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Electrochemical preparation of FeCl4−- graphite intercalation compounds in an aqueous medium
Letters to the Editor
1055
REFERENCES 5. 1. 2. 3. 4.
H.W. Kroto, J.R. Heath, SC. O’Brien, R.F. Curl and R.E. Smalley, Nature, 318, 162 (1985). W. Kraetschmer. K. Fostiropoulous and D.R. Huffman, C/rent. Phys. Lett., 170, 167 (1990). W. Kraetschmer, L.D. Lamb, K. Fostiropoulous and D.R. Huffman, Nature, 347,354 (1990). R.E. Haufler. J. Conceicao, L.P.F. Chibante, Y. Chai, N.E. Byrne, S. Flanagan, M.M. Haley, S.C. O’Brien, C. Pan, Z. Xiao, W.E. Billups, M.A. Ciufolini, R.H. Hauge, J.L. Margrave. L.J. Wilson, R.F. Curl and R.E. Smalley, J. Phys. Chem., 94, 8630 (1990).
6.
In: Mineral Powder Diffraction File, Data Book. (I%.: M.E. Mrose, B. Post, S. Weissman and H.F. McMurdie). International Center for Diffraction Data, Swarthmore, PA 19081, USA. Card 8-247. p. 937 (1980). C.S. Yannoni, R.D. Johnson, G. Meijer, D.S. Bethune, and J.R. Salem, J. Phys. Chem., 95, 9 (1991).
Electrochemical preparation of FeCl4’- graphite intercalation compounds in an aqueous medium (Received 14 June 1991; accepted 17 June 1991) Key Words - electrochemical intercalation; warn,, ferric chloride; hydrochloric acid
Compared with other preparation methods, the electrochemical preparation of graphite intercalation compounds (GIC) has several advantages. For example, the stage of the sample can be correlated with the applied potential or the charge passed during the electrochemical intercalation, and hence this process is applicable not only to the analysis of the formation process of GIC but also to the well-controlled synthesis of GIC. In addition to HzSOA-GIG, the electrochemical preparation of which has been studied in considerable detail [l-6], a number of GIC were prepared by electrochemical treatment. I-IN@-GIC[7] is one of the repesentatives of acid-GIC which can be synthesized elkochemically. Electrochemical intercalation in molten metal chlorides. such as Bit% 181.has also been performed. Alkali metals [9-lo] &d ~&etal chlorides such as FeC4- [ 111. AlC4’ or GaClq’ [ 121 dissolved in organic solvents can also be intercalated electrochemically, but owing to solvation, solvent molecules ate c&ntemalated. Water has, however, never been used as an electrolytic solvent because of its limited potential window. In 1990. Futamata 1131 eave a clue to the electrochemical inttklation of &r&into carbon plastic electrodes by repeating charge-discharge cycles in aqueous solutions, but intercalation into ordinary graphite was unsuccessful using a conventional electrochemical technique. In this letter, we present the electrochemical preparation of FeCl4’ - GIC in an aqueous medium. The solution used was composed of 2.5 moles of FeC13 and 1.75 moles of HCl to 6 moles of H20. In such a concentrated solution of hydrochloric acid, FeC14- is the average and the only important solute formed from FeCll 1141. hence it was exnected that the FeC14’ ion could be intercalated during the anodic oxidation of graphite in this solution. Union Carbide HOPG was used as the host. A slab of HOPG (ca. 10 mg) was used for the working electrode, and a glassy carbon rod was used for the counter electrode; the saturated calomel electrode (SCE)
was adopted as a reference electrode (hereafter, all potential values will be referred to the SCE). The electrochemical treatment was carried out with a combination of a triangle wave signal generator (Tacussel, type GSTP4) and a potentiostat (Tacussel, type PRT 10-O. 5). A typical cyclic voltammogram obtained during the intial potential sweep is shown in Fig. 1. In order to interpret the voltammogram, the potential sweep was stopped at several points indicated in Fig. 1 to obtain X-ray diffraction patterns of the sample. Table 1 shows the Ie value at each point and the stage assigment. These results show that anodic peak “A” in Fig. 1 corresponds to the formation of a stage 2 GIC from a stage 3 GIG, and that another peak “B” is comprised in the peaks due to the conversions from stage m+l GIC to stage m GIC (where m 2 3). As an
1hA) 1.04
-0
e
I I
r
0.8/
1.0
1.2 E
(Vvs.SCE)
Figure 1. Typical cyclic voltammogram obtained for HOPG in aqueous FeC13 - HCl solution at a sweep rate of 0.1 mV/sec.
