A Molecular Dynamics Simulation Based Investigation of the Proton Conductivity of Anhydrous Pyrazole Doped Poly(Vinylphosphonic Acid) Composite System.

Yu-Ren Huang,Cheng-Lung Chen,Chung-Te Chien

doi:10.3390/polym12122906

Yu-Ren Huang, Cheng-Lung Chen + Show 1 more

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https://doi.org/10.3390/polym12122906

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Abstract

With the recognition of the multiple advantages of proton transport membranes that can operate under anhydrous conditions and offer promising opportunities as fuel cells working at high temperatures, a number of such membranes have been developed, but the proton transport mechanism of these materials has not been fully understood. In this work, a theoretical investigation based on molecular dynamics simulations is carried out on a system that is very similar to a real anhydrous proton transport membrane. The location and type of hydrogen bonds have been precisely identified by intermolecular pair correlation functions. Furthermore, analysis of the proton coordination numbers shows that more protons are located in the neighborhood of the oxygen atoms of poly(vinyl phosphonate anion) than in the neighborhood of the nitrogen atoms of pyrazole. The proton conductivity, 1.06 × 10−3 Scm−1, is obtained by the self-diffusion coefficient of the protons at 423 K, which is reasonably close to the experimentally measured value, 2 × 10−4 Scm−1. In addition, the analysis of the proton trajectories provides us with the proton transfer mechanism in an anhydrous membrane: (a) proton hopping between the oxygen atoms of poly(vinyl phosphonate anion) and (b) proton hopping between two pyrazole molecules. Therefore, the network of the hydrogen bond is the pathway to transport protons via the processes of hydrogen bond forming and breaking.

Highlights

Polymer electrolyte membrane fuel cells (PEMFCs), or proton exchange membrane fuel cells, are a type of fuel cell being developed mainly for transport vehicles, portable devices and stationary applications
A generic force field, Dreiding, that we we chose is employed in our work because it is most suitable in predicting the structures and chose is employed in our work because it is most suitable in predicting the structures and dynamics dynamics of organic compounds involving the nonmetallic main-group elements
To elucidate the proton transport mechanism in anhydrous proton exchange membranes, a molecular dynamics simulation based on Dreiding force field has been carried out on a composite system of mixing protons, poly(vinyl phosphonate anion) and pyrazole, as a more realistic representative of anhydrous PEMs used in fuel cells

Summary

Introduction

Polymer electrolyte membrane fuel cells (PEMFCs), or proton exchange membrane fuel cells, are a type of fuel cell being developed mainly for transport vehicles, portable devices and stationary applications. They have emerged as one of the most promising candidates in power conversion devices due to advantages such as efficient power generation, less emission of pollution and a minimized design [1,2]. The proton electrolyte membrane, or proton exchange membrane, is the most critical component in PEMFCs because it plays multiple roles in an operating PEM fuel cell: as a medium for proton conduction, a gas separator between anode and cathode and a stopper for blocking fuel crossover. In a recent interesting study [9], Nafion was demonstrated

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