Rotating-frame nuclear magnetic resonance study of the superprotonic conduction in LiH2PO4

Kweon, Jin Jung; Lee, Kyu Won; Lee, Kwang Sei; Lee, Cheol Eui

doi:10.1016/j.ssc.2013.07.022

Cited by 5 publications

(8 citation statements)

References 25 publications

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“…A good protonic conductor generally involves O–H···O hydrogen bonds longer than 2.60 Å . The crystal structure of LDP determined by X-ray and neutron diffraction shows two types of O–H···O hydrogen bonds with different bond lengths of 2.677 and 2.561 Å connecting the tetrahedral PO 4 groups. , In several earlier studies of LDP, fast interbond proton hopping was suggested to be responsible for the exceptionally high protonic conductivitythis conclusion being based on the correlation between temperature-dependent 1 H spin–lattice relaxation and conductivity measurements. ,, However, in the similar compound CDP, which also contains two different H-bonding environments, the interbond proton hopping was found to be very slow, together with low protonic conductivity (10 –9 –10 –10 Ω –1 cm –1 ). , More importantly, LDP is known to be hygroscopic, but whether or not the adsorbed H 2 O plays any role in LDP’s protonic conductivity mechanism was not considered. This is important because earlier studies of several AH 2 PO 4 compounds (A = Li, K, and Cs) had indicated the role of lattice dehydration or humidity in the conductivity mechanism.…”

Section: Introductionmentioning

confidence: 97%

“…Finally, in LDP itself, the role of humidity has been noted, but surprisingly, the conductivity was reported to decrease with increase in dampness, in contrast to CDP. In addition, the earlier NMR studies on LDP were carried out at the low frequency of 200 MHz for 1 H, where spectral resolution was insufficient for assignment of peaks to specific O–H···O protons, , adding to the impetus for the present undertaking.…”

Section: Introductionmentioning

confidence: 99%

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High Field MAS NMR and Conductivity Study of the Superionic Conductor LiH₂PO₄: Critical Role of Physisorbed Water in Its Protonic Conductivity

Kweon

Steven

et al. 2014

J. Phys. Chem. C

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LiH2PO4 (LDP) is a favored candidate for hydrogen fuel cells, but the mechanism of its high protonic conductivity remains unclear. A complicating factor has been the lack of resolution in the reported proton NMR spectra. We now report multinuclear magic angle spinning NMR in LDP at magnetic fields up to 21.2 T. Well-resolved 1H NMR spectra are observed that are assignable to protons in the short and long O–H···O hydrogen bonds and a peak to physisorbed H2O. The position and intensity for the H2O peak depend on the H 2 O content, implying fast exchange between the adsorbed H2O and the O–H···O protons. 31P and 7Li NMR spectra and spin–lattice relaxation measurements showed that the proton hopping/exchange processes involve concerted hindered rotational fluctuations of the phosphate groups. Conductivity data from adsorbed H2O-controlled samples clearly suggest that the mechanism of LDP’s protonic conductivity is dominantly the exchange (and hopping) of the adsorbed H2O protons with the short O–H···O hydrogen bonds, in contrast to an earlier model that ascribed it to intermolecular hopping of O–H···O protons. The new findings enable us to modulate LDP’s protonic conductivity by several orders of magnitude via controlling physisorbed water.

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Section: Introductionmentioning

confidence: 97%

Section: Introductionmentioning

confidence: 99%

High Field MAS NMR and Conductivity Study of the Superionic Conductor LiH₂PO₄: Critical Role of Physisorbed Water in Its Protonic Conductivity

Kweon

Steven

et al. 2014

J. Phys. Chem. C

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“…Among these compounds, the most widely studied is potassium dihydrogen phosphate (KDP) for ferroelectric, piezoelectric, and electro-optic properties [3,4]. Much less investigated, LiH 2 PO 4 (LDP) has a particular interest for its relatively high protonic conductivity [5][6][7]. The structure of LDP consists into tetrahedral groups PO 4 and LiO 4 which are bonded together by oxygen ions.…”

Section: Introductionmentioning

confidence: 99%

Phase transformations in LiH 2 PO 4 (LDP) revealed by Raman spectroscopy

Dekhili

Kauffmann

Aroui

et al. 2018

Solid State Communications

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We investigate Raman scattering measurements on polycrystalline LiH 2 PO 4 (LDP) between 30 and 240°C, in order to detect phase transformations. The thermal behavior of main lines in different wavenumber ranges is discussed and analyzed. Raman spectra show two anomalies at 176°C and 210°C, reflecting changes in chemical bonds, and are attributed to progressive polymerization, in agreement with earlier electrical measurements.

