当前位置:首页 >> 能源/化工 >>

A Dielectric Polymer with High Electric Energy Density and Fast Discharge Speed


CORRECTED 29 SEPTEMBER 2006; SEE LAST PAGE
REPORTS
A
120 10 8 6 4 2 0 0 2 4 Time (h) 6 16 12 8 4 0 0 5 Time (h) 10 0 0

80

40

B

120

80

40

Given the excellent chemoselectivity of gold for reducing nitro compounds, we explored this system as an alternative catalytic route for the production of cyclohexanone oxime, an important molecule in the production of e-caprolactame. Cyclohexanone oxime is currently obtained via two different routes (Scheme 1A). In these processes, hydroxylamine, which is a toxic and unstable product, has to be used or otherwise synthesized in situ by the Sumitomo and ENICHEM procedure. However, the high activity and selectivity of gold catalysts open the possibility for an alternative process that would involve the steps given in Scheme 1B. This process requires a catalyst that selectively hydrogenates 1-nitro-1-cyclohexene into cyclohexanone oxime. Whereas Pt and Pd produce low selectivity even at relatively low levels of conversions, selectivity 990% is achieved at practically 100% conversion with the gold catalysts (Table 1).
References and Notes
1. R. S. Dowing, P. J. Kunkeler, H. van Bekkum, Catal. Today 37, 121 (1997). 2. M. Suchy, P. Winternitz, M. Zeller, World (WO) Patent 91/00278 (1991). 3. F. Kovar, F. E. Armond, U.S. Patent 3,975,444 (1976). 4. J. Butera, J. Bagli, WO Patent 91/09023 (1991). 5. A. Burawoy, J. P. Critchley, Tetrahedron 5, 340 (1959). 6. R. Braden, H. Knupfer, S. Hartung, U.S. Patents 4,002,673 and 4,051,177 (1977). 7. M. A. Narendra, O. P. Shivanand, D. R. Madhukar, WO Patent 2005.070.869 (2005). 8. W. Gerhar et al., U.S. Patent 6,395,934 (2002). 9. P. N. Rylander, Catalytic Hydrogenation in Organic Synthesis (Academic Press, New York, 1979), p. 122. 10. U. Siegrist, P. Baumeister, H.-U. Blaser, Catalysis of Organic Reactions, F. Herkes, Ed., vol. 75 of Chemical Industries (Dekker, New York, 1998). 11. H.-U. Blaser, U. Siegrist, H. Steiner, in Aromatic Nitro Compounds: Fine Chemicals through Heterogeneous

Conversion or Yield (%)

Pressure (bar)

12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27.

Conversion Hydrogen pressure

Yield 3-aminostyrene Yield 3-ethylaniline Yield intermediates

Catalysis, R. A. Sheldon, H. van Bekkum, Eds. (Wiley-VCH, Weinheim, Germany, 2001), p. 389. E. Janin, J. Catal. 215, 243 (2003). P. Concepcion, A. Corma, J. Silvestre-Albero, J. Am. Chem. Soc. 126, 5523 (2004). A. Sepulveda-Escribano, F. Coloma, F. Rodriguez-Reinoso, J. Catal. 178, 649 (1998). A. Abad, P. Concepcio ? n, A. Corma, Angew. Chem. Int. Ed. Engl. 44, 4066 (2005). A. Corma, M. E. Domine, Chem. Commun. 32, 4042 (2005). S. Naito, M. Tanimoto, J. Chem. Soc. Chem. Commun. 12, 832 (1988). S. A. Blankenship, A. Rokicki, J. A. Perkins, U.S. Patent 2003.232.719 (2003). C. Milone et al., J. Catal. 236, 80 (2005). C. Gonza ?lez-Arellano, A. Corma, M. Iglesias, Chem. Commun. 15, 3451 (2005). P. Claus, Appl. Catal. Gen. 291, 222 (2005). J. E. Bailie, G. J. Hutchings, Chem. Commun. 21, 2151 (1999). M. Ch. Daniel, D. Astruc, Chem. Rev. 104, 293 (2004). X. Lu, X. Xu, N. Wang, J. Phys. Chem. A 103, 10969 (1999). Materials and methods are available as supporting material on Science Online. Detailed product distributions with the different catalysts are given in tables S1 to S6. We thank the World Gold Council for supplying the gold catalysts that were used as well as for the corresponding transmission electron microscopy images and F. Sa ?nchez, M. Iglesias, and C. Gonza ? lez-Arellano for useful comments. This work was supported by Ministerio de Educacio ?n y Ciencia (grant MAT2003-07945-C02-01).

