There is much talking in recent days about solid metallic hydrogen and its possible uses. When was it referenced in a science fiction story for the first time? Please note that I am asking about its use as a tool.
Poul Anderson's Call Me Joe (1957) includes a reference to a level on Jupiter "where water ids a heavy mineral and Hydrogen is a metal". The speaker is told that Hydrogen is still a gas where Joe lives, and that the metallic phase is lower down.