Supported Pd–Cu Bimetallic Nanoparticles That Have High Activity for the Electrochemical Oxidation of Methanol

Monodisperse bimetallic Pd–Cu nanoparticles with controllable size and composition were synthesized by a one‐step multiphase ethylene glycol (EG) method. Adjusting the stoichiometric ratio of the Pd and Cu precursors afforded nanoparticles with different compositions, such as Pd₈₅–Cu₁₅, Pd₅₆–Cu₄₄, and Pd₃₉–Cu₆₁. The nanoparticles were separated from the solution mixture by extraction with non‐polar solvents, such as n‐hexane. Monodisperse bimetallic Pd–Cu nanoparticles with narrow size‐distribution were obtained without the need for a size‐selection process. Capping ligands that were bound to the surface of the particles were removed through heat treatment when the as‐prepared nanoparticles were loaded onto a Vulcan XC‐72 carbon support. Supported bimetallic Pd–Cu nanoparticles showed enhanced electrocatalytic activity towards methanol oxidation compared with supported Pd nanoparticles that were fabricated according to the same EG method. For a bimetallic Pd–Cu catalyst that contained 15 % Cu, the activity was even comparable to the state‐of‐the‐art commercially available Pt/C catalysts. A STEM‐HAADF study indicated that the formation of random solid‐solution alloy structures in the bimetallic Pd₈₅–Cu₁₅/C catalysts played a key role in improving the electrochemical activity.     

Uniformly dispersed copper nanoparticles onto the modified magnetically recoverable nanocatalyst for aqueous synthesis of primary amides

Magnetically recoverable and environmentally friendly Cu‐based heterogeneous catalyst has been synthesized for the one‐pot conversion of aldehydes to their corresponding primary amides. The Fe₃O₄@SiO₂ nanocomposites were prepared by synthesis of Fe₃O₄ magnetic nanoparticles (MNPs) which was then coated with a silica shell via Stöber method. Bi‐functional cysteine amino acid was covalently bonded onto the siliceous shell of nanocatalyst. The Cu^II ions were then loaded onto the modified surface of nanocatalyst. Finally, uniformly dispersed copper nanoparticles were achieved by reduction of Cu^II ions with NaBH₄. Amidation reaction of aryl halides with electron‐withdrawing or electron‐donating groups and hydroxylamine hydrochloride catalyzed with Fe₃O₄@SiO₂@Cysteine‐copper (FSC‐Cu) MNPs in aqueous condition gave an excellent yield of products. The FSC‐Cu MNPs could be easily isolated from the reaction mixture with an external magnet and reused at least 8 times without significant loss in activity.     

Carbon nanospheres with well‐controlled nano‐morphologies as support for palladium‐catalyzed Suzuki coupling reaction

Uniform carbon nanospheres (UCS) with well‐controlled nano‐morphologies were fabricated by hydrothermal carbonization of sucrose in the presence of kayexalate. Highly dispersed and ultrafine palladium nanoparticles were supported on the UCS through a facile co‐reduction process with NaBH₄ as reducing agent. The obtained Pd@UCS exhibited efficient catalytic activity for the Suzuki coupling reaction. Moreover, the as‐prepared catalyst could be recycled and reused at least five times without significant loss of its catalytic activity.     

Preparation and characterization of novel hydroxyapatite/copper assemblies with well-defined morphologies

Micrometer-sized powders with small crystallite sizes, high dispersion, and high copper contents, like Cu and/or Cu₂O assembled on core particles would find potential applications in fields of catalysts, transparent conducting films and plasmonic-based technologies. Novel hydroxyapatite (HA)/copper assemblies were synthesized via a facile glucose reduction route. During hydrothermal treatment, copper ions were firstly released after dissolution of copper-modified HA, then reduced by glucose and finally assembled as shell on HA aggregates. After 12 h, cuprous oxide grew with truncated-octahedron morphology. When the reduction time was prolonged to 24 and 36 h, Cu phase was formed in situ via glucose reduction of Cu₂O. Interestingly, HA/copper assemblies with well-defined morphologies were prepared under different reaction conditions. With presence of more Na₂CO₃, the reduction of copper ion occurred at a fast rate, which resulted in formation of spherical assemblies. Contrastingly, reduction reaction hardly occurred without Na₂CO₃ addition and assemblies with irregular morphology were prepared. Additionally, copper fibers with length of millimeters were prepared without Na₃Cit addition. The UV–Vis absorbance peak of assemblies showed a blue or red shift due to the effect of crystalline size and/or hollowing process.     

