Preparation of polybenzimidazole/ZIF-8 and polybenzimidazole/UiO-66 composite membranes with enhanced proton conductivity

Metal-organic frameworks (MOFs) are considered emerging materials as they further improve the various properties of polymer membranes used in energy applications, ranging from electrochemical storage and purification of hydrogen to proton exchange membrane fuel cells. Herein, we fabricate composite membranes consisting of polybenzimidazole (PBI) polymer as a matrix and MOFs as filler. Synthesis of ZIF-8 and UiO-66 MOFs are conducted through a typical solvothermal method, and composite membranes are fabricated with different MOF compositions (e.g., 2.5, 5.0, 7.5, and 10.0 wt %). We report a significant improvement in proton conductivity compared with the pristine PBI; for example, more than a three-fold increase in conductivity is observed when the PBI-UiO66 (10.0 wt %) and PBI-ZIF8 (10.0 wt %) membranes are tested at 160 °C. Proton conductivities of the composite membranes vary between 0.225 and 0.316 S cm −1 at 140 and 160 °C. For the comparison, pure PBI exhibits 0.060 S cm −1 at 140 °C and 0.083 S cm −1 at 160 °C. However, we also report a decrease in permeability and mechanical stability with the composite membranes. • ZIF-8 and UiO-66 MOFs are successfully synthesized and characterized. • PBI-ZIF8 and PBI-UiO66 membranes with four different loadings are fabricated. • PBI-MOF membranes can provide more than a three-fold increase in proton conductivity. • An increase in MOF amount may cause agglomeration and decrease mechanical stability.