There is an old video by Thunderf00t (Phil Mason) that shows that the explosions are not caused by the Hydrogen but for a Coulomb explosion [too many electrons go from the Sodium to the water, and then the charged Sodium nuclei repel each other very fast]. https://tldw.tube/?v=LmlAYnFF_s8 He published the result in Nature Chemistry too.

Also, he use a mix of Sodium and Potassium to get a liquid instead of a solid chuck of Sodium and in articular this avoid the oxide layer around the Sodium bar.

I'm not sure if it's possible to use that information to improve this device.