ABSTRACT The electrochemical behavior and diffusion of ferrocene and ferricenium in aqueous and organic medium was investigated by voltammetry on a platinum electrode. Both the ferrocene molecules and the ferricenium cations still show redox activity in both aqueous solution containing sulfuric acid and in dichloromethane solution containing tetrabutylammonium tetrafluoroborate. The results indicated that redox reactions of ferrocene/ ferricenium couple were a reversible process of diffusion-controlled single electron transfer in both studied solutions. The anodic and the cathodic peak potentials, as well as the corresponding anodic and cathodic peak currents, were obtained at different scan rates (0.05, 0.10, 0.30, 0.50 V.s -1 ). The diffusion coefficients have been calculated using the Randles-Sevcik equation; calculations show that the diffusion coefficients of ferrocene and ferricenium in aqueous solutions are smaller than those in organic solution

A Khelef

N S Neghmouche

T Lanez

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January – March       2010               RJPBCS            Volume 1 Issue 1               Page No. 76
Research Journal of Pharmaceutical, Biological and Chemical 
Sciences
Investigation of diffusion of ferrocene and ferricenium in aqueous and 
organic medium using voltammetry techniques 
NS.  Neghmouche, A. Khelef, T. Lanez*
VTRS laboratory, Institute of sciences and technology, University Centre of El-Oued, B.P.789, 39000, El-Oued, 
Algeria
ABSTRACT
The electrochemical behavior and diffusion of ferrocene and ferricenium in aqueous and organic 
medium was investigated by voltammetry on a platinum electrode. Both the ferrocene molecules and the 
ferricenium cations still show redox activity in both aqueous solution containing sulfuric acid and in 
dichloromethane solution containing tetrabutylammonium tetrafluoroborate.  The results indicated that redox 
reactions of ferrocene/ ferricenium couple were a reversible process of diffusion-controlled single electron 
transfer in both studied solutions. The anodic and the cathodic peak potentials, as well as the corresponding 
anodic and cathodic peak currents, were obtained at different scan rates (0.05, 0.10, 0.30, 0.50 V.s-1).  The 
diffusion coefficients have been calculated using the Randles-Sevcik equation; calculations show that the 
diffusion coefficients of ferrocene and ferricenium in aqueous solutions are smaller than those in organic 
solution. 
Keywords: Cyclic voltammetry, diffusion coefficient, ferrocene, half-wave potential, Randles-Sevcik equation. 
*Corresponding author
E-mail: t_lanez@yahoo.fr
January – March       2010               RJPBCS            Volume 1 Issue 1               Page No. 77
INTRODUCTION
Electrochemical study of organic compounds and in particular cyclic voltammetry is an efficient and 
convenient approach for the in situ characterization of mass transfer of probe molecules; it has been used to 
evaluate the diffusion of redox-active reagents in many systems [1–4]. In addition, because the redox reaction 
of ferrocene/ferricenium Fe (C5H5)/Fe(C5H5)2
+ couple is reversible and Nernstian in the majority of organic 
solutions and its redox potential is little influenced by such solvents, Fe(C5H5)2 is usually chosen as redox probe 
for non-aqueous system [5]. 
Electrochemical proprieties 
It is well known that ferrocene easily undergoes one electron oxidation to form ferricenium cation 
Fe(C5H5)2
+in a reversible manner[6-9] figure (1). Thus, we investigated the ferrocene electrochemical behaviors 
in organic and aqueous mediums.  
Figure 1: Reversible mono electronic oxidation of ferrocene 
In previous work [10] we reported the electrochemical behavior of Fe (C5H5)/Fe(C5H5)2 couple on a 
classy carbon electrode.  In present work, we report electrochemical behavior of ferrocene in dichloromethane 
