PDDA修饰的碳纳米管载铂电催化剂的合成及其在碱性条件下的氧气还原反应催化性能

采用长链聚合物聚二烯丙基二甲基氯化铵(PDDA)对多壁碳纳米管(MWCNTs)进行修饰,并将采用胶体法还原出的铂(Pt)纳米粒子通过静电作用担载于PDDA修饰的多壁碳纳米管上,从而制备出Pt/PDDA/MWCNTs复合电催化剂.透射电镜(TEM)与X射线衍射(XRD)测试结果表明, Pt纳米粒子均匀地分布在MWCNTs的表面,其平均粒径约为3.6 nm.热失重分析显示催化剂的实际负载量为36%(w).旋转圆盘电极测试结果表明, Pt/PDDA/MWCNTs催化剂对碱性条件下的氧气还原反应(ORR)具有优异的催化活性.与负载量为40%(w)的商业Pt/C催化剂相比, Pt/PDDA/MWCNTs催化剂的氧气还原反应的起始电位和半波电位均正移约30 mV,其质量比活性更大.动力学研究结果进一步证实Pt/PDDA/MWCNTs催化剂比负载量为40%(w)的商业Pt/C催化剂在碱性条件下对氧气还原反应具有更优异的催化活性.     

Cu@Pt/MWCNTs-MnO2电催化剂的制备及电催化性能研究

通过浸渍还原法,以乙二醇作为还原剂,以H2PtCl6 6H2O作为Pt的前驱体制备了Cu@Pt/MWCNTs核壳型电催化剂;通过水热法,以KMnO4和Mn(NO3)2作为锰源制备了α-MnO2和β-MnO2,并把Cu@Pt/MWCNTs核壳型电催化剂与二氧化锰进行掺杂制得Cu@Pt/MWCNTs-MnO2复合材料.利用XRD,SEM,TEM对复合材料的结构和形貌进行表征,利用循环伏安测试曲线和阴极极化曲线等电化学测试方法对电催化剂的性能进行测试.结果表明,电催化剂中Cu@Pt纳米颗粒为核壳型,粒径为6～8 nm,MnO2的晶型为α-MnO2和β-MnO2;另外,Cu@Pt/MWCNTs-MnO2复合材料具有良好的催化性能,其中Cu@Pt/MWCNTs-β-MnO2电催化剂的电化学性能较好,具有较大的电化学活性面积,为71.1 m2 g-1,同时对MnO2促进氧还原的机理进行了初步探讨.     

高催化活性Pd-Co3O4/MWCNTs催化剂对甲醇氧化的电催化性能

以Co(NO3)3·6H2O为钴源,聚乙二醇(PEG)20000为表面活性剂,与多壁碳纳米管(MWCNTs)混合后通过水热氧化法成功地合成了表面均匀分布纳米絮状Co3O4的MWCNTs复合物,进一步还原Pd的前驱体而制备得到Pd-Co3O4/MWCNTs复合催化剂.利用扫描电镜(SEM)、透射电镜(TEM)及X射线粉末衍射(XRD)等手段对样品的形貌和晶型结构进行了表征,结果表明Pd纳米粒子为面心立方晶体结构,均匀地分布在Co3O4修饰的MWCNTs表面.用循环伏安法和计时电流法表征结果表明:催化剂Pd-Co3O4/MWCNTs具有较大的电化学活性表面积,在碱性介质中对甲醇氧化具有更高的电催化活性和稳定性.研究结果表明,过渡金属氧化物纳米Co3O4颗粒在提高直接甲醇燃料电池(DMFC)催化性能研究中具有十分重要的作用,是一类很有潜力的载体催化剂.     

