• <tr id="yyy80"></tr>
  • <sup id="yyy80"></sup>
  • <tfoot id="yyy80"><noscript id="yyy80"></noscript></tfoot>
  • 99热精品在线国产_美女午夜性视频免费_国产精品国产高清国产av_av欧美777_自拍偷自拍亚洲精品老妇_亚洲熟女精品中文字幕_www日本黄色视频网_国产精品野战在线观看 ?

    Proton-Exchange Sulfonated Poly (ether ether ketone) (SPEEK)/SiOx-S Composite Membranes in Direct Methanol Fuel Cells*

    2009-05-12 03:32:50GAOQijun高啟君WANGYuxin王宇新XULi許莉WEIGuoqiang衛(wèi)國(guó)強(qiáng)andWANGZhitao王志濤
    關(guān)鍵詞:高啟王宇衛(wèi)國(guó)

    GAO Qijun (高啟君), WANG Yuxin (王宇新), XU Li (許莉), WEI Guoqiang (衛(wèi)國(guó)強(qiáng)) and WANG Zhitao (王志濤)

    ?

    Proton-Exchange Sulfonated Poly (ether ether ketone) (SPEEK)/SiO-S Composite Membranes in Direct Methanol Fuel Cells*

    GAO Qijun (高啟君)1,2, WANG Yuxin (王宇新)1,2, XU Li (許莉)1,**, WEI Guoqiang (衛(wèi)國(guó)強(qiáng))1,2and WANG Zhitao (王志濤)1,2

    1School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, China2State Key Laboratory of Chemical Engineering, Tianjin 300072, China

    sulfonated poly(ether ether ketone), functionalized silica, composite membrane, direct methanol fuel cell

    1 INTRODUCTION

    Development and research on direct methanol fuel cells (DMFCs) have been an area of active interest since the 1990s [1]. DMFC technology has made significant progress over the years, but two obstacles still need to be surmounted before DMFC commercialization [2, 3]. First, the anode catalyst is inactive and unstable enough causing a high overpotential loss of the anode. Second, severe methanol crossover of the commercially available perfluorosulfonic acid (PFSA) proton-exchange membranes (PEM) (.., Nafionò) from anode to cathode reduces fuel efficiency and increases the mixed electrode potential of the cathode, resulting in low cell performance [2, 3]. Production of the commercially available PFSA polymer membranes is costly and time-consuming. Therefore, there is an urgent need to develop PEM with improved properties, including high proton conductivity, low methanol permeability, and low cost.

    Much effort has been made in recent years to develop an alternative fluorine-free polymer membranes [4-8] and to modify PFSA polymer membranes [9]. It is widely recognized that sulfonated poly (ether ether ketone) (SPEEK) polymers are very promising materials for membranes in DMFCs [4]. SPEEK polymers can, in theory, have higher ion-exchange capacity (IEC) than PFSA polymers, which may compensate for the demerit of weaker acidity of their own sulfonic groups (SO3H). SPEEK membranes also exhibit lower methanol crossover and are less costly to produce than PFSA membranes [5]. The demand for high proton conductivity calls for SPEEK membranes to have a high degree of sulfonation (DS) and to function at high temperatures. However, highly sulfonated SPEEK membranes tend to swell excessively or even dissolve at high temperatures. There have been several attempts to overcome the excessive swelling while maintaining high proton conductivity, for example, by synthesizing SPEEK with various hydrophobic block: hydrophilic block ratios [10], by introducing cross-links between some of the sulfonic groups in the SPEEK membrane [11], and by blending the SPEEK polymer with non-conductive engineering thermoplastics (.., SPEEK/PEI, SPEEK/PES, SPEEK/PBI) [12-14].

    Addition of inorganic particles (.., ZrO2) into the SPEEK matrix is also an important approach in PEM research [15]. This approach has two objectives: one is to improve the mechanical properties of the composite membranes and the other is to physically counteract methanol crossover [16, 17]. It has also been suggested that the size of the particles (nano or micro), surface properties (acid or basic), and the functionalization determine whether the filler, besides acting as a reinforcing components as above mentioned, can impart a significant improvement in proton conductivity [16-22].

    Figure 1 Molecular structure of the functionalized silica with sulfonic acid groups (SiO-S)

    2 EXPERIMENTAL

    2.1 Materials

    2.2 Preparation of SiOx-S powder

    The SiO-S gel can be prepared from SiO-Cl hydrolyzed for 6 h at 80°C as described in a previous study [17]. The gel was washed repeatedly with deionized water until pH of the rinse water was 7 and then dried at 70°C for 24 h to remove water. The resultant SiO-S was ground to fine powder by a QM-ISP04 ball mill and finally stored in an airtight bottle before being used.

    The back-titration of sulfonic groups within the SiO-S powder was used to find whether the SiO-Cl hydrolyzed into the SiO-S completely.

    2.3 Synthesis of SPEEK

    PEEK (10g) was added gradually to 100 ml of concentrated sulfuric acid in a three-necked flask with vigorous stirring at 60°C. At a prescribed time point, the acid polymer solution was added to a large excessive ice-cold water with continuous agitation. The SPEEK precipitate was rinsed repeatedly with deionized water until the water reached pH 7. Then the SPEEK was dried at room temperature for 2 days followed by drying at 60°C for 24 h under vacuum. The IEC and DS of the sulfonated polymers were determined by a classical back-titration method as described in a previous study[23].

    2.4 Membrane preparation

    The membranes were prepared by solution casting. When the mass content of SiO-S powder is higher than 20%, the composite membrane becomes brittle in dry state at room temperature. Therefore, SPEEK/SiO-S (3%–20%) composite membranes (the degree of sulfonation for the SPEEK polymer is 55.1%, the mass content of SiO-S powder in the composite membranes is from 3% to 20%) were studied in this article.

