TTT
I wonder if you read my 3rd-to-last para above:
"There are many others, not least – as you mentioned – the recovery of hydrogen from water. That needs energy. The same amount, or slightly more, than the oxidation of hydrogen delivers in a fuel cell. "
Like batteries, a hydrogen store is essentially a way of storing energy. That's the sustainability angle. There are a number of approaches to the production of hydrogen. One is to electrolyse water to create hydrogen and oxygen, another is to put methane (natural gas) through a plasma torch to split the carbon from the hydrogen (see for example, Monolith Materials).
The process is supposed to be sustainable, so the intention is not to find a pre-existing source of energy and then convert that to motion in a once-only conversion process (such as burning gasoline).
The aim is to find a process that uses one form of energy; converts it to a different form to generate the motion, and then recycle the proceeds of that process for future use.
Hoe that answers the question.
Retrocop: I think that was a report from about 6 months ago by a consulting company called Berylls
http://www.berylls.com/wp-content/uploads/2018/03/20180323_Studie_E-Mobilitaet_DE.pdf (It's in the German language).
It's true that using electricity generated by a 'dirty' process creates pollution. As noted above, the pollutino from a power plant is focussed in one place. That may be good or bad, depending on your perspective. Any contribution by renewables reduces the pollution burden, compared with a petrol or diesel-powered car, which is 100% fossil fuel.
Furthermore, if you look at a whole-life energy analysis (including making the batteries), even the Berylls report (which is quite pessimistic) indicates that an electric car turns the energy balance positive after three to five years.
I don't claim all the probems are solved. Far from it. That will take many decades.
What I do believe is that we are close to a turning point in the energy surces for the vehiles we use.
Hope it helps