多壁碳纳米管负载高分散Pt-PrxCe1-xO2-δ复合催化剂对甲醇的电催化氧化作用研究

通过反向化学共沉淀法制备PrxCe1-xO2-δ稀土纳米复合氧化物作为助催化掺杂剂,将其包覆在多壁碳纳米管(MWCNTs)的表面作为催化剂复合载体,然后使用了柠檬酸盐-KBH4液相还原法制备了粒径分布均匀、性质稳定的Pt纳米溶胶,并沉积在上述载体中得到负载型Pt-PrxCe1-xO2-δ/CNT复合电催化剂,制备的催化剂中Pt载量为20%(质量分数).使用XRD,SEM等手段对催化剂样品进行了物相形貌表征.使用循环伏安法对催化剂的电化学性能进行了测试.结果表明,经Pr,Ce纳米复合氧化物掺杂的催化剂比传统Pt/CNT催化荆具有更低的甲醇氧化电位和更好的耐中间产物毒化能力.     

弱磁性Co0.85Se纳米片负载碳纳米管作为电催化析氢催化剂

氢气是一种环境友好可再生的清洁能源,电解水无疑是一种很好的制氢方法.然而,电催化分解水析氢受到其缓慢的动力学过程、较低的催化性能和较差的稳定性的限制.为了使整个过程更节能,具有高电流密度和低的过电势的高效电催化剂被广泛研究.非化学计量相硒化钴(Co0.85Se)作为一种重要的金属硫属化合物具有优异的催化性能而广受关注.但是低维的Co0.85Se活性位点少,分散性差,电子传递能力低,导致其电催化剂活性差.多壁碳纳米管(MWCNTs)具有多种电性能,包括金属导电性和电子存储能力等.因此,MWCNTs的特殊结构和高导电性可以有效地促进电子从电催化剂向碳纳米管的转移,实现高效电分解水制氢性能.本文在不使用表面活性剂和模板的情况下,通过一步水热溶剂热法合成弱磁性Co0.85Se纳米片负载碳纳米管电催化剂.采用磁滞回线研究Co0.85Se和MWCNTs/Co0.85Se的磁性能,结果表明其有弱顺磁性,Co0.85Se纳米片之间的空间距离增强导致粒子间偶极相互作用减弱,从而使MWCNTs/Co0.85Se纳米复合材料的矫顽力值增加到158 Oe.随着微晶尺寸的减小和纳米颗粒间距的增大,MWCNTs/Co0.85Se催化剂的比表面积增大,有利于提高其电催化活性.扫描电镜和透射电镜展示出Co0.85Se纳米片分散性较差,且团聚现象严重,而MWCNTs/Co0.85Se纳米复合催化剂显示Co0.85Se纳米片均匀分散在MWCNTs表面,且纳米片尺寸明显减小,有利于Co0.85Se纳米片暴露更多的活性位点.线性扫描伏安曲线测量表明,在酸性溶液中Co0.85Se纳米片在电流密度为10 mA cm?2时,其过电势为319 mV(vs.RHE),30 wt%MWCNTs/Co0.85Se的过电势为266 mV(vs.RHE).Co0.85Se和MWCNTs/Co0.85Se的Tafel斜率分别为92.6和60.5 mV dec?1.此外,MWCNTs/Co0.85Se的电流交换密度(j0)为0.07 mA cm?2.较小的Tafel斜率和高的电流交换密度表明,MWCNTs/Co0.85Se具有良好的反应动力学和快速的质子分离速率.交流阻抗谱表明MWCNTs/Co0.85Se比Co0.85Se电阻更小,电子传输速率更快.电化学活性表面积与双电层在固液界面处的电容测量值成正比.结果显示,30 wt%MWCNTs/Co0.85Se的双电层电容为0.22 mF cm^-2,高于Co0.85Se和15 wt%的rGO/Co0.85Se(0.04 mF cm^-2,0.17 mF cm^-2),这表明较大的电化学活性表面积有利于析氢反应进行.30 wt%MWCNTs/Co0.85Se的循环稳定测试表明其具有较好的稳定性.综上,本文介绍了通过一步水热法合成具有弱磁性的Co0.85Se和MWCNTs/Co0.85Se电催化剂,碳纳米管作为一种高导电性材料被引入Co0.85Se纳米片中以减少Co0.85Se的团聚,使Co0.85Se的活性位点增加,进而提高电催化制氢性能.     