Conversion or Yield (%)

Fig. 1. Kinetic curves for 3-nitrostyrene hydrogenation with (A) Au/TiO2 and (B) Au/Fe2O3 catalysts. Up to nearly 100% of conversion both catalytic systems provide selectivity 995%, avoiding the hydroxylamine accumulation problem (reaction conditions: for Au/TiO2, 120-C, 9 bar, and 0.23 mol % of Au; for Au/Fe2O3, 130-C, 12 bar, and 0.39 mol % of Au). Arrows indicate that the hydrogen pressure curve is referred to the right y axis, and the remaining curves are referred to the left y axis.

Pressure (bar)

Supporting Online Material
www.sciencemag.org/cgi/content/full/313/5785/332/DC1 Materials and Methods SOM Text Figs. S1 to S3 Tables S1 to S6 Schemes S1 and S2 References 5 April 2006; accepted 7 June 2006 10.1126/science.1128383

A Dielectric Polymer with High Electric Energy Density and Fast Discharge Speed
Baojin Chu,1,2 Xin Zhou,3 Kailiang Ren,3 Bret Neese,1,2 Minren Lin,2 Qing Wang,1,2 F. Bauer,4 Q. M. Zhang1,2,3* Dielectric polymers with high dipole density have the potential to achieve very high energy density, which is required in many modern electronics and electric systems. We demonstrate that a very high energy density with fast discharge speed and low loss can be obtained in defectmodified poly(vinylidene fluoride) polymers. This is achieved by combining nonpolar and polar molecular structural changes of the polymer with the proper dielectric constants, to avoid the electric displacement saturation at electric fields well below the breakdown field. The results indicate that a very high dielectric constant may not be desirable to reach a very high energy density. ielectric materials are used to control and store charges and electric energies and play a key role in modern electronics and electric power systems. As the requirements

dielectric materials becomes a major enabling technology (1–3). For example, high energy density dielectric capacitors would help to reduce the volume, weight, and cost of the electric power system in hybrid electric vehicles. Among various dielectric materials, polymers are presently the material of choice for energy storage applications because of their relatively high energy density, high electric breakdown field (Eb), low dielectric loss, fast speed, low cost, and graceful failure (i.e., high reliability) (4–6). However, dielectric polymers that are currently used for high energy density capacitors show low (G3) dielectric constants (represented by K). Consequently, the high energy density in the dielectric polymers relies on the high Eb (9500 MV/m). In general, the
1

D

grow for compact, low-cost electronic and electrical power systems, as well as for very high energy and power capacitive storage systems, the development of high power and energy density VOL 313 SCIENCE

Materials Science and Engineering Department, 2Materials Research Institute, Pennsylvania State University, University Park, PA 16802, USA. 3Electrical Engineering Department, 4 Institute Franco-Allemand de Recherches, 5 Rue du General Cassagnou, 68300 Saint-Louis, France. *To whom correspondence should be addressed. E-mail: qxz1@psu.edu

