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两种磷酸钛基质子导体的晶体结构:从头算结构解析与材料性能

Crystal Structures of Two Titanium Phosphate-Based Proton Conductors: Ab Initio Structure Solution and Materials Properties.

作者信息

Petersen Hilke, Stegmann Niklas, Fischer Michael, Zibrowius Bodo, Radev Ivan, Philippi Wladimir, Schmidt Wolfgang, Weidenthaler Claudia

机构信息

Heterogeneous Catalysis, Max-Planck-Institut für Kohlenforschung, Kaiser-Wilhelm-Platz 1, 45470 Mülheim an der Ruhr, Germany.

MAPEX Center for Materials and Processes, University of Bremen, 28334 Bremen, Germany.

出版信息

Inorg Chem. 2022 Feb 7;61(5):2379-2390. doi: 10.1021/acs.inorgchem.1c02613. Epub 2021 Nov 22.

Abstract

Transition-metal phosphates show a wide range of chemical compositions, variations of the valence states, and crystal structures. They are commercially used as solid-state catalysts, cathode materials in rechargeable batteries, or potential candidates for proton-exchange membranes in fuel cells. Here, we report on the successful ab initio structure determination of two novel titanium pyrophosphates, Ti(III)p and Ti(IV)p, from powder X-ray diffraction (PXRD) data. The low-symmetry space groups 2/ for Ti(III)p and 1̅ for Ti(IV)p required the combination of spectroscopic and diffraction techniques for structure determination. In Ti(III)p, trivalent titanium ions occupy the center of TiO polyhedra, coordinated by five pyrophosphate groups, one of them as a bidentate ligand. This secondary coordination causes the formation of one-dimensional six-membered ring channels with a diameter of 3.93(2) Å, which is stabilized by NH ions. Annealing Ti(III)p in inert atmospheres results in the formation of a new compound, denoted as Ti(IV)p. The structure of this compound shows a similar three-dimensional framework consisting of [PO] tetrahedra and TiO octahedra and an empty one-dimensional channel with a diameter of 5.07(1) Å. The PXRD of the transformation of Ti(III)p to Ti(IV)p reveals a two-step mechanism, i.e., the decomposition of NH ions in a first step and subsequent structure relaxation. The specific proton conductivity and activation energy of the proton migration of Ti(III)p, governed by the Grotthus mechanism, belong to the highest and lowest, respectively, ever reported for this class of materials, which reveals its potential application in electrochemical devices like fuel cells and water electrolyzers in the intermediate temperature range.

摘要

过渡金属磷酸盐具有广泛的化学成分、价态变化和晶体结构。它们在商业上用作固态催化剂、可充电电池的阴极材料或燃料电池中质子交换膜的潜在候选材料。在此,我们报告了从粉末X射线衍射(PXRD)数据成功从头算确定两种新型焦磷酸钛Ti(III)p和Ti(IV)p的结构。Ti(III)p的低对称空间群为2/,Ti(IV)p的为1̅,这需要结合光谱和衍射技术来确定结构。在Ti(III)p中,三价钛离子占据TiO多面体的中心,由五个焦磷酸基团配位,其中一个作为双齿配体。这种二级配位导致形成直径为3.93(2) Å的一维六元环通道,该通道由NH离子稳定。在惰性气氛中对Ti(III)p进行退火会导致形成一种新化合物,记为Ti(IV)p。该化合物的结构显示出类似的三维骨架,由[PO]四面体和TiO八面体组成,以及一个直径为5.07(1) Å的空一维通道。Ti(III)p向Ti(IV)p转变的PXRD揭示了一种两步机制,即第一步中NH离子的分解以及随后的结构弛豫。由Grotthus机制控制的Ti(III)p的比质子电导率和质子迁移活化能分别属于这类材料中报道过的最高和最低值,这揭示了其在中温范围内的燃料电池和水电解槽等电化学装置中的潜在应用。

https://cdn.ncbi.nlm.nih.gov/pmc/blobs/8201/8826274/feae8f10da35/ic1c02613_0001.jpg

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