• <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 ?

    高耐甲醇性和穩(wěn)定性的納米復(fù)合陰極催化劑

    2012-03-06 04:44:14朱春梅施祖進
    物理化學(xué)學(xué)報 2012年10期
    關(guān)鍵詞:天虹物理化學(xué)學(xué)報

    鄭 寧 朱春梅 孫 斌 施祖進 劉 巖 王 遠(yuǎn)

    (北京大學(xué)化學(xué)與分子工程學(xué)院,北京分子科學(xué)國家實驗室,北京100871)

    1 Introduction

    Because of its high energy density,simplicity of handling and processing of liquid fuel,direct methanol fuel cells(DMFCs) are promising power sources for the applications in transportation and portable electronic devices.Cathode electrocatalysts with high selectivity and high durability for the oxygen reduction reaction(ORR)in the presence of methanol are vital materials in the development of high efficient DMFCs.Cathodes based on commercial Pt/C catalysts exhibit high catalytic activity for ORR.However,the methanol crossover in DMFCs equipped with such a cathode results in the competitive oxidation reaction of methanol over the cathode,which severely decreases the cell?s performance and energy transformation efficiency.1,2Numerous efforts have been devoted to improving the performance of cathodic catalysts in the presence of methanol, including some Pt-based alloys,3-6mesoporous carbon materials as supports of Pt-based nanoparticles,6,7and non-noble metal catalysts.8-13A novel nanocomposite catalyst constructed by phthalocyanine nanocrystals and Pt nanoparticles with high methanol tolerance has been reported in our previous work.2,14Despite the advances made in this field,there are still great challenges in improving the durability of these cathode catalysts for DMFCs.

    The catalytic activity and durability of Pt-based catalysts are inherently dependent on the structures and properties of the catalytic metals and support materials,as well as the interaction between them.Single walled carbon nanohorns(SWCNHs) have been proved to be a kind of advanced support material for Pt-based nanoparticles,due to their high surface area, high electrical conductivity,and high chemical stability.15-17There has been increasing evidence showing that the electrochemical and physical properties of carbon materials are extremely sensitive to heteroatoms(N,B,S,and P)doping into the carbon structures,resulting in the improved catalytic activity and durability of electrocatalysts.13,18-21Recently,we have proved that Pt nanoclusters dispersed in the aggregate of nitrogen-doped SWCNHs(NSWCNHs)exhibit obviously enhanced durability and catalytic activity for ORR in the absence of methanol.21Herein in this paper,we designed a novel nanocomposite catalyst assembled with Pt nanoclusters,TiOPc nanocrystals,and NSWCNHs.Methanol tolerant electrocatalysts with high activity and durability are expected on the basis of the merits of these materials.

    2 Experimental

    2.1 Materials

    A carbon supported Pt catalyst(Pt/C-JM,Pt:9.4%(w)) and a Nafion?solution(5%(w))was purchased from Johnson Matthey Company(U.K.)and Aldrich(USA),respectively. H2PtCl6·6H2O(analytical reagent grade,AR grade)was supplied by Sinopharm Chemical Reagent Beijing Co.Ltd.Perchloric acid,sodium hydroxide,ethylene glycol,and ethanol of AR grade were purchased from Beijing Chemical Corp.Ultrapure water(18 MΩ),methanol(high-performance liquid chromatography grade,Fisher,USA)were used without further purification.

    2.2 Catalyst synthesis

    NSWCNHs applied in this work were prepared by a DC arc discharge method in air,and were heated at 400°C in air for 4 h to remove amorphous carbon.22TiOPc and“unprotected”Pt nanoclusters(stabilized with ethylene glycol and simple ions) with an average diameter of 1.7 nm used in this work were prepared according to the previously reported method.23-25In a typical synthesis of TiOPc-Pt/NSWCNH,45 mg of NSWCNHs powder was dispersed ultrasonically in a C2H5OH/H2O mixture (40 mL,volume ratio=1:1)for 30 min.Then a prepared colloidal solution of Pt nanoclusters(1.35 mL,Pt concentration:3.7 g·L-1)was added dropwise to the suspension under stirring, followed by ultrasonically treating the mixture for 20 min.After stirring overnight,solid in the suspension was filtered,leaving a colorless solution,washed with ultrapure water and C2H5OH,dried at 40°C,and then heated at 300°C in a tube furnace under nitrogen for 1 h to obtain Pt/NSWCNHs.50 mg of TiOPc and 50 mg of Pt/NSWCNHs were ultrasonically mixed in 30 mL of ethanol for 20 min.After stirring overnight at room temperature,the suspension was centrifuged,and the obtained precipitate was washed with C2H5OH and then dried at 50°C in a vacuum oven to obtain TiOPc-Pt/NSWCNH. TiOPc-Pt/C was prepared by the same method using Pt/C-JM and the same TiOPc as starting materials.

    2.3 Characterization

    The morphologies of catalysts were studied by transmission electron microscope(TEM,Hitachi H-9000NAR,Japan).X-ray diffraction(XRD)measurements were carried out on a Rigaku-2500Pc X-ray diffractometer(Japan)with Cu radiation at 40 kV and 300 mA.Inductively coupled plasma atomic emission spectrometry(ICP-AES,Leeman Co.,USA)was used to analyze the content of Pt in the prepared catalysts.The content of N in the prepared NSWCNH was analyzed by elementary analysis(Elementar vario MICRO CUBE,vario EL,Elementar Analysensysteme,Germany).X-ray photoelectron spectroscopy(XPS)measurements were carried out with an Axis Ultra photoelectron spectrometer with a monochromatic Al KαX-ray (1486.7 eV)source.The binding energies were referenced to the C 1s binding energy of contamination carbon at 284.5 eV.

