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Study of the proton conductor H(H2O)nBiO3
Materials
Chemistry
andphysics,
SHORT
COMMUNICATION
I.5 (1986)161-112
167
STUDY OF THE PROTON CCNDWIOR H(H.&Bs3
Q. LE THI,
J.P.
Laboratoire (U.A. 444), (France) Received
BESSE
and R. CHEVALIER
de Cristallographie et Physico-Chimie des Materiaux, Universite de Clermont-II, B.P. 45, 63170 Aubiere
7 October
; accepted
1985
4 March
1986
ABSTRACT
H(H20)Bi03 was prepared from KBi03 by ion exchange with 9N sulfuric acid. Its structure, like isotype cubic KSb03, consists of a covalent framework of octahedra sharing edges and corners bounding a network of channels in which the K8 ions are situated. Such a structure favors cation mobility and enables numerous exchange reactions. The proton exchange compound has a high proton Results are given for three hydration levels, where conductivity. conductivity varies over approximately four orders of magnitude. Comparison with the conductivity of H(H20)Sb03 isotypes is made.
INTRODUCTION Much ducting
research
has been
materials
One approach, workers,
has been
is to address emphasis
enough
to enable
Cation had been
the problem
conduction
investigated
conversion fruitful
on novel and sensor
by several
from a structural
structure
which
in a three-dimensional by us in cubic
of this work explored
by fine measurement of the materials
the various
[1,2,5,6,7,11], of electron
KSb03
ion condevices.
teams
of
standpoint,
must be open
macroanionic phases
possible
exchange
species
reac-
localized
[ 6,71, the ionic conducti-
1111 and its mechanism
applications
matrix
[.l to 111. In
cation
the mobile
density
investigated
and electrochemical
0254XX84/86/$3.50
years
ion movement.
tions were
[8,111
found
on the receptor
the course
vity
in recent
for use in energy
which
laying
done
were
studied
developed.
0 Elsevier Sequoia/Printed inThe Netherlands
168
As already observed with other types of ion exchange phases, treatment of KSbO3 with aqueous acid replaces cations by protons and water molecules
(or oxonium ions) and thereby indirectly gives
proton conductors HSb03.xH20 [6,11]. The work carried out by us on these phases 16,111 had shown that conduction depends on various factors, most obviously the volumetric proton concentration and the nature of the protonated species, but also the interatomic distances in the hydrogen bond and its polarization, which affect the energies of the processes involved. Tight control of water content is clearly essential to the study of proton conduction in these materials. The present work reports a study of H(H20),Bi03 phases undertaken to acquire fuller knowledge of ion conductors with a threedimensional matrix particularly as regards the influence of hydration on their electrical properties. Synthesis of the KBi03 phase This compound was obtained by the method described by R. Scholder and H. Stobbe [12] involving oxidation with bromine of a solution of bismuth trioxide in potassium hydroxide. A brown material was obtained which crystallized in a cubic lattice with a = 10.020 (5) i and space group Im3. This phase is an isotype of the cubic KSb03 type compounds. No line due to impurities was visible on the diffractogram. As with many other ion exchange phases the alkali metal cations of KBi03 can be exchanged for oxonium ions or protons and water molecules. Here, elution with 9N sulfuric acid for about 48 hours followed by washing with distilled water to neutrality and then drying over sulfuric acid at room temperature gave a solid exchange product. Measurement of mass loss, potassium assay by flame emission spectrophotometry of both product and filtrate and assay of Bi(V) and total Bi showed that exchange was 98 % com3fB .5@ plete, and indicated the formula H1_n(H20)Bin Bi '3+n' 1/3H20 with n = 0.1. The structure of the exchange product was of type cubic KSb03 with a = 9.815 (5) i and space group Im3.
169
Given structural results obtained previously the tunnels of 120 the anionic Bi12036 skeleton may reasonably be supposed to be oc48 cupied by both potassium ions and Bi404 units analogous to those found in the Bi3Ru3011 phase [ 131.
This result calls to mind those
of Trehoux (141 who in pyrochlor type bismuth phases found potassium and trivalent bismuth at the same crystallographic site. During the exchange, however, the existing lines widen and the relative intensities of several lines, (loo), (400) for instance (Fig. 11, change markedly. The lattice parameter a = 9.815 (5) i is smaller thanthat of the starting material, a = 10.020 (5) i.
a
0
14
18
22
26
30
34
38
42
46
50
54
58
62 2
66 THETA
C’)
b
2 0
2-
mm -f*\DID P-l.?
