In Situ Testing of Hydrogen Permeation Through Compressed O‐Rings: Experimental Innovation and Molecular Dynamics Interpretation

This study developed an in situ real‐time full‐scale O‐ring hydrogen permeation testing method, effectively overcoming the limitations of traditional stress‐free sheet sample testing. The permeation performance of HNBR and EPDM was evaluated under a hydrogen pressure of 1 MPa. The hydrogen permeation coefficient of HNBR was measured as 6.7 × 10 −18 m 3 ·m/(m 2 ·s·Pa), one order of magnitude lower than that of EPDM (2.3 × 10 −17 m 3 ·m/(m 2 ·s·Pa)). Moreover, both values were found to be 6 to 12 times lower than those reported in the literature, indicating that traditional testing methods significantly overestimate the actual leakage risk. HNBR required 186 min (1.55 ppm/min) to reach steady‐state permeation, whereas EPDM reached steady state in 131 min (5.58 ppm/min). Microstructural characterization combined with molecular dynamics simulations revealed the underlying mechanism: HNBR contains polar nitrile groups and exhibits a dense layered morphology, with a free volume fraction (4.7%) significantly lower than that of EPDM (11.3%). The “island‐like” distribution of free volume in HNBR results in a “jumping” diffusion mechanism for hydrogen molecules (diffusion coefficient: 1.02 × 10 −4 cm 2 /s), whereas the partially interconnected free volume in EPDM supports faster diffusion (3.595 × 10 −4 cm 2 /s). This study provides realistic data and practical evaluation methods for the sealing design of hydrogen energy infrastructure.