This would be an almost not terrible solution for when you need to drop in an emergency charging station (i.e. due to natural disaster) except that Hydrogen being such a pain to source, distribute, and refill, even if it still managed to be greener it would make more sense to just dump a nice big "efficient" (relative to car sized ICE) diesel genset in a crate instead.
As a standalone charging system for regular use, it's kind of silly.
Though someone pointed out the idea of using off-peak solar/wind to generate H2 and then store for later conversion to charge EVs, I suspect that while you could in theory build large hydrogen "batteries" this way, I'm not sure how economical it would be, at least with the current state of fuel cell technology. As I understand it the membranes of fuel cells have a limited lifetime ...
Hydrogen generation is an incredibly expensive way to store electricity, which is why it's never taken off in that role.