Methane hydrate formation at 1 atm and 4°C on liquid-solid interfaces reveals a climate-vulnerable carbon pool

<h2>Summary</h2> Traditional thermodynamic models of natural gas hydrate formation posit that nucleation occurs only under high-pressure and low-temperature conditions. These thermodynamic models overlook liquid-solid interfacial adsorption of gas molecules, which creates high-density surface nanobubbles in gas-liquid-solid systems, leading to significant local gas enrichment even at low pressures. This study reveals a unique nucleation pathway for methane hydrate from the three-phase contact lines of the surface methane nanobubbles under atmospheric pressure and 277.15 K. High-resolution atomic force microscopy shows hydrate crystals growing radially from nanobubbles on highly oriented pyrolytic graphite, while Raman spectroscopy confirms that the crystal is structure H (sH). This phenomenon is attributed to the high local methane concentration in the environment surrounding surface nanobubbles and a reduced nucleation energy barrier at the contact line. Our findings redefine the spatial and thermodynamic boundaries of hydrate stability, suggesting that hydrates can occur as widespread nanoscale deposits within natural reservoirs, which raises concerns about their susceptibility to releasing methane under global warming.