The palladium-hydrogen electrode (abbreviation: Pd/H₂) is one of the common

reference electrode A reference electrode is an electrode which has a stable and well-known electrode potential. The high stability of the electrode potential is usually reached by employing a redox system with constant (buffered or saturated) concentrations of each ...

s used in electrochemical study. Most of its characteristics are similar to the

standard hydrogen electrode The standard hydrogen electrode (abbreviated SHE), is a redox electrode which forms the basis of the thermodynamic scale of oxidation-reduction potentials. Its absolute electrode potential is estimated to be at 25 °C, but to form a basis ...

(with

platinum Platinum is a chemical element with the symbol Pt and atomic number 78. It is a dense, malleable, ductile, highly unreactive, precious, silverish-white transition metal. Its name originates from Spanish , a diminutive of "silver". Pla ...

). But

palladium Palladium is a chemical element with the symbol Pd and atomic number 46. It is a rare and lustrous silvery-white metal discovered in 1803 by the English chemist William Hyde Wollaston. He named it after the asteroid Pallas, which was itself na ...

has one significant feature—the capability to absorb (dissolve into itself) molecular

hydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic ...

.Palladium-hydrogen electrodes for coulometric titration
/ref>

Electrode operation

Two phases can coexist in palladium when hydrogen is absorbed: *alpha-phase at hydrogen concentration less than 0.025 atoms per atom of palladium *beta-phase at hydrogen concentration corresponding to the

non-stoichiometric In chemistry, non-stoichiometric compounds are chemical compounds, almost always solid inorganic compounds, having elemental composition whose proportions cannot be represented by a ratio of small natural numbers (i.e. an empirical formula); m ...

formula PdH_0.6 The electrochemical behaviour of a palladium electrode in equilibrium with H₃O⁺ ions in solution parallels the behaviour of palladium with molecular hydrogen :

\tfrac \mathrm_2  = \mathrm_ = \mathrm_

Thus the equilibrium is controlled in one case by the partial pressure or

fugacity In chemical thermodynamics, the fugacity of a real gas is an effective partial pressure which replaces the mechanical partial pressure in an accurate computation of the chemical equilibrium constant. It is equal to the pressure of an ideal gas whic ...

of molecular hydrogen and in other case—by activity of H⁺-ions in solution. :

E=E^0 + \ln

When palladium is electrochemically charged by hydrogen, the existence of two phases is manifested by a constant

potential Potential generally refers to a currently unrealized ability. The term is used in a wide variety of fields, from physics to the social sciences to indicate things that are in a state where they are able to change in ways ranging from the simple r ...

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

. 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

References

External links

Electrochimica Acta
Electrodes Palladium Hydrogen technologies {{electrochem-stub

Electrode operation

See also

References

External links