Development of hydrophilicity on the proton exchange using sulfonic acid on PEEK in the presence of water: a density functional theory study
The introduction of a protogenic group such as sulfonic acid enables the operation of polymer electrolyte membrane for fuel cells at intermediate temperatures (> 100 °C) and very low humidity. It has been reported that the addition of a strongly acidic sulfonic acid group to hydrophobic polyether ether ketone (PEEK) creates the water permeability and proton transfer. In order to understand how sulfonic acid develops hydrophilicity, we conducted density functional theory calculations to determine the adsorption affinity of water for sulfonated PEEK (SPEEK), which represents the binding energy and band gap between HOMO (highest occupied molecular orbital) of SPEEK and LUMO (lowest unoccupied molecular orbital) of water molecules. Moreover, we designed disulfonated PEEKs (DSPEEK) with cis- and trans-conformations and found that cis-DSPEEK exhibits higher adsorption affinity for water with strong hydrogen bonds. This is attributed to the narrow energy gap of water molecules on cis-DSPEEK. Furthermore, we investigated proton adsorption in the presence of water to determine the effect of hydrophilic environment on the proton exchange in SPEEK. We found that cis-DSPEEK shows high repulsion for hydrogen transfer and moderate adsorption affinity for protons. Theoretical findings confirm that sulfonation ultimately yields hydrophilicity and developed proton transfer ability for PEEK, leading to a suitable structure for preferable proton exchange membrane.
KeywordsPEEK Adsorption Hydrophilicity Proton transfer Density functional theory
This subject is supported by Korea Ministry of Environment (MOE) as “Public Technology Program based on Environmental Policy” (Grant Number: 2016000200003).
The manuscript was written through the contributions of all authors. All the authors have given approval to the final version of the manuscript.
Compliance with ethical standards
Conflict of interest
The authors declares that they have no conflict of interest.
- 9.Wilson MS, Decaro D, Neutzler JK, Zawodzinski C, Gottesfeld S (1996) Air-breathing fuel cell stacks for portable power applications. In: 1996 fuel cell seminar, Orlando, FL, 17–20 November, pp 314–317Google Scholar
- 15.Bauer B, Jones DJ, Roziere J, Tchicaya L, Alberti G, Casciola M, Massinelli L, Peraio A, Besse S, E. Ramunni J (2000) Electrochemical characterisation of sulfonated polyetherketone membranes. J N Mater Electrochem Syst 3:93–98Google Scholar
- 33.Stanton JF (2001) A chemist’s guide to density functional theory By Wolfram Koch (German Chemical Society, Frankfurt am Main) and Max C. Holthausen (Humbolt University Berlin). Wiley-VCH: Weinheim. 2000. xiv + 294 pp. $79.95. ISBN 3-527-29918-1. J Am Chem Soc 123 (11):2701–2701Google Scholar
- 34.Dmol3 module of Materials studio (2017) Module of materials studio. Biovia Inc, San DiegoGoogle Scholar