High temperature membranes based on PBI/sulfonated polyimide and doped-perovskite nanoparticles for PEM fuel cells

A new sulfonated aromatic diamine monomer containing nitrogen heterocycles was synthesized and employed to prepare a novel sulfonated polyimide (SPI). To develop proton exchange membranes, new nanocomposite blend membranes consist of the prepared SPI and polybenzimidazole (PBI) were fabricated with incorporation of SrCe_0.9Yb_0.1O_3-δ (SCYb) doped-perovskite nanoparticles with a solution-casting method. The goal of this work is to study the effect of SPI and SCYb doped-perovskite nanoparticles on the important parameters of the PBI membrane specially proton conductivity and fuel cell performance. The proton conductivity and phosphoric acid doping level of the PBI-SPI-SCYb nanocomposite blend membranes improved due to an interaction of –SO₃H group and thiazole rings of SPI and N–H groups of PBI in the oxygen vacancies of SCYb doped-perovskite nanoparticles. Substitution of Ce⁴⁺ by Yb³⁺ in the SCYb doped-perovskite nanoparticles produce oxygen vacancies and decrease the columbic repulsion between protons and positive ions. Furthermore at highest phosphoric acid doping level of 14 mol phosphoric acid per monomer unit, the nanocomposite blend membranes displayed proton conductivity of 131 mS/cm at 180 ^°C and 8% relative humidity. The increase in power density from 0.31 W/cm² in PBI-SPI blend membranes (SPI/PBI: 25 wt%) to 0.59 W/cm² in PBI-SPI-SCYb nanocomposite blend membranes (SPI/PBI: 25 wt% and 7 wt% of SCYb) was achieved at 0.5 V, 8% RH and 180 °C, which demonstrates that these developed nanocomposite blend membranes have a high potential to be regarded as the most promising candidates for high-temperature fuel cell with improved proton conductivity.