Cu?Cu2O?TiO2 Nanojunction Systems with an Unusual Electron–Hole Transportation Pathway and Enhanced Photocatalytic Properties

Multicomponent Cu? Cu₂O? TiO₂ nanojunction systems were successfully synthesized by a mild chemical process, and their structure and composition were thoroughly analyzed by X‐ray diffraction, transmission electron microscopy, field‐emission scanning electron microscopy, and X‐ray photoelectron spectroscopy. The as‐prepared Cu? Cu₂O? TiO₂ (3 and 9 h) nanojunctions demonstrated higher photocatalytic activities under UV/Vis light irradiation in the process of the degradation of organic compounds than those of the Cu? Cu₂O, Cu? TiO₂, and Cu₂O? TiO₂ starting materials. Moreover, time‐resolved photoluminescence spectra demonstrated that the quenching times of electrons and holes in Cu? Cu₂O? TiO₂ (3 h) is higher than that of Cu? Cu₂O? TiO₂ (9 h); this leads to a better photocatalytic performance of Cu? Cu₂O? TiO₂ (3 h). The improvement in photodegradation activity and electron–hole separation of Cu? Cu₂O? TiO₂ (3 h) can be ascribed to the rational coupling of components and dimensional control. Meanwhile, an unusual electron–hole transmission pathway for photocatalytic reactions over Cu? Cu₂O? TiO₂ nanojunctions was also identified.     

Synthesis of Tungsten Oxide Nanorods by the Controlling Precipitation Reaction: Application for Hydrogen Evolution Reaction on a WO3 Nanorods/Carbon Nanotubes Composite Film Modified Electrode

Tungsten trioxide nanorods (WO₃) were prepared by controlling the precipitation reaction of sodium tungstate dehydrates solution and hydrothermal process. The synthesized tungsten trioxide nanorods have been characterized by X‐ray diffraction (XRD), energy dispersive spectroscopy (EDS), scanning electron microscopy (SEM), cyclic voltammetry (CV) and linear sweep voltammetry (LSV). Electrochemical activity for hydrogen evolution reaction (HER) on WO₃ nanorods / carbon nanotube (WO₃/CNT) composite electrocatalyst was first studied in acid solution (0.1 M H₂SO₄) at room temperature. The overall experimental results revealed that the electrocatalytic activity for HER on WO₃/CNT is two order magnitude higher than those obtained with WO₃ nanorods and is four times than in the case of commercial WO₃ in 0.1 M H₂SO₄. On the other hand, the kinetic reaction mechanisms were discussed on WO₃/CNT electrocatalysts in acid solution for HER. However, the rate‐determining step carries through Tafel reaction on commercial WO₃, CNT, WO₃ nanorods and WO₃/CNT electrocatalysts in acidic solution was introduced.     

Solution/Ammonolysis Syntheses of Unsupported and Silica-Supported Copper(I) Nitride Nanostructures from Oxidic Precursors

Herein we describe an alternative strategy to achieve the preparation of nanoscale Cu₃N. Copper(II) oxide/hydroxide nanopowder precursors were successfully fabricated by solution methods. Ammonolysis of the oxidic precursors can be achieved essentially pseudomorphically to produce either unsupported or supported nanoparticles of the nitride. Hence, Cu₃N particles with diverse morphologies were synthesized from oxygen-containing precursors in two-step processes combining solvothermal and solid−gas ammonolysis stages. The single-phase hydroxochloride precursor, Cu₂(OH)₃Cl was prepared by solution-state synthesis from CuCl₂·2H₂O and urea, crystallising with the atacamite structure. Alternative precursors, CuO and Cu(OH)₂, were obtained after subsequent treatment of Cu₂(OH)₃Cl with NaOH solution. Cu₃N, in the form of micro- and nanorods, was the sole product formed from ammonolysis using either CuO or Cu(OH)₂. Conversely, the ammonolysis of dicopper trihydroxide chloride resulted in two-phase mixtures of Cu₃N and the monoamine, Cu(NH₃)Cl under similar experimental conditions. Importantly, this pathway is applicable to afford composite materials by incorporating substrates or matrices that are resistant to ammoniation at relatively low temperatures (ca. 300 °C). We present preliminary evidence that Cu₃N/SiO₂ nanocomposites (up to ca. 5 wt.% Cu₃N supported on SiO₂) could be prepared from CuCl₂·2H₂O and urea starting materials following similar reaction steps. Evidence suggests that in this case Cu₃N nanoparticles are confined within the porous SiO₂ matrix.     

