• <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 ?

    不同堿溶液表面處理對稀土鎂鎳基儲氫合金的影響

    2018-12-10 06:49:16苑慧萍蔣利軍
    無機(jī)化學(xué)學(xué)報 2018年12期
    關(guān)鍵詞:儲氫工程技術(shù)稀土

    苑慧萍 蔣利軍

    (有研工程技術(shù)研究院有限公司,北京 101407)

    0 Introduction

    E-Mg-Ni based AB3~3.8type alloys with higher dischargecapacitiesand fineelectrochemical properties have been developed these years.They are potential alternatives of AB5-type alloys as the negative electrode of nickel-metal hydride (Ni-MH)battery[1-7].However,the cyclic stability of such alloys is poor and it is easy to corrode in alkaline solutions.The performances of hydrogen storage alloy are related to the composition and the surface state.Alkaline treatment can improve the electrochemical properties of hydrogen storage alloy by changing the surface state,such as the high rate discharge capacity,cycle life,and electro-catalytic activity.In previous studies,alkaline aqueous solutions were mostly applied for treating AB5-type hydrogen storage alloys[8-15].The improvement of the electrochemical performances of the alloy electrodes after the treatment in alkaline solutions is attributed to the Ni enrichment and the existence of the alkaline elements in the alloy sublayers.They accelerates the H absorption on the alloy surface and helps the electron transportation between the alloy surfaces and the H2or H2O molecule[8-11].Besides,the consumption of electrolyte can be diminished after the alloy powder treated in alkaline solution when it is used as the negative electrode in nickel-metal hydride (Ni-MH)battery.

    Recently,alkaline treatment has also been applied on RE-Mg-Ni based alloys.The hydrogen storage alloy of La0.6Nd0.2Mg0.2Ni3.3Co0.3was treated in 6 mol·L-1KOH alkaline solution[16].The capacity retention rate of the alloy treated at 80℃for 1 h increased by 9.35%and the high rate discharge-ability (HRD)increased by 26.7%when the discharge current density was 900 mA·g-1.The surface treatment of the La0.7Mg0.3Ni2.4Co0.6hydrogen storage alloy with KOH solution containing KBH4exhibited excellent electrochemical properties.The hydrogen storage capacity and the high rate discharge ability of the alloy electrode were improved,and the charge-transfer resistance of the alloy electrode was reduced[17].Luo et al.[18]found with the increase of the process time of hot alkaline on La0.64Gd0.2Mg0.16Ni3.1Co0.3Al0.1alloy, the magnetization intensity of alloy increased first and then decreased.The alloy electrode performance,which changed with the hot alkali processing time,was related to the formation of enriched Ni layers and their subsequent oxidation tendency as well as the precipitation of RE oxides on the alloy surface.Young et al.[19-20]compared the AB2,AB5and A2B7type hydrogen storage alloys treated with alkaline solutions and investigated the influence of the surface oxide structure on the electrochemical properties.

    Alkaline treatment is a simple method to effectively improve the electrochemical properties.However,the kinds of alkali solutions,their concentrations,and the treating temperature and time have great effects on the properties of alloys.In our previous study,the (REMg)2(NiAl)7alloy was treated in LiOH aqueous solution[21].

    The results show that LiOH solution could effectively remove the Mg elements on the alloy surface.The LiOH solution of relative high concentration reduced the formation of oxygen species on the surface of the alloy.We think the hydrogen storage alloy treated with different alkali solutions would have different corrosion surfaces and the oxide layers.Therefore,in this work,the alkaline treatment on the RE-Mg-Ni based hydrogen storage alloy with LiOH,NaOH and KOH solutions were investigated.The effects of different alkaline solutions on the surface compositions and structures of RE-Mg-Ni-based alloys were tested. The relationship between the electrochemical character and the surface state after the alkaline treatment was analyzed.

    1 Experimental and procedures

    The commercial (REMg)2(NiAl)7hydrogen storage alloy powders were obtained from Xiamen Tungsten Co.,Ltd.RE elements in the alloy include La,Ce,Pr,Nd,etc.The phase composition of the alloy includes more than 90% (w/w)of A2B7-type crystal structure and a small amount of AB3,AB5,and A5B19phases.The alkali treatment method for the alloy powder was immersing the alloy into the alkali solution of 363 K firstly,stirring for different times,and then pouring the upper alkaline solution out,stirring and washing with distilled water until pH=7,and vacuum drying at 333 K.

    The 200 mg alloy powder was fully mixed with 800 mg nickel powder and cold pressed into a pellet of 16 mm diameter at 530 MPa pressure.The pellet was coated with nickel foam and then welded to the nickel band to make the negative electrode.The counter electrode is sintered Ni(OH)2/NiOOH.The electrolyte is 6 mol·L-1KOH solution.Electrochemical measurements were carried out in a three electrode electrolytic cell at 298 K.

    The working electrodes were charged at the current density of 60 mA·g-1for 450 min,then discharged at the current density of 60 mA·g-1to the cut-off voltage of-1.0 V.High rate discharge-ability(HRDi)was calculated by Ci/Cmax×100%,where Ciwas the discharge capacity of the discharge current density of i mA·g-1and Cmaxwas the maximum discharge capacity of the discharge current density of 60 mA·g-1.After the activation of 10 cycles,the charge and discharge current density of 300 mA·g-1were used to test the cycle lives of the metal hydride electrodes.

