Preparation and Properties of Composite Polypyrrole/Pt Catalyst Systems

Three different methods for the preparation and modification of conducting polymer/noble metal catalyst systems consisting of polypyrrole (PPy) and platinum (Pt) are described for the anodic oxidation of methanol. The first method consists of the electrochemical deposition of a thin PPy film on glassy carbon substrate, which is modified with Pt either by electroreduction of hexachloroplatinate, codeposition from a nanodispersed Pt solution, or incorporation of tetrachloroplatinate as counterion followed by cathodic reduction. A second method is based on the preparation of nanoscale PPy(PSS) particles by chemical polymerization with polystyrenesulfonate PSS^– as the counterion. This material is a favorable catalyst support for nanodispersed Pt due to its mixed electronic and cationic conductivity. To study the electrochemical properties, the particulate system PPy(PSS)/Pt is fixed in a carbon fiber electrode. A third method was developed which brings the polypyrrole in close contact to a proton exchanger membrane (Nafion) using a special chemical deposition procedure. This method is useful for preparing a membrane electrode assembly (MEA) consisting of Nafion/PPy/Pt. The structural, morphological, and electrocatalytic properties for methanol oxidation were studied depending on the preparation method applied using surface analytical techniques (TEM, SEM, and EDX) and electrochemical measurements (cyclic voltammetry and transient techniques).     

Synthesis of <Emphasis Type="Italic">N</Emphasis>-hydroxy-imidamide-functionalized graphene: an efficient metal-free electrocatalyst for oxygen reduction

Metal-free electrocatalysts for oxygen reduction reaction (ORR) are key to the development of efficient, durable, and low-cost alternatives to noble-metal-based electrocatalysts in fuel cell cathodes. In recent years, many efforts are directed to the metal-free catalyst based on heteroatom-doped graphene. In this work, we demonstrate that the graphene surface can be converted into the catalyst for the oxygen reduction by chemical functionalization. In this context, we first synthesized malononitrile-functionalized graphene oxide. Amidoximation of nitrile group and reduction in graphene oxide were then carried out by hydroxylamine in one step. The electrochemical behavior of functionalized graphene-modified electrode for the reduction in oxygen was studied. The results showed that the electrocatalyst fabricated by this method exhibited striking catalytic activities in alkaline solution. In alkaline solution, this catalyst showed a competitive activity to the commercial Pt catalyst via four-electron transfer pathway with better ORR selectivity and stability. In addition, this metal-free electrocatalyst exhibited tolerance to methanol crossover effect. Based on its outstanding performance, this functionalized graphene electrocatalyst showed the promising prospect of a metal-free catalyst for fuel cell with much lower cost than currently used Pt/C catalyst.     

Durability investigation of graphene-supported Pt nanocatalysts for PEM fuel cells

We report graphene nanosheets as a durable alternative support material for Pt nanoparticle catalysts for oxygen reduction in proton exchange membrane (PEM) fuel cells and compared them to XC-72. The materials were characterized by X-ray diffraction and transmission electron microscopy. Electrochemical surface oxidation of XC-72 and graphene, and of Pt/XC-72 and Pt/graphene has been compared following treatments for up to 120 h. The electrochemical performance of the specimens was evaluated by cyclic voltammetry and linear sweep voltammetry at different surface oxidation time intervals. Electrochemical measurements indicate that the graphene exihibits greatly enhanced electrochemical durability. It is suggested that graphene nanosheet is a promising, low-cost, and durable electrocatalyst support for oxygen reduction in the PEM fuel cell.     

Graphene supported electrocatalysts for methanol oxidation

Graphene nanosheet was prepared by modified Hummer’s chemical method and utilized as a catalyst support of PtRu nanoparticles for the electro-oxidation of methanol. Home-made graphene nanosheet was clearly characterized by Raman spectroscopy and we applied colloidal method to synthesize with high metal content of 80 wt.% Pt–Ru catalyst, which is extensively clarified by HR-TEM and XRD analysis. 80 wt.% Pt–Ru/graphene nanosheet catalyst showed superior electrochemical activity toward methanol oxidation compared to Pt–Ru/Vulcan XC-72R. It is due to the significant increase of electrochemical active surface area for better catalyst utilization.     

