MXene (Ti₃C₂T_x) as a Promising Substrate for Methane Storage via Enhanced Gas Hydrate Formation

Abstract

Methane hydrate (MH) makes it possible to store methane using the cheapest and safest solvent: water. However, the sluggish formation kinetics hinders its practical utilization. Recently, the use of nanomaterials has been suggested as a potential solution; however, there is still a lack of high-efficiency kinetic promotors, and the promoting mechanism remains unclear. Herein, we demonstrated that MXene dispersion is promising for the storage of methane via MH with rapid formation kinetics, high storage capacity, and impressive cyclic stability. MXene can significantly shorten the induction time for MH formation. The enhanced kinetics was achieved by providing extra nucleation sites and enhancing thermal conductivity, although the increased surface tension of MXene dispersion could impede the MH formation via limited mass transfer. We confirmed that the concentration-dependent promoting effect of MXene dispersions results from regulating the assembly of water molecules. The insight of this work can apply to develop high-efficiency additives to control the formation kinetics of MH.

Promoting Methane Hydrate Formation for Natural Gas Storage over Chabazite Zeolites

“…Although alluring, high water-to-hydrate conversion can be difficult to achieve in a static, pure methane and water system . Low gas-to-water contact area inhibits hydrate growth, as hydrates start forming at this interface thus limiting gas diffusion to the now trapped water phase. , Local heat of formation can slow hydrate growth if not removed, and impeded water ordering may prevent hydrate cages from forming. , …”

“…8,9 Local heat of formation can slow hydrate growth if not removed, and impeded water ordering may prevent hydrate cages from forming. 10,11 Several approaches have been proposed to overcome these barriers, such as adding chemical additives, 12,13 modifying apparatus design, 14,15 and using porous materials. In particular, porous materials provide multiple advantages for hydrate promotion: large surface area (e.g., increases gas-to-water contact area) 9 and good surface chemistry (e.g., removes local heat of formation, 11 positively affects water ordering, 10 or adsorbs methane 16 ).…”

“…10,11 Several approaches have been proposed to overcome these barriers, such as adding chemical additives, 12,13 modifying apparatus design, 14,15 and using porous materials. In particular, porous materials provide multiple advantages for hydrate promotion: large surface area (e.g., increases gas-to-water contact area) 9 and good surface chemistry (e.g., removes local heat of formation, 11 positively affects water ordering, 10 or adsorbs methane 16 ). In addition, pore size and channel shape/ topology can influence hydrate promotion.…”

Evidence of Guest–Guest Interaction in Clathrates Based on In Situ Raman Spectroscopy and Density Functional Theory

“…Most of the spectral information is well recognized; the peak at 2904.87 cm −1 can be attributed to the C−H symmetric stretching vibrational mode in the 5 12 6 2 cage, which is consistent with previous studies. 12,15,23 The symmetric stretching in the 5 12 cage around 2914 cm −1 overlapped with the CH 4 gas peak at 2916.34 cm −1 (see Figure S2). Notably, the intensity of the peak at 3053.62 cm −1 increased upon hydrate formation; it was eventually coupled with the peak at 3068.50 cm −1 to show a weak wide peak.…”

“…Raman spectra, based on molecular vibrations, have been widely used in the characterization of the hydrate composition and the acquisition of quantitative and semiquantitative structural information . It allows the spectrum across all of the physical states to be recorded without complex preprocessing, making it a convenient method for exploring the dynamic processes via monitoring the changes in the molecular vibrations of gas hydrates. , These vibrations exactly represent the state of the molecules residing under the force of the intermolecular interactions. Preliminary studies of the stretching vibration and the intensity of overtones of the gas hydrate system have indicated that the vibration of the guest molecules could impact the hydrogen-bond network .…”