Letters to the Editor
1056
Table 1 Staging of Feclq’graphite intercalation compounds; the identification of each point is explained in the text
point
E value (A,
staging of GIC expected by E graphite and higher stages
a b
26.25(=9.50+5(3.35))
6th
c
19.39(=9.34+3(3.35))
4th
d
16.16(=9.46+2(3.35))
3rd
e
16.16 and 12.71
3rd and 2nd
f
12.71(=9.36+3.35)
2nd
g
12.71
2nd
evolution of oxygen rises to about 1300 mV. The shift of the potential window did make it possible to prepare the stage n FeC4’ - GIC (n 2 2). Experiments are now under progress to analyze the materials and give their crystallographic suuctum. Acknowledgements - This work was partly supported by a grant for International Joint Research from NEDO, Japan.
C.R.M.D., CN.R.S. I b, rue de la F&rollerie 45071 Orl&ns, France
H. SHIOYAMA* M. CRESPIN R. SET-TON F. BEGUIN
*Permanent address: Government IndustrialRes. Inst., Osaka Midorigao& l-8-31, Ikeda, Osaka563, Japan
REFERENCES
example, the X-ray diffraction pattern of stage 2 GIC is shown in Fig. 2. The interplanar distance (di) of the F&4' intercalated compound is quite similar to that of the FeCl3-GIC obtained by the vapour-phase reaction of Fe@ with graphite [ 15-161 and those of the related ternary compounds obtained from organic solutions [ 11, 171. The FeCht-- GIC tends to decompose to higher stage compounds in contact with water, e.g. stage 2 GIC decomposes to stage 3 or 4; such a remarkable decomposition is not observed with the FeC13 - GIC obtained by the vapour-phase reaction. The decomposition does not take place if the FeCLt’- GIC is washed with 6M HCl, this suggesting that HCl molecules are co-intercalated into the graphite interlayer space. During the reverse potential sweep, no peak was observed in the cyclic voltammogram. This means that the intercalation of FeC4’ is not reversible, at least during a potential sweep between 800 and 1350 mV. In fact, even after a reverse potential sweep to 800 mV, the sample shows a stage 2 structute. One of the major problems of water as a solvent for electrochemical reaction is its limited potential window, i.e. the electrochemical oxidation should be performed below the potential of the evolution of oxygen. This difEculty can be overcome by controlling the acidity of the solution. As the solution used in this work contains a large amount of HCl, the potential of the
Figute 2. X-ray diffraction (MoKcc) pattern of stage 2 FeQ4’ intercalated graphite compound.
1. R. Fujii, Report. Gov. Ind. 353, (1978). 2. S. Aronson, S. Lemont and Chem., 10,1296 (1971). 3. S. Aronson, C. Frishberg and 9,715 (1971). 4. A. Metrot and H. Fuzellier,
Res. Inst., Osaka, J. Weiner, Inorg. G. Frankl, Carbon, Carbon, 22, 131
Carbon 23 449 (1985) 5. g9%hn 6. J.-O. Be&hard, H. P.‘Fritx, H. Moehwald and J. J. Nickl, Z. Naturforsch. 33b, 737 (1978). 7. P. Scharff, Z.-Y. Xu. E. Stumpp and K. Bartecxko. Carbon, 29.31 (1991). 8. E. Stumpp and K. Wloka, Synch. Metals, 3, 209 $‘908’kesenhard Carbon 14 111 (1976) 1’0: B. Marcus, Ph.’ Touxai; and J. L. Soubeyroux, Synch. Metals, 23, 13 (1988). 11. D. Billaud, A. El Haouari and R. Gerardii, Synch. Metals ,29, F241 (1989). 12. D. Billaud and A. El Haouari. Synth. Metals, 34, 79 (1989). 13. M. Futamata, Extd. Abst. Int. Syrnp. on Carbon, Tsukuba, Japan (1990) p.818. 14. M. D. Luter and D. L. Wertx, J. Phys. Chem., 85. 3542 (1981). 15. J. G. Hooley and M. Bartlett, Carbon, 5, 417 (1967). 16. D. Hohlwein, F. D. Grigutsch and A. Knappwost, Angew. Chem. (Inc. Ed.), 9,382 (1969). 17. M. Inaeaki. T. Mitsuhashi and Y. Soneda, J. Chim. Bhys:, 84, 1439 (1987).
