A process to split methane into its components, hydrogen and carbon, is advertised as a way to make hydrogen from fossil gas without emissions. Yet, claims that methane pyrolysis is free of CO₂ emissions or more efficient than water electrolysis are highly misleading.
Surplus power from anything. Existing base load power plants have periods of reduced use and do not adjust rapidly to change in load. Might as well harvest that as well. I think it is often utilized by heavy industry currently, for smelting plants and the like.
If we continue investing in wind and solar, at a certain point it will be an almost daily issue to have more power than is needed. If some of the excess could be turned into hydrogen it could be huge for decarbonizing transportation.