    Measurement of surface morphology and element content were observed using scanning electron microscopy (SEM)with EDSwith a Hitachi-S4800 Unit operating at 10 kV.The pulse heating inert gas fusion-infrared absorption method (IR)was used to test the oxygen content of the alloy powder.The magnetic properties of the alloy surfaces were measured by vibrating sample magnetometer (VSM).

    2 Results and discussion

    2.1 Surface and microstructure characteristics

    Fig.1 shows the surface states of the untreated(REMg)2(NiAl)7hydrogen storage alloy powders and the alloy powders treated with 6 mol·L-1LiOH,NaOH and KOH aqueous solutions for various times.During the treatment,some elements,such as Mg,Al,and rare-earth metal elements,dissolved in the alkaline solution.The hydroxides and oxides of the dissolved elements increased gradually in the alkaline solutions,re-precipitate on the alloy surfaces,and serve as the barrier to further corrosion[22].As can be seen in Fig.1,with the treating time increases,the amount of the rod-like and needle-like products on the alloy surfaces raise on the alloy powders treated with 6 mol·L-1NaOH and KOH solutions.On the alloy powder treated in 6 mol·L-1LiOH solution the rod-like and needle-like products raised for the first 20 min.After 60 min treatment the rod-like and needle-like products diminished and the column-shaped things appeared in some regions.

    Because of the accumulation of the hydroxides or oxides,the O content increased.Fig.2 shows the energy dispersive spectrometer (EDS)weight percentages of O elements of the (REMg)2(NiAl)7hydrogen storage alloy powders treated with 6 mol·L-1LiOH,NaOH and KOH aqueous solutions for various times.the O contents increased sharply in the first 20 min and then the rate of growth becomes slowing (Fig.2).The order of the O contents on the alloy surfaces treated in different alkaline solutions (6 mol·L-1)is LiOH<NaOH<KOH.The sample treated with 6 mol·L-1LiOH showed the lowest O content,indicating the inhibition of the oxygen containing species formation of 6 mol·L-1LiOH solution on the alloy powder.The O contents were also tested using infrared adsorption methods and were listed in Table 1,which accords well with the EDSresults.

    Fig.1 SEM images of the (REMg)2(NiAl)7 alloy powders before alkali solution treatment(a)and treated in different alkaline aqueous solutions (b)

    The porous alloy surfaces formed by the corrosion and etching of the alkaline solutions and the re-precipitation of the oxygen containing species were rich in Ni element in sub-layer.Because of its strong magnet the magnetic material content was calculated by dividing the sample magnetization by Ni powder magnetization.As shown in Table 1,the magnetic material contents of the alloy powders treated in different alkaline solutions (6 mol·L-1)increased with the treating time and were in the order of KOH>NaOH>LiOH.The Ni rich sub-layer is in favor of enhancing the activity for H absorption/desorption and the corrosion resistance of the alloy electrode.However,exorbitant Ni content could make the excessive corrosion of the alloy powder leading to the reduction of the maximum discharge capacity.

    Fig.2 EDSweight percentages of Oelement on the surfaces of the (REMg)2(NiAl)7 hydrogen storage alloy powders treated in different alkaline aqueous solutions

    Table 1 Oxygen and magnetic material contents of the alloy powders treated in different alkaline aqueous solutions

    2.2 Electrochemical properties

    Fig.3 shows the effect of the treating time on the discharge capacity and cycle life of the (REMg)2(NiAl)7hydrogen storage alloy electrode treated with different alkaline aqueous solutions.The electrochemical properties including the maximum discharge capacity at 1C,cycle life of 100 cycles,high rate dischargeability,and charge retention rate at 25℃for 180 h of the alloy electrodes treated in different alkaline aqueous solutions are listed in Table 2.The alkaline treatment corroded the alloy powder effectively.The discharge capacities of the alkaline treated alloy electrodes were all higher than that of the untreated electrode except for the alloy electrodes treated with 6 mol·L-1NaOH and KOH aqueous solution for 60 min.The alloy electrode treated in 6 mol·L-1NaOH aqueous solution for 10 min obtained the highest discharge capacity.With the treating time increases from 10 to 60 min,the maximum discharge capacity of the alloy electrode treated with 6 mol·L-1LiOH,NaOH and KOH solutions decreased from 323.10 to 319.80 mAh·g-1,from 330.36 to 309.03 mAh·g-1,and from 320.84 to 312.70 mAh·g-1,respectively.The order of the maximum discharge capacity reduction after the treatment from 10 to 60 min is NaOH>KOH>LiOH.The magnetic material contents and the oxygen contents both remarkably increased with the time for the alloy powders treated in NaOH and KOH solutions.The excessive corrosion of the alloy surface and too much oxygen containing species decreased the discharge capacity seriously[23].After 100 cycles,the alloy electrodes treated with 6 mol·L-1NaOH for 10 min and 6 mol·L-1LiOH for 10 and 20 min showed higher discharge capacities (S100).The cyclic durability of the alloy electrodes treated in LiOH solution was better than the alloy electrodes treated in NaOH and KOH solutions.

