Pt-Ru supported on double-walled carbon nanotubes as high-performance anode catalysts for direct methanol fuel cells

Pt-Ru supported on carbon nanotubes (CNTs) (single-walled nanotubes, double-walled nanotubes (DWNTs), and multi-walled nanotubes) catalysts are prepared by an ethylene glycol reduction method. Pt-Ru nanoparticles with a diameter of 2-3 nm and narrow particle size distributions are uniformly deposited onto the CNTs. A simple and fast filtration method followed by a hot-press film transfer is employed to prepare the anode catalyst layer on a Nafion membrane. The Pt-Ru/DWNTs catalyst shows the highest specific activity for methanol oxidation reaction in rotating disk electrode experiments and the highest performance as an anode catalyst in direct methanol fuel cell (DMFC) single cell tests. The DMFC single cell with Pt-Ru/DWNTs (50 wt %, 0.34 mg Pt-Ru/cm(2)) produces a 68% enhancement of power density, and at the same time, an 83% reduction of Pt-Ru electrode loading when compared to Pt-Ru/C (40 wt %, 2.0 mg Pt-Ru/cm(2)).     

Carbon nanotubes-Nafion composites as Pt-Ru catalyst support for methanol electro-oxidation in acid media

Carbon nanotubes-Nafion (CNTs-Nafion) composites were prepared by impregnated CNTs with Nafion in ethanol solution and characterized by FT-IR. Pt-Ru catalysts supported on CNTs-Nafion composites were synthesized by microwave-assisted polyol process. The physical and electrochemical properties of the catalysts were characterized by X-ray diffraction (XRD), transmission electron microscope (TEM), CO stripping voltammetry, cyclic voltammetry (CV) and chronoamperometry (CA). The results showed that the Nafion incorporation in CNTs-Nafion composites did not significantly alter the oxygen-containing groups on the CNTs surface. The Pt-Ru catalyst supported on CNTs-Nafion composites with 2 wt% Nafion showed good dispersion and the best CO oxidation and methanol electro-oxidation activities.     

Simple and controllable synthesis of highly dispersed Pt-Ru/C catalysts by a two-step spray pyrolysis process

A carbon supported Pt-Ru catalyst with uniform distribution and small average size of the Pt-Ru particles was synthesized using a two-step spray pyrolysis (SP) method; the electrocatalytic activity of the prepared catalyst for methanol oxidation is better than that of the standard commercial catalyst.     

Boosting fuel cell performance with a semiconductor photocatalyst: TiO2/Pt-Ru hybrid catalyst for methanol oxidation

A hybrid carbon fiber electrode (CFE) consisting of TiO2 semiconductor photocatalyst and Pt-Ru catalyst has been developed to boost the performance of direct methanol fuel cells (DMFC). These two catalyst nanoparticles are deposited on opposite sides of the carbon fiber paper such that methanol oxidation is carried out catalytically on Pt-Ru and photocatalytically on TiO2 under UV-light irradiation. Since both catalysts carry out methanol oxidation independently, we observe an additive effect in the current generation. The carbon support fibers provide a large network to collect the electrons from both of these catalytic processes and thus assist in efficient current generation. In addition, TiO2 improves the performance of the Pt-Ru catalyst in dark, indicating possible surface area improvement or diminished poisoning effects. The concept of incorporating a photocatalyst provides new ways to minimize precious metal content and enhance the performance of DMFCs. At low catalyst loadings (0.15 mg/cm2) at 295 K, a 25% enhancement in the peak power density is observed upon illumination with light.     

合金化程度对炭载Pt-Ru催化剂性能的影响

在含四氢呋喃(THF)的水溶液中, 室温下用NaBH₄还原H₂PtCl₆和RuCl₃制得Pt-Ru/C催化剂. 其Pt-Ru 粒子的合金化程度较高, 平均粒径较小, 相对结晶度较低. 因此对甲醇氧化的电催化活性远高于Pt-Ru 粒子的平均粒径和相对结晶度相似的, 而且Pt-Ru合金化程度低的商业化的E-TEK的Pt-Ru/C催化剂, 表明Pt-Ru的合金化程度对Pt-Ru/C催化甲醇氧化的电催化活性有很大的影响.     

