Wouldn't it be cheaper in the long run, easier and more future proof to just electrify the damn track? The tracks themselves need maintenance anyways. Having overhead electrified tracks allows you to make the electricity for it anyaway you want including hydrogen. You are also able to purchase practically any electric locomotive and the costs for those are much lower as well as maintenance.
Where does the hydrogen come from, or is this just natural gas with extra steps?<p>What's the state of the art on producing hydrogen from electricity without incredibly expensive catalysts again?
Use of hydrogen on a train is a bit stupid though - trains are the the one mobile power use where there's no real benefit to being able to dump the ash into the environment. You may as well just supply good primary battery reactants, such as zinc, or sodium and sulfur, which can be efficiently be recharged somewhere away from the train.
I would think that having a battery based train engine, that can use electricity where available and use batteries where tract electrification is not done is better than fuel based ones, no matter the source or type of fuel.