334

21 JULY 2006

www.sciencemag.org

REPORTS
energy density of a dielectric material (shaded area in Fig. 1A) is equal to the integral Ue 0 X EdD, where E is the electric field and D is the electric displacement or charge density. Therefore, besides a high Eb, a high D value is another key factor in achieving a high energy density. Furthermore, with a proper K to avoid the electric displacement saturation (Dsat) at fields well below Eb (early polarization saturation), an even higher electric energy density can be achieved (Fig. 1B). In high energy density dielectric polymers that are presently used, the level of D is low. For biaxially oriented polypropylene, which has the highest energy density (?4 J/cm3) among the known polymers, D is below 0.012 C/m2 under a field of 600 MV/m. Conversely, in polymers with high dipole density, D values higher than 0.1 C/m2 can be achieved, providing the potential of reaching an order of magnitude increase in the energy density (7). One such polarpolymer system is poly(vinylidene fluoride) (PVDF) and its copolymer with trifluoroethylene (TrFE), which is the best known ferroelectric polymer and has been used widely in electromechanical sensors and actuators (7–10). We show that, by combining the reversible nonpolar and polar molecular structural changes to realize high D with proper (or matched) K values to avoid the early D-saturation, a very high energy density (917 J/cm3) with fast discharge speed (G1 ms) and low dielectric loss can be obtained in defect-modified PVDF polymers. A typical D-E loop for a P(VDF-TrFE) copolymer is shown (Fig. 2A). Owing to the high dipole density, the polymer displays a Dsat of ?0.1 C/m2. Alternatively, the large remnant polarization in the normal ferroelectric PVDF and its copolymer P(VDF-TrFE) renders a small energy density (shaded area in Fig. 2A). Therefore, besides possessing a high D value, a polymer should also have very small remnant polarization (D , 0 at zero E), allowing for a large change in D. From the molecular point of view, in the normal ferroelectric phase of PVDF and P(VDF-TrFE), the polymer chains are already in the all-trans conformation (fig. S1A), and an applied field along the original D direction can only induce small changes in D (curve from point A to point B in Fig. 2A), which then lead to low energy density (8, 9). Recently, we demonstrated that by using defect modifications, the P(VDF-TrFE) copolymer at compositions below VDF/TrFE 70/30 mole percent (mol %) can be converted to a ferroelectric relaxor in which the remnant polarization is near zero and a large change in D can be obtained (11, 12). A D-E loop for a terpolymer of VDF-TrFE–chlorofluoroethylene (CFE) 58.3/34.2/7.5 mol % is presented in Fig. 2A (13, 14); CFE generates random defects in P(VDF-TrFE). Apparently, a much higher electric energy density can be achieved (upper shaded area in Fig. 2A). Integrating the discharge D-E curve (fig. S2) yields the electric energy density of the terpolymer. The terpolymer exhibits an electric energy density higher than 9 J/cm3 under 400 MV/m field (Fig. 2B), which is higher than known polymers and other dielectric capacitors (3, 4, 6). The discharged energy density of the terpolymer (Fig. 2B) increases in an almost linear fashion with E. This relationship contrasts with that of the linear dielectric polymer, in which the electric energy density is proportional to the square of E: Ue 0 ?K e0 E2 , where e0 is the vacuum permittivity (e0 0 8.85 ? 10j12 F/m). Indeed, this is the effect of the early D-saturation in the terpolymer; the material reaches Dsaturation at a field much lower than Eb, which reduces the energy density that can be stored in a dielectric material. As a quantitative estimation, we modeled the D-saturation as a reduction of the effective dielectric constant Keff with the field (i.e., Ue 0 ?Keff e0 E2 ). The Keff value was ?50 at low fields and decreased with E (Fig. 2B). At 400 MV/m, the terpolymer had a Keff value of ?13. In this sense, a very high K at low E is not a desirable feature for a dielectric material to achieve a very high electric energy density. Instead, a K that can maximize the electric energy density (curve II in Fig. 1B) is needed, even though that dielectric constant is lower than that of curve I. A piecewise response in D is used to approximate the real D-E response (Fig. 1B). This simple analysis illustrates the importance of a matched K to maximize the electric energy density. In the relaxor ferroelectric polymer, the change in molecular conformation between the nonpolar and polar forms at room temperature is associated with the polar-glass transition process, which is accompanied by a broad and high K peak (11, 12, 15). Because the energy difference of PVDF homopolymer between the transgauche-trans-gauche? (TGTG?) and all-trans conformations is very small, this may be used to generate a large change in D without the penalty of a high K at low E values (16, 17). The TGTG? and all-trans conformations as well as the associated a and b phases are illustrated in fig. S1. Recent simulations have shown that for the single molecular chain, a TGTG? conformation has a lower energy value compared with the all-trans conformation; however, in the crystal-

Fig. 1. (A) Schematic illustration of D and discharged energy density (shaded area) with E. Curve with arrows indicates energy release as the field is reduced. (B) Schematic illustration of the effect of K (the slope of D-E curve) on Dsat and energy density. The high K value of curve I leads to the early D-saturation and consequently to a lower energy density compared with that of curve II, despite its lower K value.

