更全的杂志信息网

Hollow Co9S8 from metal organic framework supported on r GO as electrode material for highly stable supercapacitors

更新时间:2016-07-05

Supercapacitors with attractive high power density,rapid charge and discharge and long cycling life have attracted increasing research attentions.As the key components for supercapacitors,electrode materials with high specific capacitance,good rate performance and stable cycling have been widely investigated[1-4].Porous carbons are one of the widely explored candidates due to their large specific surface area,rich porosity,high electron conductivity and ultrashort charge-discharge time,which is closely related to their energy storage mechanism,i.e.,electric double layer instead of Faradaic process[1,2].How ever,supercapacitors based on porous carbon materials show limited energy density,and then focus is turned into the investigation of pseudocapacitive materials based on the charge-transfer Faradaic reactions,i.e.,redox reactions,such as oxides and sulfides[3,4].

The fast reversible redox reactions,and/or ion intercalation/deintercalation reactions occurring on the shallow surface are supposed to be responsible for high pseudocapacitance[4].Consequently,nanoscale materials with diverse unique morphology such as hollow structure[4-6],core-shell design[7]and nanosheets[8]holding higher specific surface area compared to their bulk counterparts have been widely explored.On the other side,general pseudocapacitive materials such as metal oxides or sulfides show poor electron conductivity and/or limited cycling stability,which greatly limit their electrochemical performance and practical applications.The introduction of conductive agents such as carbon nanotubes(CNTs)[9,10]and graphene[4,11,12]enables the remarkable improvement of the electrochemical performance by increasing the electronic conductivity and preventing the collapse of nanostructures during repeated cycling process.

Recently,metal organic framework(MOF)compounds,due to their high speci fic surface area,controllable abundant porous structure and simple synthesis methods,were investigated for energy storage applications[4,13-15].For example,a composite of nanoporous Co3O4 and carbon with high capacitance was synthesized by a single MOF and ZIF-67(zeolitic imidazolate framework)was used to prepare electrode materials for supercapacitors with a high capacitance of 504 F/g[16].The metal sulfides with hollow structure possessing high specific area and ordered porous structure was synthesized via sulfidation of MOF[5,17,18].These hollow particles show better electrochemical performance compared with their bulk materials.How ever,they still present poor conductivity.Recent work show ed that sandwich-like cobalt sulfide based on reduced graphene oxides(r GO)show s high cycling stability with 99.7% capacitance retention after 4000 cycles[12].

Herein,we reported a simple hydrothermal method to prepare a composite of r GO with hollow Co9S8 particles from the reaction of uniform ZIF-67 nanoparticles with thioacetamide and results show that they can be used as superior electrode materials for supercapacitors.

Fig.1.Schematic illustration of the preparation process of r GO/Co9S8(a)and SEM images of synthesized materials in each process:(b)ZIF-67,(c)GO/ZIF-67,and(d)r GO/Co9S8.Scale bar:(a)3μm,(b)1μm,(c)3μm.

The synthetic procedure of this composite,Co9S8/r GO,is illustrated in Fig.1a and details are shown in Supporting information.Firstly,GO was prepared via a chemically modified method [19].Then,ZIF-67 was prepared by mixing the 2-methylimidazole(2-MI)solution and cobalt nitrate hexahydrate(Co(NO3)2⋅6H2O),and kept still for 24 h.Monodispersed ZIF-67 with average diameter of 200-300 nm was prepared(Fig.1b).In the case of the preparation of GO/ZIF-67,beside the addition of GO after adding 2-MI,the process was similar to that of ZIF-67.The obvious composite with uniform ZIF-67 attached to both sides of GO was achieved after the addition of GO[20].As shown in Fig.1c,a composite of perfect monodispersed dodecahedron of ZIF-67 supported on GO was prepared.The obtained GO/ZIF-67 composite was dispersed in ethanol solution by ultrasonic treatment,followed by adding thioacetamide(TAA).After hydrothermal reaction at 120°C for 3 h in a Te flon-lined stainless steel autoclave,the obtained precipitate was annealed at 500°C in argon atmosphere for 2 h.A composite of r GO with hollow Co9S8 particles was successfully prepared(Fig.1d).