    2.4 Electrochemical measurements

    Electrochemical tests of the prepared electrodes were conducted using a CHI 660C workstation at 30°C.A conventional three-compartment electrochemical cell containing an aqueous solution of HClO4(0.1 mol·L-1)was employed for the electrochemical tests,in which a reversible hydrogen electrode(RHE) was used as the reference electrode,and a platinum foil was used as the counter electrode.All potentials in this work were referred to that of RHE.The working electrodes were prepared as follows:TiOPc-Pt/NSWCNH,TiOPc-Pt/C or Pt/C-JM catalysts(10 mg),a Nafion?solution(100 μL,5%(w))and C2H5OH(5 mL)were mixed ultrasonically for 20 min.20 μL of the obtained suspension was transferred onto a freshly polished glassy carbon disk electrode(0.196 cm2),the electrodes were dried at room temperature and then heated at 120°C in a vacuum oven for 1 h.The current densities were expressed in terms of the geometric surface area of the electrodes except where otherwise indicated.

    3 Results and discussion

    Fig.1 shows the TEM images and the size distributions of Pt nanoparticles in TiOPc-Pt/NSWCNH and TiOPc-Pt/C catalysts.As shown in Figs.1(a),1(c),and 1(e),rod-like TiOPc nanocrystals were observed.NSWCNHs knitted to form electroconductive nano-nets in TiOPc-Pt/NSWCNH and most of the Pt nanoparticles with an average diameter of 1.9 nm were well dispersed in the nano-nets(Figs.1(a)and 1(d)).The average diameter of Pt nanoparticles in the TiOPc-Pt/C catalyst was 2.2 nm(Fig.1(f)).The Pt contents of TiOPc-Pt/NSWCNH and TiOPc-Pt/C were 4.6%and 4.7%(w),respectively,as measured by ICP-AES.

    Fig.2 shows the N 1s XPS of NSWCNHs.Elementary analysis indicates that NSWCNHs contain 1.6%(w)of N.The N 1s spectrum from NSWCNHs consists of two peaks,locating at 398.9 and 400.8 eV,which indicates that nitrogen atoms in NSWCNHs might mainly exist in the form of pyridinic and pyrrolic nitrogen species.26

    Fig.3 shows the XRD patterns of TiOPc-Pt/NSWCNH(I),Pt/ C-JM(II),and NSWCNH(III).The diffraction peaks at 6.9°, 15.5°,and 23.3°assignable to the signals from m-TiOPc,can be observed in the XRD pattern of TiOPc-Pt/NSWCNH.27A broad peak centered at 25°in the XRD pattern of Pt/C-JM is the signal from carbon black which is the characteristic of amorphous carbon with only small regions of ordered structures.The diffraction peaks related to the(002)and(100) planes of the hexagonal graphite structure appear at positions near 26°and 45°in the XRD patterns of TiOPc-Pt/NSWCNHs and NSWCNH.Two sharp peaks at 26.0°and 26.4°could be attributed to the signals from NSWCNH and a small amount of graphite present in the sample,which indicates a highly graphitic ordered structure in NSWCNHs.Diffraction peaks at 39.8°,46.2°,67.5°,and 81.3°assignable to the signals from the(111),(200),(220),and(311)planes of fcc Pt,respectively, can be observed in the XRD patterns of TiOPc-Pt/NSWCNH and Pt/C-JM.

    Fig.4(a)shows cyclic voltammograms(CVs)of TiOPc-Pt/ NSWCNH,TiOPc-Pt/C,and Pt/C-JM in N2-saturated HClO4(0.1 mol·L-1)aqueous solution at 30°C with a scan rate of 50 mV·s-1.The electrochemical surface areas(ESA)of Pt particles of the prepared cathodes were calculated from CVs by integrating the area in the hydrogen underpotential deposition (HUPD)region.

    Fig.3 XRD patterns of the TiOPc-Pt/NSWCNH(I),Pt/C-JM(II), and NSWCNH(III)

    where QHadsand QHdesare the charges(unit in mC)associated with the hydrogen adsorption and desorption,respectively.The value of 0.21 mC·cm-2is an average charge density associated with the formation of one monolayer hydrogen atoms on a polycrystalline platinum surface.28ESAs of TiOPc-Pt/NSWCNH,TiOPc-Pt/C,and Pt/C-JM were calculated to be 0.50, 0.54,and 2.97 cm2,respectively.The Pt active surface area of TiOPc-Pt/NSWCNH is close to that of TiOPc-Pt/C,but it is much smaller than that of Pt/C-JM.The small Pt active surface area of TiOPc-Pt/NSWCNH is due to that a part of the surfaces of Pt nanoparticles are covered by TiOPc nanocrystals.2,14

    As shown in Fig.4(b),linear sweep voltammetry(LSV)was conducted to investigate the catalytic activities for ORR in the presence of methanol over TiOPc-Pt/NSWCNH,TiOPc-PtC, and Pt/C-JM at 30°C.In the presence of methanol,the oxidation current derived from the methanol oxidation over Pt/C-JM was quite large,however,only small peaks for methanol oxidation were observed in the potential region from 0.92 to 1.1 V over TiOPc-Pt/C and TiOPc-Pt/NSWCNH.This indicates that the oxidation of methanol was obviously suppressed over the TiOPc nanocrystal-modified catalysts.Therefore,the onset potential with respect to the reduction currents over TiOPc-Pt/C and TiOPc-Pt/NSWCNH was 0.91 and 0.92 V,respectively, shifted by about 250-260 mV toward positive relative to that over Pt/C-JM(0.66 V).The mass activity and specific activity at 0.85 V of TiOPc-Pt/NSWCNH were 83.5 A·g-1and 0.294 mA·cm-2,respectively,which were much higher than those of Pt/C-JM.TiOPc-Pt/C and TiOPc-Pt/NSWCNH exhibited much higher methanol tolerance in comparison with Pt/C-JM.The catalytic activities of these three catalysts were summarized in the Table 1.

