The water thing is cool until you realize you need electricity to run the electrolysis process, most times it would be more efficient to just run the electric source directly to what you are powering than to lose it through the inefficiencies. Hydrogen Fuel Cells are basically just an attempt to find a better storage solution than batteries, the only problem is hydrogens volatility, they need to find a very safe way to store the stuff on a car so it won't explode if damaged in a collision.
I have a Hydrogen Fuel Cell Demo kit set-up right here next to my desk, We use a heat lamp to charge some photovoltaic cells that begin the electrolysis, not long and you start to see the bubbles start running through the tubes, after a few minutes enough oxygen and hydrogen has been seperated that the fuel cell on the other end is saturated enough to start making the fan connected to it start turning, but it turns slow and those little air bubbles even though they are moving pretty fast you can see them moving with your own eyes. Now if I were to take those PV cells and put them on a small battery that fan would be turning a lot faster and with enough PV cells I could keep enough charge to keep the battery up and run the fan because electrons aren't getting stuck between waiting for the air bubbles. There will be some advances in the Hydrogen fuel cell tech but I don't think it will live up to meeting our extreme addiction to energy....
As far as the welding torch, it's cool and all but most major construction uses arc welding...