High temperature properties of Rb3H(SO4)2 at ambient pressure: Absence of a polymorphic, superprotonic transition

Lisa A. Cowan; Riham M. Morcos; Naoyuki Hatada; Alexandra Navrotsky; Sossina M. Haile

doi:10.1016/j.ssi.2008.02.016

High temperature properties of Rb₃H(SO₄)₂ at ambient pressure: Absence of a polymorphic, superprotonic transition

Lisa A. Cowan, Riham M. Morcos, Naoyuki Hatada, Alexandra Navrotsky, Sossina M. Haile

Research output: Contribution to journal › Article › peer-review

23 Scopus citations

Abstract

The high temperature properties of Rb₃H(SO₄)₂ have been studied by calorimetry, impedance spectroscopy and X-ray powder diffraction under moderate humidification. At ~ 205 °C the conductivity of Rb₃H(SO₄)₂ increases sharply, rising from 3.3 × 10^{- 5} to 1.9 × 10^{- 3} S/cm, suggestive of a polymorphic, superprotonic phase transition. This conductivity anomaly is accompanied by an endothermic thermal event with a heat of transition of ~ 18 kJ/mol. The X-ray powder diffraction pattern of Rb₃H(SO₄)₂ collected at 214 °C, however, shows peaks that can be attributed to Rb₂SO₄ and an unknown solid phase. The results indicate that, rather than a polymorphic transition, the conductivity increase of Rb₃H(SO₄)₂ corresponds to solid state disproportionation, described as Rb₃H(SO₄)₂(s) → Rb₂SO₄(s) + Rb_mH_n(SO₄)_p(s), where the phase of unknown composition is rich in sulfuric acid relative to Rb₃H(SO₄⁾₂. Drop solution calorimetry, carried out using molten sodium molybdate as the solvent, revealed the enthalpy of the alternative reaction Rb₃H(SO₄)₂(s) → Rb₂SO₄(s) + RbHSO₄(s) to be essentially zero (0.9 ± 2.7 kJ/mol), supporting the assertion that the observed transformation involves different product phases. The standard enthalpy of formation of Rb₃H(SO₄)₂ from the elements at 25 °C was found to be - 2602 ± 10 kJ/mol.

Original language	English (US)
Pages (from-to)	305-313
Number of pages	9
Journal	Solid State Ionics
Volume	179
Issue number	9-10
DOIs	https://doi.org/10.1016/j.ssi.2008.02.016
State	Published - May 15 2008
Externally published	Yes

Keywords

Drop solution calorimetry
Proton conduction
RbH(SO)
RbH(SO)
RbHSO
RbSO
Solid acid
Superprotonic transition

ASJC Scopus subject areas

Chemistry(all)
Materials Science(all)
Condensed Matter Physics

Access to Document

10.1016/j.ssi.2008.02.016

Cite this

@article{7ae9691b25d0486f982284b797756946,

title = "High temperature properties of Rb3H(SO4)2 at ambient pressure: Absence of a polymorphic, superprotonic transition",

abstract = "The high temperature properties of Rb3H(SO4)2 have been studied by calorimetry, impedance spectroscopy and X-ray powder diffraction under moderate humidification. At ~ 205 °C the conductivity of Rb3H(SO4)2 increases sharply, rising from 3.3 × 10- 5 to 1.9 × 10- 3 S/cm, suggestive of a polymorphic, superprotonic phase transition. This conductivity anomaly is accompanied by an endothermic thermal event with a heat of transition of ~ 18 kJ/mol. The X-ray powder diffraction pattern of Rb3H(SO4)2 collected at 214 °C, however, shows peaks that can be attributed to Rb2SO4 and an unknown solid phase. The results indicate that, rather than a polymorphic transition, the conductivity increase of Rb3H(SO4)2 corresponds to solid state disproportionation, described as Rb3H(SO4)2(s) → Rb2SO4(s) + RbmHn(SO4)p(s), where the phase of unknown composition is rich in sulfuric acid relative to Rb3H(SO4)2. Drop solution calorimetry, carried out using molten sodium molybdate as the solvent, revealed the enthalpy of the alternative reaction Rb3H(SO4)2(s) → Rb2SO4(s) + RbHSO4(s) to be essentially zero (0.9 ± 2.7 kJ/mol), supporting the assertion that the observed transformation involves different product phases. The standard enthalpy of formation of Rb3H(SO4)2 from the elements at 25 °C was found to be - 2602 ± 10 kJ/mol.",

keywords = "Drop solution calorimetry, Proton conduction, RbH(SO), RbH(SO), RbHSO, RbSO, Solid acid, Superprotonic transition",

author = "Cowan, {Lisa A.} and Morcos, {Riham M.} and Naoyuki Hatada and Alexandra Navrotsky and Haile, {Sossina M.}",

note = "Funding Information: The authors thank Jin-Yoo Suh and Mikhail Kislitsyn for assistance with thermomechanical analysis and Prof. William Johnson for access to TMA instrumentation. Thanks are also due to Prof. Tetsuya Uda for useful discussions. Financial support from the U.S. National Science Foundation, Division of Materials Research (grant No. 0435221) at Caltech and from the U.S. Department of Energy (grant DE-FG02-03ER46053) at UC Davis is gratefully acknowledged. Additional support was provided by the National Science Foundation (DMR-0080065) via Caltech's Center for the Science and Engineering of Materials, an NSF Materials Research Science and Engineering Center (MRSEC). Copyright: Copyright 2008 Elsevier B.V., All rights reserved.",

