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nature上关于复合材料的英文文献

Short communication

Highly stabilized alpha-NiCo(OH)2nanomaterials for high performance device application

Paulo Roberto Martins,AndréLuis Araújo Parussulo,Sergio Hiroshi Toma,Michele Aparecida Rocha,Henrique Eisi Toma,Koiti Araki *

Instituto de Química,Universidade de S?o Paulo,Av.Prof.Lineu Prestes,748,S?o Paulo,SP CEP 05508-000,Brazil

h i g h l i g h t s

g r a p h i c a l a b s t r a c t

nanomaterials.

a r t i c l e i n f o

Article history:

Received 14May 2012Received in revised form 15June 2012

Accepted 18June 2012

Available online 23June 2012Keywords:

Nickel hydroxide Mixed hydroxides Alpha-polymorph Nanoparticles

Nanostructured materials

a b s t r a c t

Improving the charge capacity,electrochemical reversibility and stability of anode materials are main challenges for the development of Ni-based rechargeable batteries and devices.The combination of cobalt,as additive,and electrode material nanostructuration revealed a very promising approach for this purpose.The new a -NiCo mixed hydroxide based electrodes exhibited high speci ?c charge/discharge capacity (355e 714C g à1)and outstanding structural stability,withstanding up to 700redox cycles without any signi ?cant phase transformation,as con ?rmed by cyclic voltammetry,electrochemical quartz crystal microbalance and X-ray diffractometry.In short,the nanostructured a -NiCo mixed hydroxide materials possess superior electrochemical properties and stability,being strong candidates for application in high performance batteries and devices.

1.Introduction

Nickel hydroxides have been explored as electroactive materials of sensors [1e 6],electrochromic devices [7]and rechargeable batteries [8,9].Many efforts have been directed to improve the conductivity and reversibility of the charge/discharge processes,and to enhance the speci ?c charge capacity by incorporation of

transition and non-transition metal ions as additives (Al,Zn,Cd,Co and Mn),[10e 16]or by generating nanomaterials.Another possi-bility is by stabilizing and using the alpha-Ni(OH)2(a 4g ,433mA h g à1)instead of the conventional beta (b 4b ,289mA h g à1)polymorph,because of its superior electrochemical properties [17,18].

The addition of Co ions to Ni hydroxide electrodes is known to have bene ?cial effects,reducing the mechanical stress during charge/discharge processes,thus preventing electrode failure,and increasing the charge density [19,20].However,the absence of the characteristic cobalt waves in the mixed NiCo hydroxides

*Corresponding author.Tel.:t551130918513;fax:t551138155640.E-mail address:koiaraki@https://www.sodocs.net/doc/315328086.html,p.br (K.

Araki).Contents lists available at SciVerse ScienceDirect

Journal of Power Sources

journal h omepage:www.elsevier.co m/lo cate/jp owsou

Journal of Power Sources 218(2012)1e 4

voltammograms strengthened the hypothesis that only nickel is electrochemically active.Accordingly,the enhanced charge capacity[21]of mixed hydroxide materials was assigned to a higher conductivity and activation of more nickel sites rather than to contributions of cobalt sites[22].For example,Kim et al.[23] showed that the a-phase material obtained by co-precipitation of 10.2%of cobalt(II)hydroxide with nickel(II)hydroxide was totally converted to the b-phase after60consecutive redox cycles,but the material containing16.7%of cobalt was more stabilized.Similar results were described by Zhao et al.[24]by homogeneous co-precipitation of16.8and19.5%of aluminium hydroxide by the urea method.

The speci?c charge capacity of b-Ni(OH)2/Ni-foam electrodes is 275mA h gà1,lower than of b-Ni(OH)2nanotubes(315mA h gà1), but higher than that of nanosheets(219.5mA h gà1),commercial micrometer grade spherical powders(265mA h gà1)and micro-tubes(232.4mA h gà1)[28].New routes for preparation of alpha nickel hydroxide nanomaterials,showing enhanced electro-chemical properties and speci?c charge capacity,have also been reported[7,25e27]but none was stable enough for practical application.

Recently we showed that nanostructured materials prepared with a-Ni(OH)2nanoparticles can be stabilized[29,30],keeping the performance for at least200consecutives electrochemical cycles. In this report we demonstrate that the combination of the two strategies,more speci?cally,cobalt additivation and nano-structuration,can further enhance the stability of alpha nickel hydroxide,resulting in more robust materials for application in batteries and other devices.In special,we disclose the electro-chemical properties of nanostructured materials prepared from sol e gel nickel/cobalt mixed hydroxide nanoparticle precursors, exhibiting high speci?c charge capacity(up to714C gà1)and stability in the a-phase(over700cycles).