    Fig.4 Electrochemical properties of TiOPc-Pt/NSWCNH,TiOPC-Pt/C,and Pt/C-JM at 30°C(a)CV curves tested in N2-saturated HClO4(0.1 mol·L-1)aqueous solution with a scan rate of 50 mV·s-1;(b)ORR polarization curves tested in O2-saturated HClO4 (0.1 mol·L-1)aqueous solution containing methanol(0.5 mol·L-1)with a scan rate of 5 mV·s-1;dot lines tested after potential cycling from 0.6 to 1.0 V for 15000 cycles in an O2-saturated HClO4solution containing methanol(0.5 mol·L-1)

    Table 1 Catalytic activities of TiOPc-Pt/NSWCNH,TiOPc-Pt/C, and Pt/C-JM catalysts

    The electrochemical stability of TiOPc-Pt/NSWCNH and TiOPc-PtC was evaluated by accelerated aging tests(AAT),cycling the potential between 0.6 and 1.0 V for 15000 cycles in an O2-saturated HClO4(0.1 mol·L-1)aqueous solution containing methanol(0.5 mol·L-1)at 30°C.The dot lines show ORR polarization curves afterAAT in Fig.4(b).It was found that there was a little negative shift(30 mV)of Eonsetover TiOPc-Pt/NSWCNH (0.89 V)after AAT compared to that over the fresh catalyst (0.92 V).But for TiOPc-Pt/C,Eonsetshifted negatively by about 200 mV after the same potential cycling test.After AAT,the catalytic activity over TiOPc-Pt/NSWCNH was much higher than that of TiOPc-Pt/C,indicating that the durability of TiOPc-Pt/NSWCNH for ORR in the presence of methanol is much higher than that of TiOPc-Pt/C.

    We believe that the higher methanol tolerance of TiOPc-Pt/ NSWCNH originates from the electron transfer from the TiOPc nanocrystals to Pt nanoparticles.The Fermi level of Pt lies at-5.65 eV,29and the HOMO energy level of TiOPc locates at-5.09 eV,30so electron transfer should occur when the TiOPc nanocrystals contact Pt nanoparticles,which may accelerate the electrocatalytic reduction processes of oxygen and enhance the methanol tolerance over TiOPc-Pt/NSWCNH.2,14The high durability for ORR of TiOPc-Pt/NSWCNH is mainly derived from trapping the Pt nanoparticles in the NSWCNH nanonetwork,suppressing the migration,aggregation,and growth in size of small Pt nanoclusters during the potential cycles.21The high graphitization degree of NSWCNHs enhances the support stability against the degradation caused by Pt-catalyzed oxidation,which should be another cause of the enhanced durability relative to that of TiOPc-Pt/C.

    4 Conclusions

    In summary,a novel nanocomposite catalyst TiOPc-Pt/ NSWCNH with an excellent methanol tolerance as well as a high durability for ORR in the presence of methanol was prepared by“unprotected”Pt nanoclusters,TiOPc nanocrystal, and nitrogen-doped carbon nanohorns.In the presence of methanol(0.5 mol·L-1),the onset potential for ORR over the TiOPc-Pt/NSWCNH catalyst shifted by more than 260 mV toward positive relative to that over the Pt/C-JM catalyst.The mass activity and specific activity for ORR at 0.85 V over TiOPc-Pt/NSWCNH were 83.5 A·g-1and 0.294 mA·cm-2,respectively,which were much higher than that of Pt/C-JM.After the accelerated aging tests(0.6-1.0 V for 15000 cycles)in an O2-saturated HClO4aqueous solution with methanol,the onset potential with respect to the reduction current was 0.89 V over TiOPc-Pt/NSWCNH,shifted by 180 mV toward positive relative to that over TiOPc-Pt/C(0.71 V).The durability for ORR in the presence of methanol over TiOPc-Pt/NSWCNH is much higher than that of TiOPc-Pt/C.

    (1) Shao,M.H.;Sasaki,K.;Adzic,R.R.J.Am.Chem.Soc.2006, 128,3526.doi:10.1021/ja060167d

    (2) Liu,Y.;Zheng,N.;Chao,W.;Liu,H.;Wang,Y.Electrochim. Acta 2010,55,5617.doi:10.1016/j.electacta.2010.04.092

    (3)Li,W.Z.;Zhou,W.J.;Li,H.Q.;Zhou,Z.H.;Zhou,B.;Sun,G. Q.;Xin,Q.Electrochim.Acta 2004,49,1045.doi:10.1016/ j.electacta.2003.10.015

    (4) Gao,M.R.;Gao,Q.;Jiang,J.;Cui,C.H.;Yao,W.T.;Yu,S.H. Angew.Chem.Int.Edit.2011,50,4905.doi:10.1002/anie. v50.21

    (5)Wang,W.M.;Huang,Q.H.;Liu,J.Y.;Zou,Z.Q.;Zhao,M.Y.; Vogel,W.;Yang,H.J.Catal.2009,266,156.doi:10.1016/ j.jcat.2009.06.004

    (6) Liu,S.H.;Zheng,F.S.;Wu,J.R.Appl.Catal.B:Environ. 2011,81,108.

