Low chemical durability of proton exchange membranes is one the main factors limiting their lifetime in fuel cells. Ceria nanoparticles are the most common free radical scavengers. In this work, hybrid membranes based on Nafion-117 membrane and sulfonic or phosphoric acid functionalized ceria synthesized from various precursors were prepared by the in situ method for the first time. Ceria introduction led to a slight decrease in conductivity of hybrid membranes in contact with water. At the same time, conductivity of membranes containing sulfonic acid modified ceria exceeded that of the pristine Nafion-117 membrane at 30% relative humidity (RH). Hydrogen permeability decreased for composite membranes with ceria synthesized from cerium (III) nitrate, which correlates with their water uptake. In hydrogen-air fuel cells, membrane electrode assembly fabricated with the hybrid membrane containing ceria synthesized from cerium (IV) sulfate exhibited a peak power density of 433 mW/cm² at a current density of 1080 mA/cm², while operating at 60 °C and 70% RH. It was 1.5 times higher than for the pristine Nafion-117 membrane (287 mW/cm² at a current density of 714 mA/cm²).

The transport properties of ion-exchange membranes depend on many factors, primarily, on ion-exchange capacity and chemical composition. Therefore, the correlation of transport properties with a single particular parameter is generally not quite strict. In this study, the dependence of transport properties of several perfluorinated sulfonated cation-exchange membranes that differ in side chain length and fraction of fragments containing ether groups on ion-exchange capacity is analyzed. It is shown that, with a decrease in the ion-exchange capacity from 1.35 to 0.66 mg-equiv/g, the proton conductivity of membranes contacting water and their diffusion permeability with respect to a 0.1 M HCl solution decrease by two orders of magnitude. A decrease in relative humidity leads to the most significant decrease in the conductivity of membranes with a low ion-exchange capacity. Thus, at a relative humidity of 32%, the conductivity of the studied membranes decreases more than 600-fold with a decrease in ion-exchange capacity. In general, the oxygen permeability of membranes is characterized by a similar dependence. However, in this set of membranes, it varies as little as threefold.

Ion exchange membranes are widely used for water treatment and ion separation by electrodialysis. One of the ways to increase the efficiency of industrial membranes is their modification with various dopants. To improve the membrane permselectivity, a simple strategy of the membrane surface modification was proposed. Heterogeneous RALEX-CM membranes were surface-modified by ceria with a phosphate-functionalized surface. Despite a decrease in ionic conductivity of the prepared composite membranes, their cation transport numbers slightly increase. Moreover, the modified membranes show a threefold increase in Ca²⁺/Na⁺ permselectivity (from 2.1 to 6.1) at low current densities.