Sodium silicide

Sodium silicide (NaSi, Na4Si4) is a binary inorganic compound consisting of sodium and silicon. It is a solid black or grey crystalline material.[1] It can be synthesized by melting sodium or a sodium-potassium alloy with finely powdered silica gel. Temperature control of the reaction determine the final product's reactivity; heating above 400 °C creates an air-stable and less reducing product, while the product produced at room temperature is a pyrophoric and highly moisture-sensitive powder.[2]

Sodium silicide's empirical formula (NaSi) is deceptive, as it is a Zintl phase: instead of containing discrete Si− anions, it contains Si4−4 tetrahedra, which leads to the more descriptive formula Na4Si4. These silicon tetrahedra condense into various crosslinked silicon polymers at high pressure.[3]

Sodium silicide reacts readily with water yielding gaseous hydrogen and aqueous sodium silicate in an exothermic reaction (~175 kJ·mol−1):[4]

2 NaSi + 5 H2O → 5 H2 + Na2Si2O5

This is used in hydrogen technologies to generate hydrogen as a fuel. It is also used as high energy dense storage for hydrogen under low pressure.[5]

See also

References

  1. ^ Material Safety Data Sheet, SiGNa Chemistry, Inc.
  2. ^ Dye, J. L., Cram, K. D., Urbin, S. A., Redko, M. Y., Jackson, J. E., & Lefenfeld, M. (2005). Alkali Metals Plus Silica Gel:  Powerful Reducing Agents and Convenient Hydrogen Sources. Journal of the American Chemical Society, 127(26), 9338–9339. https://doi.org/10.1021/ja051786+
  3. ^ Cabrera, R. Q., Salamat, A., Barkalov, O. I., Leynaud, O., Hutchins, P., Daisenberger, D., Machon, D., Sella, A., Lewis, D. W., & McMillan, P. F. (2009). Pressure-induced structural transformations of the Zintl phase sodium silicide. Journal of Solid State Chemistry, 182(9), 2535–2542. https://doi.org/10.1016/j.jssc.2009.06.037
  4. ^ Hydrogen Production from Sodium Silicide Powder; Prospects for On-Board Generation, 14 July 2006
  5. ^ "Silicide-Based Hydrogen Generation for Back-Up Power and Portable Fuel Cells" (PDF). www.signachem.com/. July 2013. Archived from the original (PDF) on 25 March 2019. Retrieved 25 Mar 2019.


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