Page 33 - MODERN ASPECTS OF ELECTROCHEMISTRY

Zbigniew Koczorowski
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Figure 4. The potential changes measured at the
interfaces formed by the nonpolar solvent-water and
polar solvent-water systems.=

IV. EXPERIMENTAL METHODS FOR INVESTIGATINGI
VOLTAIC CELLSA
The electronic woÀ function maybe found byeither direct or indirect
methods. The absolute value of φ is determined bystudying the emission
x
e
of electrons from the given surface.= The indirect methods [i.e.,= investiga -
tion of the external beam of electrons, or by measuring the Volta potentials
(Sections II and III)] give the relative magnitudes (for example, the
difference in the woÀ= functions of an investigated and a reference
surface). It is worth noting that the voltaic cell gives the arithmetic mean
woÀ=function of a heterogeneous surface (for example, in the presence of
adsorbate), whereas direct methods give an average value that is weighted
in favor of low woÀ= function paths.= In contrast to the voltaic cell
measurement, emission techniques are not equilibrium methods.= Presen -
tation of emission methods is outside the scope of this review.
The main difficulty in measuring the compensation voltage of voltaic
cells is the very large resistance of the system caused by the presence of
a dielectric gas phase.= Therefore there are two possibilities for solving the
problem: reduce this resistance or measure the woÀ=of the charge transfer
across the dielectric. The first possibility is accomplished by the ionizing
method and the second by condenser and jet methods.=
The ionizing electrode method, also called the radioactivð or ionizing
probe, requires a radioactive source to ionize the gas gap and a high-