    SPEEK and SPES-C in prescribed amount were dissolved separately in DMF (10%, by mass) and then the two solutions were mixed and stirred for 6 h. The mixed solution was cast onto a glass plate and dried overnight at 60°C in a vacuum oven, followed by annealing at 100°C for 4 h. After cooling to room temperature, the membrane was peeled from the glass plate with deionized water.

    SiO-S powder in prescribed amount was uniformly dispersed in DMF solvent with mechanical stirring. The desired amount of SPEEK was then added to the solvent to make a 10% (by mass) solution. After stirring for 6 h and degassing, the solution was cast onto a glass plate and dried overnight at 60°C in a vacuum oven, followed by annealing at 100°C for 4 h. After cooling to room temperature, the membrane was peeled from the glass plate with deionized water. Finally, the membrane was treated with 1 mol·L-1sulfuric acid at room temperature for 24 h and subsequently rinsed with deionized water several times to remove acid completely. Membranes were kept in deionized water before testing. The thickness of the dried membranes was 80-95 μm.

    2.5 Membrane characterization

    Fourier transform infrared spectroscopy (FT-IR) were measured in absorbance mode by using an FT-IR spectrometer (Bio-RAD FTS 6000) in the range of wave numbers 600-4000 cm-1to compare position of IR bands and to check the presence of functional groups and their interaction in composite membranes. Prior to FT-IR measurement, the samples were dried at 80°C for 24 h.

    Thermogravimetric analysis (TGA) was used to estimate the thermal stability of the composite membranes. We used a TGA thermogravimetric analyzer (TA-50 Instrument Shimadzu TGA) at a heating rate of 10 K·min-1in nitrogen gas in the temperature range 30-800°C. All specimens were dried overnight at 90°C under vacuum before measurements.

    The morphology of the cross-section of samples was examined with an environment-scanning electron microscope (PHILIPS XL30 ESEM). The samples werecryo-fractured in liquid nitrogen to obtain fresh cross-sections, which were coated with gold before measurements.

    The swelling degree (SD) of the specimens was obtained by measuring the area difference between the dry and the wet states as described in Ref. [23]. The membranes were cut into 3 cm×4 cm rectangles and dried overnight at 90°C under vacuum before measuring the area (d). The dried membranes were immersed for 48 h in 1 mol·L-1methanol to reach equilibrium at the desired temperature. The wet membranes were wiped dry with tissue paper and the area was measured again (w). SD was calculated (in area percent) as follows:

    wheredandware the areas of dry and corresponding wet membrane sheets, respectively. Three sheets of each membrane composition were measured by the above method, and the average was calculated.

    The proton conductivity of samples in the lateral direction was measured with a measurement cell and a frequency response analyzer (FRA) (Autolab PG-STAT20). Two stainless steel electrodes connected to the FRA were pressed against the membrane to be tested. The measurement temperature was controlled from room temperature to 160°C. The conductivity,, was calculated from the impedance data, using the relation/(×), whereandare the distance between the electrodes and the cross-section area of the membrane, respectively, andwas derived from the low intersection of the high-frequency semi circle on a complex impedance plane with the() axis. For membranes that dissolved below 160°C, their dissolution was tested by measuring the weight before and after the proton conductivity measurement. Besides, the proton conductivity of SiO-S powder was obtained as described in a previous study [23]. The powder needs to be pressed into a slice before testing.

    3 RESULTS AND DISCUSSION

    3.1 Preparation of the SiOx-S

    Table 1 The back-titration results of sulfonic groups within the SiOx-S hydrolyzed at different time

    3.2 Sulfonation

    3.3 FT-IR spectra

    3.4 Thermal stability

    Figure 3 TGA curves of SiOx-S powder, SPEEK/SiOx-S (18%) composite membrane and pure SPEEK membrane

    1—SiOx-S; 2—SPEEK/SiOx-S (18%); 3—SPEEK (DS = 55.1%)

    3.5 Morphology

    The basic homogeneous distribution of SiO-S powder within the SPEEK matrix and no sign of evident aggregation can be observed from the SEM images of the SPEEK/SiO-S composite membranes at magnification of up to 10000× (Fig. 4) although the SiO-S content reaches 20%. The nominal powder size is less than 500 nm as indicated by the SEM images.

    Figure 4 Cross-section images of SPEEK/SiO-S (5%) composite membrane and SPEEK/SiO-S (20%) composite membrane

    3.6 Swelling behavior

    Figure 5 Swelling degree of Nafionò115, SPEEK membrane and SPEEK/SiO-S composite membranes in 1 mol·L-1methanol solution at different temperatures

    Figure 6 Arrehenius plots of methanol permeability for Nafionò115, pure SPEEK membrane, and SPEEK/SiO-S composite membranes

    Figure 7 Arrehenius plots of proton conductivity at 100%RH for Nafionò115, SiO-S powder, pure SPEEK membrane and SPEEK/SiO-S (15%, 20%) composite membranes under 100% RH

    3.7 Methanol permeability

    Methanol fuel is fed in the form of liquid below 80°C, thus the methanol crossover is more serious than in the form of gas at higher temperatures [2]. We analyze the methanol permeability of the membranes below 80°C here. Fig. 6 shows the methanol permeability as a function of temperature for Nafionò115, pure SPEEK and SPEEK/SiO-S composite membranes. The methanol permeability of Nafionò115 at room temperature is 1.02×10-6cm2·s-1, which is very close to the value reported by Tricoli. [24, 26, 27], while that of SPEEK and SPEEK/ SiO-S membranes are approximately an order of magnitude lower than Nafionò115.