Fig. 2. (A) D-E loops for P(VDF-TrFE) 75/25 mol% (dotted lines) and P(VDF-TrFE–CFE) 58.3/34.2/ 7.5 mol% (solid lines) measured at 10 Hz. The shaded blue areas indicate the energy density. (B) The discharged energy density measured from the D-E loops and Keff as a function of the field amplitude. The solid curves are drawn to guide eyes. SCIENCE VOL 313 21 JULY 2006

www.sciencemag.org

335

REPORTS

Fig. 3. (A) Comparison of the D-E loops of PVDF (black curves) and P(VDFCTFE) 91/9 mol% (blue curves) measured at 10 Hz. P(VDF-CTFE) shows much lower remnant polarization even though the film was uniaxially stretched. (B) D-E loops measured under a unipolar E of 10 Hz for P(VDFCTFE) 91/9 mol%. The different colored curves correspond to D-E loops

measured with different field amplitudes. The conduction contribution was subtracted. (C) The discharged energy density measured from D-E loops under unipolar fields. Open squares, uniaxially stretched films; ?, unstretched films. The uniaxially stretched P(VDF-CTFE) films exhibit much higher Eb values compared with unstretched films. the discharged energy density does not change greatly when RL is varied from 1 to 100 kilohms. These results show that the P(VDF-CTFE) copolymer capacitor possesses a low loss. Our demonstrated approach can also be applied to other polymers possessing high dipole density and high D to achieve ultra-high energy density with fast discharge time and low loss.
References and Notes
1. H. S. Nalwa, Ed., Handbook of Low and High Dielectric Constant Materials and Their Applications, Vol. 2, (Academic Press, New York, 1999). 2. Y. Cao, P. C. Irwin, K. Younsi, IEEE Trans. Dielect. Elect. Insulation 11, 797 (2004). 3. W. Sarjeant, J. Zirnheld, F. MacDougall, IEEE Trans. Plasma Sci. 26, 1368 (1998). 4. W. J. Sarjeant et al., in (1), chap. 9. 5. J. H. Tortai, N. Bonifaci, A. Denat, J. Appl. Phys. 97, 053304 (2005). 6. M. Rabuffi, G. Picci, IEEE Trans. Plasma Sci. 30, 1939 (2002). 7. H. S. Nalwa, Ed., Ferroelectric Polymers (Marcel Dekker, New York, 1995). 8. A. Lovinger, Science 220, 1115 (1983). 9. Q. M. Zhang, V. Bharti, G. Kavarnos, in The Encyclopedia of Smart Materials, Vol. 2, M. Schwartz, Ed. (Wiley, New York, 2002). 10. T. T. Wang, J. M. Herbort, A. M. Glass, Eds., The Applications of Ferroelectric Polymers (Blackie, Glasgow, 1988). 11. Q. M. Zhang, V. Bharti, X. Zhao, Science 280, 2101 (1998). 12. Q. M. Zhang, C. Huang, F. Xia, J. Su, in Electroactive Polymer Actuators as Artificial Muscles, Y. Bar-Cohen, Ed. (SPIE Press, Bellingham, WA, 2004), chap. 4. 13. J. K. Sinha, J. Sci. Instrum. 42, 696 (1965). 14. Materials and methods are available as supporting material on Science Online. 15. V. Bobnar et al., Macromolecules 36, 4436 (2003). 16. R. G. Kepler, in (7), chap. 3. 17. H. Su, A. Strachan, W. Goddard III, Phys. Rev. B70, 064101 (2004). 18. A. V. Bune et al., Nature 391, 874 (1998). 19. This work was supported by the Office of Naval Research under grant numbers N00014-05-1-0455 and N0001405-1-0541. We thank 3M for supplying P(VDF-CTFE) and PVDF powders used in this investigation.

