They will not, whole process from water to hydrogen to fuel cell to electricity is very inefficient. You only get 1/3 of input energy back (if you use 100kWh to make hydrogen, you get back from the fuel cell 35kWh)
Not to mention hydrogen is a massive pain to store, to transport, and to convert to electricity.
Hydrogen fuel cells aren't ever going to happen. [0] Power to weight sucks, energy to weight sucks, and safety sucks among other things. The supposed advantages over electric cars (infrastructure, range, refueling, longevity) don't exist, and at current rates of tech development won't ever exist. But the disadvantages (complexity, hydrogen storage, inefficiency) still do.
Hydrogen fuel cells aren't ever going to happen. [0] Power to weight sucks, energy to weight sucks, and safety sucks among other things. The supposed advantages over electric cars (infrastructure, range, refueling, longevity) don't exist, and at current rates of tech development won't ever exist. But the disadvantages (complexity, hydrogen storage, inefficiency) still do.
0: https://ssj3gohan.tweakblogs.net/blog/11470/why-fuel-cell-ca...