    The difference in methanol permeability between Nafionò115 and the SPEEK membrane can be explained qualitatively by the differences in their microstructures and the acidity of their sulfonic acid functional groups [4]. Nafionò115 macromolecules consist of very hydrophobic perfluorinated backbones and very hydrophilic side chains with sulfonic acid functional groups. The very different components lead to relatively large microphase separation in Nafionò115, which results in the low resistance to methanol permeation. The situation for SPEEK polymer is rather different. The carbon-hydrogen main chains with ether links, phenyl rings, and carbonyl groups in SPEEK make it less hydrophobic and more rigid compared with Nafionò115. Furthermore, the acidity of sulfonic acid functional groups of the SPEEK polymer is weaker than that of Nafionò115. Therefore, the microphase separation in the SPEEK membrane is not obvious and the hydrophilic ion channels are narrower, which results in low methanol permeability. This can also be proved by the results of schematic representation of the microstructure of Nafionò115 and SPEEK reported by Kreuer[4].

    As can be seen in Fig. 6, the methanol permeability of the SPEEK/SiO-S composite membranes is even lower and decreases with the increased SiO-S content in the membrane. The addition of SiO-S inhibits effectively the swelling of SPEEK matrix (Fig. 5) and thus imposes higher resistance to methanol crossover. The higher resistance to methanol crossover of the SPEEK/SiO-S composite membranes is beneficial to improve open circuit voltage (OCV) of DMFCs [2].

    3.8 Proton conductivity

    The relation between the conductivity and the reciprocal of the temperature for all the SPEEK and SPEEK/SiO-S membranes, before they dissolve, can be described by the Arrhenius equation and exhibits straight lines in a semilogarithmic graph (Fig. 7). The apparent activation energy of proton transfer, which is equal to the slope of the corresponding lines of different membranes, is obtained from the Arrhenius plot. It is noteworthy that the apparent activation energy of the SPEEK membrane has approximately 38 kJ×mol-1, in contrast to 9 kJ×mol-1for Nafionò115. The very high apparent activation energy of the SPEEK membrane is believed to be a consequence of its low swelling degree and slow variation with temperature (as shown in Fig. 7). Narrow ion channels and rich branches with dead-end “pockets” in the membrane will contribute to the high barrier to proton transfer [4].

    SPEEK and SiO-S materials are weakly acidic compared with Nafionò115. The dissociation of sulfonic acid functional groups in these materials increases at high temperatures [5, 23], whereas that of Nafionò115 approaches 100% at room temperature. Therefore, the elevation of temperature increases both the proton mobility and the proton content in the SPEEK and SPEEK/SiO-S membranes, which results in a much faster increase of proton conductivity with temperature.

    The proton conductivity of SiO-S powder is 0.018 S×cm-1at room temperature and 100% RH, and reaches 0.086 S·cm-1at 120°C. The proton conductivity of composite membranes increases slightly as mass content of SiO-S powder increases, although SiO-S powder has lower proton conductivity than the pure SPEEK membrane. The increase in conductivity upon addition of SiO-S can be rationalized based on previous studies [16-22, 28]. This phenomenon has been observed by Kim. [29] in composite PEMs based on heteropolyacid in sulfonated polysulfones. The presence of the additive was found to enhance the proton conductivity, while at the same time decrease the water uptake. In this case, it is not completely understood whether the filler participates actively in the proton conduction by enhancing proton dissociation or by providing favorable pathways for the proton along polymer-particle interfaces [16-18, 22]. The conductivity results obtained in this study are very similar to that of previous studies above, and it is likely that a similar mechanism is in place. The lower apparent activation energy of proton transfer through the composite membranes than through the pure SPEEK membrane also shows that the similar mechanism exists. The apparent activation energy of the SPEEK/SiO-S (20%) composite membrane is 33.09 kJ×mol-1. The conductivity of SPEEK/SiO-S (20%) exceeds slightly that of Nafionò115 at 145°C and 100% RH and approaches 0.17S×cm-1.

    3.9 Working temperature

    Figure 8 shows*as a function of the mass content of SiO-S in the composite membranes. SPEEK membranes of 55.1% DS is useful only below 90°C. The*of the composite membranes is, however, markedly increased as the mass content of SiO-S powder increases. As discussed in Section 3.6, the addition of SiO-S to SPEEK matrix inhibits effectively the swelling and dissolution of the membranes below 80°C. The membranes’ swelling at temperature above 100°C was quickly measured by measuring the area changes after their conductivity was tested at the temperature. It can be found that the content of SiO-S increased from 10% to 20%, the swelling degree of composite membranes decreased from 67.8% to 30.4% at 110°C and the content of SiO-S increased from 15% to 20%, the swelling degree of composite membranes decreased from 72.3% to 35.8% at 130°C. The increase of*with the increased content of SiO-S in the composite membrane should be attributed to the depressed swelling and dissolution of the composite membranes at high temperatures.

    Figure 8*of the SPEEK/SiO-S composite membranes with different SiO-S mass contents

    The extension of the working temperature of the membrane is beneficial for DMFC in many aspects. Working at higher temperature, the membrane exhibits higher proton conductivity, which leads to lower ohmic losses in DMFC. The electrocatalysts are also more active and more tolerant to carbon monoxide poisoning [30] at high temperatures. When methanol fuel is fed in the form of gas at high temperature, the methanol crossover and its negative effects can be reduced markedly. Operating at high temperature also simplifies the management of water and heat in the DMFC systems [30].

    4 CONCLUSIONS

    The results of this study indicate a strong potential of these composite membranes for use in DMFCs. SPEEK/SiO-S composite membranes with high levels of dimensional stability were prepared. The methanol permeability of the membranes was shown to be about one order of magnitude lower than that of Nafionò115, and to decrease with the increase of SiO-S content. The addition of the SiO-S into the membranes not only increases slightly the proton conductivity of composite membranes but also effectively inhibits their swelling, which enables them to be used at higher temperature, thus presenting higher proton conductivity. The results of this study indicate a strong potential of these composite membranes for use in DMFCs.

