CO2 sequestration trade-offs in polycrystalline hydrate stability

Abstract Natural gas hydrates (NGHs) offer significant potential for energy recovery and carbon sequestration, yet the thermal stability of polycrystalline CH 4 -CO 2 hydrates (PCCHs) which is critical for CO 2 -based NGH exploitation, remains poorly understood. Here, we unravel CO 2 ’s role in reshaping the thermal dissociation behaviors of PCCHs via high-throughput molecular dynamics (MD) simulations and machine learning (ML). We demonstrate that CO 2 reduces the stability of PCCHs, with a 20% increase in CO 2 concentration lowering the melting point by approximately 6 K. Microstructural analysis reveals that this destabilization arises from CO 2 -induced distortion of 5 12 cage and formation of unconventional metastable cages. Thermal dissociation occurs via cage transformations and dissociations, where 4 1 5 10 6 2 and 5 12 6 2 cages act as hubs for solid–solid restructuring pathway. Crucially, CH 4 guest molecules facilitate simpler, faster cage transformations than CO 2 , which requires complex rearrangements. We further develop a GBDT ML model that accurately predicts PCCH melting points using microstructural information, identifying 5 12 , 5 12 6 2 , and 5 10 6 3 cages as key predictors. This model provides a practical tool for guiding CO 2 -based NGH exploitation and designing hydrate storage systems. These insights advance the molecular-level understanding of hydrate stability for CO 2 sequestration and NGH recovery. Graphical Abstract