Enhanced Electrocatalytic Activity of Dual Template Based Pt/Cu‐zeolite A/Graphene for Methanol Electrooxidation

A novel Pt/Cu‐zeolite A/graphene based electrocatalyst was successfully prepared by chemical reduction method for methanol electrooxidation. Graphite oxide and Cu functionalized zeolite A were simultaneously reduced by NaBH₄ to prepare Cu‐zeolite A/graphene support which was used to deposit Pt nanoparticles. The nanostructure and composition of as‐prepared Pt/Cu‐zeolite A/graphene composites were characterized by X‐ray diffractometer, X‐ray fluorescence, Fourier transform infrared spectrometer and scanning electron microscopy. The electrocatalytic properties of Pt/Cu‐zeolite A/graphene modified electrode for methanol oxidation were investigated by cyclic voltammetry and chronoamperometry in 0.10 mol/L H₂SO₄ + 0.50 mol/L CH₃OH solution. Compared with Pt/zeolite A/graphene electrode and Pt/graphene electrode, Pt/Cu‐zeolite A/graphene based electrode exhibited obviously enhanced current and higher electrocatalytic activity for methanol electrooxidation. The increased electrocatalytic activity was attributed to the presence of zeolite A and reduced graphene oxide based dual template, which significantly increased the effective electrode surface and facilitated the diffusion of analytes into the electroactive catalyst.     

碳纳米管纯化对Pt/CNTs催化甲醇电化学氧化活性的影响

探索了一种适用于Pt/CNTs催化剂的纯化方法.利用比表面积测定、X射线衍射(XRD)、透射电子显微镜(TEM)和电化学等手段进行了表征.研究结果表明,经该方法纯化的CNTs作为载体制备的阳极催化剂表现出明显优于相应的混酸氧化法纯化的CNTs为载体的催化剂催化性能.     

PtRu/C电催化剂上甲醇吸附氧化过程的电化学原位红外光谱

采用调变的多元醇法制备了高分散的Pt/C, PtRu/C和Ru/C电催化剂. XRD计算结果表明, PtRu/C电催化剂的平均粒径和合金度分别为2.2 nm和71%. 采用电化学方法和原位傅里叶变换红外反射光谱方法(in situ FTIRS)研究了甲醇在3种电催化剂上的吸附氧化过程, 发现PtRu/C对甲醇的催化活性明显高于Pt/C, Ru的加入一方面影响了甲醇在Pt上的解离吸附性能, 另一方面提供了Ru-OH物种, 从而抑制了低电位下电催化剂中毒. 红外光谱研究结果表明, 线性吸附态CO(COL)是主要毒化物种, 反应产物主要是CO2, 还有少量的甲酸甲酯. 根据实验结果讨论了甲醇在PtRu/C电催化剂上的氧化机理.     

Carbon‐Supported Pt Particles as a Catalyst for Electrooxidation of Methanol and Cyclic Voltammetry Studies Under Acidic Conditions

Electrooxidation of methanol on glassy carbon (GC) electrode modified by optimum carbon supported Pt electrocatalyst (Pt‐C/GC) in acid media is investigated. The catalyst is prepared by ultrasonicating Pt/C powders in aqueous media. The activity of prepared Pt‐C/GC electrode is studied in potential range of 0–1000 mV (versus SCE) by cyclic voltammetry. The results showed that the Pt/C dispersed layer at the surface of glassy carbon electrode, behaves as an electrocatalyst for the oxidation of methanol in acid medium by optimum loading of Pt (0.2 mg cm^?2). The electrochemical properties of prepared electrode are studied under various conditions. However the effect of various parameters in the catalytic enhancement of Pt/C, such as platinum loading, sulfuric acid concentration, different scan rates, different final potentials, and medium temperature are considered and examined.     

Supercritical,Freezing and Thermal Drying Process of Resorcinol‐Formaldehyde Polymer based Nano‐carbons and their Highly Loaded PtRu Anode Electrocatalyst for DMFC