    Fig.3 Effect of the treating time on the discharge capacity and cycle life of the (REMg)2(NiAl)7 hydrogen storage alloy electrode treated with different alkaline aqueous solutions

    Table 2 Electrochemical properties of the alloy electrodes treated in different alkaline aqueous solutions

    As is shown in Table 2,the high rate dischargeabilities of the alloy electrodes treated for different times were in the order of NaOH>LiOH≈KOH.Only the HRD of the alloy electrode treated in 6 mol·L-1NaOH solution for 10 min is higher than that of the untreated sample indicating the good activation of NaOH solution.The HRDs of the other alloy electrodes were all worse than the untreated sample.Although the Ni rich sub-layers are formed on the other samples,the fast-growing Ocontaining species affected the HRD greatly.In addition,the alkaline treatment in our experiment did not add reducing agents[11-12].The surface oxygen species could not be effectively removed.

    As is shown in Fig.4,the charge retention rates of the treated alloy electrode were all better than that of the untreated sample.The improvement benefited from the oxidation layer and the Ni rich sub-layer on the alloy surface.With the increase of the treating time,the charge retention rate of the LiOH treated sample increased,but the charge retention rates of the NaOH and KOH treated samples decreased.This suggests that the alloy electrode treated in different alkaline solutions formed the surfaces of different compositions,which had different effects on the charge retention rate.

    Fig.4 Effect of the treating time on the charge retention rate of the (REMg)2(NiAl)7 hydrogen storage alloy electrode treated with LiOH (a),NaOH (b)and KOH (c)aqueous solutions

    In conclusion,the sample treated with 6 mol·L-1NaOH solution for 10 min shows the best electrochemical properties,including the maximum discharge capacity,the discharge capacity after 100 cycles,the HRD,and the charge retention rate.

    2.3 Surface composition

    Fig.5 shows the changes of Ni,rare-earth,Mg and Al contents by EDSanalyses on the (REMg)2(NiAl)7alloy surfaces treated with various alkaline aqueous solutions from 10 to 120 min.In order to reduce the randomness of the experimental results,several regions containing scores of alloy particles were selected,and then the average value of the test results was obtained.The surface content of oxygen varied greatly with the treating time,which had great influence on the content of other elements.Therefore,the contents of the Ni,rare-earth,Mg and Al element by EDSwere calculated by removing the O content.Fig.6 shows the ICPanalyses of Ni,RE,Mg and Al elements dissolved in 6 mol·L-1LiOH,NaOH and KOH solutions during the treatment.These results can help analyze the composition of the surface layer of the alkali treated alloy powder.In theory,with the increase of the treating time,the rare-earth,Mg and Al elements on thealloy surfacedissolved firstly and then the dissolved element ions deposited as the hydroxides or oxides.As the accumulation and growing up on the alloy surface,the deposits would break off.Therefore,the EDScontents of these elements should decrease first,then rise,and in the end fall.Nickel element is not easily dissolved in alkali solution[24].Because of the dissolution of other elements,the content of Ni on the alloy surface increased at the initial stage.With the deposition and breaking off of the oxygen containing species,the content of Ni first decreased and then increased (Fig.5a).The EDScontent of the Ni element on the most surface layer was different from the magnetic material content in Table 1,which represents the amount of the Ni atoms in the sub-layer of the alloy powders.

    Fig.5 EDSof(a)Ni,(b)rare-earth,(c)Al and (d)Mg element on the surfaces of the (REMg)2(NiAl)7 hydrogen storage alloy powders treated in different alkaline aqueous solutions

    Fig.6 ICPanalysis of(a)Ni,(b)RE,(c)Mg and (d)Al element dissolved from the alloy surface in alkaline solutions during treatment

    As can be seen in Fig.5b,the RE contents of the 6 mol·L-1LiOH and 6 mol·L-1NaOH treated samples increased first and then decrease.There was no declining process at the initial stage suggesting the dissolution and deposition process was very fast.The RE contents of the alloy surfaces treated in NaOH and KOH reversed to decline at 60 min according to the falling off of the surface RE hydroxides.However,the RE content of the alloy surface treated in LiOH had a rapid decrease after 20 min treatment.The SEM images in Fig.1 show that on the surface of sample treated with LiOH solution for 60 min the rodshaped and needle like species diminished and in some regions the column-shaped things appeared.The RE hydroxides on the alloy surface were mostly rod like and needle like.This suggests that the composition of the surface oxygen containing species were changed.Compared with the samples treated with KOH and LiOH solutions,the amount of the RE hydroxides on the sample treated with NaOH solution was larger.And the Ni content of NaOH treated sample was the smallest.

    The EDS and ICP results in Fig.5c and Fig.6c show that the dissolution and deposition of Mg element on the alloy surface treated with the alkali solutions before 20 min were both in the order of LiOH>NaOH>KOH.The Mg contents of the samples treated with LiOH and NaOH solutions at 20 min had sharp reverses at 20 min according to the falling off of the MgO or Mg(OH)2.This suggests the effective removal of the Mg element by LiOH and NaOH solutions.The EDSand ICPresults in Fig.5d and Fig.6d show that the dissolution of Al element in the alkali solutions before 20 min were also in the order of LiOH>NaOH>KOH.The EDSresults show that the Al contents on the alloy surface treated in NaOH and KOH solutions continued to decline after 20 min.The declining rate on the NaOH treated sample is much faster than that on the KOH treated sample.But the Al content on the alloy surface treated with LiOH solution raised slightly.We think the increase of the Al content was according to the deposition of the Al(OH)3.

