A ways back when looking into hydrogen as a fuel, I recall a design that manufactured hydrogen on site using nothing but water and a nominal amount of electricity.
If the electricity was from hydro power, there would be zero carbon impact.
Even if coal was used to produce the electricity, it would be a minor impact since the amount of electricity used would be nominal.
If I spent the time, I could find it, but I’m not going to. You can find it for yourselves.
My memory calls BULLSHIRT on this article.
You get less power from burning hydrogen than the power required to generate hydrogen from water using electrolysis. The loss in energy is inefficiency in the process and entropy. If it was economical then someone would be doing it by now.