    1 Kuver, A., Kamloth, K.P., “Comparative study of methanol crossover acrosselectropolymerized and commercial proton exchange membrane electrolytes for the acid direct methanol fuel cell”,., 43 (16), 2527-2535 (1998).

    2 Ren, X., Zawadzinski, T.A., Uribe, F., Dai, H., “Methanol cross-over in direct methanol fuel cells”,..., 95 (23), 284-289 (1995).

    3 Heinzel, A., Barragan, V.M., “A review of the state-of-the-art of the methanol crossover in direct methanol fuel cells”,., 84, 70-74 (1999).

    4 Kreuer, K.D., “On the development of proton conducting polymer membranes for hydrogen and methanol fuel cells”,..., 185, 29-39 (2001).

    5 Yang, B., Manthiram, A., “Sulfonated poly(ether ether ketone) membranes for direct methanol fuel cells”,.., 6, A229-A231 (2003).

    6 Wycisk, R., Lee, J.K., Pintauro, P.N., “Sulfonated polyphosphazene- polybenzimidazole membranes for DMFCs”,..., 152, A892-A898 (2005).

    7 Dai, H., Guan, R., Li, C.H., Liu, J.H., “Development and characterization of sulfonated poly(ether sulfone) for proton exchange membrane materials”,., 178, 339-345 (2007).

    8 Shahi, V.K., “Highly charged proton-exchange membrane: Sulfonated poly(ether sulfone)-silica polyelectrolyte composite membranes for fuel cells”,., 177, 3395-3404 (2007).

    9 Park, K.T., Jung, U.H., Choi, D.W., Chun, K., Lee, H.M., Kim, S.H., “ZrO2-SiO2/Nafion (R) composite membrane for polymer electrolyte membrane fuel cells operation at high temperature and low humidity”,., 177, 247-253 (2008).

    10 Zhao, C., Li, X., Na, H., “Synthesis of sulfonated poly(ether ether ketone) (S-PEEKs) material for proton exchange membrane”,..., 280, 643-650 (2006).

    11 Mikhailenko, S.U.D., Wang, K.P., Kaliaguine, S., Xing, P.X., Robertson, G.P., Guiver, M.D., “Proton conducting membranes based on cross-linked sulfonated poly(ether ether ketone) (SPEEK)”,..., 233, 93-99 (2004).

    12 Mikhailenko, S.D., Zaidi, S.M.J., Kaliaguine, S., “Electrical properties of sulfonated polyether ether ketone/polyetherimide blend membranes doped with inorganic acids”,...,:.., 33, 1386-1395 (2000).

    13 Manea, C., Mulder, M., “Characterization of polymer blends of polyether sulfone/sulfonated polysulfone and polyether sulfone/sulfonated polyetherether ketone for direct methanol fuel cell applications”,..., 206, 443-453 (2002).

    14 Zhang, H.Q., Li, X.F., Zhao, C.J., Fu, T.Z., Shi, Y.H., Na, H., “Composite membranes based on highly sulfonated PEEK and PBI: Morphology characteristics and performance”,..., 308, 67-74 (2008).

    15 Silva, V.S., Ruffmann, B., Silva, H., Gallego, Y.A., Mends, A., Madeira, L.M., Nunes, S.P., “Proton electrolyte membrane properties and direct methanol fuel cell performance/I. Characterization of hybrid sulfonated poly (ether ether ketone)/zirconium oxide membranes”,., 140, 34-40 (2005).

    16 Uchida, H., Ueno,Y., Hagihara, H., Watanabe, M., “Self-humidifying electrolyte membranes for fuel cells—Preparation of highly dispersed TiO2particles in Nafion 112”,.., 150, A57-A62 (2003).

    17 Martinelli, A., Matic, A., Jacobsson, P., borjesson, L., Navarra, M.A., Fernicola, A., Panero, S., Scrosati, B., “Structural analysis of PVA-based proton conducting membranes”,., 177, 2431-2435 (2006).

    18 Kim, D.S., Park, H.B., Rhim, J.W., Lee, Y.M., “Preparation and characterization of crosslinked PVA/SiO2hybrid membranes containing sulfonic acid groups for direct methanol fuel cell applications ”,..., 240, 37-48 (2004).

    19 Croce, F., Persi, L., Scrosati, B., Serraino-Fiory, F., Plichta, E., Hendrickson, M.A., “Role of the ceramic fillers in enhancing the transport properties of composite polymer electrolytes”,., 46, 2457-2461 (2001).

    20 Shao, Z.G.., Joghee, P., Hsing, I.M., “Preparation and characterization of hybrid Nafion-silica membrane doped with phosphotungstic acid for high temperature operation of proton exchange membrane fuel cells”,.., 229, 43-51 (2004).

    21 Xu, W.L., Liu, C.P., Xue, X.Z., Su, Y., Lv, Y.Z., Xing, W., Lu, T.H., “New proton exchange membranes based on poly (vinyl alcohol) for DMFCs ”,., 171, 121-127 (2004).

    22 Sambandam, S., Ramani, V., “SPEEK/functionalized silica composite membranes for polymer electrolyte fuel cells”,., 170, 259-267 (2007).

    23 Li, L., Wang, Y.X., “Sulfonated polyethersulfone Cardo membranes for direct methanol fuel cell”,..., 246, 167-172 (2005).

    24 Li, L., Wang, Y.X., “A hybrid membrane of poly(vinyl alcohol) and phosphotungstic acid for fuel cells”,...., 10 (5), 614-617 (2002).

    25 Zaidi, S.M.J., Mikhailenko, S.D., Robertson, G.P., Guiver, M.D., Kaliaguine, S., “Proton conducting composite membranes from polyetherether ketone and heteropolyacids for fuel cell applications”,..., 173, 17-34 (2000).

