[Joe L. Ogan (OP)]

If hydrogen is the most common element in the universe, why is it so difficult to use?  Thanks for comments.  Joe L. Ogan

[Yomi]

Already its being used...

[Joe L. Ogan (OP)]

Of course it is being used but with difficulty.  It is difficult to accumulate and dangerous to use.  It is a very good source of energy.  Thanks for comments.  Joe L. Ogan

[syhprum]

Hydrogen is not of course a primary fuel it can only be produced by the expenditure of energy.
Although it contains a lot of energy in relation to its weight it is very light and must be stored in massive high pressure containers or in a liquid form at 20°K which is not very convenient!.
There is also the difficulty caused by the H2 molecule being very small which will easily pass thru membranes that are in-permeable to other gasses, all together not a very convenient method of storing energy its only redeeming feature is that when burnt at modest temperatures the only residude is H2O

[tommya300]

http://en.wikipedia.org/wiki/Hydrogen_fuel_cell

[LeeE]

The greatest problem with using Hydrogen is, as syhprum said, the Hydrogen molecules are very small, making it difficult to store because it'll get through holes that other molecules can't.  The same, although to a slightly lesser degree, applies to helium as well, which is why it has to be regularly replenished when used as a coolant.