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Title: Hydrogen-Bond Symmetrization Breakdown and Dehydrogenation Mechanism of FeO 2 H at High Pressure

The cycling of hydrogen plays an important role in the geochemical evolution of our planet. Under high-pressure conditions, asymmetric hydroxyl bonds tend to form a symmetric O–H–O configuration in which H is positioned at the center of two O atoms. The symmetrization of O–H bonds improves their thermal stability and as such, water-bearing minerals can be present deeper in the Earth’s lower mantle. However, how exactly H is recycled from the deep mantle remains unclear. Here, we employ first-principles free-energy landscape sampling methods together with high pressure-high temperature experiments to reveal the dehydrogenation mechanism of a water-bearing mineral, FeO 2H, at deep mantle conditions. Experimentally, we show that ~50% H is released from symmetrically hydrogen-bonded ε-FeO 2H upon transforming to a pyrite-type phase (Py-phase). By resolving the lowest-energy transition pathway from ε-FeO 2H to the Py-phase, we demonstrate that half of the O–H bonds in the mineral rupture during the structural transition, leading toward the breakdown of symmetrized hydrogen bonds and eventual dehydrogenation. In conclusion, our study sheds new light on the stability of symmetric hydrogen bonds during structural transitions and provides a dehydrogenation mechanism for hydrous minerals existing in the deep mantle
Authors:
 [1] ; ORCiD logo [2] ;  [3] ;  [4] ;  [5]
  1. Center for High Pressure Science and Technology Advanced Research (HPSTAR), Shanghai (China)
  2. Center for High Pressure Science and Technology Advanced Research (HPSTAR), Shanghai (China); Stanford Univ., CA (United States). Dept. of Geological Sciences
  3. Stanford Univ., CA (United States). Dept. of Geological Sciences
  4. Center for High Pressure Science and Technology Advanced Research (HPSTAR), Shanghai (China); Carnegie Inst. of Washington, Washington, DC (United States). Geophysical Lab.
  5. Center for High Pressure Science and Technology Advanced Research (HPSTAR), Shanghai (China); George Mason Univ., Fairfax, VA (United States). Dept. of Physics and Astronomy
Publication Date:
Grant/Contract Number:
NA0001974; 21703004; U1530402
Type:
Accepted Manuscript
Journal Name:
Journal of the American Chemical Society
Additional Journal Information:
Journal Volume: 139; Journal Issue: 35; Journal ID: ISSN 0002-7863
Publisher:
American Chemical Society (ACS)
Research Org:
Carnegie Inst. of Washington, Washington, DC (United States)
Sponsoring Org:
USDOE National Nuclear Security Administration (NNSA); USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22); National Science Foundation (NSF); NSAF
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES; 37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
OSTI Identifier:
1474063

Zhu, Sheng-cai, Hu, Qingyang, Mao, Wendy L., Mao, Ho-kwang, and Sheng, Hongwei. Hydrogen-Bond Symmetrization Breakdown and Dehydrogenation Mechanism of FeO2 H at High Pressure. United States: N. p., Web. doi:10.1021/jacs.7b06528.
Zhu, Sheng-cai, Hu, Qingyang, Mao, Wendy L., Mao, Ho-kwang, & Sheng, Hongwei. Hydrogen-Bond Symmetrization Breakdown and Dehydrogenation Mechanism of FeO2 H at High Pressure. United States. doi:10.1021/jacs.7b06528.
Zhu, Sheng-cai, Hu, Qingyang, Mao, Wendy L., Mao, Ho-kwang, and Sheng, Hongwei. 2017. "Hydrogen-Bond Symmetrization Breakdown and Dehydrogenation Mechanism of FeO2 H at High Pressure". United States. doi:10.1021/jacs.7b06528. https://www.osti.gov/servlets/purl/1474063.
@article{osti_1474063,
title = {Hydrogen-Bond Symmetrization Breakdown and Dehydrogenation Mechanism of FeO2 H at High Pressure},
author = {Zhu, Sheng-cai and Hu, Qingyang and Mao, Wendy L. and Mao, Ho-kwang and Sheng, Hongwei},
abstractNote = {The cycling of hydrogen plays an important role in the geochemical evolution of our planet. Under high-pressure conditions, asymmetric hydroxyl bonds tend to form a symmetric O–H–O configuration in which H is positioned at the center of two O atoms. The symmetrization of O–H bonds improves their thermal stability and as such, water-bearing minerals can be present deeper in the Earth’s lower mantle. However, how exactly H is recycled from the deep mantle remains unclear. Here, we employ first-principles free-energy landscape sampling methods together with high pressure-high temperature experiments to reveal the dehydrogenation mechanism of a water-bearing mineral, FeO2H, at deep mantle conditions. Experimentally, we show that ~50% H is released from symmetrically hydrogen-bonded ε-FeO2H upon transforming to a pyrite-type phase (Py-phase). By resolving the lowest-energy transition pathway from ε-FeO2H to the Py-phase, we demonstrate that half of the O–H bonds in the mineral rupture during the structural transition, leading toward the breakdown of symmetrized hydrogen bonds and eventual dehydrogenation. In conclusion, our study sheds new light on the stability of symmetric hydrogen bonds during structural transitions and provides a dehydrogenation mechanism for hydrous minerals existing in the deep mantle},
doi = {10.1021/jacs.7b06528},
journal = {Journal of the American Chemical Society},
number = 35,
volume = 139,
place = {United States},
year = {2017},
month = {8}
}