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

Petersen, H., Stegmann, N., Fischer, M., Zibrowius, B., Radev, I., Philippi, W., et al. (2022). Crystal Structures of Two Titanium Phosphate-Based Proton Conductors: Ab Initio Structure Solution and Materials Properties. Inorganic Chemistry, 61(5), 2379-2390. doi:10.1021/acs.inorgchem.1c02613.

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 Creators:
Petersen, Hilke1, Author              
Stegmann, Niklas2, Author              
Fischer, Michael3, 4, Author
Zibrowius, Bodo5, Author              
Radev, Ivan6, Author
Philippi, Wladimir6, Author
Schmidt, Wolfgang2, Author              
Weidenthaler, Claudia1, Author              
Affiliations:
1Research Group Weidenthaler, Max-Planck-Institut für Kohlenforschung, Max Planck Society, ou_1950291              
2Research Group Schmidt, Max-Planck-Institut für Kohlenforschung, Max Planck Society, ou_1445618              
3MAPEX Center for Materials and Processes, University of Bremen, 28334 Bremen, Germany, ou_persistent22              
4Crystallography/Geosciences, University of Bremen, Klagenfurter Straße, 28359 Bremen, Germany, ou_persistent22              
5Service Department Farès (NMR), Max-Planck-Institut für Kohlenforschung, Max Planck Society, ou_1445623              
6The Hydrogen and Fuel Cell Center ZBT GmbH, Carl-Benz-Straße 201, 47057 Duisburg, Germany, ou_persistent22              

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 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 P21/c for Ti(III)p and P1̅ 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 TiO6 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 dmax of 3.93(2) Å, which is stabilized by NH4+ 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 [PO4]3-tetrahedra and TiIV+O6 octahedra and an empty one-dimensional channel with a diameter dmax of 5.07(1) Å. The in situ PXRD of the transformation of Ti(III)p to Ti(IV)p reveals a two-step mechanism, i.e., the decomposition of NH4+ 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.

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Language(s): eng - English
 Dates: 2021-08-242021-11-222022-02-07
 Publication Status: Published in print
 Pages: 12
 Publishing info: -
 Table of Contents: -
 Rev. Type: Peer
 Identifiers: DOI: 10.1021/acs.inorgchem.1c02613
 Degree: -

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Title: Inorganic Chemistry
  Abbreviation : Inorg. Chem.
Source Genre: Journal
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Publ. Info: Washington, DC : American Chemical Society
Pages: - Volume / Issue: 61 (5) Sequence Number: - Start / End Page: 2379 - 2390 Identifier: ISSN: 0020-1669
CoNE: https://pure.mpg.de/cone/journals/resource/0020-1669