-0 -w
2 m
58
62
22
” LB
-
13
14
10
22
26
30
34
30
42
46
50
54
66 2 THETA
--.
C9
Fig. 1. X-ray diffractograms of : a) KBi03.1/3H20; b) acid phase.
170
The exchange product H(H20)nBi03 is thermally less stable than KBi03. Loss of water occurs at room temperature and hydrolysis of the compound takes place with accompanying loss of order.
Electrical properties and discussion Measurements were made by the AC impedance method between 10 Hz and 1 MHz using a Solartron type 117A transfer function analyzer from - 40°C up to the temperature of decomposition of the material. A measuring cell developed by us was used (ANVAR 85-4832), regulated by two Peltier modules. The electrical resistance of the material was determined by extrapolating the bulk circle. Conductivity curves obtained for three different values of hydration level are given in Fig. 2, along with those obtained by Watelet 1111 for H(H20)o_8 Sb03 and H(H2G)o.33 Sb03 under the same conditions. The following conclusions may be drawn : (i) Conductivity obeys an Arrhenius type law. (ii) Conductivity depends to a great extent on the degree of hydration (4 orders of magnitude between curves 1 and 3). (iii) For equal water concentrations, the bismuth phases are less conductive than the antimony phases. This is expected given the different basicities of the anionic matrices. (iv) The presence of Bi3' along the ternary axes of the lattice does not detectably interfere with proton mobility. (v) Hydrated phases (curves 2 and 3) are sufficiently conductive -5 (u 2O'C = 1.18 x 10-5Q-1cm-1 for n = 0.95 and u 20°C = 5.9 x 10 -' for n = 1.05) to warrant consideration for use in electroS2-lcm chemical applications. This study shows the importance of hydration level for conductivity. For Grotthus type conduction to take place a high concentration of water molecules is necessary so that transfer of protons between donors and receptors can occur optimally, Further study by appropriate NMB methods 181 is required in order to investigate in detail the conduction mechanism.
171
Fi.g. 2. Conductivity curves of H(H20),Bi03 phases. 1. n = 0.20 ; 2. n = 0.95 ; 3. n = 1.05.
172
REFERENCES 1
H. Watelet, J.P. Besse, G. Baud and R. Chevalier, Mat. Res. Bull.,15
2
(1980) 875.
H. Watelet, G. Baud, J.P. Besse and R. Chevalier, Mat. Res. Bull.,17
(1982) 1155.
3
H. Watelet, J.P. Picard, J.P. Besse, G. Baud and R. Chevalier,
4
H. Watelet, J-P, Picard, G. Baud, J.P. Besse and R. Chevalier,
5
J.P. Besse, G. Baud, H. Watelet, M. Capestan and R. Chevalier,
Solid State Ionics,2 (1981) 191. Mat. Res. Bull.,16 (1981) 877. Ann. Chim. Fr.,? (1982) 35. 6
H. Watelet, J.P. Picard, G. Baud, J.P. Besse and R. Chevalier, Mat. Res. Bull.,16
7
0. M'Hamedi, J.P. Besse, G. Baud and R. Chevalier, Mat. Res. Bull .,e
8
(1981) 1131.
(1984) 487.
C. Doremieux-Morin, J.P. Fraissard, J.P. Besse and R. Chevalier, Solid State Ionics,u
9
(1985) 93.
G. Baud, J.P. Besse, M. Capestan and R. Chevalier, IIIe Protonic Workshop, Odense University Press (1985) 203.
10
J.P. Besse, G. Baud, H. Watelet, R. Chevalier and C. DoremiewMorin, 4th International Conference on Solid State Ionic%,
11
Grenoble (1983). H. Watelet, These Doctorat, Universite Clermont-Ferrand
12
R. Scholder and H. Stobbe, 2. Anorg. Allg. Chem.,E
(1983)
(1941)
403. 13
F. Abraham, D. Thomas and G. Nowagrocki, Bull. Sot. Fr. Mineral Crystallogr..98
14
(1975) 25.
