Page 27 - MODERN ASPECTS OF ELECTROCHEMISTRY

Zbigniew KoczorowskiA
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discussed. This is followed by a review of the use of voltaic cells to
determine the real potentials of ions in liquid and solid systems; the Volta
potentials of in situ, ex situ, and non situ electrodes and their importance
in determining absolute electrode potential; and the Volta potentials of
liquid-liquid systems.= Finally, the surface potential change upon adsorp-
tion of various species and the surface potentials of pure solvents are
discussed.
In addition, this review has been prepared to promote the term
“voltaic cell” in honor of Alessandro Volta, the inventor of “the pile,” i.e.,=
an electrochemical generator of electricity. Up to now this name has been
used in only a few papers. 19-21 This term is a logical analogue to the term
“galvanic cell,” particularly in discussions of “Volta potential” and “Gal-
vani potential” concepts.=

II.A ELECTRIFIED INTERFACESAAND THEIR ELECTRICALA
POTENTIALS
An electric potential drop across the boundary between two dissimiliar
phases as well as at their surfaces exposed to a neutral gas phase is the
most characteristic feature of every interface and surface electrified due
to ion separation and dipole orientation.= This charge separation is usually
described as an ionic double layer.=
The system of distinctions and terminology of the thermodynamic
and electric potentials introduced by Lange is still very useful and recom-
mended for describing all electrified phases and interphases. 1,13,22,23
Therefore these potentials can be assigned to metal/solution (M/s), as well
as the liquid/liquid boundaries 15,16,24 created at the interfaces of two
immisciblp electrolyte solutions: water (w) and an organic solvent (s).
M
The Volta potential, ∆ S Ψ,veryoften called the contactpotential, is
the difference between the outer potentials of the phases, which are in
electrochemical equilibrium in regard to the charged species, i.e.,= ions or
electrons. Each two-phase electrochemical system, including a w/s sys-
tem, may be characterized by the commonly known relation:

M M _ s
i
∆ S Ψ= –z F (α i i α ) (1)
s
M
where α and α i as are the real potentials of the charged species i, defined
i
as the sum of its chemical potential and the electrical term containing the
surface potential of the phase; e.g., for the solution: