Atomistic simulation and synthesis of novel sulfonated Polyimide polymer electrolyte membranes with facile proton transport

Polymer Electrolyte Membrane (PEM) is the most important component of the fuel cell which determines the overall performance of the PEM fuel cell. Currently, the commercially available perfluorinated membranes have limitations at higher temperatures and low humidity operations as experienced in automobile applications. Experimentation to discover alternative PEMs are extensive and time-consuming which often does not improve the proton conductivity of the developed PEM is neither at par with the perfluorinated PEMs nor is there any understanding of the exact nano-scale morphology of the PEM ionomer and behavior of proton transport in them. To this end, two novel hydrocarbon-based PEM belonging to the Sulfonated Polyimide (SPI) class of PEM ionomers- a partially fluorinated SPI and a non-fluorinated SPI have been designed in-silico and their properties compared with commercially available Nafion PFSA ionomers. In the present work, detailed all-atomistic Molecular Dynamics (MD) simulations have been used to investigate the state of nanophase segregation, the morphology of the ionic domains, and dynamics of proton transport with increasing hydration levels (λ = 1, 5, 10 and 15). The diffusion coefficients of hydronium ions and water molecules and corresponding proton conductivity owing to the transport hydronium ions in water channels were calculated. Proton conductivity values were highest for non-fluorinated SPI lying within the range 0.03–0.18 S·cm−1 for (λ = 1 to 15). Moreover, NTDA/DSDSA/MDP SPI membrane was synthesized, and proton conductivity was found to be in the range of 0.15–0.28 S·cm−1 which is exceptionally well for a PEM. Thus, a good agreement was observed between the proton conductivity values predicted using MD simulations and the values for stable stand-alone SPI PEMs.