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We have investigated systematically and statistically methanol-concentration effects on methane-hydrate nucleation using both experiment and restrained molecular-dynamics simulation, employing simple observables to achieve an initially homogeneous methane-supersaturated solution particularly favorable for nucleation realization in reasonable simulation times. We observe the pronounced “bifurcated” character of the nucleation rate upon methanol concentration in both experiments and simulation, with promotion at low concentrations and switching to industrially familiar inhibition at higher concentrations. Higher methanol concentrations suppress hydrate growth by in-lattice methanol incorporation, resulting in the formation of “defects”, increasing the energy of the nucleus. At low concentrations, on the contrary, the detrimental effect of defects is more than compensated for by the beneficial contribution of CH3in easing methane incorporation in the cages or replacing it altogether.

Electrochemical (EC) carbon dioxide (CO2) reduction, where CO2is converted to value-added products such as fuel precursors, plays a key role in helping the world’s energy system reach net-zero carbon emissions. Simulations of EC cells provide valuable insight into their operation since detailed experimental results on short length and time scales are difficult to obtain. In this work, we construct a 1D simulation of a membrane-electrode-assembly EC cell for CO2reduction, using a porous silver gas diffusion cathode. We run the simulation under different electrolyte conditions, showing how the cell performance is affected. We then perform a sensitivity analysis of all input parameters to the simulation, which has not been presented before in the literature. We show that the CO partial current density (iCO) is significantly affected by each input parameter of the simulation. iCOis most sensitive to EC kinetic parameters (i0/α) of all EC reactions, with a 1% change in α resulting in up to 6% change in iCO. Since there is uncertainty associated with the value of each input parameter, this indicates that infidelity between experiment and simulation is likely, and thus, caution should be practiced when comparing experimental results to simulation results. Further, we show that the large range of conditions simulated in literature helps to explain the large variance in reported values of i0and α. The results of this paper demonstrate the potential of sensitivity analysis methods to quickly optimize aspects of cell performance (CO2utilization, Faradaic efficiency, etc.).

The thermodynamic and kinetic properties of neon uptake and release to and from a sII clathrate hydrate were evaluated using molecular dynamics simulation in the absence and presence of an applied static electric field. In the case of neon “leakage”, neon clathrate in contact with a vacuum was simulated at temperatures ranging from 200 to 225 K for 0.5 μs, with progressive neon-emptying of cages monitored. Activation energies for release and uptake were 16.4 and 14.9 kJ/mol, respectively—consistent with experimentally determined values; for neon release in a 0.7 V/nm electric field, the value declines to 6.5 kJ/mol, suggesting its use as a control agent in facilitating gas release from already-loaded clathrates. For neon uptake into an initially empty hydrate, loading free energies for 512and 51264cages, computed via thermodynamic integration, was lower than that previously reported for methane uptake into sI hydrates.

Nonequilibrium molecular dynamics simulations have been performed to investigate both thermal- and electric field-driven breakup of planar propane hydrate interfaces with liquid water at 250–300 K and in the 0–0.7 V nm–1field intensity range. The melting temperatures of each interface were estimated, and dissociation rates were observed to be strongly dependent on temperature, with higher dissociation rates at larger overtemperatures vis-à-vis melting. It was found that externally applied electric fields below a certain intensity threshold do not lead to any marked structural distortion or dissociation effect on pre-existing bulk clathrates. However, field strengths higher than 0.7 V nm–1led to statistically significant differences in the observed initial dissociation temperature and rates. The activation energy in constant electric field was calculated based on the Arrhenius equation. The parameters of this equation, in terms of both kinetic and thermodynamics components (Aand Ea), change significantly, accelerating the dissociation process.

It is predicted herewith that the leakage of both hydrogen (H2) and deuterium (D2) from sII clathrate hydrates, borne of guest chemical-potential equalization driving enhanced nonequilibrium intercage hopping, should be observable experimentally. To this end, we have designed simulations to realize and study this process by microsecond molecular dynamics within the temperature range of 150–180 K—for which the hydrate lattice was found to be stable. In this pursuit, we considered initial large-cage (51264) guest occupancies of 1–4, with single occupation of 512cavities. Examining transient, nonequilibrium intercage hopping, we present a lattice-escape activation energy for the four nominal large-cage occupancies (1–4), by fitting to the hydrate-leakage rate. The intercage hopping of H2and D2was studied using Markov-chain models and expressed at different temperatures and large-cage occupancies. The free energy of guest “binding” in the large and small cages was also computed for all of the occupancies. Toward equilibrium, following the majority of H2/D2escape via leakage, the percentage of occupancies was calculated for both H2and D2for all of the systems for all initial nominal large-cage occupancies; here, not unexpectedly, double occupancies occurred more favorably in large cages and single occupancies dominated in small cages.