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“…As a well-established analytical technique, Nuclear Magnetic Resonance (NMR) spectroscopy is capable of providing information on structure and dynamics of solids [2,3]. Recently, the mechanism of the protonic conductivity of LDP has been investigated by 1 H NMR spectroscopy of powder samples under magic-angle spinning (MAS) [4,5]. However, not much attention has been paid to the electronic surroundings of the phosphorus and lithium atoms, which despite their light mass have been found to be quite immobile in the crystal structure at room temperature [6].…”

Section: Introductionmentioning

confidence: 99%

“…All atoms in the unit cell are located at Wyckoff position 4a, with the lithium atoms (green) and the phosphorus atoms (purple) both tetrahedrally coordinated by oxygen (red). The hydrogen atoms (ivory) stabilize the crystal structure by forming hydrogen bonds (dotted lines) between the PO 4 and LiO 4 tetrahedra. (Drawing generated with the VESTA program [8]).…”

Section: Introductionmentioning

confidence: 99%

Single-Crystal 31P and 7Li NMR of the Ionic Conductor LiH2PO4

Zeman

Kainz²,

Bräuniger

2020

Crystals

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The electronic surroundings of phosphorus and lithium atoms in the ionic conductor lithium dihydrogen phosphate (LDP) have been studied by single-crystal nuclear magnetic resonance (NMR) spectroscopy at room temperature. From orientation-dependent NMR spectra of a large homegrown LDP single crystal, the full 31 P chemical shift (CS) and 7 Li quadrupole coupling (QC) tensor was determined, using a global fit over three rotation patterns. The resulting CS tensor is characterized by its three eigenvalues: δ PAS 11 = (67.0 ± 0.6) ppm, δ PAS 22 = (13.9 ± 1.5) ppm, and δ PAS 33 = (−78.7 ± 0.9) ppm. All eigenvalues have also been verified by magic-angle spinning NMR on a polycrystalline sample, using Herzfeld-Berger analysis of the rotational side band pattern. The resulting 7 Li QC tensor is characterized by its quadrupolar coupling constant χ = Q PAS 33 = (−71 ± 1) kHz and the two eigenvalues Q PAS 11 = (22.3 ± 0.9) kHz, and Q PAS 22 = (48.4 ± 0.8) kHz. The initially unknown orientation of the mounted crystal, expressed by the orientation of the rotation axis in the orthorhombic crystal frame, was included in the global data fit as well, thus obtaining it from NMR data only.Crystals 2020, 10, 302 2 of 12 with four formula units per unit cell [6]. The PO 4 tetrahedra build a three-dimensional framework connected by two different types of hydrogen bonds. The LiO 4 coordination tetrahedra are linked by their vertices forming [100] isolated chains and share each edge with the PO 4 units. All atoms in the unit cell are located at Wyckoff position 4a with the general site symmetry 1 − C 1 [7]. As a result, no symmetry constraints affect the algebraic form of the NMR interaction tensors, as will be explained in the following.Abstract: Last thing to be done...

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Rotating-frame nuclear magnetic resonance study of the superprotonic conduction in LiH2PO4

Cited by 5 publications

References 25 publications

High Field MAS NMR and Conductivity Study of the Superionic Conductor LiH₂PO₄: Critical Role of Physisorbed Water in Its Protonic Conductivity

High Field MAS NMR and Conductivity Study of the Superionic Conductor LiH₂PO₄: Critical Role of Physisorbed Water in Its Protonic Conductivity

Phase transformations in LiH 2 PO 4 (LDP) revealed by Raman spectroscopy

Single-Crystal 31P and 7Li NMR of the Ionic Conductor LiH2PO4

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Rotating-frame nuclear magnetic resonance study of the superprotonic conduction in LiH2PO4

Cited by 5 publications

References 25 publications

High Field MAS NMR and Conductivity Study of the Superionic Conductor LiH2PO4: Critical Role of Physisorbed Water in Its Protonic Conductivity

High Field MAS NMR and Conductivity Study of the Superionic Conductor LiH2PO4: Critical Role of Physisorbed Water in Its Protonic Conductivity

Phase transformations in LiH 2 PO 4 (LDP) revealed by Raman spectroscopy

Single-Crystal 31P and 7Li NMR of the Ionic Conductor LiH2PO4

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Product

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High Field MAS NMR and Conductivity Study of the Superionic Conductor LiH₂PO₄: Critical Role of Physisorbed Water in Its Protonic Conductivity

High Field MAS NMR and Conductivity Study of the Superionic Conductor LiH₂PO₄: Critical Role of Physisorbed Water in Its Protonic Conductivity