Mechanisms of proton transport in aqueous acid solutions

Ivan Popov; Zhenghao Zhu; Harmandeep Singh; Mohanad Abdullah; Robert L. Sacci; Eugene Mamontov; Joshua T. Damron; Catalin Gainaru; Stephen J. Paddison; Alexei P. Sokolov

doi:10.1016/j.xcrp.2024.102294

Mechanisms of proton transport in aqueous acid solutions

Ivan Popov, Zhenghao Zhu, Harmandeep Singh, Mohanad Abdullah, Robert L. Sacci, Eugene Mamontov, Joshua T. Damron, Catalin Gainaru, Stephen J. Paddison, Alexei P. Sokolov

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

Abstract

The fundamental understanding of proton transport, specifically the Grotthuss-like mechanism, is critical for many technological applications. The present study presents a comprehensive analysis of proton transport in aqueous solutions of sulfuric and phosphoric acids using quasielastic neutron and light scattering, broadband dielectric spectroscopy, rheology, pulsed-field gradient-NMR measurements, and ab initio molecular dynamic simulations. Results show that in all systems, proton transport occurs through short “jumps” of ∼0.5 Å that are faster than structural relaxation. However, proton hopping appears to be coupled to structural relaxation in aqueous solutions of sulfuric acid, while these processes are decoupled in phosphoric acid. Neutron scattering indicates that all protons have the same fast mobility in phosphoric acid systems, while at least one proton per sulfuric molecule remains slower than other protons. Analysis reveals correlated proton jumps, but these correlations suppress conductivity, suggesting that expected Grotthuss-like enhancement of conductivity is unlikely in bulk liquids.

Original language	English
Article number	102294
Journal	Cell Reports Physical Science
Volume	5
Issue number	11
DOIs	https://doi.org/10.1016/j.xcrp.2024.102294
State	Published - Nov 20 2024

Funding

We acknowledge the support of the National Science Foundation (awards CHE-1764409 and CHE-2102425 ). C.G. acknowledges support for the high-frequency dielectric and rheology measurements from \u201CFast and Cooperative Ion Transport in Polymer-Based Materials (FaCT),\u201D and the Energy Frontier Research Center funded by the US Department of Energy Office of Science , Basic Energy Sciences . Research at the BASIS of the Oak Ridge National Laboratory\u2019s Spallation Neutron Source was sponsored by the Scientific User Facilities Division , Office of Basic Energy Sciences , US Department of Energy . Computing resources were provided through ACCESS allocation DMR130078 on Stampede2 at the Texas Advanced Computing Center. J.T.D. acknowledges the US Department of Energy Office of Science , Basic Energy Sciences , Materials Sciences and Engineering Division ( FWP# ERKCK60 ), under contract DE-AC05-00OR22725 with UT-Battelle, LLC , for the support of the NMR experiments. We acknowledge the support of the National Science Foundation (awards CHE-1764409 and CHE-2102425). C.G. acknowledges support for the high-frequency dielectric and rheology measurements from \u201CFast and Cooperative Ion Transport in Polymer-Based Materials (FaCT),\u201D and the Energy Frontier Research Center funded by the U.S. Department of Energy Office of Science, Basic Energy Sciences. Research at the BASIS of the Oak Ridge National Laboratory's Spallation Neutron Source was sponsored by the Scientific User Facilities Division, Office of Basic Energy Sciences, U.S. Department of Energy. Computing resources were provided through ACCESS allocation DMR130078 on Stampede2 at the Texas Advanced Computing Center. J.T.D. acknowledges the U.S. Department of Energy Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division (FWP# ERKCK60), under contract DE-AC05-00OR22725 with UT-Battelle, LLC, for the support of the NMR experiments.