Polyoxometalate-modified carbon nanotubes: new catalyst support for methanol electro-oxidation

A new catalyst support, polyoxometalate-modified carbon nanotubes, is presented in this paper through the chemisorption between polyoxometalate and carbon. Pt and Pt-Ru nanoparticles were electrochemically deposited on polyoxometalate-modified carbon nanotubes electrodes, and their electrocatalytic properties for methanol electro-oxidation are investigated in detail. Due to the unique electrical properties of carbon nanotubes and the excellent redox properties and the high protonic conductivity of polyoxometalate, for the similar deposition charge of Pt and Pt-Ru catalysts, 1.4 times larger exchange current density, 1.5 times higher specific activity, and better cycle stabilities can be obtained at polyoxometalate-modified carbon nanotube electrodes as compared to the electrodes without polyoxometalate modification. These results show that polyoxometalate-modified carbon nanotubes as a new catalyst support have good potential application in direct methanol fuel cells.     

Pt-Ru/C催化剂在甲醇电氧化过程中的组成和结构变化

本文研究了Pt-Ru/C催化剂在甲醇电催化氧化过程中组成和结构的变化。结果表明:在扫描初期,Pt-Ru催化剂的表面处于富Ru状态,Pt-Ru催化剂显示出良好的协同效应,峰电位较低,峰电流密度也较小。随着扫描圈数的增加(1~35圈),催化剂表面Ru原子逐渐溶解,Pt-Ru协同效应减弱,峰电位逐渐增大;同时,随着Ru的溶解,催化剂表面Pt原子含量的增加,催化剂对甲醇氧化的峰电流密度逐渐增大。继续增加扫描圈数(36~80圈),催化剂表面Ru原子含量趋于稳定,但Pt原子发生表面重组,粒子粒径增大,从而导致催化剂对甲醇电氧化性能下降。     

碳载体的O3处理对直接甲醇燃料电池Pt-Ru/C催化剂性能的影响

为了提高直接甲醇燃料电池阳极催化剂的催化活性, 利用O₃处理的Vulcan XC-72碳黑为载体, 制备Pt-Ru/C催化剂, 并与未经处理的Vulcan XC-72为载体制备的Pt-Ru/C催化剂的性能进行比较. 采用XPS和BET测试了O₃处理后碳粉表面的含氧浓度和比表面积, 结果表明, 随处理时间延长, 碳表面含氧浓度先减少后增加, 比表面积减小; 而随着处理温度升高, 比表面积增加, 含氧浓度先减少后增加. XRD, TEM方法对催化剂的结构及形貌的表征结果表明: O₃处理的碳黑为载体制备的Pt-Ru/C催化剂粒径均匀、分散性好. 在0.5 mol/L CH₃OH和0.5 mol/L H₂SO₄溶液中, 利用粉末微电极测试了循环伏安和稳态极化曲线, 结果表明: O₃处理碳粉为载体的催化剂比未经处理的碳粉为载体的催化剂的活性高. 研究了O₃处理碳粉的时间和温度对催化剂性能的影响, 电化学测试表明: 140 ℃处理6 min的碳粉为载体制备的催化剂对甲醇的电催化氧化活性最佳.     

Solvent effects on Pt-Ru/C catalyst for methanol electro-oxidation

Alloying degree, particle size and the level of dispersion are the key structural parameters of Pt-Ru/C catalyst in fuel cells. Solvent(s) used in the preparation process can affect the particle size and alloying degree of the object substance, which lead to a great positive impact on its properties. In this work, three types of solvents and their mixtures were used in preparation of the Pt-Ru/C catalysts by chemical reduction of metal precursors with sodium borohydride at room temperature. The structure of the catalysts was characterized by X-ray diffraction (XRD) and Transmission electron microscopy (TEM). The catalytic activity and stability for methanol electro-oxidation were studied by Cyclic Voltammetry (CV) and Chronoamperometry (CA). Pt-Ru/C catalyst prepared in H₂O or binary solvents of H₂O and isopropanol had large particle size and low alloying degree leading to low catalytic activity and less stability in methanol electro-oxidation. When tetrahydrofuran was added to the above solvent systems, Pt-Ru/C catalyst prepared had smaller particle size and higher alloying degree which resulted in better catalytic activity, lower onset and peak potentials, compared with the above catalysts. Moreover, the catalyst prepared in ternary solvents of isopropanol, water and tetrahydrofuran had the smallest particle size, and the high alloying degree and the dispersion kept unchanged. Therefore, this kind of catalyst showed the highest catalytic activity and good stability for methanol electro-oxidation.     

