A bio-based PVA/phytic acid nanocomposite film with exceptional hydrogen barrier properties via free volume control

Exploiting extremely low hydrogen permeability films is imperative for mitigating hydrogen damage and failure generated by strong hydrogen diffusion in storage vessels and pipelines. In this contribution, we have designed a simple yet effective strategy to fabricate a high-performance poly(vinyl alcohol) (PVA)-based composite thin film via a scalable spraying method, with the modification agent phytic acid (PA) incorporated to enhance crosslinking density. Various intermolecular interactions between PVA and PA form rigid structures that suppress chain mobility. Consequently, the fractional free volume (FFV) of the composite, as measured by positron annihilation lifetime spectroscopy (PALS), is reduced to merely 0.6509%. This leads to an unprecedented low H₂ gas transmission rate (GTR) of 0.518 cm³ m⁻²·24 h⁻¹·0.1 MPa⁻¹. These mutual interactions and mechanisms have also been corroborated by various simulation approaches and comprehensive experimental characterizations. Furthermore, this low H₂ GTR value exhibits no significant change even after 4 MPa hydrogen environment impact for 16 days, demonstrating high-pressure stability. Combined with a realistic coating process in the pipeline and a high mechanical tensile strength of 78 MPa, this composite thin film possesses tremendous application potential in hydrogen industries.