What is fuel rate?

Fuel cells Hydrogen consumption rate.?

• I have read a design of a car moved by fuel cells, using Hydrogen from water. This is my question: In the system they used solar cells to generate electricity and separate H from water. Then this H was used to feed the fuel cells. So... Is the energy generated from one gram of H by the fuel cell greater than the energy consumed to separate H from water? Is that possible? What about the efficiency? It wouldn't be better to run the car from the solar cells? Or if it's the opposite... Can I think about a fuel cell that produces its own fuel? So there is no need of refilling?

• Answer:

  The amount of energy generated during formation of water from H2 and separation of water into H2 would be the same provided the reaction is reversible. Also, the efficiency for the two reactions may be different (due to technological problems) because of which the actual available energy as work may be different. Probably because of this consideration it is more economical to run the car using a fuel cell instead of directly running it on the electricity. As for the 2nd question: a fuel cell producing its own fuel would not be possible. The theoretical maximum efficiency of the system cannot be 100% (2nd Law of Thermodynamics). Thus, after each cycle there would be a loss of energy which would eventually lead to zero available energy in the system.