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'All solid' pH sensor
Sensors and Actuators
215
B, 2 (1990) 215-217
‘All Solid’ pH !Semsor F. TEDJAR and L. ZERROUAL Unit6 de RPcherche Electrochimie,
Ines Chink,
Setif (Algerio)
(Received September 29, 1987; in revised form February 22, 1990; accepted February 26, 1990)
Abstract
2. Experimental
Lead dioxide is used as the inner reference for a pH sensor in an ‘all solid’ glass electrode. The response of the electrode has been studied for a and /3 forms of lead dioxide produced chemically or electrochemically.
2.1. Materials The methods of preparation of the PbGz samples included in the present study are summarized in Table 1. The samples was identified by X-ray diffraction using Ka X-rays from a Cu cathode.
1. Introduction The measurement of the proton concentration in a solution is usually carried out with a glass electrode associated with an external reference. The glass electrode is a glass membrane with an internal reference in a solution of known pH. Those reference electrodes are often a saturated calomel electrode or an Ag/AgCl electrode in KCl. From 1950, studies of replacing the ‘internal reference/liquid solution’ chain by an ‘all solid’ reference were done. Sodium, tungsten brass and insertion materials such as LixV60,3 and Li,Ti$ were used by various authors [l-5]. More recently, Deportes et al. [6] showed the possibility of using MnO, as an internal reference. However, better results were obtained with a composite electrode of y MnOJblack acetylene. The use of the black is necessary to realize a mixed (protonic/electronic) conductor. The electroactive manganese dioxides have a poor intrinsic conductivity [7j and require the use of carbon black, graphite or black acetylene, as in a Leclanchi cathode [g-lo]. In the present work lead dioxide has been tried as an ‘all solid’ internal reference for a glass electrode. PbGz exists in fi and a forms [ 11, 121, both of which are present in the positive plate of lead/acid batteries. This electrode works without carbon. It is well known that the a form of lead dioxide supplies acceptable conductivity to the electrode. On the other hand, Gamier et al. [ 131 showed by quasielastic neutron diffraction and differential scanning calorimetry that internal protons exist in lead dioxide, so that it can be used as a pH sensor [141. 09254005/90/$3.50
2.2. Apparatus and Procedure The voltage measurements were carried out in the cell shown in Fig. 1 with a high-impedance millivoltmeter (Taccussel Isis 20000). TABLE 1. Specification of materials included in the study (composition of industrial paste: 55% 3PbO.PbSO,.H,O) Samples
Preparation
Phase
Electrochemical oxidation of industrial paste in H+ media
B
Same conditions as (a) in neutral media ChemiCal oxidation of Pbz+ by S,O,- in acid media Same as (c) but in basic media
a
B a
_I
5-I
Fig. 1. Cell used for measurements. 1, saturated calomel electrode; 2, Plexiglass compartment; 3, glass electrode, internal solution; 4, solid reference; 5, copper contact.
0 Elsevier Sequoia/Printed
in The Netherlands
216 E in visce
E in v/see
I
I
::-:‘- /
040
I 10
5
-
w
(a)Eotnv/sce
E in V/SCe
I
0.80
-lo
W-
(4
\\, O
10
5
PH
IO
5
(4 0
ti
Fig. 2. Measured voltage for the indicating electrode for various samples at 25 “C. (a) and (b) are jI and a PbOz reqxctively, electrochemicaly prepared. (c) and (d) are respectively B and K pbo, chemically precipitated. Dots are experimental points and the line is a least-squams method computerized plot.
A saturated calomel electrode was used as the internal reference in a commercial full glass electrode with the calibrated solution. The solid reference was in the external compartment (Plexiglass) and the contact was ensured by the pressure obtained by the screw on the copper disk (5 in Fig. 1). The buffer solution was a commerical preparation from Ingold and was stirred with a magnetic stirrer. The temperature was kept to the required value ( f0.5 “C) by water circulation. 3. Results and Diacussioo The voltage of the electrode proton concentration is E = C -
indicating
the
determined) and the pH of the internal reference respectively; C is a constant which depends on the nature of both the reference electrodes. As we use the same internal and external reference for the same sample, the variation of E versus the external pH values is assumed to be E = A(T) - (RT/zl;)pH,
(2) From relation (2), the value of the slope must be 59 mV/pH at 25 “C. Figure 2 shows the voltage of each electrode versus the pH of the external solution. For all the samples a straight line is observed as expected, and the values of the slopes are reported in Table 2. km
pH, - pHi)
(1) where pH, and pHi are the external pH (to be (RT/ZF)(
.