Ce掺杂对碳纳米管负载Mn催化剂结构及SCR反应性能的影响

采用等体积浸渍法制备多壁碳纳米管(MWCNTs)负载Ce-Mn的催化剂,考察了Ce掺杂对Mn/MWCNTs催化剂上NH₃选择性催化还原(SCR)NO_x反应活性的影响.并运用透射电镜扫描、N₂吸附-脱附、程序升温还原、X射线光电子能谱、X射线衍射等手段,重点考察了Ce掺杂对Mn/MWCNTs催化剂结构性质的影响.结果表明,Ce掺杂能显著提高催化剂的SCR活性,其活性增量随着Ce含量的增加先增大后减小;当Ce/Mn为0.6时,催化剂活性最佳.表征结果显示,Mn/MWCNTs中添加Ce后,金属氧化物在MWCNTs上的分散程度提高;催化剂的比表面积和孔体积增大,平均孔径减小;氧化能力提高;表面氧含量增加,Mn化合价升高;结晶度降低,Mn主要以无定形或微晶形式存在,Ce主要以CeO₂物相存在.     

水合氧化钌对铂电催化剂上甲醇电氧化反应的促进作用

以多壁碳纳米管(MWCNTs)为载体,制备了Pt载量为20%的Pt-(RuOxHy)m/MWCNTs催化剂(m为Ru/Pt原子比),在m≤0.4时考察了不同电势区间循环伏安预处理对其催化性能的影响.水合氧化钌(RuOxHy)的存在明显提高了Pt催化剂抗CO毒化的能力,而在甲醇电氧化反应中Pt的质量比活性(MSA)随样品中m值增大呈先升后降趋势.经低电势区间(-0.20～0.46 V vsSCE)预处理稳定的催化剂中,Pt-(RuOxHy)0.10/MWCNTs样品中Pt的甲醇电氧化反应的MSA提高至相应单组分Pt/MWCNTs的9倍.将预处理电势区间扩展到高电势(即-0.20～0.96 V VS SCE)会造成钌组分溶解流失,导致催化剂抗CO毒化能力下降.在经过高电势区间的预处理后,Pt-(RuOxHy)0.20/MWCNTs对甲醇电氧化反应呈现出最高的催化活性,为单组分Pt催化剂的1.4倍.这些结果证实,水合氧化钌是Pt电催化剂的有效助剂.     

Zr改性MnO_x/MWCNTs催化剂的结构特征与低温SCR活性

以ZrO(NO3)2·2H2O为前驱体对多壁碳纳米管(MWCNTs)进行了改性并负载MnOx制备了MnOx/ZrO2/MWCNTs催化剂.考察了Zr对催化剂低温选择性催化还原(SCR)反应活性的影响,并通过多种分析手段对催化剂的结构进行了表征.结果表明Zr的添加对催化剂的低温SCR活性具有显著的促进作用,当Zr负载量为30%时,催化剂活性最佳.X射线衍射(XRD)、拉曼(Raman)光谱、透射电镜(TEM)、N2吸附-脱附的表征结果分析表明,适量的Zr改性促进了MnOx在载体表面的分散,增强金属氧化物与MWCNTs之间的作用,也能增加催化剂的比表面积、孔容和孔径.X射线光电子能谱(XPS)、H2程序升温还原(H2-TPR)和NH3程序升温脱附(NH3-TPD)的分析结果则显示,Zr能提高催化剂表面化学吸附氧浓度,促进Mn3+转化为Mn4+,从而使催化剂表面的活性位点增多,氧化还原能力增强,同时还提高了催化剂表面酸性位点的数量和强度,促进了NH3的吸附,是MnOx/ZrO2/MWCNTs催化剂低温SCR活性提高的主要原因.     

