Proton transfer mechanism in perfluorinated sulfonic acid polytetrafluoroethylene

The proton exchange membrane (PEM) fuel cell is one of the most promising fuel cells for wide applications, and the proton exchange membrane is one of its key components. However, the proton transfer mechanism in perfluorinated sulfonic acid polytetrafluoroethylene remains unclear for the research on PEM fuel cells. In this paper, the model of the proton transfer mechanism in perfluorinated sulfonic acid polytetrafluoroethylene is developed based on the fundamentals of the molecular dynamics, particularly the principle of energy and radial distribution function. The proton transfer process in perfluorinated sulfonic acid polytetrafluoroethylene is simulated, whereas the effects driven by the water content in the membrane and fuel cell temperature are analyzed. The results show that the water bridges developed by free water are the passage for proton transfer from one sulfonic group to its adjacent sulfonic group in perfluorinated sulfonic acid polytetrafluoroethylene. The proton transfers along the water bridge by the formation and cleavage of the H–O bond between the water from the water bridge and the proton; the increases in the water content in the membrane and the fuel cell temperature speed up the proton transfer, causing the decrease in the resistance of proton transfer. These findings are remarkably helpful to understand the working mechanism of PEM fuel cells.

► The proton transfer process in the membrane made by perfluorinated sulfonic acid polytetrafluoroethylene is simulated. ► The water bridges built by free water are the passage for proton transfer. ► By the formation and break of the H–O bond, the proton transfers along the water bridge. ► With the increase of water content, more water bridges for the proton transfer are built. ► With the increase of the temperature, the proton transfer along the water bridge becomes more ease.