In summary,we demonstrate an approach to fabricate a composite of hollow Co9S8 on r GO,in which the hollow Co9S8 is derived from the sulfidation of ZIF-67.The obtained r GO/Co9S8 exhibits excellent electrochemical performance including high specific capacitance of 575.9 F/g at 2 A/g,excellent high-rate capability of 447.7 F/g at 10 A/g and good cycling stability with 92.0%capacitance retention after 9000 cycles at 4 A/g.The outstanding electrochemical performance can be explained by the elaborately designed structure.We analyzed and summarized the relational advantages of this unique structure,and believed it could be generally extended to other hollow materials.Further work on the influence of the r GO content is needed while the insufficient and excessive addition both have negative effect on electrochemical performance.This work paved a way to design the composite structure combining r GO and nanohollow materials such as metal sulfides and oxides.

Magnified SEM image of ZIF-67(Fig.2a)show clearly that it exists as dodecahedron particles and there is little change in shape from the initial ZIF-67,and that of Co9S8 exists as hollow particles(Fig.2b).Some broken particles also verified the hollow structure of the prepared Co9S8.Noteworthy,the average diameter of the obtained Co9S8 is enlarged after the sulfidation,which can be explained by the different diffusion speed of metal ion and sulfur ion.During the sulfidation procedure,the sulfur ion dissolved from TAA diffused to the surface of the ZIF-67 and combine the cobalt ion to form a hollow Co9S8.Due to the large diameter of sulfur ion it is difficult to move inward.As a result,the smaller cobalt ion moved outward to form cobalt sulfide.Therefore,the inner side of the ZIF-67 particles becomes empty and a hollow Co9S8 is achieved(Fig.S1 in Supporting information).As shown in Fig.2c,powder X-ray diffraction(XRD)patterns for both ZIF-67 and GO/ZIF-67 show typical ZIF topologies,and no peak of GO is observed because of its low intensity.The XRD patterns of Co9S8 and r GO/Co9S8(Fig.2d)show the characteristic peaks of(311),(222),(331),(511)and(440)planes for the cobalt pentlandite(JCPDS No.86-2273,Co9S8)at 2θ values of 29.8°,31.2°,39.6°,47.6° and 52.1°,respectively.Raman spectra(Fig.S4 in Supporting information)show a clear evidence of the presences of graphene in the composites.Raman peaks at 1361.2 cm-1 and 1603.2 cm-1 could be ascribed to disordered carbon-induced D band and graphitic carbon related G band of r GO/Co9S8,respectively.

The excellent performances are mainly ascribed to the following three factors:(i)An electronic pathway is introduced by the r GO substrate.Consequently,the charge transfer resistance of the r GO/Co9S8 is smaller than that of Co9S8,which leads to higher output power.(ii)The hollow structure with its high specific surface area lowers the ion transportation distance.Due to the high surface area,the contact area between activated material and electrolyte is largely increased.Higher contact area could reduce the ion transportation distance and enhance the efficiency of ion transporting,which benefits the good high-rate performance and larger capacitance.(iii)The added r GO supports the Co9S8 hollow particle during the cycling,which promotes the cycling stability.The r GO can prevent Co9S8 from collapsing during fast charge and discharge process.The SEM image of the r GO/Co9S8 after the cycling show s the relative better retention of hollow structure than that of Co9S8(Fig.S5 in Supporting information),in spite of the inevitable slight collapsing in the r GO/Co9S8.Actually,this unique hollow Co9S8 on r GO is generally valid for other materials,such as hollow Zn S particle derived from ZIF-8[23]and Fe2O3 microboxes derived from Prussian blue[24].

As shown in Fig.3f,the r GO/Co9S8 exhibited a remarkable good capacitance retention of 92.0%after 9000 cycles at a current density of 4 A/g.In contrast,Co9S8 remained only 82.7%at the same condition and its reversible capacitance is also lower than that of r GO/Co9S8.

w here C s is the specific capacitance(F/g),I is the discharge current(A),dt is the differential of discharge time,m is the mass of the active materials(g)and d V(V)is the differential of potential.The r GO/Co9S8 electrode shows a specific capacitance of 575.9,526.0,493.7,467.2 and 447.7 F/g at a current density of 2,4,6,8 and 10 A/g,respectively(Fig.3d).The IR drop of the curves resulting from fast accumulation of charges and reactions during the charge/discharge process is relatively low even at a large current density of 10 A/g.The specific capacitance of the r GO/Co9S8 retains 59.9%with the current density ranging from 1 A/g to 20 A/g.This is illustrated from the EIS spectra of Co9S8 and the r GO/Co9S8,and their corresponding equivalent circuits shown in Fig.3e.The resistance of the system(Rs),including the ohmic resistance of electrolyte interfaces and the active materials,are 0.5Ω in r GO/Co9S8 and 1.34Ω in Co9S8.This decrease is mainly resulted from the good electronic conductivity introduced by r GO.The charge transference resistance(Rct)is only 0.89Ω after the addition of r GO,which is dramatically decreased compared with that of Co9S8,2.16Ω.The diffusion resistances(RD),indicating the migration rate of ions from the electrolyte inside the surface of Co9S8,are 1.26Ω and 1.07Ω for Co9S8 and r GO/Co9S8,respectively.This result is consistent with the above results such as excellent rate performance.

