J. Phys. Chem. 1985,89, 987-991 CHART IV
situation alumina initial coverage alumina extended coverage silica
-AH,kcal/mol reaction model this work ref 20 ref 21 ref 22 18
105
45
20-30
20-40
22
25
12
10
11-13
23
15
10
10
of ammonia on alumina can be very high (40 kcal/mol) for the first few percent of a monolayer, and that the heats then rapidly fall off to about 10-15 kcal/mol for coverages exceeding ca. 5% of a monolayer. There is essentially no ammonia chemisorption that occurs on silica with a heat of adsorption exceeding 10-15 kcal/mol, and, in contrast to alumina, the heat is virtually independent of surface coverage. This is interpreted to mean that silica has a homogeneous distribution of active sites, whereas alumina does not. The experimental results contained in ref 20-22 are for ammonia chemisorption only and do not include reactions in which the ammonia displaces other ligands from the surface. This means that only the reactions 18,22, and 23 from the present work can be compared with them. The only one of these that applies to silca is reaction 23. This suggests that ammonia chemisorbs on silica almost exclusively through hydrogen bonding, and that silica does not normally have a significant quantity of anion vacancies. Alumina, on the other hand, has a greater quantity of anion vacancies (Lewis acid sites), and these lead to the observed high initial heats of chemisorption. This situation is modeled in this (22) Stone, F. S.; Whalley, L. J . m a l . 1967, 8, 173.
987
work by reaction 18. The low heats of chemisorption on alumina at extended coverages (due to interaction with protonic acid sites) are modeled by reaction 22. A comparison of the experimental values of the heats of chemisorption with the estimated values from this study is shown in Chart IV The comparison shows that the estimated values are all too high. The directional variations from the experimental work are preserved by the models, however. The analysis by Clark et a1.20 indicates that both the isosteric heat and differential entropy of adsorption of ammonia on silica/alumina combinations remains essentially invariant with temperature. In one case discussed specifically (82% S O 2 , 18% A1203),the isosteric heat varies from -1 1.46 to -1 1.70 kcal/mol in response to a temperature variation from 100 to 300 OC. The corresponding partial molar free energies are -7.21 and -4.56 kcal/mol, respectively. The free energy values estimated for reaction 23 at 100 and 300 OC (obtained from Figure 1) are about -5 and +2 kcal/mol, respectively. This extent of agreement is probably good, considering the simplifying assumptions and the approximate bond distances used in the models.
Conclusions From the foregoing comparisons, it would appear that the utilization of Sanderson's principles to study models for surface thermochemical processes can lead to semiquantitative results. In the present case, the models permitted a distinction between the heats of chemisorption of ammonia on alumina and silica, and between the heats of initial and extended chemisorption on alumina. Extension of the method to estimate the variation of the free energy of adsorption with temperature gave results that are also in approximate- agreement with experiment. Registry No. NH3, 7664-41-7; A1203,1344-28-1; Si02,7631-86-9.
Ionically High Conductive Solid Electrolytes Composed of Graft Copolymer-Lithium Salt Hybrids Norihisa Kobayashi, Masahiro Uchiyama, Kiyotaka Shigehara, and Eishun Tsuchida* Department of Polymer Chemistry, Waseda University, Tokyo 160, Japan (Received: July 30, 1984)
Polymeric solid electrolytes with both high ionic conductivity and processibility were prepared from poly[methacryloyloligo(oxyethy1ene)l and inorganic lithium salts such as LiC104 or LiPF,. An ac conductivity as high as 2.2 X S/cm at 25 OC was observed for this hybrid film when the composition of poly(methacry1ate) and LiC104 was 70/30 wt %.
