载体表面化学状态对Pt/C催化剂结构及电催化活性的影响

对碳黑进行不同条件的氧化处理得到不同表面化学状态的载体,以甲醛为还原剂,氯铂酸为前驱体,制备Pt/C电催化剂.运用X射线光电子能谱(XPS)、X射线衍射(XRD)、透射电镜(TEM)等分析手段研究碳黑及Pt/C催化剂的化学组成、化学状态、晶体结构及表面形貌,并用循环伏安法(CV)测试Pt/C催化剂对甲醇的电催化氧化.结...     

联氨气体传感器的敏感物质的选择

通过筛选试验,并采用化学还原法制备了催化联氨氧化的Pt/C催化剂;透射电子显微镜(TEM)表明催化剂具有较小的粒径;利用电化学循环伏安法研究Pt/C催化剂催化联氨氧化的活性,担载在碳载体上的Pt催化剂对联氨的电氧化具有着更高的催化活性;电化学计时电流法表明Pt/C催化剂有着较好的工作稳定性。     

载体对铂基疏水催化剂活性的影响

为了研究载体对铂(Pt)基疏水催化剂活性的影响,分别选取了炭黑、SiC纳米粉、铈锆复合氧化物(Ce0.4Zr0.6O2-γ-Al2O3)等三种物质,在氯铂酸的乙二醇溶液中,用高压微波加热法制备了Pt基催化剂,然后将其与聚四氟乙烯一起负载于泡沫镍上,制成疏水催化剂.用X射线衍射、透射电子显微镜、X光电子能谱、扫描电子显微镜等方法分析了催化剂的结构与组成,并研究了疏水催化剂对氢-氧复合反应及氢-水交换反应的催化活性.结果表明:Pt在载体表面分布均匀,在Pt/C、Pt/SiC、Pt/Ce0.4Zr0.6O2-γ-Al2O3中Pt的平均粒径分别为4.46、1.67和1.77nm;Pt/C、Pt/SiC催化剂中Pt存在Pt(0)、Pt(Ⅱ)和Pt(Ⅳ)三种价态;Pt/C、Pt/SiC在泡沫镍表面的分布均匀,而Pt/Ce0.4Zr0.6O2-γ-Al2O3分布不均匀.Pt/C/FN对氢-氧复合反应和氢-水交换反应的催化活性都较高;Pt/SiC/FN和Pt/Ce0.4Zr0.6O2-γ-Al2O3/FN对氢-氧复合反应的催化活性高,但是对氢-水交换反应的催化活性很低.     

铁系元素掺杂的Pt基疏水催化剂的制备及活性研究

以炭黑为载体、乙二醇为溶剂, 利用高压微波加热法分别制备了铁系元素(即Fe、Co、Ni三种元素)掺杂的Pt基二元催化剂. 采用TEM、XRD、EDX、XPS等手段分析了催化剂的微观结构. 活性金属粒子在炭黑载体表面分布均匀; Fe、Co、Ni掺杂后, 催化剂中活性金属粒子的粒径分布变窄, 平均粒径明显减小(由4.57nm分别降低至2.17、2.41、2.55nm); 催化剂中Pt存在Pt(0)、Pt(II)、Pt(IV)三种价态. 将催化剂分散于聚四氟乙烯乳液中, 采用自然浸渍法负载于泡沫镍, 制得Pt基疏水催化剂, 考查了其对氢-水液相交换反应的催化活性. 与单一Pt基疏水催化剂相比, 过渡金属掺杂后的二元疏水催化剂对氢-水液相交换反应的催化活性明显提高. 其催化活性由高到低依次为: PtFe/C/FN>PtCo/C/FN>PtNi/C/FN>Pt/C/FN. 催化活性的提高可能主要来源于催化剂活性金属粒径的减小. 此外, H₂O分子在Fe系元素表面的解离行为也有一定的贡献.     

Pt/C催化剂制备及CO催化氧化性能研究

采用大气压介质阻挡放电辅助氢气热还原方法和氢气热还原方法制备Pt/C催化剂,考察了制备方法及Pt负载量对Pt/C催化性能的影响。采用X-射线衍射(XRD)、循环伏安法、CO催化氧化反应研究Pt/C催化剂的晶相结构、电催化性能和CO催化氧化活性。结果表明:大气压介质阻挡放电辅助氢气热还原所制备的样品具有更高的电化学活性和CO催化氧化活性。当Pt负载量在2%到10%之间变化时,Pt/C-PC催化活性随负载量增加而增加。XRD测试结果显示当Pt负载量为2%,5%和10%时,Pt粒径分别为:10.6 nm,9.1 nm和6.4 nm,说明采用等离子体辅助氢气热还原方法制备的Pt/C-PC催化剂,Pt负载量越大,Pt粒径越小,CO催化氧化活性更高。     