Funders	Funder number
Energy Frontier Research Centers
Basic Energy Sciences
Division of Materials Sciences and Engineering
Oak Ridge National Laboratory
U.S. Department of Energy
Texas Advanced Computing Center
Scientific User Facilities Division
Office of Science
Find A Cure Today Breast Cancer Foundation
National Science Foundation	CHE-2102425, CHE-1764409
National Science Foundation
FWP	DE-AC05-00OR22725, ERKCK60

Keywords

Grotthuss mechanism
ion-ion correlations
phosphoric acid
proton hopping
proton transport
sulfuric acid

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10.1016/j.xcrp.2024.102294

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title = "Mechanisms of proton transport in aqueous acid solutions",

abstract = "The fundamental understanding of proton transport, specifically the Grotthuss-like mechanism, is critical for many technological applications. The present study presents a comprehensive analysis of proton transport in aqueous solutions of sulfuric and phosphoric acids using quasielastic neutron and light scattering, broadband dielectric spectroscopy, rheology, pulsed-field gradient-NMR measurements, and ab initio molecular dynamic simulations. Results show that in all systems, proton transport occurs through short “jumps” of ∼0.5 {\AA} that are faster than structural relaxation. However, proton hopping appears to be coupled to structural relaxation in aqueous solutions of sulfuric acid, while these processes are decoupled in phosphoric acid. Neutron scattering indicates that all protons have the same fast mobility in phosphoric acid systems, while at least one proton per sulfuric molecule remains slower than other protons. Analysis reveals correlated proton jumps, but these correlations suppress conductivity, suggesting that expected Grotthuss-like enhancement of conductivity is unlikely in bulk liquids.",

keywords = "Grotthuss mechanism, ion-ion correlations, phosphoric acid, proton hopping, proton transport, sulfuric acid",

author = "Ivan Popov and Zhenghao Zhu and Harmandeep Singh and Mohanad Abdullah and Sacci, {Robert L.} and Eugene Mamontov and Damron, {Joshua T.} and Catalin Gainaru and Paddison, {Stephen J.} and Sokolov, {Alexei P.}",

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year = "2024",

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doi = "10.1016/j.xcrp.2024.102294",

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AU - Zhu, Zhenghao

AU - Singh, Harmandeep

AU - Abdullah, Mohanad

AU - Sacci, Robert L.

AU - Mamontov, Eugene

AU - Damron, Joshua T.

AU - Gainaru, Catalin

AU - Paddison, Stephen J.

AU - Sokolov, Alexei P.

PY - 2024/11/20

Y1 - 2024/11/20

N2 - The fundamental understanding of proton transport, specifically the Grotthuss-like mechanism, is critical for many technological applications. The present study presents a comprehensive analysis of proton transport in aqueous solutions of sulfuric and phosphoric acids using quasielastic neutron and light scattering, broadband dielectric spectroscopy, rheology, pulsed-field gradient-NMR measurements, and ab initio molecular dynamic simulations. Results show that in all systems, proton transport occurs through short “jumps” of ∼0.5 Å that are faster than structural relaxation. However, proton hopping appears to be coupled to structural relaxation in aqueous solutions of sulfuric acid, while these processes are decoupled in phosphoric acid. Neutron scattering indicates that all protons have the same fast mobility in phosphoric acid systems, while at least one proton per sulfuric molecule remains slower than other protons. Analysis reveals correlated proton jumps, but these correlations suppress conductivity, suggesting that expected Grotthuss-like enhancement of conductivity is unlikely in bulk liquids.

AB - The fundamental understanding of proton transport, specifically the Grotthuss-like mechanism, is critical for many technological applications. The present study presents a comprehensive analysis of proton transport in aqueous solutions of sulfuric and phosphoric acids using quasielastic neutron and light scattering, broadband dielectric spectroscopy, rheology, pulsed-field gradient-NMR measurements, and ab initio molecular dynamic simulations. Results show that in all systems, proton transport occurs through short “jumps” of ∼0.5 Å that are faster than structural relaxation. However, proton hopping appears to be coupled to structural relaxation in aqueous solutions of sulfuric acid, while these processes are decoupled in phosphoric acid. Neutron scattering indicates that all protons have the same fast mobility in phosphoric acid systems, while at least one proton per sulfuric molecule remains slower than other protons. Analysis reveals correlated proton jumps, but these correlations suppress conductivity, suggesting that expected Grotthuss-like enhancement of conductivity is unlikely in bulk liquids.

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Mechanisms of proton transport in aqueous acid solutions

Abstract

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Keywords

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