J. Trehoux, These Doctorat, Lille 11981).
Chemistry
andphysics,
SHORT
COMMUNICATION
I.5 (1986)161-112
167
STUDY OF THE PROTON CCNDWIOR H(H.&Bs3
Q. LE THI,
J.P.
Laboratoire (U.A. 444), (France) Received
BESSE
and R. CHEVALIER
de Cristallographie et Physico-Chimie des Materiaux, Universite de Clermont-II, B.P. 45, 63170 Aubiere
7 October
; accepted
1985
4 March
1986
ABSTRACT
H(H20)Bi03 was prepared from KBi03 by ion exchange with 9N sulfuric acid. Its structure, like isotype cubic KSb03, consists of a covalent framework of octahedra sharing edges and corners bounding a network of channels in which the K8 ions are situated. Such a structure favors cation mobility and enables numerous exchange reactions. The proton exchange compound has a high proton Results are given for three hydration levels, where conductivity. conductivity varies over approximately four orders of magnitude. Comparison with the conductivity of H(H20)Sb03 isotypes is made.
INTRODUCTION Much ducting
research
has been
materials
One approach, workers,
has been
is to address emphasis
enough
to enable
Cation had been
the problem
conduction
investigated
conversion fruitful
on novel and sensor
by several
from a structural
structure
which
in a three-dimensional by us in cubic
of this work explored
by fine measurement of the materials
the various
[1,2,5,6,7,11], of electron
KSb03
ion condevices.
teams
of
standpoint,
must be open
macroanionic phases
possible
exchange
species
reac-
localized
[ 6,71, the ionic conducti-
1111 and its mechanism
applications
matrix
[.l to 111. In
cation
the mobile
density
investigated
and electrochemical
0254XX84/86/$3.50
years
ion movement.
tions were
[8,111
found
on the receptor
the course
vity
in recent
for use in energy
which
laying
done
were
studied
developed.
0 Elsevier Sequoia/Printed inThe Netherlands
168
As already observed with other types of ion exchange phases, treatment of KSbO3 with aqueous acid replaces cations by protons and water molecules
(or oxonium ions) and thereby indirectly gives
proton conductors HSb03.xH20 [6,11]. The work carried out by us on these phases 16,111 had shown that conduction depends on various factors, most obviously the volumetric proton concentration and the nature of the protonated species, but also the interatomic distances in the hydrogen bond and its polarization, which affect the energies of the processes involved. Tight control of water content is clearly essential to the study of proton conduction in these materials. The present work reports a study of H(H20),Bi03 phases undertaken to acquire fuller knowledge of ion conductors with a threedimensional matrix particularly as regards the influence of hydration on their electrical properties. Synthesis of the KBi03 phase This compound was obtained by the method described by R. Scholder and H. Stobbe [12] involving oxidation with bromine of a solution of bismuth trioxide in potassium hydroxide. A brown material was obtained which crystallized in a cubic lattice with a = 10.020 (5) i and space group Im3. This phase is an isotype of the cubic KSb03 type compounds. No line due to impurities was visible on the diffractogram. As with many other ion exchange phases the alkali metal cations of KBi03 can be exchanged for oxonium ions or protons and water molecules. Here, elution with 9N sulfuric acid for about 48 hours followed by washing with distilled water to neutrality and then drying over sulfuric acid at room temperature gave a solid exchange product. Measurement of mass loss, potassium assay by flame emission spectrophotometry of both product and filtrate and assay of Bi(V) and total Bi showed that exchange was 98 % com3fB .5@ plete, and indicated the formula H1_n(H20)Bin Bi '3+n' 1/3H20 with n = 0.1. The structure of the exchange product was of type cubic KSb03 with a = 9.815 (5) i and space group Im3.
169
Given structural results obtained previously the tunnels of 120 the anionic Bi12036 skeleton may reasonably be supposed to be oc48 cupied by both potassium ions and Bi404 units analogous to those found in the Bi3Ru3011 phase [ 131.
This result calls to mind those
of Trehoux (141 who in pyrochlor type bismuth phases found potassium and trivalent bismuth at the same crystallographic site. During the exchange, however, the existing lines widen and the relative intensities of several lines, (loo), (400) for instance (Fig. 11, change markedly. The lattice parameter a = 9.815 (5) i is smaller thanthat of the starting material, a = 10.020 (5) i.
a
0
14
18
22
26
30
34
38
42
46
50
54
58
62 2
66 THETA
C’)
b
2 0
2-
mm -f*\DID P-l.?