9
l-
a
I
-I
900 t
TABLE 2. Slope in mV/decade from cm-ves (1) for the samples as speciiied in Fig. 2 Samples : C
d
Slope in mV/pH 54.8 54.7 46.2 48.5
I
I
20
30
40
I
so
I 1, ‘C
Fig. 3. Variation of the measured voltage with temperature at pH = 1 for samples (a), (b) and (c) as indicated in Fig 2.
217
The /3 PbQ obtained by chemical precipitation presents better linearity; a better slope is also obtained with the /I form obtained electrochemitally. The stability of the electrodes was studied and the results between 20 “C and 50 “C are stmunarized for three samples in Fig. 3. Better stability is also obtained with the electrochemically obtained /I lead dioxide. Thus the fi forms of lead dioxide seem to have the capability to be used as ‘all solid pH sensors, since they had a higher slope (54.8 mV/pH) with better stability (less than 0.5 mV/T). Studies of the stability of the electrodes at more than 100 “C and of the behaviour of the composite electrodes are in progress. References 1 B. P. Nikolsky and E. A. Materova, Solid contact in membrane ion-selective electrode, Ion-Selective Electrode Rev., 7(1985) 3. 2 G. Trumpler, Uber eine neue pestillungweisse der potentiale der Alkali metalle, Efectrochem., 30 (1924) 103. 3 M. M Schutz, 0. Ershov, P. Lepnev and A. Scrgeev, U.S.S.R. Patent, 52 (1979) 2487. 4 A. Fog and S. Athmg, Ion selective measuring electrode device, ht. Patent No. 83/03304. 5 P. Fabry, Internal ionic bridge for ionic solid state sensor, Proc hi ht. Meet. Chemical Sensors, Borhux, France, July 7-10, 1986, p. 473. 6 C. Desportes, M. Forestier and H. Kahil, to be published. 7 J. Brenet and P. Faber, Conductivity of pure and mined metal dioxides, J. Power Sources, 4 (1979) 203. 8 H. Kahil and J. G&ton, Modifications des concentrations interfaciales dans MnO,/noir d’aeetylene, Surf. Technol., 20 (1983) 181. 9 F. Tedjar and J. Guitton, Intluence de l’ion Caz+ sur le
10 11 12 13 14
comportement interfaoial de MnOs, Surf. Technoi., 24 (1985) 115. F. Tedjar and Z. Dib, Etude des properties de surface du noir d’aoctylene, Surf. TechoL, 25 (l-985) 146. J. R. Pearson. Structural studies of pbo,._. Electrochem. Technof., 5 (1967) 323. L. Zerroual. Doctorate Thesis, Grenoble, 1985. P. Boher, P. Garnier and J. R. Gavarini. Mise en evidence et localisation des protons dans PbO,, J. Solid State Chem.. 52 (1984) 146. J. Santoro, P. D’Antonio and S. Caulder, Neutron difBac+ tion studies of PbOs, J. Eleetrochem. Sot., 130( 1983) 1451.
Farouk Tedjar received the Ingenieur-Docteur and Docteur es-Sciences degrees from the Polytechnic Institute of Grenoble (France). He is presently director of the Research Unit in Electrochemistry and vice-chairman of research in the University of Setif (Algeria). Before this he was technical manager in a dry cell and lead/acid battery factory in Algeria. His special interests are MnO, and PbOz electrodes and all solid electrochemical systems and he has several publications in journals devoted to surfaces and materials. Lurbi Zerroual has the degree of Docteur in electrochemistry from Grenoble Polytechnic (France). He is assistant professor and president of the scientifk council of the Institute of Chemistry (University of Setif). He has special interest in lead dioxide structures and solid electrolytes and has previous publications in the field of surface technology.