基于Pt/CNTs催化剂的燃料电池Pt/Buckypaper催化层的制备与表征

为了提高质子交换膜燃料电池催化剂中贵金属的利用率,以碳纳米管(CNTs)负载Pt为催化剂,设计制备了具有催化剂梯度分布结构的Pt/buckypaper催化层。利用扫描电子显微镜等多种表征手段,观察与分析了催化剂和催化层的结构及Pt含量分布,并考察了它们的电化学性能。结果表明,Pt/CNTs催化剂中Pt颗粒在超声混酸氧化处理过的CNTs表面上分布均匀,平均直径为2.4nm。其电化学活性表面积(ECSA)接近于商用Pt/C催化剂的值,比质量活性(MA)则远高于商用催化剂,且具备更为优异的电化学循环稳定性。利用这种催化剂制备的Pt/buckypaper催化层保持着较大的ECSA,表明其中的Pt颗粒具有较高的利用率,体现了这种新颖结构的独特优势。     

AuPdPt-WC/C复合材料作为直接甲醇燃料电池阴极催化剂的性能研究

本实验以碳化钨(WC)增强的Au Pd Pt-WC/C复合催化剂作为直接甲醇燃料电池(DMFC)的阴极催化剂,选取了各组元比例,温度为变量,测试了其作为DMFC催化剂的性能。首先,采用了间歇微波加热法(IHM)制备了纳米级的碳化钨(WC)颗粒,并采用还原法和真空干燥法制备了Au Pd Pt-WC/C复合催化剂,控制Au、Pd、Pt的比例,制备了两组催化剂。通过循环伏安扫描,线性伏安扫描等手段进行电化学测试,表征其氧还原的性能。结果显示,复合催化剂具有高于传统Pt/C催化剂的性能,并且与实验条件息息相关。     

DBHFC阴极铂合金催化剂的制备及其电催化性能

采用浸渍还原法分别制备了两种不同铂含量的Pt/C纳米催化剂和Pt-Mn/C、Pt-Co/C纳米合金催化剂,利用XRD和TEM技术对催化剂的粒径大小、晶体结构和晶格常数进行表征,并对四种催化剂进行了循环伏安、线性扫描伏安和电流-时间测试。结果表明:四种催化剂的平均粒径均在10nm以下,且Pt-Mn/C、Pt-Co/C两种合金催化剂的粒径均小于Pt/C催化剂;四种催化剂均为面心立方晶体结构;与Pt/C催化剂相比,两种合金催化剂的晶格常数有所减小,且结晶度较低。电化学性能测试表明,两种Pt合金催化剂较相同Pt载量的纯Pt催化剂具有更高的还原峰电位和更大的还原峰电流,其中Pt-Co/C催化剂的还原峰电位和峰电流最大;在催化剂稳定性方面,两种Pt合金催化剂要优于两种纯Pt催化剂。     

微波合成条件对催化剂Pt_2Mo/C的结构和甲醇氧化催化性能的影响

为了改善Pt/C催化剂的甲醇氧化催化性能,采用快速高效的微波加热技术合成了Mo修饰的Pt基催化剂Pt2Mo/C,并对比研究了微波反应时间和超声分散时间等条件对Pt2Mo/C的晶体结构、微观形貌和甲醇氧化催化性能的影响.结果表明:Pt2Mo/C的晶体结构主要是由微波反应时间决定的,超声分散时间对其几乎没有影响;Pt2Mo/C的微观形貌受微波反应时间和超声分散时间的共同影响.在本实验的研究范围内,微波反应时间和超声分散时间对催化剂Pt2Mo/C的甲醇氧化催化性能的影响顺序分别为10min15min20min5min和60min100min30min0min;制备高活性甲醇氧化催化剂Pt2Mo/C的最佳条件为微波反应10min和超声分散60min.     

乙二醇稳定的NaBH4还原法制备纳米Pt/C催化剂

分别采用乙二醇(EG)和H2O为溶剂,通过NaBH4还原法在酸性pH≤2和碱性pH≥12条件下制备了铂担裁量为20%(质量分数)的Pt/C催化剂,利用TEM、CV及LSV等方法对催化剂进行了表征与测试,考察了EG在NaBH4还原法中对铂纳米颗粒的稳定作用.结果表明,EG作溶剂、碱性pH≥12时,通过NaBH4还原法制备得到了平均粒径约2.5nm、粒径分布窄、在碳裁体上分散均匀的Pt/C催化荆;该催化剂的电化学比表面为74.4m2/g Pt,0.8V vs NHE时通过LSV得到的单位质量铂对甲醇电催化氧化的电流密度为229.1mA/mg Pt,分别是相同条件下H2O作溶剂时制备得到的Pt/C催化剂的5.倍和5.3倍.     