Pd‐Cu alloy nanoparticle supported on amine‐terminated ionic liquid functional 3D graphene and its application on Suzuki cross‐coupling reaction

Well distributed Pd‐Cu bimetallic alloy nanoparticles supported on amine‐terminated ionic liquid functional three‐dimensional graphene (3D IL‐rGO/Pd‐Cu) as an efficient catalyst for Suzuki cross‐coupling reaction has been prepared via a facile synthetic method. The introduction of IL‐NH₂ cations on the surface of graphene sheets can effectively avoid the re‐deposition of graphene sheets, allowing the catalyst to be reused up to 10 cycles. The addition of Cu not only saves cost but also ensures high catalytic efficiency. It is worthy to note that the catalyst 3D IL‐rGO/Pd_2.5Cu_2.5 can efficiently catalyze the Suzuki cross‐coupling reaction with the yield up to 100% in 0.25 h, almost one‐fold higher than that by the pristine IL‐rGO/Pd_2.5 catalyst (52%). The Powder X‐Ray Diffraction (XRD), combining energy dispersive X‐ray spectroscopy (EDS) mapping results confirm the existence and distribution of Pd and Cu in the bimetallic nanoparticles. The transmission electron microscopy (TEM) reveals the nanoparticle size with an average diameter of 3.0 ± 0.5 nm. X‐ray photoelectron spectroscopy (XPS) analysis proved the presence of electron transfer from Cu to Pd upon alloying. Such alloying‐induced electronic modification of Pd‐Cu alloy and 3D ionic liquid functional graphene with large specific surface area both accounted for the catalytic enhancement.     

Urchin-like CoCu Bimetallic Nanocomposites for Catalytic Hydrogenolysis of Glycerol to Propanediols

Bimetallic CoCu nanocomposites were synthesized in polyol by using Ru as heterogeneous nucleation agent and stearic acid as surfactant, and their catalytic properties were investi- gated by hydrogenolysis of glycerol to propanediols. It was found that the surfactant could induce Co nanocrystals to form nanowires as structure-directing agent, while it's ineffective for Cu because only spherical Cu particles were produced under the same condition. When Co²⁺ and Cu²⁺ coexist in polyol, Cu²⁺ is firstly reduced and forms the spherical particles, and then the Cu particles afford surface for the subsequential reduction of Co²⁺ and growth of Co nanocrystals to form the nanorods, obtaining the urchin-like CoCu nanocomposites. The catalytic performance in selective hydrogenolysis of glycerol to propanediols proposed that the CoCu urchin-like nanocomposites was superior to the Co nanowires possibly due to that the synergistic effect between Co and Cu component promoted conversion of glyc-erol and obtained the higher propanediol yields based on the specific surface areas of the catalysts.     

Towards high‐performance biopackaging: barrier and mechanical properties of dual‐action polycaprolactone/zinc oxide nanocomposites

The properties of nanocomposites of biodegradable polycaprolactone containing zinc oxide (ZnO) nanoparticles with diverse morphologies, that is, ZnO nanospheres, nanorods, and nanodisks are investigated. It is demonstrated for the first time that the dual action of the ZnO nanoparticles reduces the gas permeability of the nanocomposites via two mechanisms: first by the creation of a tortuous path and second by gas adsorption. Depending on the morphology of the particles, the oxygen permeability can be reduced by more than 60%. Tensile tests show that the nanocomposites remain very ductile. The nominal strain for all nanocomposites is higher than 500% before fracture occurs. The Young's modulus and tensile strength of the nanocomposites increase at higher ZnO concentrations. This behavior is more pronounced in the case of ZnO nanorods. As a result, the incorporation of ZnO nanoparticles into (bio)polymers provides an opportunity to manufacture polymer‐based nanocomposite materials, resulting in the production of high‐performance (bio)packaging. Copyright © 2011 John Wiley & Sons, Ltd.     