1055
REFERENCES 5. 1. 2. 3. 4.
H.W. Kroto, J.R. Heath, SC. O’Brien, R.F. Curl and R.E. Smalley, Nature, 318, 162 (1985). W. Kraetschmer. K. Fostiropoulous and D.R. Huffman, C/rent. Phys. Lett., 170, 167 (1990). W. Kraetschmer, L.D. Lamb, K. Fostiropoulous and D.R. Huffman, Nature, 347,354 (1990). R.E. Haufler. J. Conceicao, L.P.F. Chibante, Y. Chai, N.E. Byrne, S. Flanagan, M.M. Haley, S.C. O’Brien, C. Pan, Z. Xiao, W.E. Billups, M.A. Ciufolini, R.H. Hauge, J.L. Margrave. L.J. Wilson, R.F. Curl and R.E. Smalley, J. Phys. Chem., 94, 8630 (1990).
6.
In: Mineral Powder Diffraction File, Data Book. (I%.: M.E. Mrose, B. Post, S. Weissman and H.F. McMurdie). International Center for Diffraction Data, Swarthmore, PA 19081, USA. Card 8-247. p. 937 (1980). C.S. Yannoni, R.D. Johnson, G. Meijer, D.S. Bethune, and J.R. Salem, J. Phys. Chem., 95, 9 (1991).
Electrochemical preparation of FeCl4’- graphite intercalation compounds in an aqueous medium (Received 14 June 1991; accepted 17 June 1991) Key Words - electrochemical intercalation; warn,, ferric chloride; hydrochloric acid
Compared with other preparation methods, the electrochemical preparation of graphite intercalation compounds (GIC) has several advantages. For example, the stage of the sample can be correlated with the applied potential or the charge passed during the electrochemical intercalation, and hence this process is applicable not only to the analysis of the formation process of GIC but also to the well-controlled synthesis of GIC. In addition to HzSOA-GIG, the electrochemical preparation of which has been studied in considerable detail [l-6], a number of GIC were prepared by electrochemical treatment. I-IN@-GIC[7] is one of the repesentatives of acid-GIC which can be synthesized elkochemically. Electrochemical intercalation in molten metal chlorides. such as Bit% 181.has also been performed. Alkali metals [9-lo] &d ~&etal chlorides such as FeC4- [ 111. AlC4’ or GaClq’ [ 121 dissolved in organic solvents can also be intercalated electrochemically, but owing to solvation, solvent molecules ate c&ntemalated. Water has, however, never been used as an electrolytic solvent because of its limited potential window. In 1990. Futamata 1131 eave a clue to the electrochemical inttklation of &r&into carbon plastic electrodes by repeating charge-discharge cycles in aqueous solutions, but intercalation into ordinary graphite was unsuccessful using a conventional electrochemical technique. In this letter, we present the electrochemical preparation of FeCl4’ - GIC in an aqueous medium. The solution used was composed of 2.5 moles of FeC13 and 1.75 moles of HCl to 6 moles of H20. In such a concentrated solution of hydrochloric acid, FeC14- is the average and the only important solute formed from FeCll 1141. hence it was exnected that the FeC14’ ion could be intercalated during the anodic oxidation of graphite in this solution. Union Carbide HOPG was used as the host. A slab of HOPG (ca. 10 mg) was used for the working electrode, and a glassy carbon rod was used for the counter electrode; the saturated calomel electrode (SCE)
was adopted as a reference electrode (hereafter, all potential values will be referred to the SCE). The electrochemical treatment was carried out with a combination of a triangle wave signal generator (Tacussel, type GSTP4) and a potentiostat (Tacussel, type PRT 10-O. 5). A typical cyclic voltammogram obtained during the intial potential sweep is shown in Fig. 1. In order to interpret the voltammogram, the potential sweep was stopped at several points indicated in Fig. 1 to obtain X-ray diffraction patterns of the sample. Table 1 shows the Ie value at each point and the stage assigment. These results show that anodic peak “A” in Fig. 1 corresponds to the formation of a stage 2 GIC from a stage 3 GIG, and that another peak “B” is comprised in the peaks due to the conversions from stage m+l GIC to stage m GIC (where m 2 3). As an
1hA) 1.04
-0
e
I I
r
0.8/
1.0
1.2 E
(Vvs.SCE)
Figure 1. Typical cyclic voltammogram obtained for HOPG in aqueous FeC13 - HCl solution at a sweep rate of 0.1 mV/sec.