Synthesis and characterization of PtSn/carbon and Pt3Sn/carbon nanocomposites as methanol electrooxidation catalysts

Two Pt-Sn/vulcan carbon nanocomposites containing nanoclusters of PtSn (niggliite) and Pt3Sn highly dispersed on a carbon powder support have been prepared using Pt(SnPh2Cl)(PPh3)2(Ph) or [Pt3[mu-(PPh2)2CH2]3(mu 3-SnF3) (mu 3-CO)][PF6] as single-source precursors of metal alloy. PtP2 or Pt metal is also present as a secondary phase. Bimetallic Pt-Sn nanoclusters with an average diameter of 5-8 nm are formed at a total metal loading of ca. 15 wt%. Evaluation of both Pt-Sn/C nanocomposites as electrooxidation catalysts in a direct methanol fuel cell gives fuel cell performances comparable to that expected for Pt-Sn catalysts prepared by more conventional methods.     

Metal–Organic Framework‐Derived Bamboo‐like Nitrogen‐Doped Graphene Tubes as an Active Matrix for Hybrid Oxygen‐Reduction Electrocatalysts

In this work, large size (i.e., diameter > 100 nm) graphene tubes with nitrogen‐doping are prepared through a high‐temperature graphitization process of dicyandiamide (DCDA) and Iron(II) acetate templated by a novel metal–organic framework (MIL‐100(Fe)). The nitrogen‐doped graphene tube (N‐GT)‐rich iron‐nitrogen‐carbon (Fe‐N‐C) catalysts exhibit inherently high activity towards the oxygen reduction reaction (ORR) in more challenging acidic media. Furthermore, aiming to improve the activity and stability of conventional Pt catalysts, the ORR active N‐GT is used as a matrix to disperse Pt nanoparticles in order to build a unique hybrid Pt cathode catalyst. This is the first demonstration of the integration of a highly active Fe‐N‐C catalyst with Pt nanoparticles. The synthesized 20% Pt/N‐GT composite catalysts demonstrate significantly enhanced ORR activity and H₂‐air fuel cell performance relative to those of 20% Pt/C, which is mainly attributed to the intrinsically active N‐GT matrix along with possible synergistic effects between the non‐precious metal active sites and the Pt nanoparticles. Unlike traditional Pt/C, the hybrid catalysts exhibit excellent stability during the accelerated durability testing, likely due to the unique highly graphitized graphene tube morphologies, capable of providing strong interaction with Pt nanoparticles and then preventing their agglomeration.     

Porous Carbon‐Hosted Atomically Dispersed Iron–Nitrogen Moiety as Enhanced Electrocatalysts for Oxygen Reduction Reaction in a Wide Range of pH

As one of the alternatives to replace precious metal catalysts, transition‐metal–nitrogen–carbon (M–N–C) electrocatalysts have attracted great research interest due to their low cost and good catalytic activities. Despite nanostructured M–N–C catalysts can achieve good electrochemical performances, they are vulnerable to aggregation and insufficient catalytic sites upon continuous catalytic reaction. In this work, metal–organic frameworks derived porous single‐atom electrocatalysts (SAEs) were successfully prepared by simple pyrolysis procedure without any further posttreatment. Combining the X‐ray absorption near‐edge spectroscopy and electrochemical measurements, the SAEs have been identified with superior oxygen reduction reaction (ORR) activity and stability compared with Pt/C catalysts in alkaline condition. More impressively, the SAEs also show excellent ORR electrocatalytic performance in both acid and neutral media. This study of nonprecious catalysts provides new insights on nanoengineering catalytically active sites and porous structures for nonprecious metal ORR catalysis in a wide range of pH.     

Precursor solvent influence on preparation and electrochemical properties of platinum nanoparticles electrodes

The crystalline sizes and loading efficiencies of metallic nanoparticles for fuel cell catalysts have been measured by changing solvent species containing precursors. By changing the solvent species containing carbon particles and metal salt, the microstructure and the according electrochemical property of catalysts could be controlled. Four kinds of solvent were investigated in this study. Pt catalysts that were deposited on carbon blacks supports by using an ethylene glycol solution showed the highest deposition efficiency, 85% and smallest crystalline size, 2.85 nm of particles. From the experimental result, it was concluded that the electrochemical performance of catalysts was dependent on the crystalline size and deposition efficiency of metal particles, by changing solvent species.     