原位合成钴/还原氧化石墨烯纳米粒子催化氨硼烷制氢

采用简单的原位还原合成方法,利用具有温和还原性能的氨硼烷作为还原剂,在室温下一步还原氧化石墨烯和氯化钴混合溶液制备了还原氧化石墨烯负载钴纳米复合材料催化剂. 利用所制备的钴/还原氧化石墨烯催化剂催化氨硼烷水解制氢,发现钴/还原氧化石墨烯具有优异的催化性能. 相对于没有负载的钴纳米粒子以及采用硼氢化钠作为还原剂制备的钴/还原氧化石墨烯催化剂,采用氨硼烷还原制备的钴/还原氧化石墨烯催化剂表现出更加优越的催化性能. 动力学测试表明,钴/还原氧化石墨烯催化氨硼烷水解反应为零级反应,同时钴/还原氧化石墨烯催化剂催化氨硼烷水解反应的活化能为27.10 kJ·mol^-1,低于大部分已报道的其它催化剂,甚至一些贵金属催化剂的活化能. 钴/还原氧化石墨烯催化剂有着稳定的循环使用性,特别是其具有的磁性使得它能够直接从溶液中通过磁力回收,极具应用前景. 这种简单有效的合成方法有望推广到其它的金属-还原氧化石墨烯纳米复合材料体系.     

MnOx/MWCNTs低温氨选择性催化还原NOx硫中毒机理

以经过浓硝酸和等离子体放电预处理后的多壁碳纳米管(MWCNTs)为载体, 锰氧化物(MnO_x)为活性组分, 采用等体积浸渍法制备MnO_x/MWCNTs 催化剂. 利用热重分析(TGA)、扫描电子显微镜(SEM)、X射线衍射(XRD)、X射线光电子能谱(XPS)、程序升温还原/脱附(TPR/TPD)以及傅里叶变换红外(FTIR)光谱对催化剂进行表征, 探讨SO₂对催化剂低温氨选择性催化还原(SCR)NO_x活性的影响及SO₂中毒机理. 结果表明, 低温下SO₂对MnO_x/MWCNTs 催化剂活性有明显毒化作用. 反应温度越高, SO₂浓度越大, 催化剂SCR活性下降越快. 活性中心Mn原子硫酸化是催化剂失活的主要原因. 另外, 催化剂表面生成硫酸铵盐以及SO₂对NO吸附的抑制作用也一定程度上造成了催化剂的失活.     

Pt-Au/CNT@TiO2作为甲醇燃料电池的高活性阳极催化剂

以TiO2包覆的多壁碳纳米管(CNT@TiO2)为载体,Pt和Au为活性物质,采用沉积紫外光催化还原法制备出高活性的甲醇阳极电催化剂Pt-Au/CNT@TiO2,并采用X射线衍射、透射电镜和X射线光电子能谱对催化剂样品的物化特征进行表征.催化剂的抗毒性能用循环伏安和交流阻抗测试来表征.结果表明,粒径为2～3nm的Pt-...     

Fabrication and characterization of bimetallic Pt-Au nanowires supported on FSM-16 and their catalytic activities toward water-gas shift reaction