    26 Tricoli, V., Carretta, N., Bartolozzi, M., “A comparative investgation of proton and methanol transport in fluorinated ionomeric membranes”,..., 147, 1286-1290 (2000).

    27 Huang, M.Y., Wang, Y.X., Cai, Y.Q., Xu, L., “Sulfonated poly(ether ether ketone)/zirconium tricarboxybutylphosphonate composite proton-exchange membranes for direct methanol fuel cells”,, 4, 337-342 (2007).

    28 Gasa, J.V., Boob, S., Weiss, R.A., Shaw, M.T., “Proton-exchange membranes composed of slightly sulfonated poly(ether ketone ketone) and highly sulfonated crosslinked polystyrene particles”,..., 269, 177-186 (2006).

    29 Kim, Y.S., Wang, F., Hickner, M., Zawodzinski, T.A., McGrath, J.E., “Fabrication and characterization of heteropolyacid (H3PW12O40)/ directly polymerized sulfonated poly(arylene ether sulfone) copolymer composite membranes for higher temperature fuel cell applications”,..., 212, 263-282 (2003).

    30 Li, Q.F., Huang, R.H., “Approaches and recent development of polymer electrolyte membranes for fuel cells operating above 100°C”,.., 15, 4896-4915 (2003).

    2008-07-24,

    2008-11-20.

    the State Key Development Program for Basic Research of China (2008CB617502), the National Natural Science Foundation of China (20606025), and Program for Changjiang Scholars and Innovative Research Team in University of China (IRT0641).