    (7)Wen,Z.H.;Liu,J.;Li,J.H.Adv.Mater.2008,20,745.

    (8) Jasinski,R.Nature 1964,201,1212.doi:10.1038/2011212a0

    (9) Vante,N.A.;Tributsch,H.Nature 1986,323,431.doi:10.1038/ 323431a0

    (10) Liu,Y.;Ishihara,A.;Mitsushima,S.;Kamiya,N.;Ota,K. J.Electrochem.Soc.2007,154,B664.

    (11) Zheng,Y.;Jiao,Y.;Chen,J.;Liu,J.;Liang,J.;Du,A.J.;Zhang, W.M.;Zhu,Z.H.;Smith,S.C.;Jaroniec,M.;Lu,G.Q.;Qiao, S.Z.J.Am.Chem.Soc.2011,133,20116.doi:10.1021/ ja209206c

    (12)Li,X.G.;Han,F.;Xing,W.;Tang,Y.W.;Lu,T.H.Acta Phys.-Chim.Sin.2003,19,380. [李旭光,韓 飛,邢 巍,唐亞文,陸天虹.物理化學(xué)學(xué)報,2003,19,380.]doi:10.3866/ PKU.WHXB20030422

    (13) Kwon,K.Y.J.;Sa,Y.J.;Cheon,J.Y.;Joo,S.H.Langmuir 2012,28,991.doi:10.1021/la204130e

    (14) Zheng,N.;Liu,Y.;Wang,Y.Chem.Res.Chin.Univ.2011,32, 748.

    (15) Iijima,S.Nature 1991,354,56.doi:10.1038/354056a0

    (16)Yoshitake,T.;Shimakawa,Y.;Kuroshima,S.;Kimura,H.; Ichihashi,T.;Kubo,Y.;Kasuya,D.;Takahashi,K.;Kokai,F.; Yudasaka,M.;Iijima,S.Physica B:Condensed Matter 2002, 323,124.doi:10.1016/S0921-4526(02)00871-2

    (17) Kosaka,M.;Kuroshima,S.;Kobayashi,K.;Sekino,S.; Ichihashi,T.;Nakamura,S.;Yoshitake,T.;Kubo,Y.J.J.Phys. Chem.C 2009,113,8660.

    (18) Zhou,Y.K.;Neyerlin,K.;Olson,T.S.;Pylypenko,S.;Bult,J.; Dinh,H.N.;Gennett,T.;Shao,Z.P.;O?Hayre,R.Energy Environ.Sci.2010,3,1437.doi:10.1039/c003710a

    (19) Ma,G.X.;Jia,R.G.;Zhao,J.H.;Wang,Z.J.;Song,C.;Jia,S. P.;Zhu,Z.P.J.Phys.Chem.C 2011,115,25148.doi:10.1021/ jp208257r

    (20) Zhao,Y.C.;Zhan,L.;Tian,J.N.;Nie,S.L.;Ning,Z.Acta Phys.-Chim.Sin.2011,27,91. [趙彥春,占 璐,田建裊,聶素連,寧 珍.物理化學(xué)學(xué)報,2011,27,91.]doi:10.3866/ PKU.WHXB20110128

    (21)Zhang,L.W.;Zheng,N.;Gao,A.;Zhu,C.M.;Wang,Z.Y.; Wang,Y.;Shi,Z.J.;Liu,Y.J.Power Sources doi:10.1016/ j.jpowsour.2012.08.009.

    (22) Li,N.;Wang,Z.Y.;Zhao,K.K.;Shi,Z.J.;Gu,Z.N.;Xu,S.K. Carbon 2010,48,1580.doi:10.1016/j.carbon.2009.12.055

    (23) Liang,D.J.;Peng,W.L.;Wang,Y.Adv.Mater.doi:10.1002/ adma.201201720

    (24) Wang,Y.;Deng,K.;Gui,L.L.;Tang,Y.Q.;Zhou,J.W.;Cai,L. Y.;Qiu,J.B.;Ren,D.Y.;Wang,Y.Q.J.Colloid Interface Sci. 1999,213,270.doi:10.1006/jcis.1999.6132

    (25)Wang,Y.;Ren,J.W.;Deng,K.;Gui,L.L.;Tang,Y.Q.Chem. Mater.2000,12,1622.doi:10.1021/cm0000853

    (26) Pylypenko,S.;Queen,A.;Olson,T.S.;Dameron,A.;O?Neill, K.;Neyerlin,K.;Pivovar,B.;Dinh,H.N.;Ginley,D.S.; Gennett,T.J.Phys.Chem.C 2011,115,13676.doi:10.1021/ jp112236n

    (27) Enokida,T.;Hirohashi,R.;Nakamura,T.J.Imaging Sci.1990, 34,234.

    (28) Sheppard,S.A.;Campbell,S.A.;Smith,J.R.;Lloyd,G.W.; Ralph,T.R.;Walsh,F.C.Analyst 1998,123,1923.doi:10.1039/ a803310b

    (29) Michaelson,H.B.J.Appl.Phys.1977,48,4729.doi:10.1063/ 1.323539

    (30) Ma,Y.;Wen,Y.Q.;Wang,J.X.;Shang,Y.L.;Du,S.S.;Pan,L. D.;Li,G.;Yang,L.M.;Gao,H.J.;Song,Y.L.J.Phys.Chem.C 2009,113,8548.

