Undesired water crossover through ion‐exchange membranes is a significant limitation in electrically driven desalination processes. The effect of mitigating water crossover is twofold: 1) The desalination degree is less reduced due to the unwanted removal of water, and 2) the brine concentration is increased due to decreased dilution by an unwanted crossover of water molecules. Hence, water crossover limits the desalination and concentration efficiency of the processes, while the energy demand to achieve a certain level of desalination or concentration increases. This effect is especially pronounced when treating high salinity solutions, which goes hand in hand with the crossover of many ions through the ion‐exchange membranes. A crosslinked coating for cation‐exchange membranes (CEMs) is presented in this work, which can significantly mitigate such undesired water crossover. The efficacy is demonstrated using the flow‐electrode capacitive deionization process applied for desalination and concentration of saline brines at feed concentrations of 60 and 120 g L⁻¹ NaCl. With just a single coated CEM, the water crossover was reduced by up to 54%.

This study tracks the physical aging behavior of coated and uncoated ultra‐thin poly(1‐trimethylsilyl‐1‐propyne) (PTMSP) films on silicon wafers based on the refractive index using ellipsometry. The measured refractive index directly correlates with the free volume and hence the physical aging progression. Plasma‐enhanced chemical vapor deposition (PECVD) creates coatings with different thicknesses and oxidation degrees onto PTMSP films. Compared to uncoated PTMSP films, the PECVD‐coated films show a reduction of the refractive index increase of more than two orders of magnitude for less than 10 nm thin SiOx coatings. In contrast, SiOCH films show only a minor impact. The results reveal the superior physical aging behavior of PECVD‐coated films compared to untreated PTMSP films.

Selective, nanometer-thin organosilica layers created by plasma-enhanced chemical vapor deposition (PECVD) exhibit selective gas permeation behavior. Despite their promising pure gas performance, published data with regard to mixed gas behavior are still severely lacking. This study endeavors to close this gap by investigating the pure and mixed gas behavior depending on temperatures from 0 °C to 60 °C for four gases (helium, methane, carbon dioxide, and nitrogen) and water vapor. For the two permanent gases, helium and methane, the studied organosilica membrane shows a substantial increase in selectivity from αHe/CH₄ = 9 at 0 °C to αHe/CH₄ = 40 at 60 °C for pure as well as mixed gases with helium permeance of up to 300 GPU. In contrast, a condensable gas such as CO₂ leads to a decrease in selectivity and an increase in permeance compared to its pure gas performance. When water vapor is present in the feed gas, the organosilica membrane shows even stronger deviations from pure gas behavior with a permeance loss of about 60 % accompanied by an increase in ideal selectivity αHe/CO₂ from 8 to 13. All in all, the studied organosilica membrane shows very promising results for mixed gases. Especially for elevated temperatures, there is a high potential for separation by size exclusion.