Is Fine‐Grained Simulation Able to Propose New Polyelectrolyte Membranes?

Abstract

International audienceAn extensive understanding in the molecular motions that occur in Nafion® should lead to important development of improved proton exchange membrane for use in fuel cells (PEMFC). As water molecules are added in the system, changes within the Nafion® chain definitely take place. To visualize such a process, molecular dynamics is especially useful. Can information gained at this level of details be useful to propose new molecules, with ultimately better physical properties, such as higher proton conductivity? For this purpose, we first computed non-bond parameters stemming from the study of the trifluorosufonic acid. They are inserted in the pcff force field. We then applied the procedure developed in our lab to extract the glass transition temperature of Nafion® with different water uptakes. The plasticization effect is first confirmed, fostering a molecular analysis. The particular behavior of the sulfur-sulfur distance is revealed, guiding the design of new monomer

Morphology of Hydrated Nafion through a Quantitative Cluster Analysis: A Case Study Based on Dissipative Particle Dynamics Simulations

“…The g CW (r) and g CC (r) peaks decrease the intensity with λ and move to larger separation. Similar weaker correlation and larger separation between the sulfonic acid groups (CC) and between the sulfonic acid groups and water beads (CW) with increasing hydration level were also observed in previous all-atom classical MD simulations 16,46,47 and mesoscale simulations. 37 Side-chain separation may impact the proton-transport mechanism in perfluorosulfonic acid materials.…”

Water nano-diffusion through the Nafion fuel cell membrane

“…Structure of hydrated Nafion is strongly investigated in order to improve its fuel cell performance but also to design new membranes. Structural studies have highlighted a complex and multi-scale structure [2,3,4,5,6,7,8,9,10,11,12].…”

Effect of Annealing on Structure and Diffusion in Hydrated Nafion Membranes

“…44,45,54 The most pronounced shift of about 50 K is clearly visible in the dry (λ = 0) sample (Figure 2a); T g = 440 K when the implemented cooling velocity is 1 K/ps and is much lower, T g = 390 K, when cooling with 0.01 K/ps is used. Still, the absolute values are slightly higher as compared to the typical experimental results which range from 373 K 61 to 405 K. 53 This is not surprising taking into account the huge difference in the simulational and experimental time scales and 50 The dashed line is the fit to the experimental results. 60 a logarithmic dependence of the glass-transition temperature on cooling rate.…”

“…Such pore sizes are also found in silica, in which water remains adsorbed on the silica surface up to high temperatures of 473 K. 51 Above this temperature water desorbs, but the clear liquid water phase was observed below 473 K. For dry Nafion samples T g in the range 373−405 K is normally reported. 50 The simulations of Fleury et al 50 show a decrease of the glasstransition temperature to ∼200 K for hydrated Nafion samples at the λ = 22.5 hydration level. MD simulations of Ozmaian and Naghdabadi 52 clearly indicated (not discussing this in detail) that both polymer and confined water thermal behavior should be taken into account when the glass transition in hydrated Nafion samples is addressed.…”