# hydrogen fuel cell

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#1
Hi,
In the spec for my chemistry exam is states that i have to explain what happens at each electrode in a hydrogen oxygen fuel cell.

My book gives me the equilibria happening at each electrode with the standard electrode potentials so you can work out the general direction of electrons which are:

H2 +2Oh- --> 2H20 + 2e- negative electrode
1/2O2 +H20 --> 2 Oh- positive electrode.

it may be that i just have to learn these equations but from these equations i can't really visualise what is happening in either of the electrodes.
I would appreciate any help with this, thanks
0
4 years ago
#2
The reason you're having trouble is probably because that second reaction (1/2O2 +H20 --> 2 OH-) is incorrect. Charge must always be the same on both sides of a reaction, and in that given reaction the left hand side has an overall charge of 0, but the right hand side has a charge of -2.The correct reaction woutl be 2e- + 1/2O2 +H20 --> 2 OH-

Think of the H2 molecule as 2H+ ions and 2 electrons. In the first reaction, these are split apart and the H+ ions react with OH- to form water, while the e- are released to be used in the second reaction.Overall this is an oxidation, as the H2 molecule has lost its electrons and oxidation is the loss of electrons.

In the second reation, the electrons from the first reaction are given to the oxygen atom, reducing it to a 2- oxidation state. It then takes away one of the H+ ions from the water, so that both of them become an OH- ion.
1
4 years ago
#3
Those equations do not balance, do they. Maybe that explains your problem.

A 'qualitative picture'; At one electrode, the hydrogen (which is fed into the cell) and the hydroxide ions (which are in the inter-electrode ion exchange medium) react to form water (an exhaust material), and an excess of electrons (if you want to describe it that way). These electrons flow around a circuit, and power whatever you've attached to it (a fan, or a motor, or a light, or whatever). Then, these electrons feed back into the positive electrode, and interact with the oxygen and water (which are fed into the cell) and produce hydroxide ions, which replenish the concentration of hydroxide ions in the inter-electrode medium that were used in the first reaction.
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