year = "2008",

month = may,

day = "15",

doi = "10.1016/j.ssi.2008.02.016",

language = "English (US)",

volume = "179",

pages = "305--313",

journal = "Solid State Ionics",

issn = "0167-2738",

publisher = "Elsevier",

number = "9-10",

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TY - JOUR

T1 - High temperature properties of Rb3H(SO4)2 at ambient pressure

T2 - Absence of a polymorphic, superprotonic transition

AU - Cowan, Lisa A.

AU - Morcos, Riham M.

AU - Hatada, Naoyuki

AU - Navrotsky, Alexandra

AU - Haile, Sossina M.

N1 - Funding Information: The authors thank Jin-Yoo Suh and Mikhail Kislitsyn for assistance with thermomechanical analysis and Prof. William Johnson for access to TMA instrumentation. Thanks are also due to Prof. Tetsuya Uda for useful discussions. Financial support from the U.S. National Science Foundation, Division of Materials Research (grant No. 0435221) at Caltech and from the U.S. Department of Energy (grant DE-FG02-03ER46053) at UC Davis is gratefully acknowledged. Additional support was provided by the National Science Foundation (DMR-0080065) via Caltech's Center for the Science and Engineering of Materials, an NSF Materials Research Science and Engineering Center (MRSEC). Copyright: Copyright 2008 Elsevier B.V., All rights reserved.

PY - 2008/5/15

Y1 - 2008/5/15

N2 - The high temperature properties of Rb3H(SO4)2 have been studied by calorimetry, impedance spectroscopy and X-ray powder diffraction under moderate humidification. At ~ 205 °C the conductivity of Rb3H(SO4)2 increases sharply, rising from 3.3 × 10- 5 to 1.9 × 10- 3 S/cm, suggestive of a polymorphic, superprotonic phase transition. This conductivity anomaly is accompanied by an endothermic thermal event with a heat of transition of ~ 18 kJ/mol. The X-ray powder diffraction pattern of Rb3H(SO4)2 collected at 214 °C, however, shows peaks that can be attributed to Rb2SO4 and an unknown solid phase. The results indicate that, rather than a polymorphic transition, the conductivity increase of Rb3H(SO4)2 corresponds to solid state disproportionation, described as Rb3H(SO4)2(s) → Rb2SO4(s) + RbmHn(SO4)p(s), where the phase of unknown composition is rich in sulfuric acid relative to Rb3H(SO4)2. Drop solution calorimetry, carried out using molten sodium molybdate as the solvent, revealed the enthalpy of the alternative reaction Rb3H(SO4)2(s) → Rb2SO4(s) + RbHSO4(s) to be essentially zero (0.9 ± 2.7 kJ/mol), supporting the assertion that the observed transformation involves different product phases. The standard enthalpy of formation of Rb3H(SO4)2 from the elements at 25 °C was found to be - 2602 ± 10 kJ/mol.

AB - The high temperature properties of Rb3H(SO4)2 have been studied by calorimetry, impedance spectroscopy and X-ray powder diffraction under moderate humidification. At ~ 205 °C the conductivity of Rb3H(SO4)2 increases sharply, rising from 3.3 × 10- 5 to 1.9 × 10- 3 S/cm, suggestive of a polymorphic, superprotonic phase transition. This conductivity anomaly is accompanied by an endothermic thermal event with a heat of transition of ~ 18 kJ/mol. The X-ray powder diffraction pattern of Rb3H(SO4)2 collected at 214 °C, however, shows peaks that can be attributed to Rb2SO4 and an unknown solid phase. The results indicate that, rather than a polymorphic transition, the conductivity increase of Rb3H(SO4)2 corresponds to solid state disproportionation, described as Rb3H(SO4)2(s) → Rb2SO4(s) + RbmHn(SO4)p(s), where the phase of unknown composition is rich in sulfuric acid relative to Rb3H(SO4)2. Drop solution calorimetry, carried out using molten sodium molybdate as the solvent, revealed the enthalpy of the alternative reaction Rb3H(SO4)2(s) → Rb2SO4(s) + RbHSO4(s) to be essentially zero (0.9 ± 2.7 kJ/mol), supporting the assertion that the observed transformation involves different product phases. The standard enthalpy of formation of Rb3H(SO4)2 from the elements at 25 °C was found to be - 2602 ± 10 kJ/mol.

KW - Drop solution calorimetry

KW - Proton conduction

KW - RbH(SO)

KW - RbHSO

KW - RbSO

KW - Solid acid

KW - Superprotonic transition

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U2 - 10.1016/j.ssi.2008.02.016

DO - 10.1016/j.ssi.2008.02.016

M3 - Article

AN - SCOPUS:41949123933

SN - 0167-2738

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EP - 313

JO - Solid State Ionics

JF - Solid State Ionics

IS - 9-10

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