215
B, 2 (1990) 215-217
‘All Solid’ pH !Semsor F. TEDJAR and L. ZERROUAL Unit6 de RPcherche Electrochimie,
Ines Chink,
Setif (Algerio)
(Received September 29, 1987; in revised form February 22, 1990; accepted February 26, 1990)
Abstract
2. Experimental
Lead dioxide is used as the inner reference for a pH sensor in an ‘all solid’ glass electrode. The response of the electrode has been studied for a and /3 forms of lead dioxide produced chemically or electrochemically.
2.1. Materials The methods of preparation of the PbGz samples included in the present study are summarized in Table 1. The samples was identified by X-ray diffraction using Ka X-rays from a Cu cathode.
1. Introduction The measurement of the proton concentration in a solution is usually carried out with a glass electrode associated with an external reference. The glass electrode is a glass membrane with an internal reference in a solution of known pH. Those reference electrodes are often a saturated calomel electrode or an Ag/AgCl electrode in KCl. From 1950, studies of replacing the ‘internal reference/liquid solution’ chain by an ‘all solid’ reference were done. Sodium, tungsten brass and insertion materials such as LixV60,3 and Li,Ti$ were used by various authors [l-5]. More recently, Deportes et al. [6] showed the possibility of using MnO, as an internal reference. However, better results were obtained with a composite electrode of y MnOJblack acetylene. The use of the black is necessary to realize a mixed (protonic/electronic) conductor. The electroactive manganese dioxides have a poor intrinsic conductivity [7j and require the use of carbon black, graphite or black acetylene, as in a Leclanchi cathode [g-lo]. In the present work lead dioxide has been tried as an ‘all solid’ internal reference for a glass electrode. PbGz exists in fi and a forms [ 11, 121, both of which are present in the positive plate of lead/acid batteries. This electrode works without carbon. It is well known that the a form of lead dioxide supplies acceptable conductivity to the electrode. On the other hand, Gamier et al. [ 131 showed by quasielastic neutron diffraction and differential scanning calorimetry that internal protons exist in lead dioxide, so that it can be used as a pH sensor [141. 09254005/90/$3.50
2.2. Apparatus and Procedure The voltage measurements were carried out in the cell shown in Fig. 1 with a high-impedance millivoltmeter (Taccussel Isis 20000). TABLE 1. Specification of materials included in the study (composition of industrial paste: 55% 3PbO.PbSO,.H,O) Samples
Preparation
Phase
Electrochemical oxidation of industrial paste in H+ media
B
Same conditions as (a) in neutral media ChemiCal oxidation of Pbz+ by S,O,- in acid media Same as (c) but in basic media
a
B a
_I
5-I
Fig. 1. Cell used for measurements. 1, saturated calomel electrode; 2, Plexiglass compartment; 3, glass electrode, internal solution; 4, solid reference; 5, copper contact.
0 Elsevier Sequoia/Printed
in The Netherlands
216 E in visce
E in v/see
I
I
::-:‘- /
040
I 10
5
-
w
(a)Eotnv/sce
E in V/SCe
I
0.80
-lo
W-
(4
\\, O
10
5
PH
IO
5
(4 0
ti
Fig. 2. Measured voltage for the indicating electrode for various samples at 25 “C. (a) and (b) are jI and a PbOz reqxctively, electrochemicaly prepared. (c) and (d) are respectively B and K pbo, chemically precipitated. Dots are experimental points and the line is a least-squams method computerized plot.
A saturated calomel electrode was used as the internal reference in a commercial full glass electrode with the calibrated solution. The solid reference was in the external compartment (Plexiglass) and the contact was ensured by the pressure obtained by the screw on the copper disk (5 in Fig. 1). The buffer solution was a commerical preparation from Ingold and was stirred with a magnetic stirrer. The temperature was kept to the required value ( f0.5 “C) by water circulation. 3. Results and Diacussioo The voltage of the electrode proton concentration is E = C -
indicating
the
determined) and the pH of the internal reference respectively; C is a constant which depends on the nature of both the reference electrodes. As we use the same internal and external reference for the same sample, the variation of E versus the external pH values is assumed to be E = A(T) - (RT/zl;)pH,
(2) From relation (2), the value of the slope must be 59 mV/pH at 25 “C. Figure 2 shows the voltage of each electrode versus the pH of the external solution. For all the samples a straight line is observed as expected, and the values of the slopes are reported in Table 2. km
pH, - pHi)
(1) where pH, and pHi are the external pH (to be (RT/ZF)(
.
