If the only byproduct of fuel cells is water, and 2/3 of water is hydrogen, then would it be possible for the exhaust water to be broken down by electrolysis that is powered by the fuel cell and re-used over and over? I am aware that due to forces like friction, it could not operate indefinitely, but could it significantly extend the range of the vehicle? Also, if it is not feasible in a car, could it be used to power other, larger vehicles like ships?
While a fuel cell produces electricity from the combination of hydrogen and water, electrolysis produces hydrogen and water by the application of electrical energy. In theory, with a perfectly efficient fuel cell and electrlysis process, you would use exactly as much energy to produce the hydrogen and oxygen as you would receive from combining it. This would leave no extra energy to power a car!
