Advances in Spectroscopic Methods for Gas Hydrate: A Review and Perspectives for Low-Carbon Energy Solutions and Applications

Gas hydrate crystalline compounds composed of gas molecules trapped within a lattice of water have garnered considerable attention due to their dual significance as a potential energy resource and their role in global climate dynamics. These ice-like structures form under specific conditions of low temperature and high pressure, involving gases such as methane (CH₄), carbon dioxide (CO₂), and nitrogen (N₂). Understanding their properties, formation mechanisms, and dissociation kinetics is essential for advancing both energy extraction technologies and climate change mitigation strategies. To this end, a range of advanced spectroscopic techniques, including neutron scattering, nuclear magnetic resonance (NMR), ultraviolet (UV), infrared (IR), and Raman spectroscopy, have been employed to probe these phenomena at the molecular level. This review focuses on the practical application of Raman and NMR (with neutron methods as a complementary probe) to micro - to millimeter-scale hydrate systems: Raman spectroscopy is used to determine structure type, quantify cage occupancy and molar composition, and monitor formation/dissociation kinetics and CH₄/CO₂ exchange in situ; NMR (both low-field and high-field) enables noninvasive quantification of hydrate saturation, phase distribution, and pore-scale dynamics in opaque sediments, while also addressing key limitations such as relaxation overlap, paramagnetic effects, and high-pressure/temperature probe compatibility. This review offers a comprehensive, and cross-technique comparison of selected spectroscopic approaches in gas hydrate research, including practical considerations for neutron facilities (e.g., beam-time competition and sample-cell constraints) and the need for improved cross-technique benchmarking. By clarifying the capabilities and limitations of these methods, the review aims to guide both new and experienced researchers in selecting appropriate tools for their studies. Through critical analysis of recent advancements, it highlights the central role of spectroscopy in uncovering fundamental aspects of gas hydrates and explicitly links these observables to low-carbon energy and CCUS objectives, offering valuable insights into their practical applications and environmental implications.