Fig.3a shows the representative cyclic voltammetric(CV)curves of the r GO/Co9S8 at various scan rates in the potential range of 0-0.55 V( vs.saturated calomel electrode,SCE).All of the curves show clear pseudocapacitance features with a similar shape,an evident oxidation peak and a large reduction one,which correspond to the reactions suggested in Eqs.(1)and(2).The curves maintained regular shapes even at a high scan rate of 100 m V/s,indicating the superb high-rate performance of r GO/Co9S8.To compare the functions of the added r GO,their CV curves at a scan rate of 10 m V/s are shown in Fig.3b.The higher area of the closed CV curve of the r GO/Co9S8 indicates its higher activities for the redox reactions due to the presence of r GO.When the current density increases from 2 A/g to 10 A/g in the potential window from 0 to 0.45 V(Fig.3c),there are no obvious potential plateaus,which are similar to those of supercapacitors and different from those of batteries[4,22].Due to the existence of pseudocapacitance from the redox reactions of Eqs.(1)and(2),their charge and discharge curves are not linearly symmetric[4].The capacitances of the electrodes were calculated from the following Eq.(3):

Fig.2.SEM images of ZIF-67(a)and Co9S8(b),XRD patterns of ZIF-67 and GO/ZIF-67(c),and Co9S8 and rGO/Co9S8(d).

Fig.3.CV curves of(a)r GO/Co9S8 at different scan rates and(b)Co9S8 and r GO/Co9S8 at the scan rate of 10 m V/s,(c)charge-discharge curves of r GO/Co9S8,(d)rate performance,(e)EIS spectra and equivalent circuits,and(f)cycling performance of Co9S8 and r GO/Co9S8.

鲁迅器重、支持聂绀弩,聂绀弩则非常敬仰尊崇鲁迅。“两个口号”论争期间,聂绀弩最早表态拥护鲁迅支持的“民族革命战争的大众文学”。对鲁迅犀利深刻的杂文,聂绀弩佩服得五体投地,他后来回忆说,鲁迅的“杂文至少很难再有了。然而这并不排斥与他同时代的人,他的后辈景仰他,学习他,学习他的思想、精神,以及他的杂文,乃至模仿他的笔调之类。我就是学习乃至仿效鲁迅杂文的一个。”他还说,我“这样一个人,虽然曾经爱好、学习、甚至模仿鲁迅的杂文,但无论内容和形式,其不会相像,毫无是处,相隔十万八千里,那是十分自然的。”[9]

For cobalt sulfide-based electrode in alkaline solution(1 mol/L KOH),the Faradaic reactions are suggested as the follow ing equations[21]:

③操作应用灵活便捷。WebGIS应用服务是将GIS的Client/Server技术与基于Web的Internet技术相结合的成果,即保留了Client/Server技术交互便捷、事务处理严谨完整的优点,又利用了Web技术分布式布设、简便灵活的特点,从而使天眼Web应用服务更加灵活,用户交互操作更加便捷,即实现了在同一窗口中的多类图像产品展示应用,便于防汛抗旱会商汇报,又将图像、数据表、气象要素柱状图(折线图)等不同风格产品多窗口展示应用,便于专业人员分析应用。

Financial support from National Key Project (No.2017YFF0210703),Distinguished Young Scientists Program of the National Natural Science Foundation of China(Nos.51425301,21374021,51673096 and U1601214)and Sanyo Chemical Co ., Ltd.is gratefully appreciated.

Acknowledgments

Appendix A.Supplementary data

(2)案例探究。B企业进行企业经营管理方法调节过程中,充分利用企业经营要点,制定经济收益与社会效益均衡性模型,设定企业经济收益为因变量,社会需求为自变量,企业管理工作的开展,必须要先寻求这一模型中的核心点,再进一步调整两者之间不相适应的部分。包括:企业某种营销方法安排是否会对企业品牌造成损害,是否会导致企业资金回笼速率减慢等方面。案例中描述的,关于均衡企业管理模式优化中,多项元素综合调控方法分析,就是对社会需求与企业利益科学调配要点的把握。

厄瓜多尔目前有5个铜矿项目正在开发,其中四个将在2021年前投产,过去一年半中有几家矿业巨头前来投资。

Supplementary data associated with this article can be found,in the online version,at https://doi.org/10.1016/j.cclet.2018.01.051.