    猜你喜歡
    天虹物理化學(xué)學(xué)報
    WANG Xiaoping. Chinese Literature and Culture in the Age of Global Capitalism:Renaissance or Rehabilitation?
    高速公路工程中瀝青混凝土拌合站配置和管理
    科學(xué)家(2022年4期)2022-05-10 02:10:11
    物理化學(xué)課程教學(xué)改革探索
    云南化工(2021年9期)2021-12-21 07:44:16
    物理化學(xué)課堂教學(xué)改進的探索
    云南化工(2021年6期)2021-12-21 07:31:42
    致敬學(xué)報40年
    Chemical Concepts from Density Functional Theory
    本刊特邀編委風(fēng)采
    給你一個島
    學(xué)報簡介
    學(xué)報簡介
    亚洲欧美日韩高清在线视频| 精品不卡国产一区二区三区| 日本精品一区二区三区蜜桃| 搡老岳熟女国产| av卡一久久| 深爱激情五月婷婷| 精品乱码久久久久久99久播| 国产黄片美女视频| 搞女人的毛片| 成熟少妇高潮喷水视频| 欧美3d第一页| 成人av在线播放网站| 国产亚洲精品久久久com| 岛国在线免费视频观看| 超碰av人人做人人爽久久| 久久久精品94久久精品| 露出奶头的视频| 欧美性猛交黑人性爽| 亚洲精品色激情综合| 丰满的人妻完整版| 午夜福利高清视频| 国产精品一区二区三区四区免费观看 | 亚洲丝袜综合中文字幕| 老师上课跳d突然被开到最大视频| 真实男女啪啪啪动态图| 一本精品99久久精品77| 国产又黄又爽又无遮挡在线| 国产在线精品亚洲第一网站| 国产v大片淫在线免费观看| 精品人妻一区二区三区麻豆 | 亚洲成人av在线免费| 国产白丝娇喘喷水9色精品| 日韩精品中文字幕看吧| 看片在线看免费视频| 99热这里只有是精品50| 级片在线观看| 日韩欧美国产在线观看| 国产av一区在线观看免费| 亚洲欧美日韩高清在线视频| 国产人妻一区二区三区在| 夜夜夜夜夜久久久久| 蜜桃久久精品国产亚洲av| 国产精品久久电影中文字幕| 观看免费一级毛片| 欧美一级a爱片免费观看看| 国产av不卡久久| 免费av毛片视频| 欧美日本亚洲视频在线播放| 国产精品亚洲一级av第二区| 男人的好看免费观看在线视频| 午夜福利视频1000在线观看| 特大巨黑吊av在线直播| 麻豆国产av国片精品| 少妇人妻一区二区三区视频| 亚洲av电影不卡..在线观看| 特大巨黑吊av在线直播| 精品久久久久久久久久免费视频| 久久久国产成人精品二区| 久久精品国产鲁丝片午夜精品| 国产亚洲欧美98| 成年女人毛片免费观看观看9| 日本一二三区视频观看| 亚洲精品456在线播放app| 亚洲人成网站在线观看播放| 成人特级黄色片久久久久久久| 嫩草影视91久久| 日韩人妻高清精品专区| 久久这里只有精品中国| 免费高清视频大片| 亚洲中文字幕日韩| 国产黄色视频一区二区在线观看 | 国产高清三级在线| 国产精品永久免费网站| 精品日产1卡2卡| 成年免费大片在线观看| 男人狂女人下面高潮的视频| 国产中年淑女户外野战色| 精品欧美国产一区二区三| 成人无遮挡网站| 久久久久九九精品影院| 观看免费一级毛片| 国产免费一级a男人的天堂| 国产欧美日韩精品亚洲av| 亚洲国产精品成人久久小说 | 欧美一区二区精品小视频在线| АⅤ资源中文在线天堂| 国产亚洲欧美98| 国产成人freesex在线 | 99精品在免费线老司机午夜| 日韩人妻高清精品专区| 国产高清有码在线观看视频| 国产精品久久电影中文字幕| 国产极品精品免费视频能看的| 亚洲av免费在线观看| 国产亚洲精品久久久com| 精品久久久噜噜| 人妻夜夜爽99麻豆av| 国产国拍精品亚洲av在线观看| 亚洲国产色片| 亚洲性久久影院| 深夜a级毛片| 日本a在线网址| 内地一区二区视频在线| 日本成人三级电影网站| 国产成人福利小说| 成人鲁丝片一二三区免费| 看免费成人av毛片| av免费在线看不卡| 99久国产av精品国产电影| 黄色欧美视频在线观看| av在线观看视频网站免费| 日韩欧美免费精品| 中文字幕人妻熟人妻熟丝袜美| 夜夜看夜夜爽夜夜摸| 亚洲18禁久久av| 国产真实乱freesex| 少妇的逼水好多| 亚洲真实伦在线观看| 免费观看人在逋| 精品99又大又爽又粗少妇毛片| 国产黄片美女视频| 男女边吃奶边做爰视频| 欧美成人精品欧美一级黄| 成年版毛片免费区| 久久久久久伊人网av| 99久久精品国产国产毛片| 