Copyright to ACS, J. Phys. Chem. C 2017, 121, 7069-7080
Polymer Electrolyte Membrane (PEM) fuel cells are electrochemical devices that can generate power with minimal impact on the environment. The choice of membrane plays a key role in magnitude of proton conductivity and hence determines the efficiency of the device. A large number of experimental techniques have focused on the characterization of polymer membrane nanostructure and dynamics of proton/molecular transport in various fuel cell operating conditions. The objective of our research program is to use computer simulations to examine structure and transport properties via Molecular Dynamics (MD) simulations and ab initio MD simulations to mimic experimental observations. To achieve this, we design several force-field parameters from quantum chemistry calculations and also optimize simulation protocols for modelling various polymer membranes. In our investigations on a variety of PEMs spanning more than a decade, we have unravelled molecular level insights to examine the effect of: side chain pendant of PFSA membranes, temperature, choice of dopant and concentration, (water, phosphoric acid, ionic liquid), membrane (PFSA, PBI, ABPBI) and polymer chain length. The simulations are used to calculate properties such as Radial Distribution Functions, Structure Factor, Diffusion coefficients, Radius of Gyration which validate experimental observations or serve as predictive insights. The effect of fillers such as Graphene Oxide and Carbon Nanotubes in polymer matrix environments has also been explored. Using quantum chemistry calculations, we have investigated proton transport pathways in proton conductors such as imidazole and imidazolium methanesulfonate. We are now investigating (using ab initio MD simulations) the structural diffusion of protons in various polymer environments and protic ionic liquids to directly correlate with proton conductivity measurements. The focus of our research is extended to explore protic ionic liquids as alternative choice of dopants for PEM in anhydrous fuel cell environments and interactions at the polymer/electrode interface. The outcome from computer simulations is expected to spur the synthesis of more efficient PEMs and exploration of proton transport carriers.