    Based on the above analyses,we find that the dissolution rates of alloy surface elements and the deposition rates of the dissolved elements were both in the order of LiOH>NaOH>KOH for the concentration of 6 mol·L-1.The LiOH solution has the smallest polarity in the three alkaline solutions.Thus we think the solubility of the dissolved ions in LiOH solution is the lowest.In our experiment,the oxides or hydroxides of RE and Mg elements are easier to deposit and fall off with the accumulation and the oxides or hydroxides of Al element is easier to deposit on the LiOH treated alloy surface than on the KOH and NaOH treated alloy surfaces.Therefore,the surface layer of LiOH treated sample had the lower oxygen content and contains more Ni or its oxidized species,and Al oxygen species.We think the oxides and hydroxides layers formed in LiOH solution were more unfavorable for H adsorption and desorption.The surface oxide layer had good corrosion resistance,which slowed down the dissolution rate of elements on the alloy surface.Thus the decrease rate of the capacity was the smallest from 10 to 60 min treatment.The alloy electrode treated in LiOH solution had high cycle stability and increasing charge retention rate with the extension of the treating time.

    The discharge capacity and the charge retention rate decreased the fastest with the increase of the treating time and the HRD property was the best for the alloy electrode treated with NaOH solution.The NaOH solution activated the surface of the alloy effectively,but also corroded the alloy powder fastest.According to the above analysis,the surface layer contained much more RE hydroxides.The loose surface layer will not prevent the further corrosion.Besides,the ICP result shows the concentration of Al ion increased fastest in NaOH solution with the increase of the treating time.The amount of dissolved Al ion was hundreds of times the amount of dissolved other ions.It has been proved Al element could relieve the alloy pulverization and the Al oxide layer on the alloy surface inhibited the alloy corrosion/oxidation in alkaline electrolyte[25-27].The high dissolution of Al in our experiment caused the decrease of Al element in the alloy powder and the serious oxidation of the alloy surface.Therefore,the discharge capacity and the charge retention rate of the alloy electrode decreased fastest (Fig.2b).The treating time in NaOH solution should not be too long.

    The dissolution and deposition rate of the alloy surface elements were both the lowest for the alloy powder treated with KOH.The activation of 6 mol·L-1KOH solution for the alloy electrode was not remarkable compared with 6 mol·L-1LiOH and NaOH solutions.The discharge capacity decreased less than the sample treated with NaOH solution during 60 min treatment.Because of the slow deposition and falling off of the hydroxides or oxides,the oxygen content was the highest for the KOH treated sample.In our experiments,the electrochemical characteristics of the alloy electrode treated in 6 mol·L-1KOH solution were not very well.The optimum treatment time and concentration of KOH solution should be further improved.

    3 Conclusions

    The (REMg)2(NiAl)7hydrogenstoragealloypowders were treated with 6 mol·L-1LiOH,NaOH and KOH aqueous solutions for different times.The alloy powder treated with 6 mol·L-1NaOH solution for 10 min shows the best electrochemical properties,including the maximum discharge capacity,the discharge capacity after 100 cycles,the HRD and the charge retention rate.Different compositions and structures of the alloy surfaces lead to different electrochemical properties of the alloy electrodes.It is found that LiOH could effectively diminish the oxygen content of the alloy surface.The surface layer of LiOH treated sample contained more Ni,Al and their oxidized species,and had good corrosion resistance.Therefore,the alloy electrode treated in LiOH solution had high cycle stability,low HRD property,and increasing charge retention rate with the extension of the treating time.The discharge capacity of the alloy electrode treated in 6 mol·L-1NaOH solution decreased remarkably with the increase of the treating time.The surface layer of NaOH treated sample contained much more RE hydroxides.At the same time,the Al element was quickly dissolved.The loose surface layer could not prevent further corrosion.The dissolution rate of the alloy surface elements and the deposition rate of the dissolved elements were both lower in 6 mol·L-1KOH solution than in the same concentration of NaOH and LiOH.

