Sodium silicide (NaSi, Na<sub>4</sub>Si<sub>4</sub>) is a binary inorganic compound consisting of sodium and silicon. It is a solid black or grey crystalline material. 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 ðC creates an air-stable and less reducing product, while the product produced at room temperature is a pyrophoric and highly moisture-sensitive powder.
Sodium silicide's empirical formula (NaSi) is deceptive, as it is a Zintl phase: instead of containing discrete anions, it contains tetrahedra, which leads to the more descriptive formula Na<sub>4</sub>Si<sub>4</sub>. These silicon tetrahedra condense into various crosslinked silicon polymers at high pressure.
Sodium silicide reacts readily with water yielding gaseous hydrogen and aqueous sodium silicate in an exothermic reaction (~175 kJ÷mol<sup>âÂÂ1</sup>):
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.