Electrochemiluminescence of Supramolecular Nanorods and Their Application in the “On–Off–On” Detection of Copper Ions

In this work, an “on–off–on” switch system has been successfully applied through the construction of an electrochemiluminscent biosensor for copper ion (Cu²⁺) detection based on a new electrochemiluminescence (ECL) emitter of supramolecular nanorods, which was achieved through supramolecular interactions between 3,4,9,10‐perylenetetracarboxylic acid (PTCA) and aniline. The initial “signal‐on” state with strong and stable ECL emission was obtained by use of the supramolecular nanorods with a new signal amplification strategy involving a co‐reaction accelerator. In addition, ECL quencher probes (Fc‐NH₂/Cu‐Sub/nano‐Au) were fabricated by immobilizing aminoferrocene (Fc‐NH₂) on Cu‐substrate strand modified Au nanoparticles. The quencher probes were hybridized with the immobilized Cu‐enzyme strand to form Cu²⁺‐specific DNAzyme. Similarly, the “signal‐off” state was obtained by the high quenching effect of Fc‐NH₂ on the ECL of the excited‐state PTCA (¹PTCA*). As expected, the second “switch‐on” state could achieved by incubating with the target Cu²⁺, owing to the Cu²⁺‐specific DNAzyme, which was irreversibly cleaved, resulting in the release of the quencher probes from the sensor interface. Herein, on the basis of the ECL intensity changes (ΔI_ECL) before and after incubating with the target Cu²⁺, the prepared Cu²⁺‐specific DNAzyme‐based biosensor was used for the determination of Cu²⁺ concentrations with high sensitivity, excellent selectivity, and good regeneration.     

A Directed Route to Colloidal Nanoparticle Synthesis of the Copper Selenophosphate Cu3PSe4

The first colloidal nanoparticle synthesis of the copper selenophosphate Cu₃PSe₄, a promising new material for photovoltaics, is reported. Because the formation of binary copper selenide impurities seemed to form more readily, two approaches were developed to install phosphorus bonds directly: 1) the synthesis of molecular P₄Se₃ and subsequent reaction with a copper precursor, (P‐Se)+Cu, and 2) the synthesis of copper phosphide, Cu₃P, nanoparticles and subsequent reaction with a selenium precursor, (Cu‐P)+Se. The isolation and purification of Cu₃P nanoparticles and subsequent selenization yielded phase‐pure Cu₃PSe₄. Solvent effects and Se precursor reactivities were elucidated and were key to understanding the final reaction conditions.     

Chrysanthemum-like Co3O4 architectures: Hydrothermal synthesis and lithium storage performances

Three-dimensional chrysanthemum-like Co₃O₄ was prepared via a facile hydrothermal route without any template, and a subsequent calcination process. With a controlled concentration of the homogeneous precipitation agent, urea, a chrysanthemum-like precursor was hydrothermally obtained at 120 °C for 20 h, and the morphology was kept for Co₃O₄ after a subsequent calcination at 300 °C for 2 h. Co₃O₄ chrysanthemum-like architectures are assemblies of nanorods radiating from a common centre, and the nanorods consisted of interconnected nanoparticles with the size of about 30 nm. When tested as an anode material of Li-ion batteries, chrysanthemum-like Co₃O₄ presented a discharge capacity of ∼450 mA h/g after 50 discharge/charge cycles.     

Core–Shell α‐Fe2O3@α‐MoO3 Nanorods as Lithium‐Ion Battery Anodes with Extremely High Capacity and Cyclability

α‐Fe₂O₃ nanoparticles are uniformly coated on the surface of α‐MoO₃ nanorods through a two‐step hydrothermal synthesis method. As the anode of a lithium‐ion battery, α‐Fe₂O₃@α‐MoO₃ core–shell nanorods exhibit extremely high lithium‐storage performance. At a rate of 0.1 C (10 h per half cycle), the reversible capacity of α‐Fe₂O₃@α‐MoO₃ core–shell nanorods is 1481 mA h g^?1 and a value of 1281 mA h g^?1 is retained after 50 cycles, which is much higher than that retained by bare α‐MoO₃ and α‐Fe₂O₃ and higher than traditional theoretical results. Such a good performance can be attributed to the synergistic effect between α‐Fe₂O₃ and α‐MoO₃, the small size effect, one‐dimensional nanostructures, short paths for lithium diffusion, and interface spaces. Our results reveal that core–shell nanocomposites have potential applications as high‐performance lithium‐ion batteries.     

