Crystal structure of ice XVII

Ice XVII is a metastable form of ice with a hexagonal structure and helical channels that was discovered in 2016. It can be formed by freezing water with hydrogen molecules at high pressure to form a filled ice, and then removing the hydrogen molecules from the structure. The form has potential for being used in hydrogen storage. Ice XVII made from heavy water[lower-alpha 1] can also be reduced to pure cubic ice.

Discovery

In 2016, the discovery of a new form of ice was announced.[1] Characterized as a "porous water ice metastable at atmospheric temperatures", this new form was discovered by taking a filled ice and removing the non-water components, leaving the crystal structure behind, similar to how ice XVI, another porous form of ice, was synthesized from a clathrate hydrate.[2][1][3][4][5]

To create ice XVII, the researchers first produced filled ice in a stable phase named C0 from a mixture of hydrogen (H2) and water (H2O), using temperatures from 100 to 270 K (−173 to −3 °C; −280 to 26 °F) and pressures from 360 to 700 MPa (52,000 to 102,000 psi; 3,600 to 6,900 atm).[1][lower-alpha 2] The filled ice is then placed in a vacuum, and the temperature gradually increased until the hydrogen frees itself from the crystal structure.[1][3][lower-alpha 3] The resulting form is metastable at room pressure while under 120 K (−153 °C; −244 °F), but collapses into ice Ih (ordinary ice) when brought above 130 K (−143 °C; −226 °F).[1][3] The crystal structure is hexagonal in nature, and the pores are helical channels with a diameter of about 6.10 Å (6.10×10−10 m; 2.40×10−8 in).[1][3]

Hydrogen storage

The discovery announcement also mentioned that ice XVII could repeatedly adsorb and release hydrogen molecules without degrading its structure.[1] The total amount of hydrogen that ice XVII can adsorb depends on the amount of pressure applied, but hydrogen molecules can be adsorbed by ice XVII even at pressures as low as a few millibars[lower-alpha 4] if the temperature is under 40 K (−233.2 °C; −387.7 °F).[1][6] The adsorbed hydrogen molecules can then be released, or desorbed, through the application of heat.[6] This was an unexpected property of ice XVII, and could allow it to be used for hydrogen storage, an issue often mentioned in environmental technology.[1][6]

Aside from storing hydrogen via compression or liquification, it can also be stored within a solid substance, either via a reversible chemical process (chemisorption) or by having the hydrogen molecules attach to the substance via the van der Waals force (physisorption).[6] The storage method used by ice XVII falls in the latter category, physisorption.[6] In physisorption, there is no chemical reaction, and the chemical bond between the two atoms within a hydrogen molecule remains intact. Because of this, the number of adsorption–desorption cycles ice XVII can withstand is "theoretically infinite".[1][6]

One significant advantage of using ice XVII as a hydrogen storage medium is the low cost of the only two chemicals involved: hydrogen and water.[6] In addition, ice XVII has shown the ability to store hydrogen at an H2 to H2O molar ratio above 40%, higher than the theoretical maximum ratio for sII clathrate hydrates, another potential storage medium.[1] However, if ice XVII is used as a storage medium, it must be kept under a temperature of 130 K (−143 °C; −226 °F) or risk being destabilized.[6]

Cubic ice

It was reported in 2020 that cubic ice based on heavy water (D2O) can be formed from ice XVII.[7] This was done by heating specially prepared D2O ice XVII powder.[7] The result was free of structural deformities compared to standard cubic ice, or ice Isd.[7][8] This discovery was reported around the same time another research group announced that they were able to obtain pure D2O cubic ice by first synthesizing filled ice in the C2 phase, and then decompressing it.[9][1][lower-alpha 2]

See also

Notes

  1. ↑ Heavy water is water based on deuterium (2H, or D), a form of hydrogen that also contains a neutron.
  2. 1 2 C0, C1, and C2 are all stable solid phases of a mixture of H2 and H2O molecules, formed at high pressures.[1][3] Although sometimes referred to as clathrate hydrates (or clathrates), they lack the cagelike structure generally found in clathrate hydrates, and are more properly referred to as filled ices.[1][3][4]
  3. ↑ If kept at a temperature range between 110 and 120 K (−163 and −153 °C; −262 and −244 °F), after about two hours, the structure will have emptied itself of any detectable hydrogen molecules.[1][3]
  4. ↑ One millibar is equivalent to 100 Pa (0.015 psi; 0.00099 atm).