    猜你喜歡
    儲氫工程技術(shù)稀土
    中國的“稀土之都”
    站用儲氫瓶式容器組缺陷及檢測方法
    我國固定式儲氫壓力容器發(fā)展現(xiàn)狀綜述
    工程技術(shù)矩陣
    工程技術(shù)研究院簡介
    稀土鈰與鐵和砷交互作用的研究進(jìn)展
    四川冶金(2019年5期)2019-12-23 09:04:36
    廢棄稀土拋光粉的綜合利用綜述
    儲氫合金La0.74Mg0.26Ni2.55Co0.55Al0.2Fe0.1的制備與電化學(xué)性能
    高比表面積活性炭吸附儲氫材料的研究進(jìn)展
    對磁浮工程技術(shù)的一些思考
    99久久99久久久精品蜜桃| 脱女人内裤的视频| 中文字幕色久视频| 中文字幕最新亚洲高清| 国产aⅴ精品一区二区三区波| 电影成人av| 9热在线视频观看99| 精品无人区乱码1区二区| 琪琪午夜伦伦电影理论片6080| 国产又爽黄色视频| 久久精品国产综合久久久| 男男h啪啪无遮挡| 亚洲国产日韩欧美精品在线观看 | 99在线人妻在线中文字幕| 日韩欧美免费精品| 视频在线观看一区二区三区| 高清在线国产一区| 欧美精品亚洲一区二区| 午夜免费观看网址| 色播亚洲综合网| e午夜精品久久久久久久| 亚洲专区字幕在线| 亚洲va日本ⅴa欧美va伊人久久| 午夜视频精品福利| 亚洲无线在线观看| 日本撒尿小便嘘嘘汇集6| 一级毛片精品| 久久久久亚洲av毛片大全| 变态另类丝袜制服| 给我免费播放毛片高清在线观看| 两个人看的免费小视频| 国产精品一区二区精品视频观看| 精品国产美女av久久久久小说| 亚洲精品中文字幕一二三四区| 高清毛片免费观看视频网站| 亚洲七黄色美女视频| 国产午夜福利久久久久久| 亚洲精品在线观看二区| 最好的美女福利视频网| 欧美在线黄色| 成人三级黄色视频| 男女做爰动态图高潮gif福利片 | 欧美成人一区二区免费高清观看 | 日本a在线网址| 欧美在线一区亚洲| 狠狠狠狠99中文字幕| 久久久久国内视频| 亚洲人成电影免费在线| 久久精品国产99精品国产亚洲性色 | 18禁国产床啪视频网站| 日韩欧美一区二区三区在线观看| 亚洲片人在线观看| 欧美黑人欧美精品刺激| 日韩av在线大香蕉| 国产国语露脸激情在线看| 97超级碰碰碰精品色视频在线观看| 老司机福利观看| 最近最新中文字幕大全电影3 | 欧美黄色淫秽网站| 亚洲精品国产色婷婷电影| 一级毛片精品| 757午夜福利合集在线观看| 老司机靠b影院| 9热在线视频观看99| 久久国产亚洲av麻豆专区| 亚洲av成人一区二区三| 亚洲一区中文字幕在线| 一级黄色大片毛片| 18禁观看日本| 国产精品久久久人人做人人爽| 国产亚洲精品久久久久5区| 很黄的视频免费| 国产成人欧美在线观看| 国产单亲对白刺激| av片东京热男人的天堂| 桃色一区二区三区在线观看| 桃色一区二区三区在线观看| 欧美成人免费av一区二区三区| 久久人人爽av亚洲精品天堂| 欧美乱码精品一区二区三区| 变态另类成人亚洲欧美熟女 | 人成视频在线观看免费观看| 99香蕉大伊视频| 午夜精品在线福利| 极品人妻少妇av视频| 首页视频小说图片口味搜索| 成人18禁高潮啪啪吃奶动态图| 淫妇啪啪啪对白视频| 成人特级黄色片久久久久久久| 亚洲激情在线av| 亚洲人成电影观看| 性少妇av在线| 成人亚洲精品av一区二区| 热re99久久国产66热| 国产欧美日韩一区二区三区在线| 香蕉丝袜av| 久久草成人影院| 欧美激情久久久久久爽电影 | 久久影院123| 黄网站色视频无遮挡免费观看| 午夜福利,免费看| 国产亚洲av嫩草精品影院| 人人澡人人妻人| 国产一级毛片七仙女欲春2 | 久久久国产成人免费| 亚洲 欧美一区二区三区| 天天躁夜夜躁狠狠躁躁| 欧美日韩乱码在线| 大码成人一级视频| 成人特级黄色片久久久久久久| 亚洲男人天堂网一区| 欧美成狂野欧美在线观看| 午夜免费鲁丝| 日本免费一区二区三区高清不卡 | 欧美在线一区亚洲| 1024视频免费在线观看| 日本一区二区免费在线视频| 亚洲一区高清亚洲精品| 黄色丝袜av网址大全| 欧美一级a爱片免费观看看 | 国产一区二区三区综合在线观看| 两个人视频免费观看高清| 国产精华一区二区三区| 国产亚洲精品综合一区在线观看 | 日日爽夜夜爽网站| 男人舔女人的私密视频| 欧美午夜高清在线| 在线天堂中文资源库| 99riav亚洲国产免费| 亚洲国产中文字幕在线视频| 麻豆一二三区av精品| 一级黄色大片毛片| 精品人妻1区二区| 久久久精品欧美日韩精品| 