Introduction Polymeric solid electrolytes such as poly(oxyethylene)/Li salt hybridk4 and polymer matrix/Li salt/additives5-' have been investigated. Especially when the ternary hybrid system took on some microphase separated structure such as a cylindrical conduction column of low T and high polarity oligomer domain, where inorganic lithium saits were solubilized in the sea of flexible polymer matrixes, flexible thin films with an ionic conductivity (1) Armand, M. B.; Chabagno, J. M.; Ducolot, M. J. 'Fast Ionic Transport in Solids"; Vashishta, P., Mundy, J. N., Shenoy, G . K., Eds.; Elsevier North-Holland: New York, 1979; p 131. (2) Weston, J. E.;Steele, B. C. H. Solid Srare Ionics 1982, 7 , 81. (3) Dupon, R.; Papke, B. L.; Ratner, M. A., Whitmore, D. H.; Shriver, D. F. J . Am. Chem. Soc. 1982,104, 6247. (4) 'Proceedings of the 4th International Conference on Solid State Ionics, Grenoble, France, July, 1983" Solid State Ionics, 1983, 9Br10, 1101-1 166. (5) Tsuchida, E.; Ohno, H.; Tsunemi, K. Electrochim. Acta 1983,28, 591. (6) Tsuchida, E.; Ohno, H.; Tsunemi, K. Electrochim. Acta 1983,28,833.
0022-3654/85/2089-0987$01.50/0
of more than S/cm at 25 OC were realized.8 In order to design a suitable polymer matrix for polymersalt hybrid formation, we prepared poly(methacry1ate) with side chains of oligooxyethylene. Side chains with an average number of oxyethylene unit ranging from 3 to 18 were used to investigate the effect of side chain length on ionic conductivity.
Experimental Section Materials. Li Salts. LiC104 was purchased from Kanto Chemical Co. Ltd. and was purified by recrystallization with acetone and dried in vacuo at 160 O C for 2 days. Moisture was excluded by storing the LiC104 in a sealed ampule before use. LiPF, was purchased from Alfa Chemical Co. Ltd., and the same purification method of LiC104 was employed. IR spectra were used to verify the absence of water. Endo-Acetylated Oligo(oxyethylene) [ OEsA]. Oligo(oxyethylene) with an average number of oxyethylene units, n, of 8 purchased from Kanto Chemical Co. Ltd. was esterified with acetic 0 1985 American Chemical Society
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Kobayashi et al.
The Journal of Physical Chemistry, Vol. 89, No. 6, 1985 -2
I
n=7
-5
-5
0
2
4 ILlC1041
8
7
6
5
4
3
2
6
( P P ~ )
1
0
Figure 1. NMR spectrum of MEO, monomer in CDCI,.
acid anhydride, and the resulting OE8A was purified by passing the reaction mixture through a basic alumina (Merck, Grade-I) column as described earlier’ and drying in vacuo at 180 OC for 1 day because. of dehydration. The degree of esterification of O b A was determined to be 98% according to the method described in the l i t e r a t ~ r e . ~ Methacryloyl Oligo(oxyethy1ene) Monomethyl Ether (MEO,). Oligo(oxyethy1ene) monomethyl ether derivatives with n values of 3 [tri(oxyethylene) monomethyl ether], 7, 12, and 17 purchased from Aldrich Chemical Co. were allowed to react with a large excess amount of metallic lithium at reflux in dry THF for typically 3 days. After the unreacted metallic lithium was removed, the dry THF solution with an excess of methacryloyl chloride was added dropwise to the solution at 0-5 OC. The mixture was allowed to react further for 0.5 day at 0-5 OC and then for another day a t room temperature. The solution was concentrated by evaporation at lower than 30 OC, and then the solvent was replaced by dry chloroform. Complete evaporation was avoided, because this leads to spontaneous polymerization. The solution was passed through a basic alumina (Merck, Grade-I; typically 10 cm diameter X 30 cm for 40 g purification) and eluted with chloroform in order to remove unreacted methacryloyl chloride or lithium chloride precipitate. The resulting MEO, (n = 3 , 7, 12, and 17) solution with a concentration lower than 40 wt % was stored in the refrigerator at 0 OC. The yields of MEO, were 6040%. The structures were confirmed by the N M R spectra, one example of which was shown in Figure 1. Other Chemicals. Solvents were distilled and stored over molecular sieves, and used after filtration. Film Preparation. A chloroform solution of MEO, was evaporated at temperatures below 40 OC and dry methanol was continuously added in order to prepare a methanolic solution of MEO,. The desired inorganic lithium salt was then dissolved in the resulting solution. The mixture was allowed to evaporate under a flow of dry nitrogen. The resulting viscous liquid was placed on a Teflon plate and evacuated at room temperature over P205 for 1 day. Spontaneous polymerization commenced during the evacuation. Further polymerization occurred upon raising the temperature to 60 (n = 3 and 7) and 80 OC ( n = 12 and 17) on the second day. Except for the inorganic lithium salt involved, the resulting polymer matrix, poly(MEOJ(PME0,) hybrid films were insoluble in common organic solvents. The completion of polymerization was confirmed by N M R spectroscopy of the methanolic Soxhlet extract of the hybrid films. Measurements. Ionic Conductivity of Lithium Salt-OE Fluid Solutions. A given amount of inorganic lithium salt was dissolved in dehydrated OE8 or OE8A and dried in vacuo a t 60 OC for 1 day over P205. The ionic conductivity of the resulting fluid solution was measured under a dry argon atmosphere at a given temperature by an ac (3 V) method at 50 H z with a digital con-
0
(mol*)
2
4
6
IL1C1041
8
1
0
(moa)
Dependence of the ac ( 3 V) ionic conductivity of R(OCH2CH2)80R-LiC104fluid solution on salt content: (a) R = H; (b) R = COCH,. Figure 2.
