Effective ion mobility in anion exchange ionomers: Relations with hydration, porosity, tortuosity, and percolation

The effective mobility of hydroxide, chloride and fluoride ions is reported in various anion exchange membranes (AEM) with a backbone polysulfone (PSU) or poly (2,6-dimethyl-1,4-phenylene)oxide (PPO). concentration dependence the used to derive porosity (?), tortuosity (?), percolation thresholds plot ionic conductivity vs hydration number. Semi-logarithmic plots ion u(i) square root ?c(i) for PSU- PPO-based ionomers at 25 60 °C show linear relations, from which ratio ?/? can be determined. This existence = f(?c(i)) related very particular boundary conditions experienced by mobile ions, migrating close vicinity immobile grafted counter-ions placed interfaces between polymer domains electrolyte solution. values PSU-QA (0.29) PPO-QA (0.38) are consistent relatively low hydrophilic-hydrophobic nanophase separation, leads channels diameter high tortuosity. determined Bruggeman-type relation 1.9 1.6 PPO-QA. ?H2O,p, universal equation near above water volume fraction 0.07 PSU-TMA 0.03 indicating that these AEM have two-dimensional structure hydrated domains. prefactor, should represent good indication as maximum achievable conductivity, slightly below 100 mS/cm both ionomers. Plots experimental computed hydroxide conductivities function number (?) value around 60, corresponding optimal conditions. At ? 100, (OH? form) (Cl? indicates degree dissociation pairs about 30% lower than radii Cl? OH?.