In Science Behind Hydrogen Hybrid Cars - The water electrolysis we discussed the basic composition of a hydrogen fuel cell and how it works, now we should look at the actual scientific equations in the process. (This will be a bit advanced so pull out your old paper books!)
At the negatively charged cathode (electrode plate) in the water of your hydrogen cell car, a reduction reaction happens. The electrons (e) from the cathode turn into hydrogen ions (positively charged ion which is attracted to a negative electrode in an electrolyte) which then forms the hydrogen gas (half the reaction balanced with acid):
Cathode (reduction): 2H + (aq) + 2e → H2 (g)
An oxidation reaction happens on the positively charged anode (electrode plate) in the water of your hydrogen cell car. This gives oxygen and gives electrons to the cathode to complete the circuit:
Anode (oxidation): 2H2O (1) → 02 (g) (+) 4H + (aq) (+) 4-
You can balance these half reactions in your hydrogen cell car with a base like those listed below. You do not need to balance all of these half reactions with a base or acid, although many like the improvement of the reduction or oxidation of the water. For half reactions, they must both balance with either base or acid:
Cathode (reduction): 2H2O (1) (+) 2e → H2 (g) (+) 2OH- (aq)
Anode (oxidation): 4OH- (aq) → O2 (g) (+) 2H2O (1) + 4e
You can combine any of these half reactions to get the same total degradation of water in hydrogen and oxygen:
Overall reaction: 2H2O (1) → 2H2 (g) (+) O2 (g)
As mentioned before, you get twice as many hydrogen molecules as you get oxygen molecules. If everything is equal to the pressure and temperature of both gases, the hydrogen produced will have twice as much as the oxygen volume. Therefore, the number of electrons that shoot through the water will be twice as many generated hydrogen molecules and four times as many as the number of oxygen molecules
If we look at the electrode's thermodynamics in the hydrogen cell, we see that normal temperatures and pressures do not give the best results. Based on "Nernst Equation", the normal potential for the fuel cell is:
-1.23 V at 25 ° C at pH 7 (H + = 1.0x10-7 M) or -1.23 V at 25 ° C at pH 0 (H + = 1.0 M)
The negative voltage shows that the energy for electrolysis of water is more than zero. This is shown by the G = -nFE equation from the kinetics of the chemicals, where "n" corresponds to the moles of electrons and "F" is equal to the Faraday constant. This reaction will not occur without the supplied energy, usually from an external power source.
Please stay with us for the Science behind Waterhousing cars - Electrolytes and electrolysis when we talk more about how the electrolytes affect the process in your hydrogen cell car.