久久午夜亚洲精品久久| 亚洲成国产人片在线观看| 精品久久久久久久久久免费视频| 岛国在线观看网站| 不卡一级毛片| 日韩精品青青久久久久久| 在线观看一区二区三区| 99在线人妻在线中文字幕| 99国产精品一区二区蜜桃av| 黄色片一级片一级黄色片| 大码成人一级视频| 不卡一级毛片| 国产精品自产拍在线观看55亚洲| 久久午夜亚洲精品久久| 精品熟女少妇八av免费久了| 天堂动漫精品| 人人妻人人爽人人添夜夜欢视频| 日韩三级视频一区二区三区| 色播亚洲综合网| 老司机午夜福利在线观看视频| 免费一级毛片在线播放高清视频 | 国产午夜精品久久久久久| 中文字幕人妻熟女乱码| 99国产精品一区二区三区| avwww免费| 一本久久中文字幕| 一级毛片精品| 精品一品国产午夜福利视频| 三级毛片av免费| 99国产精品一区二区三区| 亚洲视频免费观看视频| 精品一区二区三区四区五区乱码| 777久久人妻少妇嫩草av网站| 精品乱码久久久久久99久播| 欧美中文日本在线观看视频| 亚洲精品在线美女| 两个人视频免费观看高清| 最新美女视频免费是黄的| 久久久久久人人人人人| 亚洲欧美一区二区三区黑人| 50天的宝宝边吃奶边哭怎么回事| 丁香欧美五月| 99在线视频只有这里精品首页| 丝袜美足系列| 在线永久观看黄色视频| 极品人妻少妇av视频| 亚洲一区中文字幕在线| 免费高清视频大片| 熟女少妇亚洲综合色aaa.| 一边摸一边做爽爽视频免费| 丝袜美腿诱惑在线| 正在播放国产对白刺激| av天堂在线播放| 欧美在线一区亚洲| 色综合婷婷激情| avwww免费| 真人一进一出gif抽搐免费| 韩国av一区二区三区四区| 久久婷婷人人爽人人干人人爱 | 亚洲自拍偷在线| 亚洲黑人精品在线| 夜夜躁狠狠躁天天躁| 亚洲欧美日韩无卡精品| 真人一进一出gif抽搐免费| 女人爽到高潮嗷嗷叫在线视频| 一区二区日韩欧美中文字幕| 老司机午夜十八禁免费视频| 久久精品91蜜桃| 淫秽高清视频在线观看| av天堂久久9| 欧美+亚洲+日韩+国产| 男女之事视频高清在线观看| 日日夜夜操网爽| 精品国产一区二区三区四区第35| 国产极品粉嫩免费观看在线| 国产亚洲精品久久久久久毛片| 国产三级黄色录像| 高清在线国产一区| 搡老岳熟女国产| 久久性视频一级片| 免费无遮挡裸体视频| 黄色视频不卡| 高清在线国产一区| 国产精品久久久av美女十八| 在线观看日韩欧美| 女同久久另类99精品国产91| 国内毛片毛片毛片毛片毛片| 欧美一级a爱片免费观看看 | av中文乱码字幕在线| 一级,二级,三级黄色视频| 一级毛片高清免费大全| 国产高清激情床上av| 在线观看免费午夜福利视频| 国产精品1区2区在线观看.| 国产一区二区在线av高清观看| 老司机午夜福利在线观看视频| 亚洲精品国产区一区二| 老鸭窝网址在线观看| 久久 成人 亚洲| 黄色女人牲交| 国产亚洲欧美98| 精品少妇一区二区三区视频日本电影| 亚洲九九香蕉| 精品高清国产在线一区| 99精品欧美一区二区三区四区| 老司机午夜十八禁免费视频| 久久香蕉精品热| av在线天堂中文字幕| 亚洲欧洲精品一区二区精品久久久| 伊人久久大香线蕉亚洲五| 国产精品 国内视频| 级片在线观看| 欧美日韩精品网址| 最好的美女福利视频网| 亚洲熟妇熟女久久| 亚洲人成电影观看| 日韩欧美在线二视频| 欧美乱色亚洲激情| 成人三级黄色视频| 黄色视频,在线免费观看| 亚洲欧美激情综合另类| 欧美乱码精品一区二区三区| 免费少妇av软件| 免费搜索国产男女视频| 中文字幕最新亚洲高清| 亚洲中文字幕一区二区三区有码在线看 | 女同久久另类99精品国产91| 精品卡一卡二卡四卡免费| 亚洲五月色婷婷综合| 亚洲片人在线观看| www.www免费av| 女人被狂操c到高潮| 国产精品国产高清国产av| 日韩欧美一区二区三区在线观看| 免费看十八禁软件| 久久青草综合色| 无遮挡黄片免费观看| 亚洲av熟女| 国内久久婷婷六月综合欲色啪| 亚洲最大成人中文| 亚洲精品一区av在线观看| 变态另类丝袜制服| 国产国语露脸激情在线看| www.