9
l-
a
I
-I
900 t
TABLE 2. Slope in mV/decade from cm-ves (1) for the samples as speciiied in Fig. 2 Samples : C
d
Slope in mV/pH 54.8 54.7 46.2 48.5
I
I
20
30
40
I
so
I 1, ‘C
Fig. 3. Variation of the measured voltage with temperature at pH = 1 for samples (a), (b) and (c) as indicated in Fig 2.
217
The /3 PbQ obtained by chemical precipitation presents better linearity; a better slope is also obtained with the /I form obtained electrochemitally. The stability of the electrodes was studied and the results between 20 “C and 50 “C are stmunarized for three samples in Fig. 3. Better stability is also obtained with the electrochemically obtained /I lead dioxide. Thus the fi forms of lead dioxide seem to have the capability to be used as ‘all solid pH sensors, since they had a higher slope (54.8 mV/pH) with better stability (less than 0.5 mV/T). Studies of the stability of the electrodes at more than 100 “C and of the behaviour of the composite electrodes are in progress. References 1 B. P. Nikolsky and E. A. Materova, Solid contact in membrane ion-selective electrode, Ion-Selective Electrode Rev., 7(1985) 3. 2 G. Trumpler, Uber eine neue pestillungweisse der potentiale der Alkali metalle, Efectrochem., 30 (1924) 103. 3 M. M Schutz, 0. Ershov, P. Lepnev and A. Scrgeev, U.S.S.R. Patent, 52 (1979) 2487. 4 A. Fog and S. Athmg, Ion selective measuring electrode device, ht. Patent No. 83/03304. 5 P. Fabry, Internal ionic bridge for ionic solid state sensor, Proc hi ht. Meet. Chemical Sensors, Borhux, France, July 7-10, 1986, p. 473. 6 C. Desportes, M. Forestier and H. Kahil, to be published. 7 J. Brenet and P. Faber, Conductivity of pure and mined metal dioxides, J. Power Sources, 4 (1979) 203. 8 H. Kahil and J. G&ton, Modifications des concentrations interfaciales dans MnO,/noir d’aeetylene, Surf. Technol., 20 (1983) 181. 9 F. Tedjar and J. Guitton, Intluence de l’ion Caz+ sur le
10 11 12 13 14
comportement interfaoial de MnOs, Surf. Technoi., 24 (1985) 115. F. Tedjar and Z. Dib, Etude des properties de surface du noir d’aoctylene, Surf. TechoL, 25 (l-985) 146. J. R. Pearson. Structural studies of pbo,._. Electrochem. Technof., 5 (1967) 323. L. Zerroual. Doctorate Thesis, Grenoble, 1985. P. Boher, P. Garnier and J. R. Gavarini. Mise en evidence et localisation des protons dans PbO,, J. Solid State Chem.. 52 (1984) 146. J. Santoro, P. D’Antonio and S. Caulder, Neutron difBac+ tion studies of PbOs, J. Eleetrochem. Sot., 130( 1983) 1451.
Farouk Tedjar received the Ingenieur-Docteur and Docteur es-Sciences degrees from the Polytechnic Institute of Grenoble (France). He is presently director of the Research Unit in Electrochemistry and vice-chairman of research in the University of Setif (Algeria). Before this he was technical manager in a dry cell and lead/acid battery factory in Algeria. His special interests are MnO, and PbOz electrodes and all solid electrochemical systems and he has several publications in journals devoted to surfaces and materials. Lurbi Zerroual has the degree of Docteur in electrochemistry from Grenoble Polytechnic (France). He is assistant professor and president of the scientifk council of the Institute of Chemistry (University of Setif). He has special interest in lead dioxide structures and solid electrolytes and has previous publications in the field of surface technology.