在仿真实现过程中,发现由于数值计算误差的累积,经常出现协方差矩阵非正定导致Cholesky分解无法进行,递推中断。因此,对代码实现进行了优化:

References

[1]F.X.Wang,S.Y.Xiao,Y.Y.Hou,et al.,RSC Adv.3(2013)13059-13084.

[2]M.Winter,R.J.Brodd,Chem.Rev.104(2004)4245-4269.

[3]B.E.Conway,W.G.Pell,J.Solid State Electrochem.7(2003)637-644.

[4]F.X.Wang,X.W.Wu,X.H.Yuan,et al.,Chem.Soc.Rev.46(2017)6816-6854.

[5]X.Y.Yu,L.Yu,X.W.D.Lou,Adv.Energy Mater.6(2016)1501333.

[6]M.Xu,L.Kong,W.Zhou,et al.,J.Phys.Chem.C 111(2007)19141-19147.

[7]X.Lu,M.Yu,G.Wang,et al.,Adv.Mater.25(2013)267-272.

[8]M.Acerce,D.Voiry,M.Chhow alla,Nat.Nanotechnol.10(2015)313-318.

[9]J.Yan,Z.Fan,T.Wei,et al.,J.Pow er Sources 194(2009)1202-1207.

[10]C.Peng,S.Zhang,D.Jew ell,et al.,Prog.Nat.Sci.18(2008)777-788.

[11]X.C.Dong,H.Xu,X.W.Wang,et al.,ACS Nano 6(2012)3206-3213.

[12]Y.Wang,B.Chen,Z.Chang,J.Mater.Chem.A 5(2017)8981-8988.

[13]H.Li,M.Eddaoudi,M.O’Keeffe,et al.,Nature 402(1999)276-279.

[14]D.Y.Lee,S.J.Yoon,N.K.Shrestha,et al.,Microporous Mesoporous Mater.153(2012)163-165.

[15]A.Morozan,F.Jaouen,Energy Environ.Sci.5(2012)9269-9290.

[16]R.R.Salunkhe,J.Tang,Y.Kamachi,et al.,Acs Nano 9(2015)6288-6296.

[17]X.Y.Yu,L.Yu,B.H.Wu,et al.,Angew.Chem.Int.Ed.54(2015)5331-5335.

[18]Z.Jiang,W.Lu,Z.Li,et al.,J.Mater.Chem.A 2(2014)8603-8606.

[19]A.Fasolino,J.H.Los,M.I.Katsnelson,Nat.Mater.6(2007)858-861.

[20]L.Jiao,Y.X.Zhou,H.L.Jiang,Chem.Sci.7(2016)1690-1695.

[21]J.Yu,H.Wan,J.Jiang,et al.,J.Electrochem.Soc.161(2014)A996-A1000.

[22]Z.Chang,Y.Q.Yang,M.X.Li,et al.,J.Mater.Chem.A 2(2014)10739-10755.

[23]Z.Jiang,H.Sun,Z.Qin,et al.,Chem.Commn.48(2012)3620-3622.

[24]L.Zhang,H.B.Wu,S.Madhavi,et al.,J.Am.Chem.Soc.134(2012)17388-17391.

PengWang,ChunyangLi,WeigangWang,JingWang,YusongZhu,YupingWu
《Chinese Chemical Letters》2018年第4期文献
Supercapacitors 作者:Zhiqiang Shi,Zhong-Shuai Wu,Zhiqiang Niu,Jinping Liu,Xiaowei Yang,Wei Lv

服务严谨可靠 7×14小时在线支持 支持宝特邀商家 不满意退款

本站非杂志社官网,上千家国家级期刊、省级期刊、北大核心、南大核心、专业的职称论文发表网站。
职称论文发表、杂志论文发表、期刊征稿、期刊投稿,论文发表指导正规机构。是您首选最可靠,最快速的期刊论文发表网站。
免责声明:本网站部分资源、信息来源于网络,完全免费共享,仅供学习和研究使用,版权和著作权归原作者所有
如有不愿意被转载的情况,请通知我们删除已转载的信息 粤ICP备2023046998号