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| The '''palladium-hydrogen electrode''' (abbreviation: Pd/H<sub>2</sub>) is one of the common [[reference electrode]]s used in [[electrochemistry|electrochemical study]].<ref>[http://www.cormet.fi/pdf/PDF_Pd-H2.pdf Operation principle of Pd/H2 reference electrode]</ref> 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]].<ref>[http://www.iop.org/EJ/abstract/0022-3735/1/6/424 A palladium-hydrogen probe electrode for use as a microreference electrode]</ref><ref>[http://neon.otago.ac.nz/research/mfc/pubs/co2-ph/pdh-electrode.pdf Palladium-hydrogen electrodes for coulometric titration]</ref>
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| ==Electrode operation==
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| Two phases can coexist in palladium when hydrogen is absorbed:
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| *alpha-phase at hydrogen concentration less than 0.025 atoms per atom of palladium
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| *beta-phase at hydrogen concentration corresponding to the [[non-stoichiometric]] formula PdH<sub>0.6</sub>
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| 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
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| :<math>\tfrac{1}{2} \mathrm{H}_2 = \mathrm{H}_{ads} = \mathrm{H}_{abs}</math>
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| Thus the equilibrium is controlled in one case by the partial pressure or [[fugacity]] of molecular hydrogen and in other case—by [[activity (chemistry)|activity]] of H<sup>+</sup>-ions in solution.
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| :<math>E=E^0 + {RT \over F}\ln {a_{\mathrm{H}^+} \over (p_{\mathrm{H}2})^{1/2}}</math>
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| When palladium is electrochemically charged by hydrogen, the existence of two phases is manifested by a constant [[potential]] of approximately +50 mV compared to the [[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]].
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| ==See also==
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| *[[Dynamic hydrogen electrode]]
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| *[[Reversible hydrogen electrode]]
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| ==References==
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| {{reflist}}
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| [[Category:Electrodes]]
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| [[Category:Palladium]]
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| [[Category:Hydrogen technologies]]
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| {{physical-chemistry-stub}}
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Latest revision as of 02:41, 16 October 2014
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