Imagine - a mobile drone factory, digging itself in in the hinterlands, harvesting solar energy and water, producing mobile hydrogen-IEDs - the minefields of the future will be hard to undo.
Now a much better thing to do instead of making IED drones would be to melt sand or rock into appropriately formed projectiles so that one has an autonomous artillery piece that does not require reloading.
There are much better explosives to use than hydrogen. One could use the haber process to make ammonia and use some biological carbon sources to make pretty much any explosive worth using.
Landmines are probably cheaper though.