Nanostructure and surface composition of Pt and Ru binary catalysts on polyaniline-functionalized carbon nanotubes

Pt-Ru binary catalysts were prepared on a polyaniline-functionalized multiwalled carbon nanotube (PANi/MWCNT). PANi/MWCNT composites were synthesized by the polymerization of aniline in the presence of a carbon nanotube suspension using FeSO(4) and (NH(4))(2)S(2)O(8) as the oxidants. The Pt-Ru/PANi/MWCNT catalysts were formed by the chemical reduction of H(2)PtCl(6) and RuCl(3) using NaBH(4) as the reducing agent. The binary component catalyst is sharply distributed, with particle sizes ranging from 2.0 to 4.0 nm, and the Pt and Ru distributions are homogeneous when supported on PANi/MWCNT. In comparison, the binary catalyst supported on bare MWCNT displayed a Pt-rich core and a Ru-rich shell nanostructure. The surface composition deduced from CO stripping potentials confirms that the Ru surface content (χ(Ru)) is approximately 50% for the Pt-Ru alloy on PANi/MWCNT, and the catalyst on bare MWCNT shows nearly 70% Ru on the surface. Pt-Ru binary catalysts supported on PANi/MWCNT have higher activity, a higher Pt utilization efficiency, and much better durability when compared to other catalyst supports on bare MWCNT or on Vulcan XC-72.     

In situ muSR and NMR investigation of methanol dissociation on carbon-supported nanoscaled Pt-Ru catalyst

In situ muSR and nuclear magnetic resonance (NMR) experiments on the investigation of methanol decomposition on Pt-Ru nanoscaled catalyst supported on Vulcan XC-72 carbon black (Pt-Ru/Vulcan XC-72) are presented. Avoided-level-crossing muon spin resonance measurements reveal the resonance line at magnetic field 2.018 T, we assign to transient CH₂?OMu? formaldehyde muonated radical. Results obtained allow us to estimate the contribution of chemical decomposition reaction process for the formaldehyde—carbon oxide—hydrogen conversion on Pt-Ru/Vulcan XC-72 catalytic material. NMR spectrum of the methanol covered Pt-Ru/Vulcan XC-72 consists of three broad resonance lines. Two of them are assigned to OH and CH₃ groups of methanol bound to the carbon black surface. Following the existing literature, which indicates that polymerization of formaldehyde readily takes place when the monomer is adsorbed on some active surface, the third one is assigned to the resonance signal of oligomeric species of formaldehyde. Taking into account the results of our experiments on electrochemical hydrogenation of carbon nanotubes, we do not exclude that the hydrogen arising as a result of methanol decomposition would also contribute to this signal. The high surface area of amorphous carbon nanoparticles of Vulcan XC-72 is favourable to adsorb the hydrogen on their surface.     

Preparation of High-alloying Pt-Ru/CMK-3 Catalysts in THF-H2O-EtOH Ternary Solution System

The Pt-Ru particles of the Pt-Ru/CMK-3 catalyst were found to possess high degree of alloying, small average size, and low relative crystallinity when the Pt-Ru/CMK-3 catalyst was prepared using the general chemical reduction method in the ternary solution system containing tetrahydrofuran (THF), H₂O, and ethanol. The Pt-Ru/CMK-3 catalyst showed high electrocatalytic activity for methanol oxidation. It indicated that the alloying of Pt-Ru could significantly affect the electrocatalytic activity for methanol oxidation. The Pt-Ru/CMK-3 catalyst with high alloying degree can be obtained because THF and H₂PtCl₆ can form a complex leading to the reduction potentials of H₂PtCl₆ and RuCl₃, which are close to each other in the aqueous solution with THF.     