久久久精品大字幕| 自拍偷自拍亚洲精品老妇| 亚洲av熟女| 国内久久婷婷六月综合欲色啪| 午夜福利在线观看免费完整高清在 | 一a级毛片在线观看| 国产精品爽爽va在线观看网站| 丝袜美腿在线中文| 非洲黑人性xxxx精品又粗又长| 国国产精品蜜臀av免费| 99九九线精品视频在线观看视频| 51国产日韩欧美| 精品国内亚洲2022精品成人| 欧美三级亚洲精品| 亚洲成人中文字幕在线播放| 丰满乱子伦码专区| 91在线精品国自产拍蜜月| 久久午夜福利片| 一级av片app| 在线播放无遮挡| 日产精品乱码卡一卡2卡三| 男女边吃奶边做爰视频| 能在线免费观看的黄片| 国产在线精品亚洲第一网站| h日本视频在线播放| 精品人妻视频免费看| 国产成人福利小说| 久久天躁狠狠躁夜夜2o2o| 可以在线观看的亚洲视频| 欧美色欧美亚洲另类二区| 日本三级黄在线观看| 免费一级毛片在线播放高清视频| 成人欧美大片| 欧美日本视频| 三级国产精品欧美在线观看| 一进一出抽搐gif免费好疼| 亚洲美女黄片视频| 高清日韩中文字幕在线| 少妇的逼好多水| 欧美精品国产亚洲| 国产毛片a区久久久久| 中文字幕免费在线视频6| 亚洲精品乱码久久久v下载方式| 亚洲av成人精品一区久久| 可以在线观看毛片的网站| 国产精品久久电影中文字幕| 欧美日本视频| 国语自产精品视频在线第100页| 久久热精品热| www日本黄色视频网| 久久国产乱子免费精品| 女生性感内裤真人,穿戴方法视频| 久久久久九九精品影院| 色av中文字幕| 日本在线视频免费播放| 亚洲成av人片在线播放无| 亚洲经典国产精华液单| 亚洲美女黄片视频| 久久中文看片网| 成人特级av手机在线观看| 国产精品一区二区三区四区久久| 久久精品综合一区二区三区| 春色校园在线视频观看| 在线播放国产精品三级| 日韩精品中文字幕看吧| 国产精品av视频在线免费观看| а√天堂www在线а√下载| 久久久久性生活片| 老女人水多毛片| 国产毛片a区久久久久| 国产不卡一卡二| 狂野欧美激情性xxxx在线观看| 免费人成视频x8x8入口观看| 可以在线观看的亚洲视频| 国产精品永久免费网站| 亚洲精华国产精华液的使用体验 | 亚洲精品456在线播放app| 精品一区二区三区av网在线观看| 黄色配什么色好看| h日本视频在线播放| 又粗又爽又猛毛片免费看| 久久精品国产亚洲av香蕉五月| 一级毛片电影观看 | 国产高清不卡午夜福利| 国产不卡一卡二| av在线天堂中文字幕| 少妇人妻精品综合一区二区 | 国内少妇人妻偷人精品xxx网站| 亚洲av第一区精品v没综合| 国产高清三级在线| 国产一区二区三区av在线 | 人妻丰满熟妇av一区二区三区| 国产男靠女视频免费网站| 午夜福利在线观看吧| 亚洲精华国产精华液的使用体验 | 亚洲欧美清纯卡通| 伦理电影大哥的女人| 国国产精品蜜臀av免费| 观看免费一级毛片| av国产免费在线观看| 麻豆国产av国片精品| 黄色一级大片看看| 国产av不卡久久| 成人亚洲精品av一区二区| 一区二区三区高清视频在线| 一本久久中文字幕| 国产精品一区二区三区四区免费观看 | 国产69精品久久久久777片| 免费观看在线日韩| 午夜福利在线观看吧| 欧美高清成人免费视频www| 国产蜜桃级精品一区二区三区| 秋霞在线观看毛片| 国产午夜福利久久久久久| 少妇裸体淫交视频免费看高清| 久久久a久久爽久久v久久| 91av网一区二区| 可以在线观看的亚洲视频| 变态另类成人亚洲欧美熟女| 男女之事视频高清在线观看| 国产亚洲精品综合一区在线观看| 麻豆国产97在线/欧美| 国产精品久久电影中文字幕| 亚洲国产精品sss在线观看| 亚洲国产精品成人久久小说 | 丰满的人妻完整版| 亚洲人成网站在线播| 波多野结衣高清无吗| 成人无遮挡网站| 成人永久免费在线观看视频| 国国产精品蜜臀av免费| 大又大粗又爽又黄少妇毛片口| 搡女人真爽免费视频火全软件 | 国产极品精品免费视频能看的| 亚洲七黄色美女视频| 成人精品一区二区免费| 少妇的逼好多水| 国产av一区在线观看免费| 午夜影院日韩av| 在线免费十八禁| 亚洲色图av天堂| 成年女人永久免费观看视频| 国产在线精品亚洲第一网站| 国产成人91sexporn| 成年免费大片在线观看| 神马国产精品三级电影在线观看| 一本久久中文字幕| 日本成人三级电影网站| av卡一久久| 国产伦一二天堂av在线观看| 久久久精品欧美日韩精品| 又黄又爽又刺激的免费视频.