The round trip is a net loss isn't it? We use electricity to convert H2O into H and O.

Then in a hydrogen fuel cell car, we RE-convert the H and O back into H2O again.

So it is a round trip.

But since every mechanical device LOSES energy through friction and heat and waste, the round trip from H2O to H & O and back to H2O LOSES energy.

Isn't this right? So how will a hydrogen economy run the country or replace oil-burning cars?