The mechanism underlying the stability of bulk nanobubbles has been a long-standing and contentious topic, with recent studies emphasizing the role of external pressure in nanobubble dynamics. However, there remains a lack of experimental evidence to unravel the complexities of bulk nanobubble behavior under elevated external pressures. In this study, we investigated the effect of external pressure on the stability of bulk hydrogen nanobubbles in both water and methanol liquid media using a nanobubble experimental system, with the external pressure up to 0.9 MPa. Our results show that nanobubble concentration increases linearly with pressure, and the nanobubbles exhibit longer lifetimes under high-pressure storage conditions, indicating enhanced stability. Notably, the effect of external pressure on surface charge is negligible, ruling out the hypothesis that surface charge dominates nanobubble stability. All-atom molecular dynamics (MD) simulations were conducted to elucidate the nanobubble evolution under varying external pressures. It demonstrates that elevated external pressure does not diminish the internal-external pressure differential. Increased supersaturation, reduced gas molecular diffusion, and reinforced hydrogen bond network were identified as primary factors for the stability enhancement at high external pressures. This study provides insights and experimental findings regarding the impact of external pressure on the dynamic behaviors of bulk nanobubbles.

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• Bubble dynamics
• High-pressure studies
• Nanobubbles