ductometer (Toa Electronics Ltd., Model CM-20). Ionic Conductivity of Solid Hybrid Films. Metallic lithium electrodes were used for the measurement of the ac ionic conductivity. A metallic lithium anode and a stainless steel cathode were employed in the dc electrolysis. Details were described previo~sly.~’All measurements were conducted under dry argon to avoid moisture. The current density passing through the hybrid films sandwiched between the metallic lithium electrodes was measured by the ac (1 V) method with a Yokogawa-Hewlett Packard multifrequency LCR meter (Model 4274A) at frequencies between lo2 and lo5 Hz. The ac ionic conductivity of the hybrid films was calculated from the resulting complex impedance plane plots (Cole-Cole plots)1° with computer-controlled curve fitting. For the dc (3 V) conductivity measurements or dc electrolysis, a Kikusui dc power supply (Model PAC 7-10) and a Keithley solid-state electrometer (Model 610C) were employed. Determination of the Amount of Lithium Deposited on a Stainless Steel Cathode (Determination of Lithium Ion Transport Number in This System). After dc electrolysis with a metallic lithium anode and a stainless steel cathode, the hybrid films were removed from the cathode. The metallic lithium deposited on the cathode was dissolved in pure water and the resulting concentration of lithium ion was determined by atomic absorption spectroscopy. The lithium ion transport number was determined from the fraction of the amount of electrodeposited metallic lithium and amount of charge through the cell. X-ray Diffraction. The X-ray diffraction patterns of the hybrid films and the lithium salts were measured by an X-ray diffractometer (Rigaku Denki Co. Ltd., Model 2026) with Cu K a irradiation. Differential Scanning Calorimetry. Thermograms of the hybrid films were obtained with a Perkin-Elmer differential scanning calorimeter (Model DSC-2) under a dry helium atmosphere.
Results and Discussion LiX-OE8 or -OE8 A Fluid Solution Systems. Ionic Conductivity of LiX-OE8 or -0EsA Fluid Solutions. Figure 2 illustrates the dependence of the ionic conductivity of LiC1044E8or - O E g A fluid solutions on the concentration of the lithium salt. All the curves show a maximum conductivity. As deduced from the eq 1,” this is due to two opposing effects on the ionic conductivity e2
ui = (Kono)l’za6nrq exp[-V/2tkT]
(ai): Increasing the concentration of lithium salt increases the number of carrier ions (increase ai)and also increases the viscosity of the solution (decrease ai). KO,no, a , r , q , W, t, and k denote the intrinsic dissociation constant of the lithium salt, the number of total ions, the activity coefficient, the radius of the ion, the viscosity of the solution, the dissociation energy of the lithium salt, __
__
~~
(IO) Cole, K. S.; Cole, R. H. J . Chem. Phys. 1941, 9, 341. (7) Tsuchida, E.; Ohno, H.; Tsunemi, K.; Kobayashi, N. Solid State Ionics 1983, 1 I , 227. ( 8 ) Shigehara, K.; Kobayashi, N.; Tsuchida, E. Solid State Ionics 1984, 14, 8 5 . (9) Stetzler, R. S.; Smullin, C. F. Anal. Chem. 1962, 34, 194.
(1 1) u, = Zq,n,,u, (q is the charge of carrier ion, n the carrier concentration, u the carrier mobility) and u = eD/KT (Nernst-Einstein equation, D =
~ T / 6 r R q(Stokes-Einstein equtation), so u = e / 6 r r q (Walden’s rule). Considering n = [(K&)’/*a] exp(-W/ZwT), the combination with the first and the last equation gives eq 1.