and in aqueous ethanol.  Electrochemical behavior of ferrocene and ferricenium couple in both solutions was 
investigated by cyclic voltammetry using conventional platinum (Pt) electrode.
EXPERIMENTAL
Materials 
Electrochemical experiments were carried out using a potentiostat type voltalab 40. All experiments 
were carried out in dichloromethane or in aqueous ethanol. tetrabutylammonium tetrafluoroborate Bu4NBF4
was used as supporting electrolyte 10-1 M. A three electrode configuration was used. The working electrode 
was a platinum disc (diameter 2 mm) sealed in glass. The reference electrode was a saturated calomel 
electrode (SCE). The counter electrode was a platinum wire. Potentials were calibrated against ferrocene. The 
experiments were carried out under a moisture free argon atmosphere. Cyclic voltammetry was measured for 
a dichloromethane and aqueous ethanol solutions of ferrocene (10-3 M) at scan rates equal to 0.05, 0.10, 0.30 
and 0.50 V.s-1.
Chemicals
Ferrocene (Fluka, 98% purity) and sulfuric acid (Fluka, 99% purity ) were used as received, the 
electrolyte salt tetrabutylammonium tetrafluoroborate Bu4NBF4 (Fluka, electrochemical grade 99% purity) was 
dried for 1 h at 105 °C before use. Dichloromethane (Sigma–Aldrich, 99.9% purity) was dried over molecular 
sieves before use. Argon plunging tube bottle was provided by Linde (Linde gas algérie). All the freshly 
prepared solutions were degassed under argon gas flow before experiments.    
January – March       2010               
Cyclic voltammetry  
Cyclic voltammograms of ferrocene were performed at concentration of 
dichloromethane and in aqueous ethanol solutions with respectively 10
supporting electrolyte, each solution was scanned at scan rate
resultant CV curves and the electrochemical parameters 
Figure 2:  Cyclic voltammetry of ferrocene  1  mM and 100 mM Bu
of ferrocene in ethanol/aq.H2SO4 (
electrode, and CSE reference electrode at 
Epa
v(mV/s)
                         medium 
Organic
50 526
100 542
300 -
500 -
Table 1: electrochemical parameters obtained from 
The peak potential spacing (ΔEp)
and 0.064 V for the ferrocene in ethanol/water
ΔEp = 0.059 V at 298 K [11]. The discrepancy
solution resistance. 
The anodic and the cathodic peak heights as function of the square ro
platinum electrode are shown in figure 
RJPBCS            Volume 1 Issue 1               Page No. 
RESULTS AND DISCUSSION
10-3 M of ferrocene in deoxygenated 
-1 M of Bu4NBF4
equal to 0.05, 0.10, 0.30 and 0.50 V.s
are shown respectively in figure 2 and table 1
4NBF4 in CH2Cl2 (left
right) at 2 mm diameter platinum working electrode, Pt counter 
(0.05, 0.10, 0.30, 0.50 V.s-1).
(mV) Epc (mV) ΔEp
Aqueous Organic Aqueous Organic
290 403 226 123
291 399 217 143
303 - 213 -
310 - 210 -
voltammograms of figure 2
, at scan rate equal to 0.05 V.s-1 is 0.123 V for the ferrocene 
. A fast, reversible, one-electron transfer would ideally have
from this ideal value is attributed to slow electron
ot of the scanning rate for 
3. The obtained linear relationship indicates clear diffusion character.  
78
and H2SO4 as 
-1. The 
.
) and 1  mM 
(mV)
Aqueous 
64
74
90
100
in CH2Cl2
a 
transfers and 
January – March       2010               RJPBCS            Volume 1 Issue 1               Page No. 79
As it can be seen from figure 3, the ratio of the anodic and cathodic current peak heights is close to one for 
both solutions; this indicates the reversible character of the oxidation of ferrocene in both studied medium. 
7 . 0 7 . 5 8 . 0 8 . 5 9 . 0 9 . 5 1 0 . 0. . . . . . .
- 1 0
- 8
- 6
- 4
- 2
0
2
4
6
8
1 0
v
1 / 2
( m V / s )
1 / 2
i p
(µ
A
/c
m
2
)
6 8 1 0 1 2 1 4 1 6 1 8 2 0 2 2 2 4
- 3 0
- 2 5
- 2 0
- 1 5
- 1 0
- 5
0
5
1 0
1 5
2 0
2 5
3 0
-
-
-
-
i p(
µ
A
/c
m
2 )
v 1 / 2 ( m V / s ) 1 / 2
              
