Molecular level knowledge of nucleation and growth of clathrate hydrates is of importance for advancing fundamental understanding on the nature of water and hydrophobic hydrate formers, and their interactions that result in the formation of ice-like solids at temperatures higher than the ice-point. The stochastic nature and the inability to probe the small length and time scales associated with the nucleation process make it very difficult to experimentally determine the molecular level changes that lead to the nucleation event. Conversely, for this reason, there have been increasing efforts to obtain this information using molecular simulations. Accurate knowledge of how and when hydrate structures nucleate will be tremendously beneficial for the development of sustainable hydrate management strategies in oil and gas flowlines, as well as for their application in energy storage and recovery, gas separation, carbon sequestration, seawater desalination, and refrigeration. This article reviews various aspects of hydrate nucleation. First, properties of supercooled water and ice nucleation are reviewed briefly due to their apparent similarity to hydrates. Hydrate nucleation is then reviewed starting from macroscopic observations as obtained from experiments in laboratories and operations in industries, followed by various hydrate nucleation hypotheses and hydrate nucleation driving force calculations based on the classical nucleation theory. Finally, molecular simulations on hydrate nucleation are discussed in detail followed by potential future research directions.

Significant efforts are being made to make natural gas processing energy-efficient and environmentally friendly by utilizing membrane based separation processes. While membranes (polymer/zeolite/metal-organic framework) are effective in separating CO₂ and N₂ from CH₄, their separation performance is negatively affected when natural gas contains high concentrations of higher hydrocarbons (propane, butane, etc.) and H₂S. Interestingly, higher hydrocarbons and H₂S form gas (clathrate) hydrates at much milder conditions compared to CH₄, CO₂, and N₂ and could thus act as a separation step before membranes. In this perspective, gas separation using membranes and gas hydrates is briefly reviewed, and the challenges of developing an integrated gas hydrate-membrane process are discussed. Such a process could be an energy efficient approach to reduce the costs associated with natural gas purification. The proposed system can also serve as a model for other challenging molecular gas separations relevant to the energy and environmental arenas, including flue gas treatment and hydrogen purification.

Development of novel energy storage techniques is essential for the development of sustainable energy resources. Li-ion batteries have the highest rated energy density among rechargeable batteries and have attracted a lot of attention for energy storage in the last 15–20 years. However, significant advancements are required in anode materials before Li-ion batteries become viable for a wide variety of applications, including in renewable energy storage, grid storage, and electric vehicles. While graphite is the current standard anode material in commercial Li-ion batteries, it is Si that exhibits the highest specific energy density among all materials considered for this purpose. Si, however, suffers from significant volume expansion/contraction and the formation of a thick solid-electrolyte interface layer. To resolve these issues, Si clathrates are being considered for anode materials. Clathrates are inclusion compounds and contain cages in which Li could be captured. While Si clathrates offer promising advantages due to their caged structure which enables negligible volume change upon Li insertion, there remains scientific challenges and knowledge gaps to be overcome before these materials can be utilized for Li-ion battery applications, i.e., understanding lithiation/de-lithiation mechanisms, optimizing guest concentrations, as well as safe and economic synthesis routes.