2.Materials and methods

All reagents and solvents were of analytical grade and used as received.Isopropyl alcohol,n-butyl alcohol and potassium hydroxide were purchased from Synth.Anhydrous glycerin was purchased from Sigma e Aldrich,whereas nickel acetate tetrahy-drate and cobalt acetate hydrate were obtained from Vetec.

The nickel/cobalt mixed hydroxide precursors were prepared by dissolving4.82mmol of the metal acetates in25mL of glycerin and adding9.64mmol of KOH in n-butanol,at room temperature.Four samples were prepared and named according to the Ni:Co molar ratio as follows:Ni(OH)2,NiCo-80:20,NiCo-60:40and NiCo-50:50.

X-ray analyses were performed using a Higaku Mini?ex powder diffractometer equipped with a Cu K a radiation source(1.541 A, 30kV,15mA,step?0.02 ),in the2q range from1.5to70 .

Cyclic voltammograms(à0.15e0.44V,20mV sà1)were registered on an Autolab PGSTAT30potentiostat/galvanostat using a conventional three electrodes arrangement with a NiCo(OH)2 modi?ed?uorine doped tin oxide(FTO)as working electrode,

a coiled platinum wire as auxiliary and an Ag/AgCl(in

1.0mol dmà3KCl,0.222V vs SHE)reference electrode,using 1.0mol dmà3KOH as electrolyte solution.

Electrochemical quartz crystal microbalance(EQCMB) measurements were carried out simultaneously with CV,using AT-cut quartz crystal electrodes(5MHz,25.4mm diameter,working area?1.37cm2)covered with a thin platinum layer,and a Maxtek PM-710equipment coupled with the Autolab PGSTAT30potencio-stat/galvanostat,using a conventional three electrodes arrangement.

FTO glass plates were carefully washed with isopropanol and water,dried in air and modi?ed by spin-coating the nickel/cobalt mixed hydroxide sol e gel nanoparticle precursors,at2500rpm. These electrodes were dried under vacuum and calcined at240 C for30min.The speci?c charge capacities per gram of nickel were determined using1.0cm2electrodes,where the amounts of nickel and cobalt were measured by ICP-AES(Arcos-SOP e Spectro)using the solutions obtained by dissolving the NiCo hydroxide?lms with a0.1mol dmà3nitric acid solution,from the working electrodes after700cycles.The quartz crystal electrodes were modi?ed in

a similar way,except for the exclusion of the heat treatment.

3.Results and discussion

Mixed alpha-NiCo(OH)2sol e gel precursors(a-NiCo-80:20, a-NiCo-60:40and a-NiCo-50:50)are convenient row materials for the preparation of nanostructured?lms by methods as simple as dip-coating and spin-coating.In fact,porous?lms constituted by agglomerated5e15nm nanoparticles,resembling sponge like nanostructures,were obtained in all cases.A typical SEM image of a NiCo-50:50sample is shown in Fig.1A where the particle size and morphology are clearly depicted.The vacuum dried material was stable enough to be washed and submitted to electrochemical cycling without signi?cant lixiviation or?aking,but the calcined materials are more stable and used throughout,except for

the Fig.1.(A)SEM image of a NiCo-50:50electrode calcined at240 C,and(B)XRD of the nanostructured nickel and cobalt mixed hydroxide materials.

P.R.Martins et al./Journal of Power Sources218(2012)1e4

samples for EQCMB measurements which were not submitted to heat treatment to avoid damaging the quartz crystal.

The polymorphic phases of nickel hydroxide materials can be readily distinguished by X-ray diffractometry(XRD)by evaluating the inter-slab distances and the degree of organization of the lamella along the crystallographic c axis.The disordered turbos-tratic structure of a-Ni(OH)2presents inter-slab distances higher than about8 A,whereas the structure of the beta polymorph is more compact and organized presenting a much shorter inter-slab distance of4.6 A.

X-ray diffractograms of Ni(OH)2,NiCo-80:20,NiCo-60:40and NiCo-50:50nanostructured materials are shown in Fig.1B.Only the 003peak was observed in the low angle region at7.91 ,7.55 ,8.16 and8.64 ,respectively corresponding to inter-slab distances of11.2, 11.7,10.9and10.3 A,in addition to lower intensity and broadened 101(34.5 )and110(60.3 )peaks,con?rming that the nano-structured materials are constituted by rather small sized crystal-lites of the a-polymorph.A tendency of decrease of inter-slab distances was observed as a function of cobalt content,but no signi?cant shift of the101and110peaks could be observed precluding the comparison of lattice parameters.However,the substitution of Ni(II)by cobalt ions in the lattice should have con-trasting effects depending on its oxidation state and extent of substitution since Ni(II)ionic radii(83pm)is in between that of Co(II)and Co(III)(88.5and68.5pm,respectively).