Fig. 4. Discharge energy density as a function of time measured from the direct discharge of the P(VDF-CTFE) polymer films to RL of 1 kilohm. The E value is 253.5 MV/m. line phase, the interchain coupling lowers the energy of the all-trans conformation with respect to the TGTG? conformation (17). Therefore, defects that expand the interchain lattice spacing may lower the energy of the TGTG? conformation and achieve a reversible change in conformations between the nonpolar and polar phases. This can also lead to a substantial change in D in the absence of a very high value of K at low E and the early D-saturation. Based on these considerations, we examined random copolymers of VDF-chlorotrifluoroethylene (CTFE), in which the bulkier size of CTFE compared with VDF may expand the interchain space and distort the crystalline ordering (14). As previously observed for the PVDF homopolymer, the films prepared from the solution cast are in the a phase, whereas, after mechanical stretching, the films are converted to b phase, which is the thermodynamically lower energy phase for PVDF (16, 17). In contrast, both of the films EP(VDFCTFE) 91/9 mol%, unstretched and uniaxially stretched^ exhibited an x-ray pattern of mostly the a phase (fig. S3), indicating that the small amount of bulky CTFE stabilizes the TGTG? confor-

mations and the a phase. In addition, the D-E hysteresis loop, measured from the uniaxially stretched P(VDF-CTFE) 91/9 mol% films, also exhibited much smaller remnant polarization as compared with that of PVDF (Fig. 3A). The discharged energy density from the films of P(VDF-CTFE) 91/9 mol% was measured by the use of the Sawyer-Tower circuit under unipolar Es of 10 Hz (Fig. 3B) (13, 14). The data indicate that P(VDF-CTFE) 91/9 mol% copolymer does not show D-saturation as seen in the terpolymers (fig. S2A). The discharged energy density as a function of E is presented in Fig. 3C, and the copolymer exhibited an energy density of more than 17 J/cm3 under a field of 575 MV/m. Furthermore, the discharged energy density increased with the square of E, which suggests that, by improving the film quality so that Eb can be further raised to 9575 MV/m, a much higher energy density can be achieved (Ue ? E2). For instance, Eb in the LangmuirBlodgett films of P(VDF-TrFE) copolymer has been shown to be higher than 1000 MV/m (18). For many applications to energy storage capacitors, a fast discharge time is required (1, 5, 6). We measured the discharge speed of these copolymer films by using a specially designed, high-speed capacitor discharge circuit in which the discharged energy was measured from a load resistor (RL) in series with the polymer capacitor (fig. S4). For P(VDF-CTFE) capacitor films of 0.16 nF (measured at low field and 1 kHz) discharging to a 1 kilohm load, the energy discharging time is well below 1 ms (Fig. 4). As the RL value changed from 1 to 100 kilohms, the discharge time increased by a factor of 100 (fig. S5). This finding indicates that the discharge time is controlled mainly by the capacitance of the film and external RL and that the P(VDF-CTFE) copolymer capacitor can have very fast discharge time (G1 ms). Indeed, the fitting to the voltage change V(t) across the RL yields the time constant that is nearly the same as that deduced from RLC (fig. S6), where C is the capacitance. Furthermore, VOL 313 SCIENCE

Supporting Online Material
www.sciencemag.org/cgi/content/full/313/5785/334/DC1 Materials and Methods Figs. S1 to S6 References 23 March 2006; accepted 13 June 2006 10.1126/science.1127798

336

21 JULY 2006

www.sciencemag.org

CORRECTIONS & CLARIFICATIONS

ERRATUM

Post date 29 September 2006

Reports: “A dielectric polymer with high electric energy density and fast discharge speed” by B. Chu et al. (21 July 2006, p. 334). The affiliations were incorrect. They should appear as follows: Baojin Chu,1 Xin Zhou,2 Kailiang Ren,2 Bret Neese,1,3 Minren Lin,1 Qing Wang,1,3 F. Bauer,4 Q. M. Zhang1,2,3* 1Materials Research Institute, 2Electrical Engineering Department, 3Materials Science and Engineering Department, Pennsylvania State University, University Park, PA 16802, USA. 4Institute Franco-Allemand de Recherches, 5 Rue du General Cassagnou, 68300 Saint-Louis, France.

