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Journal of Electroanalytical Chemistry 486 (2000) 85–90
Short Communication
On the work function of the gas exposed electrode surfaces in
solid state electrochemistry
C.G. Vayenas *
Department of Chemical Engineering, 1 Caratheodory St ., Uniersity of Patras, Patras 26500, Greece
Received 8 March 2000; accepted 20 March 2000
In his book review [1] of Modern Aspects of Electro-
chemistry No. 29 edited by J.O’M. Bockris, B.E. Con-
way and R.E. White, Plenum Press, NY 1996 Professor
Roger Parsons wrote, referring to pages 70–100 of
Chapter 2 by C.G. Vayenas, M.M. Jaksic, S.I. Bebelis
and S.N. Neophytides [2], that ‘‘ T his section includes
the erroneous claim that work function changes can be
measured from the potential difference of a galanic cell.
This rests on the argument that the outer potential of a
catalyst particle remains unchanged as charge is supplied
to it because all the charge remains located at the
interface with the support .’’
The purpose of this short communication is to ad-
dress the above point and show that the above state-
ment is not an erroneous claim but an experimental fact
in solid state electrochemistry that has been confirmed
by several electrochemical and surface science
laboratories.
We denote, as in Ref. [2], by e
c
the work function of
the gas exposed electrode surface and by V
WR
the poten-
tial of the working (W) catalyst electrode with respect
to a reference (R) electrode (Fig. 1).
What is stated in Ref. [2] and contested in Ref. [1] is
the equation:
(e
c
) =e V
WR
(1)
where (e
c
) and V
WR
are, respectively, the changes
in the gas-exposed catalyst–electrode surface work
function and ohmic drop free catalyst–electrode poten-
tial induced either by using a potentiostat or by chang-
ing the gaseous composition over the catalyst electrode.
1. Experimental evidence
The validity of Eq. (1) has been shown using both the
Kelvin probe technique [3–7] and the UPS technique
[8] (use of the electron cutoff energy in UPS experi-
ments) to measure the work function of the gas exposed
electrode surfaces (Pt [3,4,7], Ag [8], IrO
2
[5,6]) in
contact with Yttria-stabilized-Zirconia (YSZ), an O
2 -
conductor [3 – 8], and -Al
2
O
3
, a Na
+
conductor
[3,4,6,7], at temperatures of 200–550°C. In addition to
the group which first reported this experimental finding
[2–4] the groups of Go ¨pel [8], Comninellis [5,6], Haller
[7] and Imbihl [9] have confirmed its validity (Fig. 2).
Torkelsen and Raaen [10] have found up to 1 eV
change in e upon changing the catalyst-counter elec-
trode potential by 6 V (no reference electrode was
used), while significant deviations from Eq. (1) have
been reported only by Emery et al. [11]. In this study,
however, it is not clear if the uncompensated IR drop
has been subtracted from the measured V
WR
values as
was done in all other studies [3–8]. The point is that in
all studies significant reversible changes in e have been
observed, and in most cases Eq. (1) has been found to
hold very well (Fig. 2). Eq. (1) holds not only at steady
state (Fig. 2) but also reasonably well during galvanos-
tatic transients (Fig. 3). As every experimental ‘law’,
Eq. (1) has its limitations: Deviations for high anodic
or cathodic overpotentials exist (Fig. 2), and this has
also been observed by the groups which have estab-
lished its validity.
2. Theoretical implications
We denote by ¯ and the electrochemical and
chemical potential, respectively, of electrons in the
* Tel.: +30-61-997576; fax: +30-61-997269.
E -mail address: cat@zeus.chemeng.upatras.gr (C.G. Vayenas)
0022-0728/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved.
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