A facile, previously unexplored, method to synthesize bimetallic Pt-Au nanowires (20nm diameter×120-170nm long) on mesoporous FSM-16 (2.7nm) was fabricated by co-impregnation of H(2)PtCl(6) with HAuCl(4) followed by evacuation at 300K and finally exposure to the CO/H(2)O gas mixture (60:5Torr) at 323K for 1.0h. On the other hand, spherical monometallic nanoparticles of pure Pt (7.0nm diameter) and Au (7-26nm diameter) were synthesized as well, by impregnation, at the same reaction conditions. The catalysts were characterized by in situ FTIR spectroscopy, UV-vis absorption spectroscopy, TEM, TPR and TPCOR. The catalytic activities toward the water-gas shift reaction (WGSR) were also examined under atmospheric pressure and at the margin of 323-373K. The optical absorption spectra showed a remarkable shift and broadening of Pt-Au surface Plasmon resonance band at 515nm apart from those of individual analogue emphasizing bimetallic formation. Results from in situ FTIR spectroscopy indicated that incorporation of Au assisted and stabilized the formation of carbonyl clusters of Pt-Au-CO (2084cm(-1)) and Pt-CO (1888cm(-1)) inside the host FSM-16. The Pt-Au carbonyl clusters built up at the moment of vanishing the linear carbonyl band of the charged Au (Au(+)-CO, 2186cm(-1)) along with a concomitant increase in the reduced gold (Au(0)-CO, 2124cm(-1)) species. TPR profiles showed that the H(2) consumed was higher for Pt/FSM-16 than for Pt-Au/FSM-16 verifying the facile reduction of Pt moieties after addition of Au. The CO adsorption peak maximum, in TPCOR, for Pt/FSM-16 occurred at higher temperature than that of Pt-Au/FSM-16, which exhibited higher amounts of CO(2) produced. The relative decrease in CO bindings on bimetallic surface was responsible for increasing the CO oxidation activity mainly through an association mechanism. Accordingly, the activity of Pt-Au/FSM-16 towards WGS showed a marked increase (8-23 times) compared with those of monometallics emphasizing the dependence of this reaction on the electronic defects of the nanowires. A straightforward reduction mechanism was deduced for Pt-Au alloy formation in view of the results obtained.     

Activity of platinum-gold alloys for glucose electrooxidation in biofuel cells

Carbon supported Pt-Au catalysts with different bimetallic compositions were prepared by water in oil (w/o) microemulsion. Carbon Vulcan XC-72 was added during the synthesis of particles in order to obtain their good dispersion and a mean particle size distribution of 5.02 +/- 0.56 nm. Structural characterization was performed using XRD at wide angles (WAXS), which showed that Pt-Au particles exhibited alloy properties. Electrochemical characterization allowed to estimate the surface composition of Pt-Au alloys, which was close to that of the bulk material Pt(20)Au(80). This catalyst composition displayed the best catalytic activity in steady-state conditions in comparison with Pt(50)Au(50) or Pt and Au alone. Moreover, a Pt-Au/C catalyst with a metal loading of 40 wt % was immobilized onto a carbon porous tube as anode. A membrane-less biofuel cell was tested using laccase/ABTS biocathode in phosphate buffer (pH 5).     

The mechanical and electrical properties of carbon nanotube‐grafted polyimide nanocomposites

Polyimide (PI)‐based nanocomposites containing aminophenyl functionalized multiwalled carbon nanotubes (AP‐MWCNTs) obtained through a diazonium salt reaction was successfully prepared by in situ polymerization. PI composites with different loadings of AP‐MWCNTs were fabricated by the thermal conversion of poly(amic acid) (PAA)/AP‐MWCNTs. The mechanical and electrical properties of the AP‐MWCNTs/PI composites were improved compared with those of pure PI due to the homogeneous dispersion of AP‐MWCNTs and the strong interfacial covalent bonds between AP‐MWNTs and the PI matrix. The conductivity of AP‐MWNTs/PI composites (5:95 w/w) was 9.32 × 10^?1 S/cm which was about 10¹⁵ times higher than that of Pure PI. The tensile strength and tensile modules of the AP‐MWCNTs/PI composites with 0.5 wt % of AP‐MWCNTs were increased by about 77% (316.9 ± 10.5 MPa) and 25% (8.30 ± 1.10 GPa) compared to those of pure PI, respectively. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 960–966     

Catalysis of Multi‐walled Carbon Nanotubes Supported PdxCoy Nanoparticles Prepared by a Pyrolysis Method Using Ionic Liquids as the Solvent toward Ethanol Oxidation Reaction