-0 -w
2 m
58
62
22
” LB
-
13
14
10
22
26
30
34
30
42
46
50
54
66 2 THETA
--.
C9
Fig. 1. X-ray diffractograms of : a) KBi03.1/3H20; b) acid phase.
170
The exchange product H(H20)nBi03 is thermally less stable than KBi03. Loss of water occurs at room temperature and hydrolysis of the compound takes place with accompanying loss of order.
Electrical properties and discussion Measurements were made by the AC impedance method between 10 Hz and 1 MHz using a Solartron type 117A transfer function analyzer from - 40°C up to the temperature of decomposition of the material. A measuring cell developed by us was used (ANVAR 85-4832), regulated by two Peltier modules. The electrical resistance of the material was determined by extrapolating the bulk circle. Conductivity curves obtained for three different values of hydration level are given in Fig. 2, along with those obtained by Watelet 1111 for H(H20)o_8 Sb03 and H(H2G)o.33 Sb03 under the same conditions. The following conclusions may be drawn : (i) Conductivity obeys an Arrhenius type law. (ii) Conductivity depends to a great extent on the degree of hydration (4 orders of magnitude between curves 1 and 3). (iii) For equal water concentrations, the bismuth phases are less conductive than the antimony phases. This is expected given the different basicities of the anionic matrices. (iv) The presence of Bi3' along the ternary axes of the lattice does not detectably interfere with proton mobility. (v) Hydrated phases (curves 2 and 3) are sufficiently conductive -5 (u 2O'C = 1.18 x 10-5Q-1cm-1 for n = 0.95 and u 20°C = 5.9 x 10 -' for n = 1.05) to warrant consideration for use in electroS2-lcm chemical applications. This study shows the importance of hydration level for conductivity. For Grotthus type conduction to take place a high concentration of water molecules is necessary so that transfer of protons between donors and receptors can occur optimally, Further study by appropriate NMB methods 181 is required in order to investigate in detail the conduction mechanism.
171
Fi.g. 2. Conductivity curves of H(H20),Bi03 phases. 1. n = 0.20 ; 2. n = 0.95 ; 3. n = 1.05.
172
REFERENCES 1
H. Watelet, J.P. Besse, G. Baud and R. Chevalier, Mat. Res. Bull.,15
2
(1980) 875.
H. Watelet, G. Baud, J.P. Besse and R. Chevalier, Mat. Res. Bull.,17
(1982) 1155.
3
H. Watelet, J.P. Picard, J.P. Besse, G. Baud and R. Chevalier,
4
H. Watelet, J-P, Picard, G. Baud, J.P. Besse and R. Chevalier,
5
J.P. Besse, G. Baud, H. Watelet, M. Capestan and R. Chevalier,
Solid State Ionics,2 (1981) 191. Mat. Res. Bull.,16 (1981) 877. Ann. Chim. Fr.,? (1982) 35. 6
H. Watelet, J.P. Picard, G. Baud, J.P. Besse and R. Chevalier, Mat. Res. Bull.,16
7
0. M'Hamedi, J.P. Besse, G. Baud and R. Chevalier, Mat. Res. Bull .,e
8
(1981) 1131.
(1984) 487.
C. Doremieux-Morin, J.P. Fraissard, J.P. Besse and R. Chevalier, Solid State Ionics,u
9
(1985) 93.
G. Baud, J.P. Besse, M. Capestan and R. Chevalier, IIIe Protonic Workshop, Odense University Press (1985) 203.
10
J.P. Besse, G. Baud, H. Watelet, R. Chevalier and C. DoremiewMorin, 4th International Conference on Solid State Ionic%,
11
Grenoble (1983). H. Watelet, These Doctorat, Universite Clermont-Ferrand
12
R. Scholder and H. Stobbe, 2. Anorg. Allg. Chem.,E
(1983)
(1941)
403. 13
F. Abraham, D. Thomas and G. Nowagrocki, Bull. Sot. Fr. Mineral Crystallogr..98
14
(1975) 25.
J. Trehoux, These Doctorat, Lille 11981).