    ** To whom correspondence should be addressed. E-mail: xuli620@eyou.com

    猜你喜歡
    高啟王宇衛(wèi)國(guó)
    基于ShuffleNet V2算法的三維視線估計(jì)
    A novel low-loss four-bit bandpass filter using RF MEMS switches
    許衛(wèi)國(guó)書(shū)法作品選
    我相信
    高啟與北郭詩(shī)社成員交游考
    Cavitation erosion in bloods*
    我的同桌
    高啟對(duì)李白詩(shī)歌藝術(shù)特點(diǎn)的繼承
    Evaluation on nitrogen isotopes analysis in high-C/N-ratio plants using elemental analyzer/isotope ratio mass spectrometry
    A Support Vector Machine Based on Bayesian Criterion
    日本-黄色视频高清免费观看| 中文乱码字字幕精品一区二区三区| 国产av国产精品国产| 日本av手机在线免费观看| 中文精品一卡2卡3卡4更新| 欧美精品高潮呻吟av久久| 亚洲国产av影院在线观看| 日本免费在线观看一区| 男人添女人高潮全过程视频| 国产精品麻豆人妻色哟哟久久| 97在线人人人人妻| 午夜福利视频在线观看免费| 亚洲无线观看免费| 成人手机av| 国产精品欧美亚洲77777| 国产免费一区二区三区四区乱码| 久久精品国产a三级三级三级| 在线精品无人区一区二区三| 黄片无遮挡物在线观看| 青青草视频在线视频观看| 51国产日韩欧美| 欧美精品高潮呻吟av久久| 久久久久久久久久人人人人人人| 又大又黄又爽视频免费| 免费观看无遮挡的男女| 久久久久久久大尺度免费视频| 亚洲欧美成人精品一区二区| 成人手机av| 亚洲av电影在线观看一区二区三区| 国产精品久久久久久精品电影小说| 涩涩av久久男人的天堂| 免费观看av网站的网址| 啦啦啦在线观看免费高清www| 亚洲国产最新在线播放| 亚洲国产毛片av蜜桃av| 国产女主播在线喷水免费视频网站| 日韩大片免费观看网站| 老司机影院成人| 丝袜喷水一区| 精品熟女少妇av免费看| 18禁裸乳无遮挡动漫免费视频| 美女内射精品一级片tv| videos熟女内射| 成人亚洲精品一区在线观看| 美女国产视频在线观看| 亚洲四区av| 丁香六月天网| 99国产综合亚洲精品| 视频区图区小说| 高清不卡的av网站| 亚洲图色成人| 一级毛片黄色毛片免费观看视频| 少妇人妻久久综合中文| 国内精品宾馆在线| 亚洲精品久久成人aⅴ小说 | 国产欧美日韩综合在线一区二区| 男男h啪啪无遮挡| 纯流量卡能插随身wifi吗| 日日摸夜夜添夜夜添av毛片| 国产熟女午夜一区二区三区 | 国产白丝娇喘喷水9色精品| 国产一区二区三区av在线| 久久久久人妻精品一区果冻| 蜜桃国产av成人99| 国产白丝娇喘喷水9色精品| 国产国语露脸激情在线看| 黄色怎么调成土黄色| 在线观看www视频免费| 日韩成人伦理影院| 一区二区三区精品91| 久久久久人妻精品一区果冻| 午夜精品国产一区二区电影| 一级毛片黄色毛片免费观看视频| 啦啦啦在线观看免费高清www| 美女国产高潮福利片在线看| 日韩在线高清观看一区二区三区| 街头女战士在线观看网站| 亚洲国产精品一区三区| 久久精品国产亚洲网站| 久久久久久久亚洲中文字幕| 国产女主播在线喷水免费视频网站| 国产亚洲欧美精品永久| 国产精品国产三级国产专区5o| kizo精华| av免费观看日本| 日本爱情动作片www.在线观看| 亚洲av不卡在线观看| 黄色一级大片看看| 99热国产这里只有精品6| 日日爽夜夜爽网站| 亚洲av成人精品一区久久| 日本黄大片高清| 午夜激情久久久久久久| 亚洲成人一二三区av| 精品少妇黑人巨大在线播放| 日韩制服骚丝袜av| 在线 av 中文字幕| 人人妻人人爽人人添夜夜欢视频| 国产国语露脸激情在线看| av国产久精品久网站免费入址| 日日啪夜夜爽| 男的添女的下面高潮视频| av一本久久久久| 99热全是精品| 看十八女毛片水多多多| 又粗又硬又长又爽又黄的视频| 最近手机中文字幕大全| 赤兔流量卡办理| 亚洲精品日韩在线中文字幕| 91精品国产国语对白视频| 亚洲图色成人| 天天躁夜夜躁狠狠久久av| 国产视频首页在线观看| 国产爽快片一区二区三区| 波野结衣二区三区在线| av免费在线看不卡| 亚洲欧美日韩另类电影网站| 少妇高潮的动态图| 亚洲av男天堂| 色婷婷久久久亚洲欧美| 另类亚洲欧美激情| 亚洲国产av新网站| 熟女人妻精品中文字幕| 国产伦理片在线播放av一区| 亚洲综合色惰| 韩国av在线不卡| 国产精品99久久久久久久久| av福利片在线| 色婷婷久久久亚洲欧美| 国产成人午夜福利电影在线观看| 亚洲av成人精品一二三区| 午夜老司机福利剧场| 久久久a久久爽久久v久久| 性高湖久久久久久久久免费观看| 大香蕉久久网| 国产免费现黄频在线看| 久久久国产一区二区| av在线播放精品| 欧美xxxx性猛交bbbb| 久久精品国产亚洲av天美| 特大巨黑吊av在线直播| 香蕉精品网在线| 乱人伦中国视频| 久久久久久久久久成人| 涩涩av久久男人的天堂| 久久久久久人妻| 婷婷色av中文字幕| 成年女人在线观看亚洲视频| 午夜福利,免费看| 肉色欧美久久久久久久蜜桃| 视频在线观看一区二区三区| av又黄又爽大尺度在线免费看| 夫妻午夜视频| 一级a做视频免费观看| 好男人视频免费观看在线| 蜜桃国产av成人99| 亚洲丝袜综合中文字幕| 熟女电影av网| 国产 一区精品| 一区二区三区免费毛片| 久久婷婷青草| 又大又黄又爽视频免费| 一边摸一边做爽爽视频免费| 国产高清不卡午夜福利| 美女xxoo啪啪120秒动态图| 免费黄网站久久成人精品| 欧美三级亚洲精品| 久久99热这里只频精品6学生| 老熟女久久久| 日本-黄色视频高清免费观看| 99久久中文字幕三级久久日本| 欧美性感艳星| a级毛片黄视频| 如何舔出高潮| 