Experimental study and modeling of proton conductivity of phosphoric acid doped PBI-Fe 2 TiO 5 nanocomposite membranes for using in high temperature proton exchange membrane fuel cell (HT-PEMFC)

In this study, phosphoric acid doped PBI-Fe2TiO5 nanocomposite membranes were prepared by dispersion of various amounts of Fe2TiO5 nanoparticles in PBI polymer matrix followed by phosphoric acid doping and they were applied into high temperature proton exchange membrane fuel cells (HT-PEMFCs). Effects of phosphoric acid doping level (PAdop), Fe2TiO5 mass fraction (Wd), and temperature on proton conductivity of the membranes were evaluated. The highest proton conductivity of 0.078 S/cm was obtained for the membranes containing 4 wt% of Fe2TiO5 nanoparticles with the highest value of phosphoric acid doping level (PAdop). Furthermore, a simple semi-empirical model was developed to predict the proton conductivity of the nanocomposite membranes at elevated temperatures (100–180 °C) and dry conditions. The effects of PAdop, Wd, and temperature on proton conductivity of the membranes were accounted in the model. The model was defined based on the volume fraction of free phosphoric acid inside the nanocomposite membrane structure which showed to be a determining factor in proton conduction of the membranes. The obtained proton conductivities by the model at various temperatures and phosphoric acid doping levels were in good agreement with the experimental results (average relative error <4%), indicating the reliability of the model.