Standard hydrogen electrode

From Academic Kids

A standard hydrogen electrode (abbreviated SHE) is a redox electrode which is placed in the basis of the thermodynamic scale of oxidation-reduction potentials. Its standard electrode potential (E0) is declared to be zero. Potentials of any other electrodes are compared with the standard hydrogen electrode.

Missing image
Standard_hydrogen_electrode.jpg


Hydrogen electrode is based on the redox half cell:
2H+(aq) + 2e- → H2(g)

This redox reaction occurs at platinized platinum electrode. Usage of such electrode is caused by several factors:

  • necessity to employ electrode with very large square. The more electrode square, the faster electrode kinetics.
  • necessity to use electrode material which can adsorb hydrogen at its interface. This factor also improve electrode kinetics.


Nernst equation should be written as:
<math>E={RT \over F}\ln {a_{H^+} \over (p_{H2})^{1/2}}<math>
or
<math>E=-{RT \over F}pH - {RT \over 2F}\ln {p_{H2}}<math>
where

Interference

Because of the high adsorption activity of the platinized platinum electrode, it's very important to protect electrode surface and solution for the presence of organic substances as well as oxygen of atmosphere.

Construction

The scheme of the standard hydrogen electrode:
1 - platinized platinum electrode
2 - hydrogen blow
3 - solution of the acid with activity of H+ = 1 mol/l
4 - hydroseal for prevention of the oxygen inteference
5 - reservoir through the which the second half-element of the galvanic cell should be attached

See also

Template:Chem-stubnl:Waterstof-elektrode

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