精华液| 亚洲三区欧美一区| 欧美黑人欧美精品刺激| 无人区码免费观看不卡| 亚洲国产日韩欧美精品在线观看 | ponron亚洲| 国产成年人精品一区二区| 亚洲一卡2卡3卡4卡5卡精品中文| 久久人人爽av亚洲精品天堂| 日本免费一区二区三区高清不卡 | 亚洲国产日韩欧美精品在线观看 | 亚洲av成人一区二区三| 国产精品久久久久久亚洲av鲁大| 麻豆国产av国片精品| 成年版毛片免费区| 51午夜福利影视在线观看| 一级毛片精品| 亚洲精品美女久久久久99蜜臀| 国产精品亚洲av一区麻豆| 精品国产超薄肉色丝袜足j| 搡老妇女老女人老熟妇| 国产成+人综合+亚洲专区| 女性生殖器流出的白浆| 一级毛片女人18水好多| 亚洲av美国av| 制服人妻中文乱码| 国产不卡一卡二| 99久久精品国产亚洲精品| 妹子高潮喷水视频| 青草久久国产| 国产精品亚洲一级av第二区| 亚洲精品久久国产高清桃花| www日本在线高清视频| 在线天堂中文资源库| 精品第一国产精品| 少妇被粗大的猛进出69影院| 亚洲国产中文字幕在线视频| 国产精品久久久av美女十八| 非洲黑人性xxxx精品又粗又长| 成人特级黄色片久久久久久久| 日本 欧美在线| 欧美国产精品va在线观看不卡| 国产一区二区三区综合在线观看| 黄色a级毛片大全视频| 日韩 欧美 亚洲 中文字幕| 日韩一卡2卡3卡4卡2021年| 国产高清视频在线播放一区| 午夜福利视频1000在线观看 | 久久香蕉激情| 精品不卡国产一区二区三区| 亚洲精品中文字幕一二三四区| 在线国产一区二区在线| 国产成人精品在线电影| 色播在线永久视频| 露出奶头的视频| 丁香六月欧美| 国产一区二区激情短视频| 黑人欧美特级aaaaaa片| 免费在线观看完整版高清| 久久伊人香网站| 免费少妇av软件| 操美女的视频在线观看| 91字幕亚洲| 男人操女人黄网站| 亚洲成人久久性| 91国产中文字幕| 亚洲欧美精品综合一区二区三区| 麻豆av在线久日| 美女国产高潮福利片在线看| 日本a在线网址| 精品久久久久久久人妻蜜臀av | 精品久久久久久成人av| 午夜a级毛片| 大码成人一级视频| 亚洲美女黄片视频| 大码成人一级视频| 午夜a级毛片| 欧美一级毛片孕妇| 国产一区在线观看成人免费| 成熟少妇高潮喷水视频| 99re在线观看精品视频| 中文字幕色久视频| 免费少妇av软件| 最新在线观看一区二区三区| av天堂在线播放| 热99re8久久精品国产| 18禁观看日本| 日韩一卡2卡3卡4卡2021年| 亚洲av成人不卡在线观看播放网| 国产精品秋霞免费鲁丝片| 亚洲国产欧美日韩在线播放| 欧美色视频一区免费| 精品一区二区三区视频在线观看免费| 两性夫妻黄色片| 在线观看www视频免费| 99riav亚洲国产免费| 国产亚洲精品久久久久久毛片| 丝袜人妻中文字幕| 亚洲五月色婷婷综合| 这个男人来自地球电影免费观看| 一边摸一边做爽爽视频免费| 午夜精品在线福利| 99久久久亚洲精品蜜臀av| 久久香蕉激情| 久久欧美精品欧美久久欧美| 亚洲一区高清亚洲精品| 亚洲国产看品久久| 欧美中文综合在线视频| 国产高清激情床上av| 国产亚洲欧美精品永久| 国产精品久久久人人做人人爽| www.精华液| 久久亚洲精品不卡| 99久久综合精品五月天人人| 国产精品综合久久久久久久免费 | 夜夜看夜夜爽夜夜摸| 亚洲国产精品sss在线观看| 搡老妇女老女人老熟妇| av片东京热男人的天堂| 夜夜看夜夜爽夜夜摸| 一二三四社区在线视频社区8| 97超级碰碰碰精品色视频在线观看| 欧美绝顶高潮抽搐喷水| 欧美黑人欧美精品刺激| 欧洲精品卡2卡3卡4卡5卡区| 亚洲精品在线观看二区| 国产av又大| 一二三四在线观看免费中文在| 久久人妻熟女aⅴ| 国产精品电影一区二区三区| 纯流量卡能插随身wifi吗| 99国产精品免费福利视频| 性欧美人与动物交配| 精品卡一卡二卡四卡免费| 在线观看免费视频网站a站| 国产精华一区二区三区| 女性被躁到高潮视频| 亚洲熟妇熟女久久| 国产高清videossex| 亚洲国产精品sss在线观看| 久久久国产成人免费| 国产精品98久久久久久宅男小说| 欧美激情高清一区二区三区| 99国产精品一区二区蜜桃av| 正在播放国产对白刺激| 日本五十路高清| 欧美乱妇无乱码| 国产亚洲精品久久久久久毛片| 欧美成人一区二区免费高清观看 | 久久国产精品人妻蜜桃| ponron亚洲| 午夜福利视频1000在线观看 | 国产精品爽爽va在线观看网站 | 国产国语露脸激情在线看| 久久国产精品影院| 亚洲精品中文字幕一二三四区| 丁香六月欧美| 久久精品国产清高在天天线| 少妇的丰满在线观看| 美女大奶头视频| 亚洲国产中文字幕在线视频| 1024香蕉在线观看| 夜夜躁狠狠躁天天躁| 一级作爱视频免费观看| 露出奶头的视频| 搡老熟女国产l中国老女人| 精品免费久久久久久久清纯| 国产精品免费视频内射| 制服诱惑二区| 波多野结衣高清无吗| 亚洲一区高清亚洲精品| 婷婷六月久久综合丁香| 亚洲欧洲精品一区二区精品久久久| 人人妻人人爽人人添夜夜欢视频| 精品高清国产在线一区| 18禁美女被吸乳视频| av免费在线观看网站| 