碱性介质中W,Ni和Sn掺杂的Pt-Ru/C电催化氧化甲醇的性能

直接以Pt, Ru, W, Ni和Sn的金属盐为前驱体, 通过溶胶法制备了不同原子比的Pt-Ru-M/C(M=W, Ni, Sn)碳载纳米合金催化剂, 用X射线衍射(XRD)和X光电子能谱(XPS)表征催化剂的晶相结构、表面组成及价态形式, 采用循环伏安法测试催化剂电催化氧化甲醇活性. 结果表明, 掺杂Ni和W可明显提高Pt-Ru/C催化活性, 掺杂Sn则降低了Pt-Ru/C催化活性. 其中Pt5-Ru4-Ni0.7/C的活性最高, 在1.0 mol/L NaOH＋1.0 mol/L CH3OH溶液中峰电流达835.2 mA/mg, 甲醇起始氧化电位比Pt5-Ru5/C低约0.11 V.     

Combinatorial optimization of ternary Pt alloy catalysts for the electrooxidation of methanol

We report the combinatorial and high-throughput optimization of improved ternary Pt alloy electrocatalysts for the oxidation of methanol for use in direct methanol fuel cell (DMFC) anodes. Following up on the discovery of a ternary Pt20Co60Ru20 catalyst with significantly improved electrocatalytic activity for methanol oxidation over standard Pt-Ru catalysts, we optimize the electrocatalytic activity of this composition using a closely sampled Pt-Co-Ru "optimization library". We also screen for compositional and structural stability using high-throughput methods. Composition-activity maps confirmed improved activity in compositional neighborhood of the Pt20Co60Ru20 catalyst. Activity trends of Pt-Ru binary alloys were in excellent agreement with fundamental surface electrochemical studies. Structural and compositional catalyst stability was probed using X-ray diffraction (XRD) and energy dispersive X-ray analysis (EDX). Combination of the stability-composition and activity-composition maps resulted in "consensus maps" pointing to a new optimized ternary alloy electrocatalyst for methanol electrooxidation with an overall composition of Pt18Co62Ru20.     

一种制备碳载高合金化Pt-Ru催化剂的方法

提出了在四氢呋喃(THF)和H₂O混合溶液中用一般的化学还原法在室温下制备碳载Pt-Ru(Pt-Ru/C)催化剂的新方法。与在纯水中制得的Pt-Ru/C催化剂相比，其Pt-Ru粒子的合金化程度高、平均粒径较小且相对结晶度低，因此，该催化剂对甲醇氧化的电催化活性远高于在纯水中制得的Pt-Ru/C催化剂。高合金化程度的原因是H₂PtCl₆和RuCl₃在THF和H₂O混合溶液中的起始还原电位相近。此外，在THF和H₂O混合溶液中，THF和H₂O的体积比的改变并不影响制得的Pt-Ru/C催化剂中Pt-Ru粒子的合金化程度，但对Pt-Ru粒子的粒径以及相对结晶度有较大影响。     

四氢呋喃-水-乙醇三元溶液体系制备高合金化Pt-Ru/CMK-3催化剂

提出了在四氢呋喃(THF)、H2O和乙醇三元体系中用一般的化学还原法在室温下制备高合金化Pt-Ru/CMK-3催化剂的新方法. 与在纯水中制得的商品化ETEK催化剂相比, 其Pt-Ru粒子的合金化程度高、平均粒径较小且相对结晶度低, 因此, 该催化剂对甲醇氧化的电催化活性远高于在纯水中制得的Pt-Ru催化剂. 高合金化程度的原因是H2PtCl6和RuCl3在THF、H2O和乙醇三元溶液体系中的起始还原电位相近. 此外, CMK-3以其规整的二维有序孔道结构, 为直接甲醇燃烧电池(DMFC)中电子和物质的传输提供了方便的路径, 其巨大的比表面积也为Pt-Ru 纳米粒子的均匀分散提供了良好的载体.     

Sensitive and selective electrochemical detection of carbon monoxide in saline at a Pt-Ru/Nafion/MnO2-modified electrode

We fabricated a sensitive and selective electrochemical carbon monoxide (CO) sensor for physiological conditions based on the Pt-Ru system. At a bare Pt-Ru electrode, a linear amperometric response to CO concentration was obtained in the range of 0.9-9 μM. However, significant current response to model electroactive interferents for physiological conditions, uric acid (UA), ascorbic acid (AA) and hydrogen peroxide (HP), was also recorded at the Pt-Ru electrode. The response to UA and AA was highly suppressed by coating the Pt-Ru electrode surface with a Nafion layer, and the response to HP was almost completely eliminated by the additional coating with a MnO(2)/chitosan layer. Finally, at the Pt-Ru/Nafion/MnO(2) electrode, amperometric CO detection with a sensitivity of 173 nA cm(-2) μM(-1) was obtained in the concentration range of 0.9-9 μM with the UA, AA and HP signal being below 1.7% at the same concentration of CO.     

