Molecular Dynamics Study Of The Confined Proton Structure And Diffusion In Perfluorosulphonic Acid Membrane

Fuel cell is regarded as a major energy conversion technology in the future.Proton exchange membrane fuel cell?PEMFC?is getting increasingly academic attention and research because of its high power density and short starting time.It is also ideal emerging technology in hydrogen generation.Proton exchange membrane?PEM?is the key of PEMFC.The perfluorinated sulfonic acid membrane?PFSA?is the preferred PEM.But,the PFSA often confront some deficiencies that sharply declined proton conductivity at elevated temperature because undesirable dehydration.Now,short side chain PFSA and composite membrane by adding hydrophilic inorganic materials into PFSA membrane shows a well performance at elevated temperature PEMFC?HT-PEMFC?.SiO₂ nanoparticle with silanol has excellent hydrophility,the effect of doped SiO₂ nanoparticle on the mechanism of proton transport is still unclear.Therefore,short side chain PFSA?Hyfion?and hybrid membrane?Hyfion/Si O₂?added SiO₂ nanoparticle were studied by classical molecular dynamics simulation in our paper.The pure Hyfion membrane was constructed in order to elucidate the proton transport structural and dynamic properties.It was found that the phase separation into hydrophilic and hydrophobic regions clearly produced water networks with a wide range of topologies in hydrated Hyfion membrane.The hydrophilic region consists of water,hydronium and sulphonic group.The hydrophobic region consists of polymer chains.The simulated values of Dw were 0.11×10-5 cm2/s for ?=3.2 and 0.37×10-5 cm2/s for ?=5.8.These values are quite similar to the experimental results.The hydrogen bonding interaction between water and hydronium led to the formation of the hydrated hydronium complexes,H3O+·?H2O?n,where n=1–3.The self-diffusion coefficients of these hydrated hydronium complexes are different at each hydration level.The probability structure of H7O3+ was about 0.38 at each hydration level.Then,SiO₂ nanoparticle was directly doped in the constructed Hyfion membrane to study the interaction between SiO₂ and water molecules.In the Hyfion/SiO₂ hybrid membrane,the results show that the self-diffusion coefficients of hydronium was higher than in pure Hyfion membrane.The SiO₂ nanoparticles were surrounded by water molecules.We found that hydrogen bond?H-bond?interaction between silanol and water in the proton exchange channels.The silanol not only as a donor for the H-bond,but also as an accept.The H-bond ofsilanol-water reduced the diffusion of water near the SiO₂ nanoparticle and improved more free hydronium for the conductivity of proton.The results from MD simulations provide molecular insight into the proton transport mechanism in the PEMFC,which present some theoretical guidance for the preparation of HT-PEM and design of HT-PEMFC.