How to build a Hydrogen generator?

The "easiest" is using electrolysis. It is essentially two electrodes (graphite will work, gold, platinum or palladium metal are better), each in it's own "cell", with controlled electric current flowing to each cell, and the salt solution (not table salt) able to "communicate" thru a membrane. Oxygen comes off of one cell and hydrogen off the other. You can buy an electroysis unit cheaper than you can build one. The energy efficiency is terribly low - you end up using electricity, which is created at as much as 30% efficiency from the thermal source (the power plant, burning natural gas, coal, etc.), and the hydrogen production and capture is maybe 25% efficient. It's enormously more efficient and much cheaper to burn gasoline or diesel (if you have a diesel engine). The hydrogen can't be used in a gasoline engine. It will destroy the engine from a variety of means - the hydrogen itself will enbrittle the metal, ruin the seals, and it will burn extra hot. If it was efficient, inexpensive and easy, everyone would be doing it!

Cars that run on hydrogen simply use a very high pressure storage tank for the hydrogen. If you bring along all the stuff to generate the hydrogen as you go, it will all weigh to much and destroy the efficiency of the system. An alternate method of storing hydrogen is in the form of a hydride filled tank that must be heated to release the stored hydrogen.

The "easiest" is using electrolysis. It is essentially two electrodes (graphite will work, gold, platinum or palladium metal are better), each in it's own "cell", with controlled electric current flowing to each cell, and the salt solution (not table salt) able to "communicate" thru a membrane. Oxygen comes off of one cell and hydrogen off the other. You can buy an electroysis unit cheaper than you can build one. The energy efficiency is terribly low - you end up using electricity, which is created at as much as 30% efficiency from the thermal source (the power plant, burning natural gas, coal, etc.), and the hydrogen production and capture is maybe 25% efficient. It's enormously more efficient and much cheaper to burn gasoline or diesel (if you have a diesel engine). The hydrogen can't be used in a gasoline engine. It will destroy the engine from a variety of means - the hydrogen itself will enbrittle the metal, ruin the seals, and it will burn extra hot. If it was efficient, inexpensive and easy, everyone would be doing it!

Cars that run on hydrogen simply use a very high pressure storage tank for the hydrogen. If you bring along all the stuff to generate the hydrogen as you go, it will all weigh to much and destroy the efficiency of the system. An alternate method of storing hydrogen is in the form of a hydride filled tank that must be heated to release the stored hydrogen.

Do you need the formula for nuclear warhead too?