| 搡老岳熟女国产| 热99re8久久精品国产| 国产熟女欧美一区二区| av视频在线观看入口| 国产在线男女| 精品久久久久久久久av| 在线播放国产精品三级| 少妇人妻一区二区三区视频| 欧美丝袜亚洲另类| 成人av一区二区三区在线看| 好男人在线观看高清免费视频| 亚洲av五月六月丁香网| 日本a在线网址| 日韩欧美在线乱码| 亚洲无线在线观看| 亚洲欧美日韩高清在线视频| 久久中文看片网| 精品久久久久久成人av| 欧美bdsm另类| 老司机午夜福利在线观看视频| 日韩欧美 国产精品| 中国美女看黄片| 日韩,欧美,国产一区二区三区 | 色5月婷婷丁香| 亚洲精品色激情综合| 久久精品国产鲁丝片午夜精品| 国产精品福利在线免费观看| 夜夜夜夜夜久久久久| 悠悠久久av| 日本一二三区视频观看| 欧美日韩一区二区视频在线观看视频在线 | 精品一区二区免费观看| 午夜精品国产一区二区电影 | 久久精品国产清高在天天线| av黄色大香蕉| 日韩制服骚丝袜av| 国产精品伦人一区二区| 97人妻精品一区二区三区麻豆| 最近的中文字幕免费完整| 日本-黄色视频高清免费观看| 久久午夜福利片| 大香蕉久久网| 91久久精品国产一区二区成人| 国产亚洲精品av在线| 国产成人福利小说| 国产色婷婷99| 国产黄a三级三级三级人| 亚洲av成人精品一区久久| 亚洲综合色惰| 国产又黄又爽又无遮挡在线| 在线免费观看的www视频| 欧洲精品卡2卡3卡4卡5卡区| 久久婷婷人人爽人人干人人爱| 老司机福利观看| 亚洲国产精品sss在线观看| 欧美色欧美亚洲另类二区| 欧美+亚洲+日韩+国产| 简卡轻食公司| 男女啪啪激烈高潮av片| 国产黄色视频一区二区在线观看 | 99视频精品全部免费 在线| 亚洲aⅴ乱码一区二区在线播放| 亚洲成av人片在线播放无| 久久精品综合一区二区三区| 在线国产一区二区在线| 俄罗斯特黄特色一大片| 国产精品不卡视频一区二区| 中国国产av一级| 日日摸夜夜添夜夜添小说| 亚洲精品色激情综合| 观看免费一级毛片| 国产精品一区二区三区四区久久| 精品一区二区三区av网在线观看| 国产国拍精品亚洲av在线观看| 99热这里只有是精品50| 99在线人妻在线中文字幕| 尤物成人国产欧美一区二区三区| 久久中文看片网| 午夜久久久久精精品| 3wmmmm亚洲av在线观看| 国产久久久一区二区三区| eeuss影院久久| 特大巨黑吊av在线直播| 搡女人真爽免费视频火全软件 | 亚洲欧美日韩无卡精品| 女的被弄到高潮叫床怎么办| 久久精品国产自在天天线| 色av中文字幕| 精品一区二区免费观看| 国产高清三级在线| 九色成人免费人妻av| 日韩大尺度精品在线看网址| 99热网站在线观看| 亚洲av成人精品一区久久| 黑人高潮一二区| 丝袜喷水一区| АⅤ资源中文在线天堂| 波多野结衣巨乳人妻| 丰满乱子伦码专区| 免费av观看视频| 亚洲精品国产成人久久av| 国产精品人妻久久久久久| 欧美一区二区国产精品久久精品| 人人妻人人看人人澡| 激情 狠狠 欧美| 18+在线观看网站| 舔av片在线| 国产午夜精品论理片| 成人漫画全彩无遮挡| av在线亚洲专区| 日本免费a在线| 久久鲁丝午夜福利片| 日韩av在线大香蕉| 亚洲色图av天堂| 一区二区三区免费毛片| 国产成人精品久久久久久| 国产欧美日韩一区二区精品| 22中文网久久字幕| 久久久久性生活片| 婷婷色综合大香蕉| 尤物成人国产欧美一区二区三区| 我的女老师完整版在线观看| 免费观看精品视频网站| 嫩草影院精品99| 成人永久免费在线观看视频| 免费搜索国产男女视频| 熟女电影av网| 最近在线观看免费完整版| 两个人的视频大全免费| 久久精品夜色国产| 亚洲国产精品sss在线观看| 色av中文字幕| 99久久中文字幕三级久久日本| 最近最新中文字幕大全电影3| 五月玫瑰六月丁香| 免费观看精品视频网站| 嫩草影院精品99| 搞女人的毛片| 久久天躁狠狠躁夜夜2o2o| 你懂的网址亚洲精品在线观看 | 午夜老司机福利剧场| 国产视频一区二区在线看| 亚洲av免费高清在线观看| 国产高潮美女av| 99热6这里只有精品| 免费看a级黄色片| 老司机午夜福利在线观看视频| avwww免费| 久久久久久久久久久丰满| 日韩欧美三级三区| 小蜜桃在线观看免费完整版高清| 搡老妇女老女人老熟妇| 亚洲成人av在线免费| 高清毛片免费观看视频网站| 12—13女人毛片做爰片一| 麻豆国产av国片精品| 日本成人三级电影网站| 一区二区三区免费毛片| 99久久久亚洲精品蜜臀av| 99久国产av精品国产电影| 国产精品1区2区在线观看.