The electrochemical quartz crystal microbalance(EQCMB) experiments were carried out to shed light on possible structural changes that may be occurring along the successive charge/ discharge processes.This technique is quite sensitive and conve-nient to distinguish the alpha and beta polymorphic phases.The a-

Ni II(OH)2is characterized by a positive mass change whereas the b-Ni II(OH)2shows exactly the opposite behavior associated with the oxidation process but the mechanism is not clearly de?ned.Eq.(1) can be used to explain that behavior,but the incorporation of hydrated cations and hydroxide anion concomitantly with the release of water molecules during the oxidation process have also been proposed[23].

aàNieOHT

$H2OtOHà?g NiOOH$eH2OTe1txTte1àxTH2Oteà

(1)

A typical EQCM

B experiment for the NiCo nanomaterials is illustrated in Fig.2where the results for the NiCo-50:50and the simultaneously measured CVs are depicted.The oxidation at E ap?t0.28V(Fig.2A)is associated with a positive mass change that parallels the current rise in the respective voltammogram, indicating that both are correlated and the corresponding cathodic wave at E cp?t0.23V is associated with a negative mass change,as expected for nickel hydroxide nanomaterials in the alpha poly-morphic phase.Surprisingly,the charge capacity and the EQCMB pro?le after50and200cycles were very similar clearly re?ecting the electrochemical stability of the nanomaterial(Fig.2B).

FTO electrodes modi?ed with the nanomaterials were prepared by de?ning1.0cm2areas using Scotch tape,depositing the mixed NiCo hydroxide sol e gel nanoparticle precursors,drying under vacuum and?ring at240 C.The CVs(Fig.3)are characterized by low intensity redox waves that become well de?ned in the 0.2e0.4V range after about ten redox cycles for electrode conditioning.The peak currents associated with the Ni II(OH)2/ Ni III OOH redox pair increased dramatically while small shifts on the anodic and cathodic peak potentials were observed, indicating an increase of the electroactive sites concentration as a function of the number of successive scans.

The voltammetric behavior of the thermally treated mixed hydroxides was strongly dependent on the amount of cobalt ion present in the nanomaterials(Fig.3A e D).For example,the E ap and E cp of pure Ni(OH)2were found respectively att0.39andt0.30V. However,they were signi?cantly shifted to lower potentials as the amount of cobalt was increased,such that E ap was cathodically shifted to0.37,0.31and0.29V respectively after incorporation of 20,40and50%of cobalt to the Ni(OH)2,improving the reversibility and decreasing the possibility of oxygen gas evolution during the charging process.Two successive CVs were always superimposable, except for a small increase in current,indicating that all electro-chemically active sites were recovered during the

reduction Fig.2.Cyclic voltammogram(black line)and voltamassogram(red line)of a-NiCo-50:50after(A)50and(B)200scan cycles,in1mol dmà3KOH electrolyte solution,at 20mV sà1.(For interpretation of the references to color in this?gure legend,the reader is referred to the web version of this

article.)

Fig.3.Successive cyclic voltammograms of FTO electrodes modi?ed with A)Ni(OH)2, B)a-NiCo-80:20,C)a-NiCo-60:40and D)a-NiCo-50:50and submitted to heat treat-ment at240 C for30min,in1mol dmà3KOH and scan rate?20mV sà1.

P.R.Martins et al./Journal of Power Sources218(2012)1e43

(discharge)process despite the slower kinetics,as indicated by the less intense and broader cathodic wave.The charge/discharge curves become more symmetric as the cobalt content was increased (Figs.3and 4).

The Ni:Co molar ratios in the modi ?ed electrodes were deter-mined before (77.7:22.3,56.4:43.6and 47.3:52.7)and after 700redox cycles (79.0:21.0,58.1:41.9and 53.3:46.7),and the speci ?c charge and discharge capacities per gram of nickel were evaluated from the amounts of charge under the voltammetric waves (esti-mated by integration of CVs in Fig.3)and the respective mass of nickel in the electrode determined by ICP-AES.It should be noticed that the charge capacity of the pure Ni(OH)2remained more or less constant (147C g à1(Ni))whereas those of mixed hydroxides increased progressively as a function of the number of successive charge/discharge cycles,reaching limit values as high as 355,714,and 609C g à1(Ni),respectively for the NiCo-80:20,NiCo-60:40and NiCo-50:50nanomaterials,after 700cycles.The exception seems to be the NiCo-60:40,which should reach a limit value as high as ?ve times the charge capacity of a -Ni(OH)2.This behavior suggests that the diffusion of electrolyte and consequent activation of nickel hydroxide sites is somewhat slower in this material.