Magnetically recyclable nano copper/chitosan in O‐arylation of phenols with aryl halides

Interaction of chitosan (CS) with Fe₃O₄, followed by embedding Cu nanoparticles (NPs) on the magnetic surface through adsorption of Cu²⁺, and its reduction to Cu^o via NaBH₄, offers a reusable efficient catalyst (Fe₃O₄/CS‐Cu NPs) that is employed in cross‐coupling reactions of aryl halides with phenols, which affords the corresponding diaryl ethers, with good to excellent yields. The catalyst is completely recoverable from the reaction mixture by using an external magnet. It can be reused four times, without significant loss in its catalytic activity.     

The composite catalysts of Cu/CuxO nanoparticles supported on the carbon fibers were prepared for styrene oxidation reaction

In this paper a novel simple method for preparing two different catalysts with various‐valences copper was reported. Carbon nanofibers supported copper‐cuprous oxide nanoparticles (Cu‐Cu₂O NPs/CNFs) and copper oxide nanoparticles (CuO NPs/CNFs) through electrospinning, adsorption and reduction in the high‐pressure hydrogenation and the high‐temperature calcination methods. These catalysts were investigated by a series of characterizations and were applied in reaction in nitrogen atmosphere, which had a good catalytic activity and selectivity of benzaldehyde for the reaction. Above all, the new study has been certified clearly, in which Cu‐Cu₂O NPs/CNFs and CuO NPs/CNFs composite catalysts enhanced the generation of benzaldehydeand the excellent catalytic properties were exhibited.     

Co3O4纳米催化剂催化CO的形貌效应：合成过程和催化活性

通过催化剂将CO转化为无毒气体仍然是目前减少CO污染的主要手段.随着纳米技术的快速发展,纳米催化剂因其在催化反应中呈现出的独特结构效应（如形貌效应、尺寸效应等）而受到人们的广泛关注.已有大量研究表明,纳米Co3O4作为一种非贵金属氧化物催化剂具有强烈的催化形貌效应,展现出优异的CO低温催化活性.因此,通过合理的设计来调控催化剂粒子的形貌,从而进一步改善催化剂的性能已成为近年来催化剂领域的重要研究方向.对于Co3O4纳米催化剂的可控制备,水热法具有反应温和、操作简便和产品形貌易控等特点.早期的研究主要围绕于Co3O4形貌的可控合成以及不同形貌Co3O4催化剂对其催化活性产生的影响,较少有对其形貌形成机制的报道.特别是在水热反应中,系统研究各反应参数对催化剂各异形貌的形成影响鲜有报道.
　　本文在前人的研究基础上,重点研究了水热反应过程中各主要反应参数对产品形貌控制的影响,绘制了一副不同形貌Co3O4材料的合成过程图,并研究了Co3O4纳米催化剂催化CO氧化的形貌效应.通过水热法先成功合成了三种不同形貌(纳米棒、纳米片和纳米立方)的碱式碳酸钴纳米粒子,然后将其焙烧得到了Co3O4纳米粒子.采用扫描电子显微镜(SEM),透射电子显微镜(TEM), X射线粉末衍射仪(XRD),程序升温还原(H2-TPR和CO-TPR),氮气吸附-脱附比表面积测试(BET),氧气程序升温脱附(O2-TPD), X射线光电子能谱(XPS)等表征手段研究了不同反应参数对纳米碱式碳酸钴前驱体形貌形成的作用和各异形貌Co3O4纳米粒子在催化CO氧化反应中催化性能的差异及原因.
　　结果表明, Co3O4较好地继承了碱式碳酸钴的形貌,在较低温度条件下(≤140°C),钴源(CoCl2或Co(NO3)2)是影响前驱体形貌的关键因素,反应时间只对粒子的尺寸产生较大影响.低温下, CoCl2作为钴源易诱导生产纳米棒状碱式碳酸钴,而Co(NO3)2则有利于纳米片状生成.当温度高于140°C后,无论何种钴源,最终均制得纳米立方体.表面活性剂CTAB对前驱体的均一性和粒子的分散性产生重要影响,加入CTAB后得到的产品尺寸更均一,形貌更加规整.对比于其他两种形貌的样品, Co3O4纳米片显示出更好的CO催化氧化活性.
　　 XPS结果表明,各形貌Co3O4纳米材料的表面组成存在明显差异,活性物种Co3+含量的不同是影响催化活性差异的重要原因. Co3O4纳米片具有更多的Co3+活性位,立方纳米Co3O4表面吸附氧含量较高, Co3O4纳米棒则暴露出相对更多的Co2+.因此,在三种形貌催化剂上CO氧化反应中, Co3O4纳米片表现出最优的催化活性,纳米立方次之,而纳米棒最差. H2-TPR, CO-TPR和O2-TPD等结果也表明, Co3O4纳米片拥有更强的还原性能和脱附氧能力,其次是纳米立方Co3O4.这与XPS结果一致,证实了不同形貌Co3O4纳米催化剂上暴露活性位的数量和表面氧物种的不同是造成彼此间催化CO氧化活性差异的重要原因.此外,通过稳定性测试发现Co3O4纳米片具有较高的催化稳定性,在水蒸气存在的情况下Co3O4纳米片逐渐失活,但随后在干燥条件下其催化活性又逐渐得到恢复.     