www.sciencemag.org

SCIENCE

ERRATUM POST DATE

29 SEPTEMBER 2006

1


相关文章:
...polymer with high electric energy density and fa....pdf
accepted 7 June 2006 10.1126/science.1128383 A Dielectric Polymer with High Electric Energy Density and Fast Discharge Speed Baojin Chu,1,2 Xin Zhou,3 ...
PZNT_LSCO异质结的制备与反铁电性能研究_图文.pdf
使用原子力显微镜 ( Seiko, SP I3800N - SPA - 300HV AFM ) 接触模式对 ...A dielectric polymer w ith high electric energy density and fast discharge ...
BST纳米线 超高储能密度_图文.pdf
strength polymer and high dielectric permittivity ...elds which require greater energy density with a ...ultrahigh energy density and fast discharge time....
PPEK_图文.pdf
dielectric properties over a broad frequency and ...of storing high-density electric energy (1, 2)...Remarkable energy densities and fast discharge speed...
PVDF-P(VDF-HFP)_图文.pdf
with high energy density and fast exhibited improved crystallinity of a-phase...The dielectric constant of the desired properties of polymer systems, based ...
超高击穿场强,低损耗聚合物_图文.pdf
M. Zhang* Dielectric materials with high electric energy density and low ...dielectric polymer based on aromatic polythiourea (ArPTU), which is a ...
High%20Dielectric%20Constant%20Polymer%20Film%20Cap....pdf
M. Zhang. “A Dielectric Polymer with High Electric Energy Density and Fast Discharge Speed”, Science 313, 334 (2006). Baojin Chu, Xin Zhou, B. ...
Introduction of dielectric elastomers_图文.pdf
Basic mechanism and applications ? Dielectric ...Large deformation (>100%) ?High energy density ...a Q a C = = ε0 l Φε0 E= Electric ...
英文原文和中文译文.doc
electric current, the frequency, the pulse and ...Making the capacitor the high polymer dielectric ...reduce the airplane weight, reduces the energy. ...
英文翻译.doc
the electric field with the energy up to 10eV ...discharge point, heat up to medium high ...and dielectric loss, thus creating a vicious ...
传感器新技术外文资料.doc
Making the capacitor the high polymer dielectric ...and so on the temperature, pres-sure, electric ...reduce the airplane weight, reduces the energy. ...
复合材料课件11_图文.pdf
Similarly, to address the high capacitance density...Fig.11.20 Variation of (a) dielectric constant,...magneticelectric energy conversion and thus is ...
Science-2013-Bonnell-401-2.pdf
nanolithography and high-density memory applications...with no electric ?eld applied), high dielectric ...polymer ferroelectric compounds by a factor of 10...
Sentaurus.pdf
fast response, high light sensitivity and high-de...Lee reported ZnO-TFTs with a polymer dielectric ...energy to migrate and crystallize at room ...
北京化工大学正志鹏电子材料论文.doc
Array/Polymer Core/Shell Structured Composites with High Dielectric Permittivity,Low Dielectric Loss, and Large Energy Density[J].Adv Mater.2011,23,5104-...
科技文献.doc
Making the capacitor the high polymer dielectric ...and so on the temperature, pressure, electric ...reduce the airplane weight, reduces the energy. ...
8.外文文献英文.doc
electric current, the frequency, the pulse and ...Making the capacitor the high polymer dielectric ...may reduce theairplane weight, reduces the energy...
Supercapacitor Devices Based on Graphene Materials.pdf
conventional dielectric capacitors.2 Furthermore, ...with energy density of 28.5 Wh/kg, which are...c surface area and high electric conductivity (?...
Electrochemical supercapacitors Energy storage.pdf
with pseudocapacitors employing certain high surface...and positive electric charges on the plates of a...capacitors have a substantially low energy-density....
Thermally conducting aluminum nitride polymer-matri....pdf
Thermally conducting aluminum nitride polymer-matrix ...high electrical resistivity, a low dielectric ...thermal interface material and electric cable insulation...