This research addresses the critical challenge of energy conversion and hydrogen storage as a key low-carbon energy carrier for modern transportation. The primary objective of this study is to provide a comprehensive analysis of the thermomechanical properties and molecular-level interaction mechanisms of a novel composite material, designed to optimize the operational performance and enhance the structural integrity of hydrogen transport pipelines and storage vessels within next-generation energy systems. This study involved the fabrication of five composite series with reduced graphene oxide (rGO) contents ranging from 0 to 2 wt%, utilizing a strategic partial curing agent substitution to examine its impact on the cross-linking density and thermomechanical performance of the epoxy matrix. A comprehensive experimental methodology was applied, including static flexural (ISO 178) and compression (ISO 604) strength tests, Vickers hardness measurements (ISO 6507), and differential scanning calorimetry (DSC) analysis. These empirical investigations were complemented by advanced quantum chemical simulations using the PM6 semi-empirical method within the Scigress software, facilitating the analysis of macromolecular electron distribution and physicochemical interactions at the epoxy–graphene interface. The results demonstrate a dual effect of the nanofiller: at low concentrations (0.25 wt%), increased material plasticity was observed due to reduced cross-linking density, whereas higher concentrations (≥ 0.5 wt%) led to significant mechanical reinforcement and restricted polymer chain mobility. Although rGO integration reduced flexural strength by 1.3-6.6%, the 2 wt% loading enhanced Vickers hardness by 7.5% and Young’s modulus by 6.9%, reducing deflection by 22.2%. Integrated DSC and mechanical analyses identified 0.5 wt% as the critical threshold, where peak crystallinity optimized compressive strength to 89.7 MPa, notwithstanding a 5°C depression in the glass transition temperature (Tg). This phenomenon, combined with the "labyrinth effect" providing a superior diffusion barrier, significantly enhances the durability of hydrogen installations.