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https://ecomento.com/guide/hydrogen-fuel-cell-vs-battery-electric-cars-greener/ Having tested a Toyota Mirai and my brother owning a Prius...which he just replaced the batterie$$ on:

In both cases, one must consider the total environmental impact of energy production. This is known as “well-to-wheels” emissions. Electricity has to be generated, while hydrogen has to be separated from other elements and transported to filling stations. California has one of the cleanest grids in the country, and the most electric cars. It also has nine of the 10 public hydrogen fueling stations currently operating. Right now, the Golden State is essentially a “best-case scenario” for electric cars, and an “only-case scenario” for fuel cells.
According to the 2010 California Low Carbon Fuel Standard Final Regulation Order, fuel-cell cars have an average lifetime greenhouse gas emissions rate of 61.83 grams of carbon dioxide per megajoule. This is for hydrogen produced through the popular natural gas reforming process.
Electricity, on the other hand, was determined to have average lifetime greenhouse gas emissions of 41.37g/mj.
All things considered, the inherently simpler process of storing energy in a battery and using it to power a car makes electricity greener than hydrogen.
The myriad variables of the isolation, packaging, transport, and consumption of hydrogen mean its well-to-wheels emissions can vary wildly, while those of battery-electric cars tend to remain consistently low regardless of where the electricity comes from.
That’s not to say that fuel-cell cars don’t have other advantages, but in the emissions battle, the batteries appear to be on top.
There you have it, in a nutshell.