Multi‐walled carbon nanotubes (MWCNTs) decorated with Pd_xCo_y (the nominal atomic ratios of Pd to Co were 3:1, 3:1.5, 3:2, 3:3, respectively) nanoparticles (denoted as Pd_xCo_y/MWCNTs ) were fabricated by a simple pyrolysis process, in which room temperature ionic liquids (RTILs) of butyl‐3‐methylimidazolium hexafluorophosphate (denoted as [BMIM]PF₆) was used as the solvent. X‐ray diffraction (XRD) and transmission electron microscopy (TEM) were all used to characterize the Pd_xCo_y/MWCNTs catalysts, showing that the Pd_xCo_y particles were dispersed on the surface of the MWCNTs with an average particle size of ～25.0 nm. The electro‐catalytic activity of the Pd_xCo_y/MWCNTs catalysts toward ethanol oxidation reaction (EOR) was examined by cyclic voltammetry (CV). It was revealed that the onset potential was ～90 mV lower and the peak current was about four times higher for ethanol oxidation for Pd₃Co_1.5/MWCNTs compared to those of Pd₃Co₁/MWCNTs. The possible catalysis mechanisms of the Pd₃Co_1.5/MWCNTs toward EOR were also discussed.     

Dispergation and modification of multi-walled carbon nanotubes in aqueous solution

Multi-walled carbon nanotubes (MWCNTs) are widely applied in development of composite materials. However, their properties are directly influenced by the degree of uniformity of dispersion of MWCNTs in the material’s matrix. In this paper, the dispersing of raw MWCNTs (R-MWCNTs) and decorated MWCNTs (D-MWCNTs) was studied in aqueous solution. The D-MWCNTs were obtained by chemical modification method by treatment of initial MWCNTs with the mixture of concentrated nitric and sulfuric acids (3: 1 vol/vol). To achieve a good dispersion of the MWCNTs, a method utilizing ultrasonic processing and surfactant (polyvinylpyrrolidone, PVP) was employed. MWCNTs were characterized by Fourier transform infrared spectroscopy (FT–IR) and X-ray diffraction (XRD). The prepared MWCNTs suspensions were investigated by UV spectroscopy, zeta potential measurements, surface tension and transmission electron microscopy (TEM). The D-MWCNTs have better dispersibility in aqueous solution; this attributed to the functional groups formed on their surface during chemical modification. The PVP surfactant in a certain concentration of 0.6 g/L has the maximum dispersing effect on MWCNTs in aqueous solution, the optimum concentration ratio of PVP and MWCNTs was 3: 1.     

The effect of different treatment methods of multiwalled carbon nanotubes on thermal and flexural properties of their epoxy nanocomposites

Multiwalled carbon nanotubes (MWCNTs) were oxidized using four different acid‐treatment methods followed by their functionalization with 3‐aminopropyltriethoxysilane (3‐APTES). Diglycidyl ether of bisphenol A (DGEBA) nanocomposites with unmodified and silanized MWCNTs (0.2 wt %) were prepared by a cast molding method. The effect of functionalization of MWCNTs on thermal, flexural, and morphological properties of the epoxy nanocomposites were studied. The epoxy/MWCNTs nanocomposites were characterized by thermogravimetric analysis, flexural testing, and field emission electron microscopic analysis. The results showed that the silanization of MWCNTs which were oxidized by a two‐step process using nitric acid and hydrochloric acid showed better thermal and flexural properties due to good interfacial adhesion between MWCNTs and the epoxy matrix. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1175–1184, 2010     

Highly dispersed sulfur in multi-walled carbon nanotubes for lithium/sulfur battery