The capillary condensation is affected by micropore and nanopore of catalyst layer on fuel cell. Due to limitation of sluggish mass transport and electrocatalytic activity, to retain the pore skeleton of carbon and metal nanoparticles are very significant for enhanced utilizations of pore structure in electrochemical reaction. Besides, thickness of electrocatalyst layer is very crucial due to one of the factor affected by cell performance of direct methanol fuel cell. Highly loaded four Pt?Ru anode catalysts supported on resorcinol‐formaldehyde (RF) polymer based on meso‐porous carbons (80 wt.% Pt?Ru/carbon cryogel, 80 wt.% Pt?Ru/carbon xerogel and 80 wt.% Pt?Ru/carbon aerogel) and conventional carbon (80 wt.% Pt?Ru/Vulcan XC‐72) were prepared by colloidal method for direct methanol fuel cell. These catalysts were characterized by X‐Ray diffraction (XRD), High resolution transmission electron microscopy (HR‐TEM) and X‐ray photoemission (XPS). The results of CO stripping voltammetry, cyclic voltammetry (CV) and single cell test performed on DMFC show that Pt?Ru/carbon cryogel and Pt?Ru/carbon aerogel exhibits better performances in comparison to Pt?Ru/carbon xerogel and Pt?Ru/Vulcan XC‐72. It is thus considered that particle size, oxidation state of metal and electrochemical active surface area of these catalysts are important role in electrocatalytic activity in DMFC.     

A novel Pt/Au/C cathode catalyst for direct methanol fuel cells with simultaneous methanol tolerance and oxygen promotion

A novel Pt/Au/C catalyst was prepared by depositing the Pt and Au nanoparticles on the carbon support. The synthesized catalysts were characterized by energy-dispersive X-ray (EDX) and transmission electron microscopy (TEM), and electrochemically analyzed for activity towards oxygen-reduction reaction and methanol oxidation reaction. EDX and TEM results reveal that Pt nanoparticles supported on carbon supports were separated by Au nanoparticles. The electrochemical analysis indicate that the novel catalyst showed the enhanced methanol tolerance while maintaining a high catalytic activity for the oxygen-reduction reaction, which could be attributed to the less methanol adsorption on Pt/Au/C catalyst.     

Electrocatalytic oxidation of methanol onto platinum particles decorated nanostructured poly (1,5-diaminonaphthalene) film

In this work, platinum particles decorated nanostructured poly (1,5-diaminonaphthalene) modified glassy carbon electrode (Pt/Nano-PDAN/MGCE) is prepared. The composite catalysts are characterized by scanning electron microscopy, energy dispersive spectroscopy, and electrochemical methods. The electrochemical methanol oxidation reaction is studied at the surface of this modified electrode. At same Pt loading, the Pt/Nano-PDAN/MGCE can act as higher efficient catalyst for methanol oxidation than that Pt/MGCE. Then, the influence of some parameters such as potential scan rates, switching potential, and methanol concentration on its oxidation as well as long-term stability of the modified electrode have studied by electrochemical methods. Also, ability of the modified electrode toward electrocatalytic oxidation of formaldehyde as an intermediate in methanol oxidation has been investigated.     

Electrochemical Catalytic Properties of Pt/FeSnO(OH)_5 towards Methanol Oxidation

The Pt/FeSnO(OH)_5 catalyst has been prepared by depositing Pt nanoparticles on the synthesized FeSnO(OH)_5 nanoboxes and demonstrates excellent performance towards methanol oxidation reaction(MOR) in direct methanol fuel cells(DMFCs).The Pt/FeSnO(OH)_5 catalyst exhibits a higher mass activity(1182.35 mA/mgPt) compared with Pt/C(594.57 mA/mgPt) catalysts.The X-ray powder diffraction,field emission scanning electron microscope,field emission transmission electron microscopy,X-ray photoelectron spectroscopy and electrochemical experiments have been employed to explore the relationships between the crystal structure and electrochemical properties.The increased activity and resistance of CO poisoning for Pt/FeSnO(OH)_5 catalyst can be attributed to the strong interaction between the transition metal in the hydroxide and Pt and the bifunctional effect.The higher relative concentration of Pt~0 in Pt/FeSnO(OH)_5 also contributes to the MOR activity.Moreover,the charge transfer resistance of Pt/FeSnO(OH)_5 is lower than that of Pt/C.Therefore,Pt/FeSnO(OH)_5 has great application prospect as a high-performance electrocatalyst in DMFCs.     