日韩在线高清观看一区二区三区| 国产成人精品久久久久久| 免费观看a级毛片全部| 久久影院123| 久久久久久久精品精品| 最后的刺客免费高清国语| 国产成人av激情在线播放 | 精品视频人人做人人爽| 插逼视频在线观看| 亚洲一区二区三区欧美精品| 日日撸夜夜添| 国产高清有码在线观看视频| 人妻系列 视频| 亚洲三级黄色毛片| 日本免费在线观看一区| 国产极品粉嫩免费观看在线 | 中文字幕人妻熟人妻熟丝袜美| 两个人的视频大全免费| 国产成人免费无遮挡视频| 亚洲av成人精品一区久久| 在线观看免费日韩欧美大片 | 欧美精品一区二区大全| xxxhd国产人妻xxx| 秋霞伦理黄片| 午夜av观看不卡| 夜夜骑夜夜射夜夜干| 日日摸夜夜添夜夜添av毛片| 久久久国产一区二区| 飞空精品影院首页| 久久免费观看电影| 日韩欧美精品免费久久| 一个人看视频在线观看www免费| 欧美bdsm另类| 日韩成人av中文字幕在线观看| 欧美 亚洲 国产 日韩一| 在线 av 中文字幕| 成人综合一区亚洲| .国产精品久久| 一区在线观看完整版| 亚洲内射少妇av| 99九九线精品视频在线观看视频| 大香蕉97超碰在线| 精品亚洲乱码少妇综合久久| videosex国产| 精品国产乱码久久久久久小说| 国产精品免费大片| 国产精品熟女久久久久浪| 国产精品麻豆人妻色哟哟久久| 高清午夜精品一区二区三区| 亚洲av成人精品一二三区| 国产成人a∨麻豆精品| 国产无遮挡羞羞视频在线观看| 国产伦理片在线播放av一区| av福利片在线| 亚洲欧美一区二区三区国产| 99国产综合亚洲精品| 欧美性感艳星| 欧美变态另类bdsm刘玥| 成人国语在线视频| 精品99又大又爽又粗少妇毛片| 91久久精品电影网| 国产免费视频播放在线视频| 亚洲,欧美,日韩| 一级毛片 在线播放| a级毛色黄片| 亚洲第一区二区三区不卡| 久久青草综合色| 亚洲丝袜综合中文字幕| 亚洲精品乱久久久久久| 精品亚洲乱码少妇综合久久| 成人手机av| 五月天丁香电影| 国产欧美亚洲国产| 亚洲av电影在线观看一区二区三区| av在线老鸭窝| 亚洲综合色惰| 免费黄网站久久成人精品| 久久久午夜欧美精品| 高清欧美精品videossex| 国产在线视频一区二区| 一级a做视频免费观看| 伊人久久国产一区二区| 婷婷色综合大香蕉| 建设人人有责人人尽责人人享有的| 熟女电影av网| 国产免费一区二区三区四区乱码| 岛国毛片在线播放| xxxhd国产人妻xxx| 高清视频免费观看一区二区| 一级毛片电影观看| 亚洲丝袜综合中文字幕| 又粗又硬又长又爽又黄的视频| 高清毛片免费看| 超色免费av| 国产片特级美女逼逼视频| .国产精品久久| 在线观看美女被高潮喷水网站| 夜夜爽夜夜爽视频| 久久久久视频综合| 在线亚洲精品国产二区图片欧美 | 午夜激情久久久久久久| tube8黄色片| 日韩中字成人| 国产精品久久久久久久久免| 日本av免费视频播放| 美女国产高潮福利片在线看| 99国产精品免费福利视频| 国产亚洲欧美精品永久| 在线观看一区二区三区激情| www.色视频.com| 国产精品蜜桃在线观看| 亚洲av中文av极速乱| 日本欧美国产在线视频| 国产av精品麻豆| 视频中文字幕在线观看| 亚洲精品一二三| 在线观看三级黄色| 九九爱精品视频在线观看| 大香蕉久久成人网| 青春草国产在线视频| 中文天堂在线官网| 亚洲欧美中文字幕日韩二区| 纵有疾风起免费观看全集完整版| 夜夜骑夜夜射夜夜干| 女性生殖器流出的白浆| 久久97久久精品| 人妻一区二区av| 亚洲综合色网址| 乱人伦中国视频| 国产一区二区在线观看日韩| 欧美亚洲日本最大视频资源| 国产精品偷伦视频观看了| 成年人午夜在线观看视频| 99国产综合亚洲精品| 在线观看免费高清a一片| 色5月婷婷丁香| 激情五月婷婷亚洲| 久久久欧美国产精品| 国产一区亚洲一区在线观看| 涩涩av久久男人的天堂| 亚洲欧洲国产日韩| 亚洲图色成人| 精品久久久久久电影网| 十八禁高潮呻吟视频| 69精品国产乱码久久久| 18禁动态无遮挡网站| 国产午夜精品久久久久久一区二区三区| 51国产日韩欧美| 人成视频在线观看免费观看| 色婷婷久久久亚洲欧美| 午夜福利网站1000一区二区三区| 亚洲国产精品成人久久小说| 母亲3免费完整高清在线观看 | 大片电影免费在线观看免费| 国产淫语在线视频| 久久久国产一区二区| 国产一区有黄有色的免费视频| 亚洲国产精品专区欧美| 精品人妻一区二区三区麻豆| 欧美人与性动交α欧美精品济南到 | 国产精品人妻久久久久久| 色哟哟·www| 三上悠亚av全集在线观看| 亚洲精品日韩av片在线观看| 欧美日韩亚洲高清精品| 久久精品国产自在天天线| 国产视频内射| 91国产中文字幕| 99热6这里只有精品| 人成视频在线观看免费观看| 九色亚洲精品在线播放| 亚洲国产精品一区二区三区在线| 中文字幕精品免费在线观看视频 | 亚洲综合色惰| 久久久a久久爽久久v久久| 美女国产视频在线观看| 少妇精品久久久久久久| 亚洲国产欧美在线一区| 亚洲国产毛片av蜜桃av| 精品午夜福利在线看| 乱码一卡2卡4卡精品| 亚洲av.av天堂| 新久久久久国产一级毛片| 菩萨蛮人人尽说江南好唐韦庄| 自线自在国产av| 日韩精品有码人妻一区| 久久久久久人妻| 亚洲欧洲国产日韩| 新久久久久国产一级毛片| 久久久久久伊人网av| 亚洲精品一区蜜桃| 一级毛片 在线播放| 91成人精品电影| 国产成人91sexporn| 亚洲图色成人| 一本色道久久久久久精品综合| av黄色大香蕉| 成人国语在线视频| 亚洲三级黄色毛片| 男女国产视频网站| 欧美+日韩+精品| 人人妻人人添人人爽欧美一区卜| 久久精品国产亚洲av涩爱| 日本爱情动作片www.在线观看| 一个人看视频在线观看www免费| 色视频在线一区二区三区| 亚洲国产精品999| 黄片播放在线免费| 国产一区二区三区综合在线观看 | 精品99又大又爽又粗少妇毛片| 国产极品天堂在线| 夜夜骑夜夜射夜夜干| 国产不卡av网站在线观看| 18在线观看网站| 日日爽夜夜爽网站| 又黄又爽又刺激的免费视频.| 亚洲av中文av极速乱| 嫩草影院入口| 精品人妻在线不人妻| 亚洲av成人精品一二三区| 国产精品99久久99久久久不卡 | 免费高清在线观看视频在线观看| 91精品国产国语对白视频| 又黄又爽又刺激的免费视频.