High Conductive Solid Electrolytes the dielectric constant of the solution, and the Boltzmann constant, respectively. For example, the viscosities of the LiC104-OEsA fluid solutions (from an Ostwald viscometer) at [LiClO,] = 2.5 and 4.0 mol % were larger by a factor of 2 (152.4 cP) and 5 (340.8 cP), respectively, than that of pure OEsA (69.7 cP) at 26 "C. Although the viscosity of OEs (87.9 cP, 26 "C) is larger by a factor of 1.3 than that of OEsA, the ionic conductivity of the LiC1O,-OEs system is almost the same as that of the LiC10,OEBA system. This is not expected on the basis of the considerations described above as the ionic conductivity is inversely proportional to the viscosity of the solution. The limit of solubility of LiC104 in OEs and OEgA is ca. 10 and 7 mol %, respectively, so it is thought that the endo-hydroxy groups of OEs enhance the dissociation of the lithium salt. Indeed, from 'H N M R spectroscopy in deuterio T H F solution, the proton signal of the endo-hydroxy groups of OEs at 4.9 ppm in the absence of LiClO, is shifted to lower field, 5.7 ppm, in the presence of 5.0 mol % of LiClO,. This is obvious evidence that the endo-hydroxy groups of OEs are interacting with LiC10, and that they possibly enhanced the degree of dissociation of LiClO,. It may also be that the endo-hydroxy protons participate in ionic conduction by proton hopping, as the N M R shift to lower field presumably represents formation of the bond between the oxygen atom and the terminal proton. At any rate, if such endo-hydroxy POE or O E is used as the polymer matrix or oligomer solvent, the endo-hydroxy group of POE or O E reacts with the electrode. The resulting hybrid film or viscous solution of LiX causes the corrosion of metal electrodes, especially alkali metal electrodes. A profile similar to that in Figure 2 is also obtained when Lic104 is replaced by LiPF,. Due to the better solubility of LiPF6 in the oligomer solvent (limit ca.15 mol % in Ob,), the maximum of the ionic conductivity of about 4 X lo-, S/cm appeared, for instance, at ca. 5 mol% in LiPF6-OEsA system. PME0,-LiX Hybrid Systems (Solid Films). Ionic Conductivity of the PME0,-LiC104 Hybrid. Poly(oxyethylene), a kind of linear poly(ether) often called "podand", is a well-known material which can interact with alkali metal cations to enhance the dissociation of their salts.'*J3 For this reason, considerable work has been done on POE-MX (M, alkali metal ion) hybrid systems: despite the low ionic conductivity ( Tgand T < Tg, for ion hopping from one free volume site to another, respectively. go corresponds with (Kono)1/2ae/(6?rrq) in eq 1 . Hence, in earlier reports,57 low Tgvalues were sought by adding polar solvents or OESA to M X hybridized with a solid polymer matrix and the authors have made a ternary hybrid polymeric solid electrolyte. Although ionic conductivities of more than lod S/cm were found in some hybrid systems such as polymer/ MX/solvent or oligomer, their longevity was not satisfactory ~~~
(12) Fendler, J. H. 'Membrane Mimetic Chemistry"; p 184-208 and references therein. (13) Smid, J. Macromolecules 1983, 16, 1382. (14) (a) Kaeble, D. H. 'Rheology, Theory and Application"; Academic Press: New York, 1969; Vol. 5. (b) Cohen, M. H.; Turnbull, D. J . Chem. Phys. 1959, 31, 1164. (c) Miyamoto, T.; Shibayama, K. J. Appl. Phys. 1973, 44,5372. (d) Miyamoto, T.; Shibayame, K. Kobunshi Kagaku 1973,30, 103. (e) Williams, M. L.; Landel, R. F.; Ferry, J. D. J . Am. Chem. SOC.1955, 77, 3701.
