Molecular dynamics simulations of triflic acid and triflate ion/water mixtures: A proton conducting electrolytic component in fuel cells

Abstract

Triflic acid is a functional group of perflourosulfonated polymer electrolyte membranes where the sulfonate group is responsible for proton conduction. However, even at extremely low hydration, triflic acid exists as a triflate ion. In this work, we have developed a force-field for triflic acid and triflate ion by deriving force-field parameters using ab initio calculations and incorporated these parameters with the Optimized Potentials for Liquid Simulations - All Atom (OPLS-AA) force-field. We have employed classical molecular dynamics (MD) simulations with the developed force field to characterize structural and dynamical properties of triflic acid (270-450 K) and triflate ion/water mixtures (300 K). The radial distribution functions (RDFs) show the hydrophobic nature of CF(3) group and presence of strong hydrogen bonding in triflic acid and temperature has an insignificant effect. Results from our MD simulations show that the diffusion of triflic acid increases with temperature. The RDFs from triflate ion/water mixtures shows that increasing hydration causes water molecules to orient around the SO(3)(-) group of triflate ions, solvate the hydronium ions, and other water molecules. The diffusion of triflate ions, hydronium ion, and water molecules shows an increase with hydration. At λ = 1, the diffusion of triflate ion is 30 times lower than the diffusion of triflic acid due to the formation of stable triflate ion-hydronium ion complex. With increasing hydration, water molecules break the stability of triflate ion-hydronium ion complex leading to enhanced diffusion. The RDFs and diffusion coefficients of triflate ions, hydronium ions and water molecules resemble qualitatively the previous findings using per-fluorosulfonated membranes.

Molecular dynamics simulations of side chain pendants of perfluorosulfonic acidpolymer electrolyte membranes

“…The density prole for the Dow, Aciplex and Naon side chain pendant-water mixtures (shown in Fig. 3) closely resemble the density prole of our previous work 59 on triate ion-water mixtures. The density proles at 300 K in Fig.…”

Atomistic simulations of structure and dynamics of hydrated Aciplex polymer electrolyte membrane

“…The coordination number calculated at the first minima from the S-S RDFs (as seen in Table 2) decreases with increasing hydration which suggests that water mediates the sulfonate-sulfonate interactions. 84 The sulfonate-water interactions are characterized by the S-O w RDF shown in Fig. 2b.…”

Effects of chloride ions in acid-catalyzed biomass dehydration reactions in polar aprotic solvents

“…Molecular interactions of fructose and GVL molecules were adapted from an all-atom version of Optimized Potentials for Liquid Simulations 49,50 (OPLS-AA) force field. Literature force fields were implemented for the hydronium ion 51 , chloride anion 52 , bisulfate anion 53 , triflate anion 54 , and water 55 .…”