I'll nit pick here. Oxygen generation occurs when the potential of the positive electrode exceeds the oxidation potential of the electrolyte.
Heh heh. Thank you for supplying the extra detail.
Agreed, except at that OH-, not hydrogen gas, is generated along with oxygen due to the high pH of the electrolyte.
However, if we look at the whole cell, and look at both half reactions together, there has to be charge balance. Since the oxygen gas is neutral and comes from the water in the electrolyte, the other reaction product must be neutral too. If we add together the two electrode half reactions we have in total:
4M + 2H
2O + [energy] => 4MH + O
2
The hydrogen is produced and then absorbed at the negative metal hydride electrode. The energy in this equation comes from the supplied electric current.
Later on, the oxygen diffuses across to the negative electrode and is catalytically recombined with the hydrogen, reversing the above reaction to form water again:
4MH + O
2 => 4M + 2H
2O + [energy]
In this reaction the energy is liberated as heat and the cell warms up. But the heat originally came from the electrical energy used to split the water into hydrogen and oxygen.
We may have different ways of talking about the same thing.
Quite. In science there are always different ways of looking at and understanding what is going on. That is the beauty of it.
In terms of physics we have an energy balance:
[energy supplied] = (I^2) x R = [energy stored] + [energy dissipated]
So in our cell we find the electrical energy supplied is either stored internally as chemical energy or dissipated as heat. When the cell can accept no more charge then all energy supplied is being converted into heat. Internally the oxygen recombination cycle may be taking place, but when looking at the cell from the outside we don't need to know about that. Chemistry may happen, but physics cannot be denied.