The Journal of Physical Chemistry, Vol. 89, No. 6,1985 989 lLiC1041 (mol% vs. OE unit for PMEO 7 ) 10 20 30 I
-
I
8
C PMEO7 -012 -O17 I
10
20
30
IL i C l aI
50 (wt%)
40
Figure 3. Dependence of the ac ( 1 V) ionic conductivity of PME0,LiC104 hybrid solid films on salt content.
because of the slow vaporization of the solvent from the hybrid films or of localization of the oligomer on the anode. Also, as the solvent or oligomer moieties needs to be connected across the hybrid films in order to form the MX-solvent or -oligomer conduction pathways in the solid hybrid film, the addition of large amounts of solvent or oligomer caused the films to become too soft. When the self-segregated structures of perfluoro polyelectrolytes, the lithium salt of Nafion15or Hemion,', and ternary hybrid systems such as the "lithium salt of Nafion or Flemion/LiX/ ObA"were used high ionic conductivities of more than S/cm were obtained.8 The LiX-OEsA mixture was believed to be inserted into the cylindrical domains of the perfluoro polyelectrolytes to establish continuous ionic conduction pathways acrms the hybrid films. If this is true, it will be very interesting to prepare a hybrid composed of LiX and a graft copolymer possessing flexible main chains for processibility and oxyethylene side chains to provide ionic conduction columns. MEO, or the methacryloyl oligo(oxyethy1ene) macromer, here the subscript n denotes the average number of oxyethylene unit of oligomer chains, is one of the plausible precursors to yield such graft copolymers. MEO, is spontaneously polymerizable under an inert atmosphere even at room temperature and even in the presence of LiX. The PME0,-LiX hybrid films thus obtained by the spontaneous casting polymerization procedure described in Experimental Section was sandwiched between metallic lithium electrodes, and the ionic conductivity was determined from the complex impedance plant plots. As it was noticed that the present hybrid systems were ohmic conductors at the potentials applied in the experiment (0.5-5.0 V), the subsequent measurements were done at an electrode potential of 1V ac. The results are summarized in Figure 3. One can notice that the conductivity maxima appear at lower concentrations of LiC104 when PMEO, with a larger n is employed. The appearance of ionic conductivity maxima is very similar to that observed in the corresponding fluid solution systems LiC104-OEs or LiC10,(15) Mauritz, K. A.; Hopfinger, A. J. "Modern Aspects of Electrochemistry"; Bockris, O M . , Conway, B. E., White, R. E., Eds.; Plenum Press: New York, 1982; Vol. 14, p 425 and references therein. (16) Ukihashi, H. CHEMTECH 1980, 118 and references therein.
990
Kobayashi et al.
The Journal of Physical Chemistry, Vol. 89, No. 6, 1985 I LiPF6 1
(mol% vs.OE unit)
0 -5
-C-
PMEO
,
-25 wt% LiC104
I
L
0
Fr
10
20 30 1 LiPF61
40 50 (wt%)
60
Figure 4. Dependence of ac (1 V) ionic conductivity of PME0,-LiPF6 hybrid solid films on salt content.
OESA. As the LiC104 concentration is increased, the number of carrier ions increases while the microviscosity at the conduction column in the hybrid film increases (decreases the mobility of carrier ions). The increment of microviscosity is probably more extensive in PMEO, hybrids with larger n; besides the microviscosity increases resulting from entanglements among the longer oxyethylene side chains, the stronger interaction between the lithium cation and the longer side chains12 further increases the microviscosity. Indeed, DSC thermograms of PMEO, (without salt) revealed that Tgincreases from -90 to -70 OC according to the n value. Therfore, as the oxyethylene side chains became longer, the maxima in the ionic conductivity appeared at lower LiC104 content. The PME0,-LiC104 hybrid system with a larger n value exhibited a higher ionic conductivity at low LiCI04 content. As mentioned above, in solution systems, podand-like polymers with longer ether chains interact with alkali metal cations more strongly than those with shorter to enhance the dissociation of salts. The descending order of ionic conductivities of PMEO17, PMEO12,PMEO,, and P M E 0 3is ascribable to the difference in the number of dissociated carrier ions compared to the same low content of LiC104. At the very high LiC104 content, the ionic conductivity is further decreased by the formation of microcrystals of LiX besides the