| 久久久久久久午夜电影| 国产综合懂色| 成年女人永久免费观看视频| 久久精品国产亚洲av涩爱 | 久久精品国产鲁丝片午夜精品| 亚州av有码| 一级毛片aaaaaa免费看小| 日韩强制内射视频| 成人高潮视频无遮挡免费网站| 久久天躁狠狠躁夜夜2o2o| 不卡一级毛片| 成年免费大片在线观看| 久久99热这里只有精品18| 亚洲人成网站高清观看| 有码 亚洲区| 亚洲欧美成人精品一区二区| 久久6这里有精品| 熟女电影av网| 非洲黑人性xxxx精品又粗又长| 91av网一区二区| 国产av一区在线观看免费| 长腿黑丝高跟| 搞女人的毛片| 一本久久中文字幕| 波多野结衣高清无吗| 女的被弄到高潮叫床怎么办| 国产成年人精品一区二区| a级一级毛片免费在线观看| 国产黄色小视频在线观看| 国产白丝娇喘喷水9色精品| 给我免费播放毛片高清在线观看| 看黄色毛片网站| 偷拍熟女少妇极品色| h日本视频在线播放| 久久久色成人| 国产精品无大码| 久久久久精品国产欧美久久久| 波多野结衣高清作品| 中国美白少妇内射xxxbb| av视频在线观看入口| 亚洲国产高清在线一区二区三| 99久久精品国产国产毛片| 男人舔奶头视频| 午夜精品国产一区二区电影 | 美女xxoo啪啪120秒动态图| 国产毛片a区久久久久| 日韩av在线大香蕉| 少妇高潮的动态图| 欧美激情在线99| 两性午夜刺激爽爽歪歪视频在线观看| 久久综合国产亚洲精品| 中文资源天堂在线| 国产精品爽爽va在线观看网站| 欧美潮喷喷水| 有码 亚洲区| 欧美潮喷喷水| 有码 亚洲区| 午夜视频国产福利| 欧美一区二区国产精品久久精品| 成人欧美大片| 久久久久久大精品| 可以在线观看毛片的网站| 久久精品国产自在天天线| 99久国产av精品国产电影| 三级经典国产精品| 欧美激情在线99| 天天一区二区日本电影三级| 国产一区二区三区在线臀色熟女| 精品久久久久久久久久久久久| 国产真实伦视频高清在线观看| 在线免费十八禁| 亚洲国产高清在线一区二区三| 99久久无色码亚洲精品果冻| 18+在线观看网站| 淫秽高清视频在线观看| 午夜精品一区二区三区免费看| 国产高清视频在线观看网站| 国产色爽女视频免费观看| 婷婷色综合大香蕉| 亚洲精品456在线播放app| 欧美日本亚洲视频在线播放| 麻豆成人午夜福利视频| 国产老妇女一区| 免费搜索国产男女视频| 大香蕉久久网| 亚洲国产精品成人综合色| 网址你懂的国产日韩在线| 欧美激情在线99| 国产黄片美女视频| 久久午夜福利片| 国产老妇女一区| 18禁裸乳无遮挡免费网站照片| 高清午夜精品一区二区三区 | 久99久视频精品免费| 男女啪啪激烈高潮av片| 99热全是精品| 国产一区二区三区av在线 | av在线老鸭窝| 长腿黑丝高跟| 久久久久久久久中文| 亚洲无线在线观看| 国产白丝娇喘喷水9色精品| 国产精品美女特级片免费视频播放器| 亚洲欧美成人综合另类久久久 | 十八禁国产超污无遮挡网站| 在线观看美女被高潮喷水网站| 欧美不卡视频在线免费观看| 精品久久久久久久末码| 网址你懂的国产日韩在线| 18禁在线无遮挡免费观看视频 | 特级一级黄色大片| 亚洲性夜色夜夜综合| 国产午夜精品论理片| 日日干狠狠操夜夜爽| 精品不卡国产一区二区三区| 亚洲国产精品成人久久小说 | 美女黄网站色视频| 国产伦精品一区二区三区四那| 我要看日韩黄色一级片| 搡老熟女国产l中国老女人| 少妇猛男粗大的猛烈进出视频 | 伊人久久精品亚洲午夜| 六月丁香七月| 国内精品美女久久久久久| 一进一出抽搐动态| 亚洲乱码一区二区免费版| 久久草成人影院| 色综合亚洲欧美另类图片| 淫妇啪啪啪对白视频| 精品久久国产蜜桃| 国产午夜精品论理片| 一个人观看的视频www高清免费观看| 国产精品亚洲一级av第二区| 国产真实乱freesex| 国产真实伦视频高清在线观看| 直男gayav资源| 国产成人91sexporn| 日本一本二区三区精品| 国产精品三级大全| 欧美高清成人免费视频www| 欧美性猛交╳xxx乱大交人| 少妇熟女aⅴ在线视频| 男女视频在线观看网站免费| av天堂中文字幕网| 男插女下体视频免费在线播放| 寂寞人妻少妇视频99o| 中文字幕精品亚洲无线码一区| 深夜a级毛片| 直男gayav资源| 美女黄网站色视频| 精品久久久久久久人妻蜜臀av| 日本a在线网址| 亚洲国产高清在线一区二区三| 非洲黑人性xxxx精品又粗又长| 亚洲欧美成人综合另类久久久 | 国产精品日韩av在线免费观看| 赤兔流量卡办理| а√天堂www在线а√下载| 欧美区成人在线视频| 熟女人妻精品中文字幕| 亚洲真实伦在线观看| 成人亚洲精品av一区二区| 亚洲av免费在线观看| 欧美高清成人免费视频www| 久久韩国三级中文字幕| 亚洲一区二区三区色噜噜| 日本撒尿小便嘘嘘汇集6| 国产精品av视频在线免费观看| 联通29元200g的流量卡| 天美传媒精品一区二区| 你懂的网址亚洲精品在线观看 | 深夜精品福利| 午夜免费男女啪啪视频观看 | 伊人久久精品亚洲午夜| 春色校园在线视频观看| 日产精品乱码卡一卡2卡三|