Palladium-hydrogen electrode
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2008-04-02T03:14:36Z
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Spell aprox => approx.
The '''Palladium-Hydrogen electrode''' (Abbreviation: Pd/H<sub>2</sub>) is one of the common [[reference electrode]]s used in [[electrochemistry|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 PdH<sub>0.6</sub>
The electrochemical behaviour of a palladium electrode in equilibrium with H<sub>3</sub>O<sup>+</sup> ions in solution parallels the behaviour of palladium with molecular hydrogen<br>
1/2H<sub>2</sub> = H<sub>ads</sub> = H<sub>abs</sub><br>
Thus the equilibrium is controlled in one case by the partial pressure of [[fugacity]] of molecular hydrogen and in other case - by [[activity]] of H<sup>+</sup>-ions in solution.<br>
<math>E=E^0 + {RT \over F}\ln {a_{H^+} \over (p_{H2})^{1/2}}</math><br>
When palladium is electrochemically charged by hydrogen, the existence of two phases is manifested by a constant [[potential]] of approx. +50 mV vs [[standard hydrogen electrode|reversible hydrogen electrode]]. This potential is independent of the amount of hydrogen absorbed over a wide range. This property has been utilized in the construction of a palladium/hydrogen [[reference electrode]]. The main feature of such electrode is an absence of non-stop bubbling of molecular hydrogen through the solution as it is absolutely necessary for the [[standard hydrogen electrode]].
==References==
* [[Eliezer Gileadi|E. Gileadi]], E.Kirowa-Eisner, J.Penciner ''Experiments in interfacial electrochemistry''. Institute of Chemistry, Tel-Aviv Univ., part 2, pp. 247-249
[[Category:Electrodes]]
[[Category:Electrochemistry]]
[[Category:Palladium]]
[[Category:Hydrogen technologies]]