Considering nickel hydroxide as electrochemically active species,the coulombic ef ?ciencies were estimated as 8.9,21.6,43.4and 37.0%,respectively for a -Ni(OH)2,a -NiCo-80:20,a -NiCo-60:40and a -NiCo-50:50,indicating that almost half of the nickel hydroxide sites are electrochemically active.These results are inconsistent with a signi ?cant increase of the degree of crystallinity and conversion of the material to the b -phase polymorph,con-?rming the electrochemical stability and reversibility of the mixed hydroxide nanomaterials,in striking contrast with previously reported analogous materials.4.Conclusion

Mixed nickel and cobalt hydroxide nanomaterials exhibiting enhanced electrochemical reversibility and speci ?c charge and discharge capacity as a function of cobalt molar proportion up to

50%were successfully prepared from sol e gel precursors.Interest-ingly,the speci ?c charge capacity increased progressively until up to 700cycles and no change in the EQCMB pro ?le was observed con ?rming their high structural stability in the alpha polymorphic phase.The a -NiCo-60:40showed the best performance exhibiting at least four and six times higher speci ?c charge capacity than pure a -Ni II (OH)2and b -Ni II (OH)2,respectively.Summarizing,the mixed hydroxide nanomaterials showed superior electrochemical prop-erties and phase stability making them suitable for high charge device applications.Acknowledgements

To Funda??o de Amparo àPesquisa do Estado de S?o Paulo (FAPESP)and Conselho Nacional de Desenvolvimento Cientí?co e Tecnológico (CNPq)for the ?nancial support.Appendix A.Supplementary material

Supplementary material associated with this article can be found,in the online version,at https://www.sodocs.net/doc/315328086.html,/10.1016/j.jpowsour.2012.06.065.References

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Fig.4.Plots of the speci ?c charge and discharge capacities per gram of nickel of FTO electrodes modi ?ed with stabilized pure and mixed alpha nickel hydroxides (a -Ni(OH)2,a -NiCo-80:20,a -NiCo-60:40and a -NiCo-50:50),?red at 240 C for 30min,as a function of the number of consecutive scan cycles in 1mol dm à3KOH,at 20mV s à1.

P.R.Martins et al./Journal of Power Sources 218(2012)1e 4

碳纤维复合材料英文文献

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资者的利益。这些功能已被的广泛普及内部控制系统架构设计的广泛认可，并指出了内部控制是用以促进效率，减少资产损失风险，帮助保证财务报告的可靠性和对法律法规的遵从（COSO,1992）。尽管有其相关性，但投资者不能直接观察，因此也无法得到内部控制系统设计和发挥功能的信息，因为它们都是组织内的内在机制、活动和过程（Deumes and Knechel,2008）。由于投资者考虑到成本维持监控管理其声称的（Jensen and Meckling，1976）,内部控制系统在管理激励信息沟通上的特性，以告知投资者内部控制系统的有效性,是当其他监控机制（该公司的股权结构和董事会）比较薄弱，从而为其提供便捷的监控（Leftwich et等, 1981）。存在的替代机制一直是人们在不同公司治理文献中争论的话题（Rediker and Seth, 1995；Fernandez and Arrondo，2005），基于威廉姆森（1983年）的替代假说认为，特定控制机制的边际作用取决于其在公司治理制度的相对重要性。在本文中，我们认为披露内部控制系统的特点是在管理者选择的监控机制时存在一个可替代治理机制。Leftwich（1981）认为“管理者选择一个监控包，监测包的组成取决于各种监控机制的成本与效益”（P.59）。特别是，我们重点关注内部控制系统和监控包的另外两个机制 (公司的所有权结构和董事会) 间的关系，根据有关文献（Jensen and Meckling，1976；Fernandez and Arrondo，2005；Gillan，2006）它们在管理行为监控方面发挥相关作用。我们假设认为，内部控制系统的特性取决于激励由企业的股权结构和董事会发挥监督作用。因此,我们研究了三年间在四个不同的证券交易所上市（伦敦、巴黎、法兰克福和米兰）160家欧洲公司内部控制系统披露程度，通过利用这个国际范例,我们能够描绘出不同的体制环境的某些功能。我们发现证据表明内部控制系统披露代替了监测方面所发挥的作用与所有制结构、制度所有权、在董事会上独立董事比例和会计审计委员会的专家成员的比率相关。我们再加上通过内部会计控制的披露所发挥的管理作用，采用以往文献的完整披露架构，使我们能够详细地从内容和信息管理的程度上内制披露上进行交流。而公司治理的最佳做法要求披露内部控制系统的特性，他们没有提供管理应该披露和披露程度的指令。这样的管理缺乏指示使内部控制系统存在随意性。本文提供了实证支持威廉姆森（1983年成立）在不同的治理机制下的替代假说，它有相应的政策含义。虽然大多数公司治理研究考虑一个互补的披露机制管理采用强化公

