The diffusion and interfacial dynamics of balanced hydrogen nanobubble in water: Continuous phase state recognition based on convolution analysis

Hydrogen nanobubbles (HNBs) are widely used in hydrogen production, fuel cells, and catalytic due to their efficient mass transfer and oxidation resistance. However, in molecular dynamics simulations, the distinct mass transfer behaviors of hydrogen in the bubble and aqueous phases, coupled with continuous interfacial exchange, hinder accurate calculation of its self-diffusion coefficient. To address this, we classify hydrogen molecules into confined (c-H2) and free states (f-H2) and introduce a convolution-based method for phase identification. Using this approach, we examine temperature effects on HNBs. As temperature increases from 300 to 350 K, HNB volume expands, and internal and external hydrogen densities decrease by up to 24.76% and 29.34%, respectively, while the gas–liquid interface thickness remains stable. The gas inside the nanobubble can be described by the van der Waals equation of state. The self-diffusion coefficient of dissolved hydrogen is comparable to that in pure water, with deviations of 4.66%, 8.76%, 13.76%, and 29.06% for systems with N = 800, 1000, 1500, and 2000. These results deepen understanding of HNB thermodynamic behavior and provide guidance for applications in mass transfer, catalysis, and biomedicine.