Hydrogen as a fuel

chound

Is it possible to create a structure where
1)water is electrolysed into oxygen and hydrogen
2)Hydrogen is burnt in the same oxygen obtained from step 1
3)This releases lot of energy and forms water
4)This energy can be used to rotate the armature of an electric generator
5)Electricity can be produced
6)The water in step 3 can be used in step 1

Bystander

Yup, yup, yup, yup, yup, and yup. Will "5" take care of "1"? Nope.

russ_watters

Since the reaction is symmetrical (water+energy=hydrogen+oxygen=water+energy, etc, etc, etc.), even if you had perfect efficiency, you'd still never get more energy out than you put in.

Chronos

Let's do the math here and see what falls out. Per Faradays constant of electrolysis, it takes about 96,500 coulombs to generate 1 mole of hydrogen gas. After a couple of crunches, it appears to require about 32.9 kilowatts to generate 1 kilogram of hydogen gas. The electrical energy equivalent of a kilogram of hydrogen gas is 33.5 kilowatts. That looks promising, 102% efficiency!

Aye, but there is a rub, as usual. Those are idealized numbers - i.e., they assume 100% efficiency. You can take 17% straight off the top in heat loss. Now the numbers look like this 32.9 x 1.17 and 33.5 x 0.83 = 38.5 kw to get 29.1 kw.. down to 75% efficiency. And this is at laboratory efficiencies. In the real world, the true loss is about 1/3, so the real world efficiency is in the neighborhood of 50%. The bad news is you will run out of gas. The good news is it ain't all that bad a return.