increment in microviscosity. The solubility limit of LiC104 in PMEO, is about 18 (n = 17), 22 (12), 25 (7), and 40 wt % (3) as obtained from the results of X-ray diffractometry at room temperature. This is almost the same as the solubilities in OE,, fluid solution. For instance, comparing P M E 0 7 with OESA, the solubility limit of LiC104 in OEgA is 7 mol % (corresponding to ca. 20 wt %) which is very similar to that found in the P M E 0 7 system. Ionic Conductivity of the PME@-LiPF6 System. The ac ionic conductivity of P M E 0 7 hybrid films, when the lithium salt was replaced by LiPF6, was also examined (Figure 4). As the solubility of LiPF6 in OEsA is much larger than that of Lic104, the dissociation energy of LiPFs is probably lower than that of LiC104 and it was expected that the ionic conductivity of the P M E 0 7 system could be improved by utilizing LiPF6 instead of LiC104. Despite this consideration, the ionic conductivity maximum was lower than that of LiCIO, system (Figures 3 and 4). This might be due to the biionic property of the present hybrid systems; Le., the perchlorate anion was also participating in the ionic conduction. This is strongly related to the dc ionic conductivity and will be further discussed in the following paragraphs. dc Ionic Conductivity of PMEO,-LiX Systems. In Figure 5 is illustrated the time dependence of dc (3 V) ionic conductivity in several PME07-LiX systems. From the X-ray diffractometry of the hybrids observed after 10-min of dc electrolysis, the initial steep decrease of the dc conductivity is revealed to be caused by the local crystallization of LIX at the inner-most a few layers adjacent to the anode. The present hybrid systems are intrinsically
1
I
I
0
10
20 Time
50
(hr)
Figure 5. Time dependence of the dc (3 V) ionic conductivity in
PME0,-LiX systems.
70
I
60
Temperature 50 40
('C ) 30
20
1(
'
I
-C+
PMEO
-15wt%LiC1O4
-0-
WE0
-15wt%LiPFg
-A-
PMEO,* - 1 5 w t ~ L i C I O ~
I
29
3.0
31
1OOO/T
32
33
3.4
3.5
(K-l)
Arrhenius plots for the ac (1 V) ionic conductivity in PME0,-LiX systems. Figure 6.
biionic, Le., both Li+ and X- are mobile although the mobilities are different. When the X- ions moved toward the anode, the electrolyzed Li' ions from the metallic lithium anode encounter each other yielding a local high concentration of LiX crystals which block the further Li' movement, and this is the major reason for the initial steep decrease of dc ionic conductivity. For LiC104 systems, a further slow accumulation of LiC104 crystals near the anode surface is observed in accordance with a slow decrease of the dc ionic conductivity. While, after the initial steep decrease, the dc ionic conductivity of the PME0,-LiPF6 systems reaches a constant value, showing no further accumulation of LiPF6 crystals. This difference is attributed to the higher mobility of ClO4- than PF6-. From the measurement of the amount of metallic lithium deposited on the stainless steel cathode during dc electrolysis and the measurement of charges passed through the hybrid film, the apparent transport number of Li+ is obtained. The transport number in the time range corresponding to the initial steep decrease of dc ionic conductivity is 0.6-0.7 and 0.8, while that at the stationary state is 0.95 and almost 1.0, respectively, for the PME07-LiC104 and -LiPF6 systems with the limit of error of f0.05. This result explains why the ac ionic conductivity of PME07-LiC104 systems is higher than that of the PME07-LiPF6 system in Figure 4 and suggests that lithium salts with larger (immobile) anions are to be used in order to get a Li+ single-ion
J . Phys. Chem. 1985,89, 991-996 30
the existence of Tg).However, when Tgis far lower than the I temperature employed for the conductivity measurement, the first
-
5 25-
E
- 1.0
1
-E
B
& 0
-20-
m
- 0.8 - LiClO4
15 -
-LiClO,
l0I
10
ci
=
exP[ -
E 4- W / 2 c kT
]
(3)
1
m
W
5
0
term in the parentheses becomes negligibly small. In such cases, eq 2 can be simplified to
0
\
W
99 1
20
ILixl (mol% vs.OE unit) Figure 7. Activation energy of the ac (1 V) ionic conductivity in
PMEO,,-LiX systems. conductor. The dc ionic conductivity of thus polarized hybrid films can be recovered temporarily by a prolonged ac potential supply. Activation Energy f o r Ionic Conduction in PME0,-LiX Systems. The temperature dependence of the ionic conductivity of PME0,-LiX systems is shown in the linear Arrhenius-type plots, in Figure 6. Generally, in polymer/MX hybrid log q vs. T’, solid-state ionic conductors, such plots show curved lines due to the contribution of the first term in parentheses in eq 2 (due to