Figure 3: The anodic and the cathodic peak heights as function of the square root of the scanning 
rate for platinum electrode in CH2Cl2 (bleu) and in ethanol/H2SO4 (red) at 2 mm diameter Pt 
working electrode.
Diffusion of ferrocene and ferricenium 
In general, the peak current of diffusion controlled reversible or quasi-reversible electrochemical 
reaction follows Randles–Sevcik equation [12]:
i_p = 0.4463nF√nFD / RT) AC √v                          (1)
Where ip: the peak current, n: the number of electrons, F: Faraday constant, T: the temperature in Kelvin, R: 
the gas constant, A: the surface area of the working electrode, D: the diffusion coefficient of the electroactive 
species, C: the bulk concentration of the electroactive species and v: the scan rate of voltammograms. Thus, 
the diffusion coefficients for ferrocene and ferricenium at 298K are calculated from the slope of the plot of ip 
versus √ . Table 2 lists calculated diffusion coefficients for ferrocene and ferricenium in both aqueous and 
organic solutions.
Medium Dferricenum x 10
6cm2/s Dferricenum x 10
6cm2/s
CH2Cl2 19.21 22.47
ethanol/aq.H2SO4 12.35 14.45
Table 2: Diffusion coefficients of ferrocene and ferricenium in organic and aqueous medium at 
298K
Electrochemical measurement on rotating disk electrode
The diffusion coefficients of ferrocene organic and aqueous medium were also measured on a 
rotating disk electrode using the same conditions as used for voltammetry cyclic. 
The calculations were based on the Randles-Sevcik equation. That means the anodic peak height of 
ferrocene oxidation (obtained from voltammetry cyclic measurements) was measured in quiescent solutions 
on both electrodes and in both medium. The obtained polarogramme are showed in figure 4. 
January – March       2010               RJPBCS            Volume 1 Issue 1               Page No. 80
0.0 0.2 0.4 0.6 0.8
0
5
10
15
20
25
 400 rpm
 600 rpm
 800 rpm
 1000 rpm i(
µ
A
/c
m
2
)
E(V/ECS)
Figure 4:  Polarogramme of ferrocene  1  mM and 100 mM Bu4NBF4 in CH2Cl2 (left) and 1  mM of 
ferrocene in ethanol/H2SO4 (right) at 2 mm diameter platinum  working electrode, Pt counter 
electrode, and CSE reference electrode at 0.50 V.s-1. (Rotating rate 400, 600, 800, 1000 rpm)
The anodic peak heights as function of the square root of the rotating disk electrode rate for platinum 
electrode are shown in figure 4. The coefficient diffusion for ferrocene is calculated from figure 4 as follows:
20 22 24 26 28 30 32
18,5
19,0
19,5
20,0
20,5
21,0
21,5
i lim
(µ
A
/c
m
2
)
1/2
12 14 16 18 20 22 24 26 28 30 32 34
10
12
14
16
18
20
22
i lim
(µ
A
/c
m
2 )
1/2
Figure 5: The diffusion current as function of the square root of the rotating rate for platinum 
electrode in CH2Cl2 (bleu) and in ethanol/H2SO4 (red)
From Figure 5 the slope of the line gives
P = i/ ω^ (1/2)                  (2)
On another hand the limited current is given by,
I = nFADC/δ             (3)
Whereas: n, number of electrons
          F: is the Faraday (9.65.104 C/mol)
          A: is the area of the working electrode (cm2). 
          D: is the coefficient diffusion (cm2.s-1)
         C: is the concentration (mol/cm3), in our case is equal to10-3 mol/l 
Replacing equations 2 and 3 in 4 gives,
January – March       2010               RJPBCS            Volume 1 Issue 1               Page No. 81
D^ (2/3) = (P1.61γ^ (1/6)/(nFAC√2π)       (4)
For a rotating rate of the working electrode equal to 400 t/min., the coefficient diffusion of ferrocene in 
dichlormethane is.
D = 19.21 x 10-6cm2.s-1
The coefficient diffusion of ferrocene in aqueous ethanol is calculated as above. Table 3 summarize the 
obtained values.  
Medium Dferricenum x 10
6cm2/s
CH2Cl2 1.95 19.21
ethanol/aq.H2SO4 1.34 12.35
Table 3: Diffusion coefficients of ferrocene calculated from polarogramme of figure 
CONCLUSION
Voltammetry analysis on a fixed and on a rotating electrode of ferrocene in aqueous and organic 
solutions indicates that the electrochemical reaction of ferrocene in both studied solutions  is a diffusion 
controlled process, namely, single electron transfer reversible electrochemical process. The diffusion 
coefficients of ferricenium and ferrocene in both organic and aqueous solutions are almost in the same order 
of magnitude. This is most probably because the size of the solvated ferricenium and ferrocene is much 
smaller than the size of the pores of three-dimensional networks.
ACKNOWLEDGMENTS
Support of the work by the laboratoire de valorisation et promotion des resources sahariennes is 
gratefully acknowledged. We would like to thank Professor M. SAIDI, for his help. 
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[9]  Simenel AA, Kuzmenko YV, Morozova EA, Ilyin MM, Gun’ko IF, Snegur LV. Journal of Organometallic 
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Investigation of diffusion of ferrocene and ferricenium in aqueous and organic medium using voltammetry techniques

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Investigation of diffusion of ferrocene and ferricenium in aqueous and organic medium using voltammetry techniques

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