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The Palladium-Hydrogen electrode (Abbreviation: Pd/H2) is one of the common reference electrodes used in electrochemical study. Most of its characteristics are similar to the standard hydrogen electrode (with platinum). But palladium has one significant feature - the capability to absorb (dissolve into itself) molecular hydrogen.

Two phases can coexist in palladium when hydrogen is absorbed:

• alpha-phase at hydrogen concentration <0.3 atom percent
• beta-phase at hydrogen concentration corresponds to the non-stoichiometric formula PdH0.6

The electrochemical behaviour of a palladium electrode in equilibrium with H3O+ ions in solution parallels the behaviour of palladium with molecular hydrogen
$E=E^0 + {RT \over F}\ln {a_{H^+} \over (p_{H2})^{1/2}}$