亚洲五月婷婷丁香| 天天躁夜夜躁狠狠躁躁| 久久草成人影院| 久久婷婷人人爽人人干人人爱 | 婷婷精品国产亚洲av在线| 狂野欧美激情性xxxx| 婷婷六月久久综合丁香| 99精品在免费线老司机午夜| 免费观看人在逋| 免费无遮挡裸体视频| 大香蕉久久成人网| 久久欧美精品欧美久久欧美| 美女扒开内裤让男人捅视频| 十八禁网站免费在线| 日韩大尺度精品在线看网址 | 国产精品98久久久久久宅男小说| 国产欧美日韩一区二区精品| 91成人精品电影| 色尼玛亚洲综合影院| 久久精品影院6| 国产亚洲精品一区二区www| 色播亚洲综合网| 欧美日韩黄片免| 很黄的视频免费| av在线播放免费不卡| 最新美女视频免费是黄的| 色综合站精品国产| 又黄又爽又免费观看的视频| 大香蕉久久成人网| 国产男靠女视频免费网站| 国产成人啪精品午夜网站| 亚洲av成人av| 午夜福利影视在线免费观看| 免费看十八禁软件| www.自偷自拍.com| 欧美日韩亚洲国产一区二区在线观看| 精品乱码久久久久久99久播| 国产亚洲精品av在线| 男女之事视频高清在线观看| 一区二区三区激情视频| 精品国产一区二区久久| 国产xxxxx性猛交| 亚洲情色 制服丝袜| 国产亚洲欧美在线一区二区| 在线十欧美十亚洲十日本专区| 黄片大片在线免费观看| av天堂在线播放| 日本在线视频免费播放| 欧美日韩中文字幕国产精品一区二区三区 | 久久精品91蜜桃| 国内精品久久久久久久电影| 99国产极品粉嫩在线观看| 别揉我奶头~嗯~啊~动态视频| 亚洲精品国产区一区二| 亚洲aⅴ乱码一区二区在线播放 | 中国美女看黄片| 成年版毛片免费区| 老鸭窝网址在线观看| 国产精品免费视频内射| 视频在线观看一区二区三区| 午夜激情av网站| 日本免费a在线| 精品久久久精品久久久| 91成年电影在线观看| 久久国产亚洲av麻豆专区| 久久久水蜜桃国产精品网| 50天的宝宝边吃奶边哭怎么回事| 99热只有精品国产| 久久热在线av| 欧美黑人欧美精品刺激| 黄片播放在线免费| 99精品欧美一区二区三区四区| 脱女人内裤的视频| 亚洲一码二码三码区别大吗| 久久婷婷成人综合色麻豆| 桃色一区二区三区在线观看| 黄片小视频在线播放| 亚洲一区二区三区不卡视频| 男人的好看免费观看在线视频 | 一区二区三区激情视频| 亚洲一区高清亚洲精品| 欧美黑人欧美精品刺激| 欧美性长视频在线观看| 国产熟女午夜一区二区三区| 国产不卡一卡二| 一级毛片精品| a级毛片在线看网站| 亚洲全国av大片| 日本在线视频免费播放| 嫩草影院精品99| 亚洲人成网站在线播放欧美日韩| 桃色一区二区三区在线观看| 亚洲av美国av| 不卡av一区二区三区| 亚洲色图 男人天堂 中文字幕| 无遮挡黄片免费观看| 黄色a级毛片大全视频| 亚洲精品中文字幕一二三四区| 老司机靠b影院| 色av中文字幕| 视频区欧美日本亚洲| 黄色成人免费大全| 亚洲成a人片在线一区二区| 日韩欧美三级三区| 天天一区二区日本电影三级 | 美女大奶头视频| 久久青草综合色| 久久亚洲真实| www.自偷自拍.com| 久久午夜综合久久蜜桃| 少妇裸体淫交视频免费看高清 | 九色国产91popny在线| 午夜亚洲福利在线播放| 免费在线观看影片大全网站| 一卡2卡三卡四卡精品乱码亚洲| av有码第一页| 黑人巨大精品欧美一区二区mp4| 国产区一区二久久| 亚洲男人天堂网一区| www日本在线高清视频| 国产熟女午夜一区二区三区| 亚洲片人在线观看| 91在线观看av| 国产av又大| 在线观看免费视频网站a站| 午夜日韩欧美国产| 亚洲人成电影观看| 亚洲第一av免费看| 91精品国产国语对白视频| 久久精品成人免费网站| 人人妻人人澡欧美一区二区 | 叶爱在线成人免费视频播放| 黄网站色视频无遮挡免费观看| 中出人妻视频一区二区| 国产三级黄色录像| 国产视频一区二区在线看| 亚洲一区高清亚洲精品| 亚洲精品粉嫩美女一区| 亚洲专区国产一区二区| 十分钟在线观看高清视频www| 中文字幕人妻丝袜一区二区| 美女国产高潮福利片在线看| 亚洲人成伊人成综合网2020| 亚洲男人天堂网一区| 色老头精品视频在线观看| 一进一出抽搐动态| 精品乱码久久久久久99久播| 色老头精品视频在线观看| 亚洲成av人片免费观看| 亚洲精品在线观看二区| 这个男人来自地球电影免费观看| 亚洲 欧美 日韩 在线 免费| 国产男靠女视频免费网站| x7x7x7水蜜桃| 欧美在线黄色| 亚洲第一电影网av| 国产午夜精品久久久久久| 色婷婷久久久亚洲欧美| 99riav亚洲国产免费| 久久欧美精品欧美久久欧美| 中出人妻视频一区二区|