so that linear Arrhenius plots are obtained. From Figure 7 it is noticed that (i) the activation energy for ionic conduction, E, increases with an increase of LiX content, (ii) the increasing feature of E , is more outstanding in the PME0,-LiClO, systems than that in the PMEO,-LiPF, systems, (iii) the E, of the PME0,-LiC104 systems is much larger than that in the PME0,-LiPF6 systems, and (iv) there is a relatively small difference in E, among PME0,-LiC104 systems with different n if the same lithium salt is used. (i) is related to the increase of microviscosity with increasing the salt content. (ii) and (iii) reflect the fact that the increment in microviscosity on adding LiX is more drastic in the PME0,-LiC104 systems and that the solubility of LiC10, is worse than that of LiPF6. (iv) suggests that the ionic conductivity of PME0,-LiX systems is mostly influenced by the preexponential term of eq 3, as the large difference in the ionic conductivity (especially see the ionic conductivity at low [LiClO,] in Figure 3) is not reflected in the E , value. Acknowledgment. This work is partially supported by a Grant-in-Aid for Scientific Researches from the Ministry of Education, Science and Culture, Japan. Registry No. LiC104, 7791-03-9; LiPF,, 21324-40-3; poly(oxyethy1ene)monomethyl ether methacrylate polymer, 87105-87-1; poly(oxyethylene)acetate, 2761 3-77-0.
Formation of a Polymer-Supported Catalyst from Anchored Rhos, Clusters: Aggregation with Segregation of the Metals J. Lieto,t M. Wolf,+*B. A. Matrana,t M. Prochazka,t B. Tesche,I H. Knozinger,f and B. C. Gates*+ Center f o r Catalytic Science and Technology, Department of Chemical Engineering, University of Delaware, Newark, Delaware 1971 6, and Physikalisch-Chemisches Institut der Universitat, 8000 Miinchen 2, West Germany, and Fritz-Haber-Institut der Max-Planck-Gesellschaft, 1000 Berlin 338 FRG (Received: August 24, 1984)
Supported molecular metal clusters were prepared by the ligand association reaction involving the phosphine groups of poly(styrene-co-divinylbenzene-co-p-styryldipheny1phosphine)and [H2RhOs3(acac)(CO)lo]to give [H2RhOs3(acac)(CO)loPh2P-@]. This molecular analogue was used as a precursor of a supported metal catalyst, its activity being probed with the isomerizations of but- 1-ene and the hydrogenation of ethylene, and its structure being characterized by infrared spectroscopy, X-ray photoelectron spectroscopy, and transmission electron microscopy. The results show that the initial bimetallic cluster broke up with segregation of the metals. The infrared spectra show that the cluster breakup gave stable triosmium carbonyl clusters, which account for the isomerization activity. The activity for hydrogenation is attributed to Rh metal; the electron microscopy suggested the presence of metal particles C1.0 nm in diameter.
Introduction supported bimetallic catalysts are finding an increasing number of technological applications, including re-forming of light petroleum fractions.’ Since the metal species on the support are typically aggregates or crystallites with diameters of only 1-1 0 nm, which are nonuniform in size, shape, and catalytic activity, it is difficult to obtain precise structural characterizations and to measure relations between structure and catalytic performance. t University of Delaware.
* Physikalisch-Chemisches Institut der UniversitBt. I Fritz-Haber-Institut
der Max-Planck-Gesellschaft.
0022-3654/85/2089-0991$01.50/0
Our objective was to investigate a supported bimetallic catalyst initially having a simple structure-analogous to that of a molecular metal cluster. The evolution Of the structure was followed With both SPtroscoPic and catalytic reaction Pro&. The support was chosen to be PolY(StYrene-co-divinYlbenzene), Since this Polymer is nearly inert and allows straightforward Synthesis of bound organometallics;2 the metal cluster precursor was chosen (1) Sinfelt, J. H. “Bimetallic Catalysts- -Discoveries, Concepts, and Applications”; Wiley: New York, 1983. (2) Lieto, J.; Milstein, D.; Albright, R. L.; Minkiewicz, J. V.;Gates, B. C. CHEMTECH 1983, 13, 46.
0 1985 American Chemical Society
