Regarding this topic, Ed Storms asked me to post the following:
A common mistake is being made here. In electrochemistry, when deuterium is generated at the cathode, it produces gas at ambient pressure and an activity of D in the Pd. In chemistry, activity is made equal to the IDEAL pressure when making calculations of Gibbs energy. However, in the real world activity and pressure are NOT the same phenomenon and are frequently not equal. For example, although the activity of D in Pd can be calculated and presented as 10e47 atm, this is NOT the pressure in the material. There is no gas pressure in the Pd because D2 does not exist there as gas. If a cavity exists and gas is generated to fill the cavity, the pressure will rise in the cavity. However, it will not rise to a value equal to the activity because H2 becomes nonideal at high pressure. As a result, the measured pressure will be much smaller than the activity.
