In this Empyrion Galactic Survival gameplay video I just gather pentaxid on the moon.
Pentaxid (refined) is the fuel required for the operation of warp drives. It is created by processing Pentaxid (raw material) crystals in a Constructor. The crystals can be found underwater on Akua, in Mist biomes on Skillon, and possibly other places. Once created, the fuel is stored in stacks of 1 in the Warp Drive Tank.
Note that multiple refined pentaxid will be required per warp, likely 1 unit per AU. Warping to Aestus from Akua (which are 2.8 AU apart) and back using a modified Tier 1 Starter Capital ship (available in blueprints) requires 3 refined pentaxid, and thus 3 raw pentaxid, each way.
Pentaxid (refined) used to be known as Pentaxit.