Gas hydrates offer solutions in areas like CO 2 sequestration and desalination. However, their formation is severely limited by long induction (wait) times for nucleation, which range from hours to days. Many existing nucleation promotion techniques involve chemical additives, which invite environmental and process-related concerns. Here, we report a simple, passive, and environmentally friendly technique to significantly promote the nucleation of CO 2 hydrates: magnesium (in pure and alloy forms) triggers nucleation almost instantaneously. We report induction times of less than 1 min, which is the fastest induction time reported for any gas hydrate under stagnant conditions. This translates to Mg-promoted nucleation rates being 3000 times higher than the baseline. Statistically meaningful measurements of nucleation kinetics (in milliliter and liter-scale reactors), direct visualization of nucleation, and X-ray photoelectron spectroscopy (XPS)/Fourier-transform infrared spectroscopy (FTIR) analysis uncover several chemistry-related insights associated with Mg-based promotion. Importantly, the three-phase line of magnesium−water−CO 2 gas is key to promotion. Porous oxide layers, generation of H 2 nanobubbles, and chemisorption of CO 2 on Mg surfaces are other factors responsible for accelerated nucleation. Interestingly, Mg alloys exhibit faster nucleation promotion than pure Mg, which is significant in salt water medium. Overall, our work opens up pathways for faster synthesis of hydrates, which is critical to realizing applications.

Gas hydrate formation has several applications in CO2 sequestration, flow assurance, and desalination. Nucleation of hydrates is constrained by very high induction (wait) times, which necessitates the use of complex nucleation promotion techniques to form hydrates. Presently, we report the discovery of a simple, passive nucleation promotion technique, wherein an aluminum surface significantly accelerates nucleation of CO2hydrates. Statistically meaningful measurements of induction times for CO2 hydrate nucleation were undertaken using water droplets as individual microsystems for hydrate formation. The influence of various metal surfaces, droplet size, CO2 dissolution time, and the presence of salts in water on nucleation kinetics was characterized. Interestingly, we observe nucleation initiation only on aluminum surfaces, the influence of which cannot be replicated by salts of aluminum. We discover that the aluminum–water interface is responsible for nucleation promotion. We hypothesize that hydrogen bubbles generated at the aluminum–water interface are responsible for nucleation promotion.

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