室温制备高合金化Pt-Ru/CMK-3催化剂及其对甲醇的电催化氧化

通过低温络合反应制备了高分散高合金化的Pt-Ru固溶体, 并将其均匀地担载在有序介孔碳CMK-3上, 以形成二元复合金属催化剂. XRD谱图表明,fcc结构的Pt原子部分被hcp结构的Ru原子取代形成置换固溶体， 而且几乎没有未形成合金的Ru存在. TEM和XRD研究结果表明， Pt-Ru/CMK-3催化剂中Pt-Ru合金粒子的平均粒径为27 nm, 且具有良好的均一度. 还研究了催化剂对甲醇的电催化氧化性能, 并与E-TEK公司同类催化剂进行了对比, 研究结果表明, Pt-Ru/CMK-3催化剂具有较大的电化学活性面积, 对甲醇的电催化氧化性能和抗CO中毒能力明显优于其它同类催化剂.     

The carbon nanotubes-polyaniline composites and their effect on catalytic properties of deposited catalysts

Composites of functionalized single-wall carbon nanotubes and polyaniline are deposited onto electrodes by in situ electrochemical polymerization. Their electrochemical behavior and differential capacitance are studied by cyclic voltammetry, electrochemical impedance spectroscopy, and chronovoltamperometry. The differential capacitance of the composite electrode exceeds that of pure polyaniline film deposited onto electrode, which can be explained by the nanotubes’ loosening effect on the polyaniline structure. The composite-electrode capacitance is as large as 1000 F g⁻¹ or higher. Thus obtained composite films were used as a support for deposited platinum-ruthenium catalyst. The Pt-Ru structure and catalytic properties in the methanol oxidation reaction are studied. It is shown that the specific current of methanol oxidation at Pt-Ru is larger by a factor of 7–15 than those measured when pure polyaniline, pure carbon nanotubes, or standard Vulcan XC-72 carbon black are used as supports. It is found that the catalytic activity is the same for all studied supports, provided the current is reduced to the unit of Pt-Ru true surface area. Thus, the observed large catalytic effect is associated with the structure and high dispersivity of the electrodeposited metals incorporated to the single-wall carbon nanotubes-polyaniline composite.     

Electrocatalytic oxidation of ethylene glycol on Pt and Pt-Ru nanoparticles modified multi-walled carbon nanotubes

The synthesis and characterization of catalysts based on nanomaterials, supported on multi-walled carbon nanotubes (CNT) for ethylene glycol (EG) oxidation is investigated. Platinum (Pt) and platinum-ruthenium (Pt-Ru) nanoparticles are deposited on surface-oxidized multi-walled carbon nanotubes [Pt/CNT; Pt-Ru/CNT] by the aqueous solution reduction of the corresponding metal salts with glycerol. The electrocatalytic properties of the modified electrodes for oxidation of ethylene glycol in acidic solution have been studied by cyclic voltammetry (CV), and excellent activity is observed. This may be attributed to the small particle size of the metal nanoparticles, the efficacy of carbon nanotubes acting as good catalyst support and uniform dispersion of nanoparticles on CNT surfaces. The nature of the resulting nanoparticles decorated multiwalled carbon nanotubes are characterized by scanning electron microscopy (SEM) and transmission electron microscopic (TEM) analysis. The cyclic voltammetry response indicates that Pt-Ru/CNT catalyst displays a higher performance than Pt/CNT, which may be due to the efficiency of the nature of Ru species in Pt-Ru systems. The fabricated Pt and Pt-Ru nanoparticles decorated CNT electrodes shows better catalytic performance towards ethylene glycol oxidation than the corresponding nanoparticles decorated carbon electrodes, demonstrating that it is more promising for use in fuel cells.