The transition toward a hydrogen-based economy necessitates the development of advanced materials capable of mitigating hydrogen permeation in Type IV high-pressure storage tanks. This study investigates the synthesis and characterization of silica-based barrier coatings produced via the sol-gel method and applied to PET substrates.

Permeability tests were conducted across a wide pressure range, from low-pressure conditions (2 bar) to high-pressure environments (400 bar). Results demonstrate that the amorphous silica network significantly enhances its barrier properties. Moreover, it was shown that modifications introduced to the silica network, such as doping or aging, improve the barrier properties of the coatings even more. Tests revealed a significant reduction in the permeability coefficient for multilayered and doped coatings, with some samples showing up to 40% improvement in gas transmission rate compared to standard configurations. These findings highlight the strong potential of sol–gel-derived silica-based coatings as effective barrier solutions for next-generation hydrogen storage systems, contributing to improved safety, durability, and performance of Type IV tanks.