| 亚洲精品自拍成人| 激情五月婷婷亚洲| av在线老鸭窝| 国产熟女午夜一区二区三区 | 欧美日韩综合久久久久久| 久久久久人妻精品一区果冻| 中文字幕人妻熟人妻熟丝袜美| 免费高清在线观看视频在线观看| 99久久精品国产国产毛片| 日韩在线高清观看一区二区三区| 亚洲精品久久午夜乱码| 免费高清在线观看日韩| 午夜老司机福利剧场| 欧美xxⅹ黑人| 少妇 在线观看| 91国产中文字幕| 女的被弄到高潮叫床怎么办| 99热网站在线观看| 久久精品熟女亚洲av麻豆精品| 丰满乱子伦码专区| 国产毛片在线视频| 国精品久久久久久国模美| 人人妻人人澡人人爽人人夜夜| 一区二区三区免费毛片| 我的老师免费观看完整版| 欧美日韩av久久| 蜜臀久久99精品久久宅男| 日韩一区二区三区影片| 26uuu在线亚洲综合色| 伊人久久国产一区二区| 一边亲一边摸免费视频| 欧美激情 高清一区二区三区| 久久综合国产亚洲精品| 五月开心婷婷网| 国语对白做爰xxxⅹ性视频网站| av.在线天堂| 人妻少妇偷人精品九色| 日本av免费视频播放| 免费黄网站久久成人精品| 成人国产av品久久久| 一级毛片 在线播放| 国产免费又黄又爽又色| av天堂久久9| 欧美+日韩+精品| 国精品久久久久久国模美| 久久国产精品大桥未久av| 免费日韩欧美在线观看| 2022亚洲国产成人精品| 99热这里只有精品一区| 欧美+日韩+精品| 欧美日韩视频高清一区二区三区二| 精品酒店卫生间| 能在线免费看毛片的网站| 我的老师免费观看完整版| 人妻一区二区av| 十八禁网站网址无遮挡| 黄色怎么调成土黄色| 亚洲欧美日韩另类电影网站| av在线老鸭窝| 久久亚洲国产成人精品v| 亚洲经典国产精华液单| 2022亚洲国产成人精品| 国产精品一区二区在线不卡| 国产黄色视频一区二区在线观看| 午夜免费观看性视频| 黄片无遮挡物在线观看| 王馨瑶露胸无遮挡在线观看| tube8黄色片| 久久人妻熟女aⅴ| 国产亚洲最大av| 99热这里只有精品一区| 欧美xxⅹ黑人| 在线观看美女被高潮喷水网站| 欧美成人午夜免费资源| 成人毛片a级毛片在线播放| 精品少妇久久久久久888优播| 日本91视频免费播放| 街头女战士在线观看网站| 最后的刺客免费高清国语| 青春草视频在线免费观看| 一区在线观看完整版| 国产精品熟女久久久久浪| 国产探花极品一区二区| 免费不卡的大黄色大毛片视频在线观看| 韩国av在线不卡| 成人亚洲欧美一区二区av| a级毛片免费高清观看在线播放| 中文字幕免费在线视频6| 成人毛片a级毛片在线播放| 卡戴珊不雅视频在线播放| h视频一区二区三区| 久久久久精品久久久久真实原创| 简卡轻食公司| 国产白丝娇喘喷水9色精品| 精品久久国产蜜桃| 高清毛片免费看| 国产黄色免费在线视频| 丰满少妇做爰视频| 久久av网站| 亚洲一级一片aⅴ在线观看| 国产亚洲一区二区精品| 免费观看av网站的网址| 久久久久久久精品精品| 夜夜爽夜夜爽视频| 精品国产乱码久久久久久小说| 欧美日韩av久久| 久久女婷五月综合色啪小说| 国产精品女同一区二区软件| 国产成人精品一,二区| 最黄视频免费看| 秋霞在线观看毛片| 日本免费在线观看一区| 国产黄片视频在线免费观看| 成年女人在线观看亚洲视频| 国产成人91sexporn| 啦啦啦啦在线视频资源| 欧美精品人与动牲交sv欧美| 嫩草影院入口| 午夜福利,免费看| 大片电影免费在线观看免费| 免费黄网站久久成人精品| 免费高清在线观看视频在线观看| 高清欧美精品videossex| 免费大片黄手机在线观看| 91久久精品国产一区二区三区| 91成人精品电影| 看非洲黑人一级黄片| 亚洲欧美日韩另类电影网站| 国产成人精品久久久久久| 美女福利国产在线| 人妻制服诱惑在线中文字幕| 黄色怎么调成土黄色| 国产精品人妻久久久久久| 精品久久国产蜜桃| 日本91视频免费播放| 亚洲欧美成人综合另类久久久| 青春草国产在线视频| 人成视频在线观看免费观看| 最近手机中文字幕大全| 大香蕉久久网| 亚洲情色 制服丝袜| av专区在线播放| 18禁裸乳无遮挡动漫免费视频| 九九爱精品视频在线观看| 欧美日韩在线观看h| 久久精品国产亚洲网站| 在线看a的网站| 午夜91福利影院| 国产在线免费精品| 人人澡人人妻人| 久久久欧美国产精品| 多毛熟女@视频| 欧美一级a爱片免费观看看| 极品人妻少妇av视频| 女的被弄到高潮叫床怎么办| 免费高清在线观看视频在线观看| 国产黄色视频一区二区在线观看| 亚洲国产精品一区二区三区在线| 国产免费一区二区三区四区乱码| 日韩,欧美,国产一区二区三区| av天堂久久9| 80岁老熟妇乱子伦牲交| 国产男人的电影天堂91| 国产日韩欧美亚洲二区| 免费播放大片免费观看视频在线观看| 热re99久久精品国产66热6| 国产精品成人在线| 亚洲一区二区三区欧美精品| 久久国内精品自在自线图片| 色94色欧美一区二区| 日本爱情动作片www.在线观看| 亚洲精华国产精华液的使用体验| 国产男人的电影天堂91| 国产日韩欧美在线精品| 女人精品久久久久毛片| 自线自在国产av| 亚洲av成人精品一二三区| 午夜精品国产一区二区电影| 黄片无遮挡物在线观看| 日本黄色片子视频| freevideosex欧美| 少妇人妻精品综合一区二区| 欧美精品人与动牲交sv欧美| 欧美日韩av久久| 日韩一本色道免费dvd| 久久久久精品性色| 欧美xxⅹ黑人| 五月天丁香电影| 亚洲av日韩在线播放| 国产亚洲精品久久久com| 大话2 男鬼变身卡| 大香蕉97超碰在线| av.在线天堂| 在现免费观看毛片| 男的添女的下面高潮视频| 色婷婷久久久亚洲欧美| 国产免费福利视频在线观看| 一本久久精品| 日本黄大片高清| 老司机影院成人| 两个人的视频大全免费| 男人爽女人下面视频在线观看| 久久99一区二区三区| 大香蕉97超碰在线| 中文天堂在线官网| 99热6这里只有精品| 成人手机av| 亚洲国产成人一精品久久久| 久久精品国产自在天天线| 在线亚洲精品国产二区图片欧美 | 国产成人aa在线观看| 亚洲av国产av综合av卡| 妹子高潮喷水视频| 五月伊人婷婷丁香| 18禁观看日本| 国产一区二区在线观看av| 三上悠亚av全集在线观看|