Letters to the Editor
1056
Table 1 Staging of Feclq’graphite intercalation compounds; the identification of each point is explained in the text
point
E value (A,
staging of GIC expected by E graphite and higher stages
a b
26.25(=9.50+5(3.35))
6th
c
19.39(=9.34+3(3.35))
4th
d
16.16(=9.46+2(3.35))
3rd
e
16.16 and 12.71
3rd and 2nd
f
12.71(=9.36+3.35)
2nd
g
12.71
2nd
evolution of oxygen rises to about 1300 mV. The shift of the potential window did make it possible to prepare the stage n FeC4’ - GIC (n 2 2). Experiments are now under progress to analyze the materials and give their crystallographic suuctum. Acknowledgements - This work was partly supported by a grant for International Joint Research from NEDO, Japan.
C.R.M.D., CN.R.S. I b, rue de la F&rollerie 45071 Orl&ns, France
H. SHIOYAMA* M. CRESPIN R. SET-TON F. BEGUIN
*Permanent address: Government IndustrialRes. Inst., Osaka Midorigao& l-8-31, Ikeda, Osaka563, Japan
REFERENCES
example, the X-ray diffraction pattern of stage 2 GIC is shown in Fig. 2. The interplanar distance (di) of the F&4' intercalated compound is quite similar to that of the FeCl3-GIC obtained by the vapour-phase reaction of Fe@ with graphite [ 15-161 and those of the related ternary compounds obtained from organic solutions [ 11, 171. The FeCht-- GIC tends to decompose to higher stage compounds in contact with water, e.g. stage 2 GIC decomposes to stage 3 or 4; such a remarkable decomposition is not observed with the FeC13 - GIC obtained by the vapour-phase reaction. The decomposition does not take place if the FeCLt’- GIC is washed with 6M HCl, this suggesting that HCl molecules are co-intercalated into the graphite interlayer space. During the reverse potential sweep, no peak was observed in the cyclic voltammogram. This means that the intercalation of FeC4’ is not reversible, at least during a potential sweep between 800 and 1350 mV. In fact, even after a reverse potential sweep to 800 mV, the sample shows a stage 2 structute. One of the major problems of water as a solvent for electrochemical reaction is its limited potential window, i.e. the electrochemical oxidation should be performed below the potential of the evolution of oxygen. This difEculty can be overcome by controlling the acidity of the solution. As the solution used in this work contains a large amount of HCl, the potential of the
Figute 2. X-ray diffraction (MoKcc) pattern of stage 2 FeQ4’ intercalated graphite compound.
1. R. Fujii, Report. Gov. Ind. 353, (1978). 2. S. Aronson, S. Lemont and Chem., 10,1296 (1971). 3. S. Aronson, C. Frishberg and 9,715 (1971). 4. A. Metrot and H. Fuzellier,
Res. Inst., Osaka, J. Weiner, Inorg. G. Frankl, Carbon, Carbon, 22, 131
Carbon 23 449 (1985) 5. g9%hn 6. J.-O. Be&hard, H. P.‘Fritx, H. Moehwald and J. J. Nickl, Z. Naturforsch. 33b, 737 (1978). 7. P. Scharff, Z.-Y. Xu. E. Stumpp and K. Bartecxko. Carbon, 29.31 (1991). 8. E. Stumpp and K. Wloka, Synch. Metals, 3, 209 $‘908’kesenhard Carbon 14 111 (1976) 1’0: B. Marcus, Ph.’ Touxai; and J. L. Soubeyroux, Synch. Metals, 23, 13 (1988). 11. D. Billaud, A. El Haouari and R. Gerardii, Synch. Metals ,29, F241 (1989). 12. D. Billaud and A. El Haouari. Synth. Metals, 34, 79 (1989). 13. M. Futamata, Extd. Abst. Int. Syrnp. on Carbon, Tsukuba, Japan (1990) p.818. 14. M. D. Luter and D. L. Wertx, J. Phys. Chem., 85. 3542 (1981). 15. J. G. Hooley and M. Bartlett, Carbon, 5, 417 (1967). 16. D. Hohlwein, F. D. Grigutsch and A. Knappwost, Angew. Chem. (Inc. Ed.), 9,382 (1969). 17. M. Inaeaki. T. Mitsuhashi and Y. Soneda, J. Chim. Bhys:, 84, 1439 (1987).