Mixed Grotthuss and Vehicle Transport Mechanism in Proton Conducting Polymers from Ab initio Molecular Dynamics Simulations

Abstract

We elucidate the microscopic mechanism of long-range proton conduction in poly[vinyl phosphonic acid] (PVPA), a highly promising proton conducting polymer. Using a steered ab initio molecular dynamics approach, we characterize the charge transport functionality of acid groups interacting with nonbulk water molecules intercalated in the polymer. Our results show that in PVPA, unlike in Nafion, water has a local vehicle/carrier function for excess protons. This function must however be combined with the Grotthuss-type conduction mechanism that is supplied by the acid groups in order to yield long-range charge transport. As an additional aspect, we find that contrary to common intuition, systems with disordered/amorphous morphology leave a considerably more pronounced functionality than well-ordered crystalline systems.

Atomic scale characterization and surface chemistry of metal modified titanate nanotubes and nanowires

“…More recent results suggest that adsorbed molecules at the S/G interface can actively participate in Grotthuss-type proton conduction [151]. Several variants of this process were published: the one occuring in hydrated poly (vinyl-phosphonic acid) polymers is denoted as carrier mediated [152], while the one found in hydrated boehmite is called interfacial Grotthuss mechanism [153].…”

Imidazole-doped nanocrystalline cellulose solid proton conductor: synthesis, thermal properties, and conductivity

“…Generally, the higher activation energy (i.e. 0.5-0.9 eV) reflects other than Grotthuss conduction mechanism like the vehicle (Knauth et al 2008;Kreuer et al 1982Kreuer et al , 1996 or proton hopping mechanism (Eikerling et al 2001;Luduena et al 2011). The latter mechanism was well proved and described for microcrystalline Cell-Im composites (Zhao et al 2016) in which Im molecules formed a dynamic hydrogen bond network with residual water molecules and hydroxyl groups of cellulose chains.…”

Microscopic properties of liquid water from combined ab initio molecular dynamics and energy decomposition studies

“…The propagation scheme in second-generation CPMD relies on the appropriate usage of the information about the electrons from the previous MD steps and, in contrast to CPMD, does not require a fictitious mass parameter to maintain the accuracy of the Born-Oppenheimer dynamics. The superior efficiency of this new approach, which, depending on the system, varies between one to two orders of magnitude, has been demonstrated for a large variety of different systems [15][16][17][18][19][20] .…”