A facile method is developed for homogeneous dispersion of sulfur (S) nanoparticles in multi-walled carbon nanotubes (MWCNTs). The process involves the modification of MWCNTs via oxidation catalyzed by acid and the introduction of sulfur nanoparticles into the MWCNTs through direct precipitation. The resulting sample (precipitated S/MWCNTs) is characterized with scanning electron microscopy and thermogravimetric analysis, and its performance as cathode of lithium/sulfur battery is investigated with a comparison of the sample prepared by ball-milling (ball-milling S/MWCNTs). It is found that the precipitated S/MWCNTs exhibit better battery performance than the ball-milling S/MWCNTs. The initial discharge capacity is 1,299 mA?h?g^?1 for the precipitated S/MWCNTs but only 839 mA?h?g^?1 for ball-milling S/MWCNTs at 0.02 C. The capacity remains 800 mA?h?g^?1 for the precipitated S/MWCNTs but only 620 mA?h?g^?1 for ball-milling S/MWCNTs at 0.05 C after 50 cycles. The better performance of the precipitated S/MWCNTs results from the improved uniformity of S dispersed in MWCNTs through precipitation.     

Durable electrocatalytic-activity of Pt-Au/C cathode in PEMFCs

Longevity remains as one of the central issues in the successful commercialization of polymer electrolyte membrane fuel cells (PEMFCs) and primarily hinges on the durability of the cathode. Incorporation of gold (Au) to platinum (Pt) is known to ameliorate both the electrocatalytic activity and stability of cathode in relation to pristine Pt-cathodes that are currently being used in PEMFCs. In this study, an accelerated stress test (AST) is conducted to simulate prolonged fuel-cell operating conditions by potential cycling the carbon-supported Pt-Au (Pt-Au/C) cathode. The loss in performance of PEMFC with Pt-Au/C cathode is found to be ～10% after 7000 accelerated potential-cycles as against ～60% for Pt/C cathode under similar conditions. These data are in conformity with the electrochemical surface-area values. PEMFC with Pt-Au/C cathode can withstand >10,000 potential cycles with very little effect on its performance. X-ray diffraction and transmission electron microscopy studies on the catalyst before and after AST suggest that incorporating Au with Pt helps mitigate aggregation of Pt particles during prolonged fuel-cell operations while X-ray photoelectron spectroscopy reflects that the metallic nature of Pt is retained in the Pt-Au catalyst during AST in comparison to Pt/C that shows a major portion of Pt to be present as oxidic platinum. Field-emission scanning electron microscopy conducted on the membrane electrode assembly before and after AST suggests that incorporating Au with Pt helps mitigating deformations in the catalyst layer.     

Synthesis of MWCNTs doped sodium silicate based aerogels by ambient pressure drying

The successful incorporation of multiwalled carbon nanotubes (MWCNTs) into silica aerogels prepared by sol–gel method is reported herein. Pure silica aerogels prepared using sodium silicate precursor by ambient pressure drying are so fragile that they cannot be used easily. MWCNTs were used as reinforcements to improve the mechanical properties of silica aerogels. Results show that inserting small amounts of MWCNTs in the gels causes enhanced dimensional stability of silica aerogels. The silica aerogels were prepared by doping MWCNTs in silica matrix before gelation. The influence of MWCNTs on some microstructural aspects of silica matrix has been studied using nitrogen adsorption–desorption isotherms. From SEM study it is confirmed that the silica particles get capped on the surface of MWCNTs suggesting an enhanced toughness. Further, FTIR, Raman, EDAX, thermal conductivity and hydrophobicity studies of these doped aerogels were carried out. By addition of MWCNTs, silica aerogels were formed with 706 m²/g BET and 1,200 m²/g Langmuir surface areas and 149^o contact angle. Low density (0.052 g/cc) and low thermal conductivity (0.067 W/m K) MWCNTs doped silica aerogels were obtained for the molar ratio of Na₂SiO₃::H₂O::MWCNTs::citric acid::TMCS at 1::146.67::2.5 × 10⁻³::0.54::9.46 respectively with improved mechanical strength.