Pt and Pt–Ru nanoparticles decorated polypyrrole/multiwalled carbon nanotubes and their catalytic activity towards methanol oxidation

Conducting polymer composite films comprised of polypyrrole (PPy) and multiwalled carbon nanotubes (MWCNTs) [PPy–CNT] were synthesized by in situ polymerization of pyrrole on carbon nanotubes in 0.1 M HCl containing (NH₄)S₂O₈ as oxidizing agent over a temperature range of 0–5 °C. Pt nanoparticles are deposited on PPy–CNT composite films by chemical reduction of H₂PtCl₆ using HCHO as reducing agent at pH = 11 [Pt/PPy–CNT]. The presence of MWCNTs leads to higher activity, which might be due to the increase of electrochemically accessible surface areas, electronic conductivity and easier charge-transfer at polymer/electrolyte interfaces allowing higher dispersion and utilization of the deposited Pt nanoparticles. A comparative investigation was carried out using Pt–Ru nanoparticles decorated PPy–CNT composites. Cyclic voltammetry demonstrated that the synthesized Pt–Ru/PPy–CNT catalysts exhibited higher catalytic activity for methanol oxidation than Pt/PPy–CNT catalyst. Such kinds of Pt and Pt–Ru particles deposited on PPy–CNT composite polymer films exhibit excellent catalytic activity and stability towards methanol oxidation, which indicates that the composite films is more promising support material for fuel cell applications.     

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.     

Bimetallic Pt-Au nanocatalysts electrochemically deposited on graphene and their electrocatalytic characteristics towards oxygen reduction and methanol oxidation

The burgeoning demand for clean and energy-efficient fuel cell system requires electrocatalysts to deliver greater activity and selectivity. Bimetallic catalysts have proven superior to single metal catalysts in this respect. This work reports the preparation, characterization, and electrocatalytic characteristics of a new bimetallic nanocatalyst. The catalyst, Pt-Au-graphene, was synthesized by electrodeposition of Pt-Au nanostructures on the surface of graphene sheets, and characterized by scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), X-ray powder diffraction (XRD), and voltammetry. The morphology and composition of the nanocatalyst can be easily controlled by adjusting the molar ratio between Pt and Au precursors. The electrocatalytic characteristics of the nanocatalysts for the oxygen reduction reaction (ORR) and the methanol oxidation reaction (MOR) were systematically investigated by cyclic voltammetry. The Pt-Au-graphene catalysts exhibits higher catalytic activity than Au-graphene and Pt-graphene catalysts for both the ORR and the MOR, and the highest activity is obtained at a Pt/Au molar ratio of 2:1. Moreover, graphene can significantly enhance the long-term stability of the nanocatalyst toward the MOR by effectively removing the accumulated carbonaceous species formed in the oxidation of methanol from the surface of the catalyst. Therefore, this work has demonstrated that a higher performance of ORR and the MOR could be realized at the Pt-Au-graphene electrocatalyst while Pt utilization also could be greatly diminished. This method may open a general approach for the morphology-controlled synthesis of bimetallic Pt-M nanocatalysts, which can be expected to have promising applications in fuel cells.     

一步法制备还原态氧化石墨烯载铂纳米粒子及其对甲醇氧化的电催化性能

以天然石墨为原料,采用改进的Hummers法制备氧化石墨.然后采用简单的一步化学还原法在乙二醇(EG)中同时还原氧化石墨烯(GO)和H₂PtCl₆制备高分散的铂/还原态氧化石墨烯(Pt/RGO)催化剂.采用傅里叶变换红外(FTIR)光谱、X射线衍射(XRD)和透射电子显微镜(TEM)对催化剂的微结构、组成和形貌进行表征.结果表明, GO已被还原成RGO, Pt纳米粒子均匀分散在RGO表面,粒径约为2.3 nm.采用循环伏安法和计时电流法评价催化剂对甲醇氧化的电催化性能,测试结果表明, Pt/RGO催化剂对甲醇氧化的电催化活性和稳定性与Pt/C和Pt/CNT相比有了很大提高.另外其对甲醇电催化氧化的循环伏安图中正扫峰电流密度(I_f)和反扫峰电流密度(I_b)的比值高达1.3,分别是Pt/C和Pt/CNT催化剂的2.2和1.9倍,表明Pt/RGO催化剂具有高的抗甲醇氧化中间体CO_ad的中毒能力.     