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BN 氮化硼 BNE 新型环氧树脂 BNS β－萘磺酸甲醛低缩合物 BOA 己二酸辛苄酯 BOP 邻苯二甲酰丁辛酯 BOPP 双轴向聚丙烯 BP 苯甲醇 BPA 双酚A BPBG 邻苯二甲酸丁(乙醇酸乙酯)酯 BPF 双酚F BPMC 2-仲丁基苯基-N-甲基氨基酸酯 BPO 过氧化苯甲酰 BPP 过氧化特戊酸特丁酯 BPPD 过氧化二碳酸二苯氧化酯 BPS 4，4’-硫代双(6-特丁基-3-甲基苯酚) BPTP 聚对苯二甲酸丁二醇酯 BR 丁二烯橡胶 BRN 青红光硫化黑 BROC 二溴(代)甲酚环氧丙基醚 BS 丁二烯-苯乙烯共聚物 BS-1S 新型密封胶 BSH 苯磺酰肼 BSU N，N’-双(三甲基硅烷)脲 BT 聚丁烯-1热塑性塑料 BTA 苯并三唑 BTX 苯-甲苯-二甲苯混合物 BX 渗透剂 BXA 己二酸二丁基二甘酯 BZ 二正丁基二硫代氨基甲酸锌 C 英文缩写全称 CA 醋酸纤维素 CAB 醋酸-丁酸纤维素 CAN 醋酸-硝酸纤维素 CAP 醋酸-丙酸纤维素 CBA 化学发泡剂

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中英文翻译内部控制爆炸① 摘要：Power的1997版书以审计社会为主题的探讨使得审计活动在联合王国（英国）和北美得到扩散。由审计爆炸一同带动的是内部控制制度的兴起。审计已经从审计结果转向审计制度和内部控制，它已然成为公众对公司治理和审计监管政策的辩论主题。Power表示对什么是有效的内部控制各方说法不一。本人对内部控制研究方面有一个合理的解释。内部控制对非常不同概念的各个领域的会计进行探究，并研究如何控制不同水平的组织。因此，内部控制研究的各类之间的交叉影响是有限的，而且，许多内部会计控制是研究是再更宽广的公司治理问题的背景下进行的。所以，许多有关内部控制制度对公司治理的价值观点扔需要进行研究。关键词：机构理论；公司治理；外部审计；内部审计；内部控制制度；管理控制 1 概述 Power的1997版书以审计社会为主题的探讨使得审计活动在联合王国（英国）和北美得到扩散。由审计爆炸一同带动的是内部控制制度的兴起。审计已经从审计结果转向审 ①Maastricht Accounting and Auditing Research and Education Center (MARC), Faculty of Economics and Business Administration, Universiteit Maastricht, P.O. Box 616, 6200 MD Maastricht, The Netherlands s.maijoor@marc.unimaas.nl Fax: 31-43-3884876 Tel: 31-43-3883783

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https://www.sodocs.net/doc/315328086.html,/Journal of Reinforced Plastics and Composites https://www.sodocs.net/doc/315328086.html,/content/30/19/1621The online version of this article can be found at: DOI: 10.1177/0731684411426810 2011 30: 1621 originally published online 7 November 2011 Journal of Reinforced Plastics and Composites N. Venkateshwaran, A. ElayaPerumal and M. S. Jagatheeshwaran Effect of fiber length and fiber content on mechanical properties of banana fiber/epoxy composite Published by: https://www.sodocs.net/doc/315328086.html, can be found at: Journal of Reinforced Plastics and Composites Additional services and information for https://www.sodocs.net/doc/315328086.html,/cgi/alerts Email Alerts: https://www.sodocs.net/doc/315328086.html,/subscriptions Subscriptions: https://www.sodocs.net/doc/315328086.html,/journalsReprints.nav Reprints: https://www.sodocs.net/doc/315328086.html,/journalsPermissions.nav Permissions: https://www.sodocs.net/doc/315328086.html,/content/30/19/1621.refs.html Citations: What is This? - Nov 7, 2011 OnlineFirst Version of Record - Dec 16, 2011 Version of Record >>

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