Aluminium hydrogen threshold?

While refining some NaOH/Al/Cu batteries I have made for charging nicads and ultracaps,I noticed that at a certain low cell voltage the aluminium electrode ceased to give off hydrogen, even though the cell was producing wattage that varied predictably above and below this voltage, as if there was no electrochemical change. (The non-linear factor was the anode/cathode area ratio.)

Some weeks ago I came across a reference to the "hydrogen threshold", and what this voltage was for different elements. Now I can't find it again!

I am interested because such a cell that does not produce potentially explosive hydrogen, nor a fine mist of caustic vapour is a much friendlier device.

So:

1. What effect have I stumbled upon

2. If no hydrogen is evolved, what effect would this have on cell chemistry? Perhaps it is absorbed by the aluminium causing

hydrogen embrittlement?