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Title: Quantum Chemical Prediction of p K a Values of Cationic Ion-Exchange Groups in Polymer Electrolyte Membranes

Abstract

The durability of anion-exchange membranes (AEMs) in alkaline fuel cells is largely determined by the stability of anion-exchange groups. Despite continuous research efforts, the commonly employed cations still have limited stability against hydroxide that can act as a strong base and nucleophile. This work is concerned with base-catalyzed degradation of organic cations initiated by proton abstraction to form reactive ylides or carbenes. We report on the performance of 24 methods combining density functional theory and electronic structure methods with implicit solvation calculations for predicting pK a values of organic cations in water and DMSO. The most accurate computational protocols are obtained using a combination of M06-2X/6-311++G** with the SMD solvation model for water (the mean absolute error of 0.4 pK a units) and B3LYP/aug-cc-pVTZ with the IEFPCM solvation model for DMSO (the mean absolute error of 1.4 pK a units). The aqueous pK a calculation protocol is cross-validated against the experimental C–H acidity constants outside the conventional range of 0–14 pK a values. In conclusion, this study rationalizes alkaline degradation of imidazolium cations with C2-alkyl substituents and provides a theoretical scale of C–H acidity for potential anion-exchange groups in AEMs.

Authors:
 [1];  [1]; ORCiD logo [1]; ORCiD logo [1]
  1. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Chemical Sciences Division
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
1458374
Grant/Contract Number:
AC05-00OR22725; AC02-05CH11231
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Journal of Physical Chemistry. C
Additional Journal Information:
Journal Volume: 122; Journal Issue: 5; Journal ID: ISSN 1932-7447
Publisher:
American Chemical Society
Country of Publication:
United States
Language:
English
Subject:
25 ENERGY STORAGE; 36 MATERIALS SCIENCE

Citation Formats

de Paul Nzuwah Nziko, Vincent, Shih, Jiun-Le, Jansone-Popova, Santa, and Bryantsev, Vyacheslav S. Quantum Chemical Prediction of pKa Values of Cationic Ion-Exchange Groups in Polymer Electrolyte Membranes. United States: N. p., 2018. Web. doi:10.1021/acs.jpcc.7b09828.
de Paul Nzuwah Nziko, Vincent, Shih, Jiun-Le, Jansone-Popova, Santa, & Bryantsev, Vyacheslav S. Quantum Chemical Prediction of pKa Values of Cationic Ion-Exchange Groups in Polymer Electrolyte Membranes. United States. doi:10.1021/acs.jpcc.7b09828.
de Paul Nzuwah Nziko, Vincent, Shih, Jiun-Le, Jansone-Popova, Santa, and Bryantsev, Vyacheslav S. Tue . "Quantum Chemical Prediction of pKa Values of Cationic Ion-Exchange Groups in Polymer Electrolyte Membranes". United States. doi:10.1021/acs.jpcc.7b09828.
@article{osti_1458374,
title = {Quantum Chemical Prediction of pKa Values of Cationic Ion-Exchange Groups in Polymer Electrolyte Membranes},
author = {de Paul Nzuwah Nziko, Vincent and Shih, Jiun-Le and Jansone-Popova, Santa and Bryantsev, Vyacheslav S.},
abstractNote = {The durability of anion-exchange membranes (AEMs) in alkaline fuel cells is largely determined by the stability of anion-exchange groups. Despite continuous research efforts, the commonly employed cations still have limited stability against hydroxide that can act as a strong base and nucleophile. This work is concerned with base-catalyzed degradation of organic cations initiated by proton abstraction to form reactive ylides or carbenes. We report on the performance of 24 methods combining density functional theory and electronic structure methods with implicit solvation calculations for predicting pKa values of organic cations in water and DMSO. The most accurate computational protocols are obtained using a combination of M06-2X/6-311++G** with the SMD solvation model for water (the mean absolute error of 0.4 pKa units) and B3LYP/aug-cc-pVTZ with the IEFPCM solvation model for DMSO (the mean absolute error of 1.4 pKa units). The aqueous pKa calculation protocol is cross-validated against the experimental C–H acidity constants outside the conventional range of 0–14 pKa values. In conclusion, this study rationalizes alkaline degradation of imidazolium cations with C2-alkyl substituents and provides a theoretical scale of C–H acidity for potential anion-exchange groups in AEMs.},
doi = {10.1021/acs.jpcc.7b09828},
journal = {Journal of Physical Chemistry. C},
number = 5,
volume = 122,
place = {United States},
year = {Tue Jan 09 00:00:00 EST 2018},
month = {Tue Jan 09 00:00:00 EST 2018}
}

Journal Article:
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