The only manufacturer in the world going down the IC Hydrogen path with diesels is JCB in the U.K. Anthony (Lord) Bamford is pushing the IC Hydrogen engine with a £100M investment. He's even built JCB Hydrogen refuelling vehicles.
But nowhere is it mentioned where a constant, cheap source of hydrogen for the long-term, is coming from. I don't know where JCB is getting their hydrogen, but I'll wager it's a refinery by-product - and no cost of the hydrogen is mentioned.
https://www.jcb.com/en-au/campaigns/hydrogen/hydrogen-truck
Bamford claims it's a no-brainer to use hydrogen in current IC engines, because the development costs are low, and he doesn't have to add serious strength to his machines to carry the batteries needed for electric drive.
He says if went to electric motive power on a 20 tonne digger, the battery would add 8 tonnes in weight to the machine and he'd have to install a heavier undercarriage and frame.
But there are already pure electric motive power machines appearing in the construction industry, and I think Bamford has taken a major detour that is going to lead him into a cul-de-sac for the long-term.
The problem with hydrogen is, although it's very energy intensive, carrying 33.33 kWh per kg - as against about 12 kWh per kg for petrol and diesel - it's hydrogen TRANSPORTATION, that is the giant bugbear.
Hydrogen rates poorly for volumetric efficiency in transportation, even when pressurised to 700 kPa. It can be pressurised to much greater levels - but at what cost and safety level?
So hydrogen has to be LIQUIFIED to be transported efficiently. But when it's liquified, it takes around 36% of its available energy to liquify it.
Current research is all about trying to reduce the cost of hydrogen liquifaction - but no-one has come up with a cheap liquifaction method yet - and no-one has produced cheap and substantial supplies of hydrogen - even though we've been promised cheap, GREEN hydrogen for a couple of decades now.
https://www.idealhy.eu/index.php?page=lh2_outline
Note that the hydrogen liquifaction project in the last link above, was completed in 2013 and nothing further has come from all their research. In the meantime, battery design has improved in leaps and bounds, tripling and quadrupling energy storage abilities in just a few short years, and with more substantial advances in the near future.
You'll be flying an electric aircraft long before you'll be flying a hydrogen fuel cell one - and you'll be able to recharge in a myriad of places with ease.