Photochemical Synthesis and Spectral-Optical Characteristics of ZnO/Cu and ZnO/Ag/Cu Nanoheterostructures

The photoreduction of Cu²⁺ at the surface of ZnO nanoparticles and ZnO/Ag nanostructures was investigated. The spectral characteristics of the obtained ZnO/Cu and ZnO/Ag/Cu composites were studied in relation to the reaction conditions. It was shown that the ZnO/Ag nanoparticles have higher photocatalytic activity in the reduction of Cu²⁺ ions than the individual ZnO particles.     

Facilely anchoring Cu2O nanoparticles on mesoporous TiO2 nanorods for enhanced photocatalytic CO2 reduction through efficient charge transfer

Semiconductor-employed photocatalytic CO₂ reduction has been regarded as a promising approach for environmental-friendly conversion of CO₂ into solar fuels. Herein, TiO₂/Cu₂O composite nanorods have been successfully fabricated by a facile chemical reduction method and applied for photocatalytic CO₂ reduction. The composition and structure characterization indicates that the Cu₂O nanoparticles are coupled with TiO₂ nanorods with an intimate contact. Under light illumination, all the TiO₂/Cu₂O composite nanorods enhance the photocatalytic CO₂ reduction. In particular, the TiO₂/Cu₂O-15% sample exhibits the highest CH₄ yield (1.35 µmol g^-1 h^-1) within 4 h irradiation, and it is 3.07 and 15 times higher than that of pristine TiO₂ nanorods and Cu₂O nanoparticles, respectively. The enhanced photoreduction capability of the TiO₂/Cu₂O-15% is attributed to the intimate construction of Cu₂O nanoparticles on TiO₂ nanorods with formed p-n junction to accelerate the separation of photogenerated electron-hole pairs. This work provides a reference for rational design of a p-n heterojunction photocatalyst for CO₂ photoreduction.     

Investigation on the Growth Mechanism of Cu2MoS4 Nanotube,Nanoplate and its use as a Catalyst for Hydrogen Evolution in Water

Cu₂MoS₄ is a ternary transition‐metal sulfide that shows great potential in the field of energy conversion and storage, namely catalytic H₂ evolution in water and Li‐, Na‐ or Mg‐ion battery. In this work, we report on a growth mechanism of the single‐crystalline Cu₂MoS₄ nanotube from (NH₄)₂MoS₄ salt and Cu₂O nanoparticle. By probing the nature and morphology of solid products generated in function of reaction conditions we find that the crystalline Cu(NH₄)MoS₄ nanorod is first generated at ambient conditions. The nanorod is then converted into Cu₂MoS₄ nanotube under hydrothermal treatment due to the Kirkendall effect or a selective etching of the Cu₂MoS₄ core. Extending the hydrothermal treatment causes a collapse of nanotube generating Cu₂MoS₄ nanoplate. The catalytic activities of these sulfides are investigated. The Cu₂MoS₄ shows superior catalytic activity to that of Cu(NH₄)MoS₄. Catalytic performance of the former largely depends on its morphology. The nanoplate shows superior catalytic activity to the nanotube, thanks to its higher specific electrochemical surface area.