How are alkali-metal hydrides produced from hydrogen gas?

Alkali-metal hydrides are produced through the direct combination of their constituent elements—the alkali metal and hydrogen gas—at elevated temperatures, typically ranging from 300 to 700 °C (570 to 1,300 °F).12

These compounds, classified as saline (ionic) hydrides, contain hydrogen as a negatively charged ion ($H^{-}$). While pure samples appear as white crystalline solids, they often have a gray appearance due to trace metal impurities. Because these hydrides react instantly and vigorously with water to release large volumes of hydrogen gas, they serve as useful, portable sources of hydrogen.12