References

  1. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 del Rosso, Leonardo; Celli, Milva; Ulivi, Lorenzo (7 November 2016). "New porous water ice metastable at atmospheric pressure obtained by emptying a hydrogen-filled ice". Nature Communications. 7 (1): 13394. arXiv:1607.07617. Bibcode:2016NatCo...713394D. doi:10.1038/ncomms13394. PMC 5103070. PMID 27819265.
  2. ↑ Chaplin, Martin. "Ice-seventeen (Ice XVII)". Archived from the original on 2022-09-11. Retrieved 2022-09-11.{{cite web}}: CS1 maint: bot: original URL status unknown (link)
  3. 1 2 3 4 5 6 7 Chaplin, Martin. "Ice-seventeen (Ice XVII)". Archived from the original on 2022-09-11. Retrieved 2022-09-11.{{cite web}}: CS1 maint: bot: original URL status unknown (link)
  4. 1 2 Liu, Yuan; Huang, Yingying; Zhu, Chongqin; Li, Hui; Zhao, Jijun; Wang, Lu; Ojamäe, Lars; Francisco, Joseph S.; Zeng, Xiao Cheng (25 June 2019). "An ultralow-density porous ice with the largest internal cavity identified in the water phase diagram". Proceedings of the National Academy of Sciences. 116 (26): 12684–12691. Bibcode:2019PNAS..11612684L. doi:10.1073/pnas.1900739116. PMC 6600908. PMID 31182582.
  5. ↑ Falenty, Andrzej; Hansen, Thomas C.; Kuhs, Werner F. (December 2014). "Formation and properties of ice XVI obtained by emptying a type sII clathrate hydrate". Nature. 516 (7530): 231–233. Bibcode:2014Natur.516..231F. doi:10.1038/nature14014. PMID 25503235. S2CID 4464711.
  6. 1 2 3 4 5 6 7 8 Del Rosso, Leonardo; Celli, Milva; Ulivi, Lorenzo (June 2017). "Ice XVII as a Novel Material for Hydrogen Storage". Challenges. 8 (1): 3. doi:10.3390/challe8010003.
  7. 1 2 3 del Rosso, Leonardo; Celli, Milva; Grazzi, Francesco; Catti, Michele; Hansen, Thomas C.; Fortes, A. Dominic; Ulivi, Lorenzo (June 2020). "Cubic ice Ic without stacking defects obtained from ice XVII". Nature Materials. 19 (6): 663–668. arXiv:1907.02915. Bibcode:2020NatMa..19..663D. doi:10.1038/s41563-020-0606-y. PMID 32015533. S2CID 195820566.
  8. ↑ Chaplin, Martin. "Stacking disordered ice; Ice Isd". Archived from the original on 2022-09-11. Retrieved 2022-09-11.{{cite web}}: CS1 maint: bot: original URL status unknown (link)
  9. ↑ Komatsu, Kazuki; Machida, Shinichi; Noritake, Fumiya; Hattori, Takanori; Sano-Furukawa, Asami; Yamane, Ryo; Yamashita, Keishiro; Kagi, Hiroyuki (3 February 2020). "Ice Ic without stacking disorder by evacuating hydrogen from hydrogen hydrate". Nature Communications. 11 (1): 464. arXiv:1909.03400. Bibcode:2020NatCo..11..464K. doi:10.1038/s41467-020-14346-5. PMC 6997176. PMID 32015342.
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