Sr 2 TiO 3 FH 0.48的附加对称性降低,并由中子粉末衍射证实。通过X射线吸收光谱,电子顺磁共振和磁测量来检查和确认Ti氧化态和配位环境的变化。此外,我们通过X射线光电子能谱研究发现,这类化合物的表面化学性质与本体性质大不相同,表明Sr 2 TiO 3 F和Sr 2 TiO 3与Ti 3+和Ti 2的表面组成+可以分别在反应中获得两种。我们进一步强调指出,使用相同的方法不可能将氧化物前体Sr 2 TiO 4直接还原为Sr 2 TiO 3。因此,Sr 2 TiO 4的两步改性允许在迄​​今为止用于氢化物还原含钛氧化物的最低温度下(300°C,而以前使用的〜600°C)制备具有低氧化态的化合物。基于氧化物的DFT计算形成能很好地支持了所观察到的与氧化物相比,氟氧化物的反应性差异。他们表明,NaF的形成是强大的驱动力,与纯氧化物化合物的Na 2 O的endergonic形成相比,导致exergonic还原/氢化物-氟化物取代反应。
更新日期:2018-05-04
down
wechat
bug