http://www.spiritofmaat.com/archive/watercar/h20car2.htm
*Fuel Cells:* This method uses oxygen from the atmosphere to complete the burning of the hydrogen in the fuel cell. What comes out of the tail pipe is oxygen and water vapor, but the oxygen originally came from the atmosphere, not from the fuel. And so the use of fuel cells neither takes away nor contributes to the oxygen content of the air. *Hydrogen: *This fuel is complete in itself. It does not need oxygen from the atmosphere to burn, which is an improvement over fossil fuels in saving the oxygen in our air supply. In fact, when hydrogen burns perfectly, nothing at all comes out of the tail pipe. If salt and metal alloy are used to create hydrogen, then there will be residues of that in the exhaust, but hydrogen fuel does not contribute oxygen to the atmosphere. *Brown's gas:* This is the most perfect fuel of all for running our vehicles. Like pure hydrogen, it is made from water, i.e., hydrogen and oxygen, but it burns in the combustion engine so that, depending on the setup, it may actually release oxygen into the atmosphere. In that case, what comes out of the tail pipe is oxygen and water vapor, just as with fuel cells; but the oxygen comes from the water that's being used to create the Brown's gas fuel. So burning Brown's gas as fuel can add oxygen to the air and thus increase the oxygen content of our atmosphere.