Effect of Pt/alumina catalyst preparation method on sensing performance of thermoelectric hydrogen sensor

We fabricated three different Pt/alumina catalysts for micro-thermoelectric hydrogen sensor (micro-THS). In the three Pt/alumina catalysts, two were prepared by impregnation of a commercial alumina with an aqueous solution of platinum (IV) chloride pentahydrate, and the third was prepared by impregnation of commercial alumina and nano-Pt with isobornyl acetate solution. To fabricate the micro-THS, the three Pt/alumina catalysts were integrated on thin membrane of the micro-THS, and its hydrogen sensing properties were investigated. The micro-THS with nano-Pt loaded alumina catalyst showed better sensing performance than those with Pt/alumina catalysts prepared by an aqueous solution of platinum (IV) chloride pentahydrate, because of effectively dispersed nano-Pt metal grain on the surface alumina grain observed by TEM. Its voltage signal was 15.7 mV for hydrogen concentration of 1% in dry air at catalyst temperature of 100°C.     

Characterization of Pt-Cu binary catalysts for oxygen reduction for fuel cell applications

Nanostructured Pt-Cu/C alloy catalysts synthesized by a reduction procedure with different reducing agents are investigated to find the origin of the enhanced activity of the oxygen reduction reaction for fuel cell applications. Prepared catalysts are characterized by various techniques, such as energy dispersive X-ray spectrometry, X-ray diffraction, transmission electron microscopy (TEM) and cyclic voltammetry. XRD analysis shows that all prepared catalysts exhibit face-centered cubic structures and have smaller lattice parameters than pure Pt catalyst. TEM images show that the particle size of the catalysts increases with the heat treatment temperature, and that different reducing agent causes different particle size and dispersion of the binary catalysts on XC-72R. Using the polyol method with CuSO₄ as the precursor, the Pt-Cu/C sample is found to have good dispersion and high Cu loading. The Pt-Cu/C sample has a slightly higher specific activity value than that of Pt/C. The catalytic activity can be enhanced greatly with hydrogen reduction at 300 °C. Higher reduction temperatures cause the catalytic particles to agglomerate and therefore decreased catalytic activity.     

Development of a simple method for the preparation of novel egg-shell type Pt catalysts using hollow silica nanostructures as supporting precursors

A simple method for the preparation of novel egg-shell type platinum catalysts was developed and achieved by utilizing unique hollow silica nanostructures, i.e., hollow silica nanospheres and nanotubes, as supports. The observation by transmission electron microscopy indicated that the well-dispersed hollow silica supported Pt catalysts with a Pt particle diameter of 8-14 nm can be successfully prepared by wet impregnation process and heat treatment. The Pt-loaded hollow silica nanostructures were also characterized by inductively coupled plasma, X-ray diffraction, specific surface area, Fourier transformation infrared spectroscopy, X-ray photoelectron spectroscopy and energy dispersive spectroscopy. It was thus demonstrated that a higher Pt loading amount (0.392%) could be obtained under the same conditions except the addition of ammonia, which was found to be more effective than that (0.061%) with the addition of HCl in the immobilization of Pt. In addition, the effect of soaking time, Pt precursor concentration and calcination temperature on the loading of Pt in hollow silica nanostructures were investigated as well.     

Characterization of platinum–iron catalysts supported on MCM-41 synthesized with rice husk silica and their performance for phenol hydroxylation

Abstract

Mesoporous material RH-MCM-41 was synthesized with rice husk silica by a hydrothermal method. It was used as a support for bimetallic platinum?iron catalysts Pt–Fe/RH-MCM-41 for phenol hydroxylation. The catalysts were prepared by co-impregnation with Pt and Fe at amounts of 0.5 and 5.0 wt.%, respectively. The RH-MCM-41 structure in the catalysts was studied with x-ray diffraction, and their surface areas were determined by nitrogen adsorption. The oxidation number of Fe supported on RH-MCM-41 was + 3, as determined by x-ray absorption near edge structure (XANES) analysis. Transmission electron microscopy (TEM) images of all the catalysts displayed well-ordered structures, and metal nanoparticles were observed in some catalysts. All the catalysts were active for phenol hydroxylation using H₂O₂ as the oxidant at phenol : H₂O₂ mole ratios of 2 : 1, 2 : 2, 2 : 3 and 2 : 4. The first three ratios produced only catechol and hydroquinone, whereas the 2 : 4 ratio also produced benzoquinone. The 2 : 3 ratio gave the highest phenol conversion of 47% at 70 °C. The catalyst prepared by co-impregnation with Pt and Fe was more active than that prepared using a physical mixture of Pt/RH-MCM-41 and Fe/RH-MCM-41.