Hydrothermal Syntheses of NiO−GO Nanocomposite on 3D Nickel Foam as a Support for Pt Nanoparticles and its Superior Electrocatalytic Activity towards Methanol Oxidation

In this project, Pt/NiO?GO nanocatalyst is grown on nickel foam (NF) and, its catalytic activity towards electrochemical oxidation of methanol in acidic media is studied. The first step is devoted to the synthesis of NiO?GO support by a hydrothermal method. Then Pt nanoparticles (～34.3 nm) are electrodeposited on this supporting material. Hydrothermal and electrochemical deposition conditions are optimized. Surface of modified NF was inspected for physical characterization and Chemical composition by some techniques such as field emission scanning electron microscopy (FESEM), energy‐dispersive X‐ray spectra (EDS), and X‐ray diffraction (XRD). In the electrochemical section, the catalytic performance of Pt/NiO?GO/NF towards methanol oxidation is investigated by cyclic voltammetry and chronoamperometry measurements. The electrochemical impedance spectroscopy (EIS) is elected to deliberate charge transfer resistance on the catalyst surface. Mass activity, electrochemical surface area (ECSA) and durability of prepared catalysts are compared with commercial Pt/C. Deliberations prove the superiority of Pt/NiO?GO/NF towards methanol oxidation in acidic media. The Superior quality of synthesized nanocatalyst that is attributed to the synergetic effect of the NiO?GO support material and Pt nanoparticles, indicate that Pt/NiO?GO/NF can be successfully used as the anode in the direct methanol fuel cell (DMFC).     

MoP-NC纳米球负载Pt纳米粒子用于高效甲醇电解

实现绿色甲醇电解制氢需要高效的双功能催化剂。本文采用热处理结合乙二醇还原法成功制备了MoP-NC纳米球负载的超细Pt纳米粒子(平均粒径为2.53 nm)复合催化剂(Pt/MoP-NC)用于高效甲醇电解制氢。MoP-NC纳米球不仅能提高Pt纳米粒子的分散性并且增强Pt的抗中毒能力。电化学测试表明Pt/MoP-NC催化剂在酸性甲醇氧化反应(MOR)和析氢反应(HER)中具有较高的催化性能;其中,MOR的正向扫描峰值电流密度为90.7 mA∙cm⁻²,是商业Pt/C催化剂的3.2倍,在10 mA∙cm⁻²的电流密度下,HER的过电位低至30 mV,与商业Pt/C接近。由Pt/MoP-NC||Pt/MoP-NC组装的两电极电解槽驱动10 mA∙cm⁻²的电流密度仅需要0.67 V的电压,比相同条件下电解水的电压低1.02 V,大大降低了能量输入。Pt/MoP-NC的高催化性能主要来源于Pt活性中心与相邻层状多孔球形结构的MoP-NC载体之间电子效应及配体效应引起的抗一氧化碳中毒能力的提升和含氧物种的容易生成。     

Neutral red as electron transfer mediator: enhanced electrocatalytic activity of platinum catalyst for methanol electro-oxidation

Organic molecule neutral red (NR), as electron transfer mediator, was introduced in the anodic electrocatalyst system for methanol oxidation and the resulting electrode was investigated by cyclic voltammetry, polarization method, and electrochemical impedance spectroscopy. For the same loading mass of platinum catalyst, 1.25 times larger exchange current density, 1.83 times higher specific activity, and better long-term cycle stability can be obtained at Pt/NR/graphite electrode, as compared to the electrode without NR. These results indicate that neutral red plays an important role on the enhanced electrocatalytic activity of platinum catalyst for methanol oxidation.     

Pt/RuO2/CNTs纳米催化剂中RuO2含量对甲醇电催化氧化性能的影响

制备了一种新的甲醇直接燃料电池Pt/RuO2/CNTs阳极催化剂,在相同Pt负载量下,其甲醇电催化氧化活性是Pt/CNTs的3倍.采用循环伏安法研究发现Pt/RuO2/CNTs纳米催化剂中RuO2含量对甲醇电催化氧化活性有明显影响,当Pt和RuO2在碳纳米管上含量分别为15%和9.5%时,Pt/RuO2/CNTs催化剂具有最佳的甲醇电催化氧化活性.RuO2负载在碳纳米管上比电容的变化,反映了水合RuO2结构中质子与电子传输平衡的能力,分析表明,催化剂中RuO2含量不同导致电容的变化是影响甲醇电催化氧化活性的主要原因.当催化剂结构中质子与电子传输达到平衡时,催化剂比电容最大,电催化氧化活性最高.这种基于电容关联电催化剂的观点对甲醇直接燃料电池阳极催化剂的设计非常有意义.