Hydrothermal synthesis of PtRu nanoparticles supported on graphene sheets for methanol oxidation in direct methanol fuel cell

Platinum–ruthenium (PtRu) nanoparticles are dispersed on graphene nanosheets and multi-walled carbon nanotubes (MWCNTs) via a hydrothermal method. Transmission electron microsocopy (TEM) observation shows the uniformly dispersed nanoparticles and the average nanoparticle size has been calculated. The electrochemical measurements demonstrate that the Pt–Ru/graphene catalyst exhibits about two times higher mass activity and better tolerance to poisoning species in methanol electro-oxidation than the Pt–Ru/MWCNTs catalyst. This study indicates that the PtRu anodic catalyst synthesized by hydrothermal method can be applied for direct methanol fuel cells (DMFC).     

熔盐电解制备Zr基低价金属氧化物担载铂催化剂催化氧化甲醇和CO

通过在700℃下的CaCl_2和NaCl混合熔盐中电化学还原ZrO_2制备得到了Zr的低价金属氧化物ZrO0.35,该低价金属氧化物作为铂催化剂载体催化甲醇显示了很高的催化活性和稳定性。分析了该催化剂的组成结构和电化学行为。结果显示,在酸性介质中该载体能够有效地提高铂纳米颗粒对甲醇和CO的催化活性。有两种机制可以解释其表现:一是电子协同效应,即Zr原子的电子转移到Pt原子,Pt与CO的相互作用力减弱,从而抑制了Pt中毒;另外一方面是Pt和金属载体的协同效应,它可以有效地移除和氧化CO的中间体。     

Method for preparing highly dispersed Pt catalysts on mesoporous carbon support

Two Pt catalysts supported on template-synthesized mesoporous carbons (MC) were prepared by the conventional wet-impregnation method (Pt-impreg/MC) and by the less commonly used colloidal deposition method (Pt-coll/MC) to examine the effect of preparation method on catalyst performance. The catalysts were characterized by transmission electron microscopy, field-emission electron microscopy, thermogravimetric analysis and X-ray diffraction. The electro-oxidation of methanol in acidic solutions for direct methanol fuel cells at room temperature was used as the test reaction. CO anodic stripping voltammetry and cyclic voltammetry both recorded enhanced performance for Pt-coll/MC relative to Pt-impreg/MC. The poorer application performance of Pt-impreg/MC can be attributed to the transport resistance in the mesopores, and to the entrapment of a sizable fraction (40%) of Pt nanoparticles in the mesopores which are not readily accessible to the reactants under the reaction conditions.     

Simple preparation of tungsten carbide supported on carbon for use as a catalyst support in a methanol electro-oxidation

Two types of supported tungsten carbides were prepared via the impregnation of tungsten precursors on carbon support followed by heat treatment. Depending on whether ammonium metatungstate (AMT) or tungsten chloride (WCl₆) was used as the precursor, this process resulted in samples that are referred to as either WC-A or WC-W, respectively. Both WC-A and WC-W showed tungsten subcarbide (W₂C) as the major crystalline phase, with tungsten monocarbide (WC) as a minor phase. More amount of tungsten carbide being formed when WCl₆ was used as the precursor. This increased formation has occurred because the thermodynamically favorable properties of WCl₆ caused the contact area between the tungsten precursor and the carbon support to promote formation of tungsten carbide. The prepared tungsten carbides were used as a catalyst support of the Pt catalyst in a methanol electro-oxidation. The metal dispersion and the catalytic performance were increased as follows: Pt/C<Pt/WC-A<Pt/WC-W. It is believed that the tungsten carbides supported on the carbon support improved the dispersion of Pt and the activation of water for removal of intermediate CO, which enhanced the catalytic performance during the methanol electro-oxidation.     

Microwave-assisted synthesis of high-loading, highly dispersed Pt/carbon aerogel catalyst for direct methanol fuel cell

A Pt supported on carbon aerogel catalyst has been synthesized by the microwave-assisted polyol process. The Pt supported on carbon aerogel catalyst was characterized by high resolution transmission electron microscopy and X-ray diffraction. The results show a uniform dispersion of spherical Pt nanoparticles 2·5–3·0 nm in diameter. Cyclic voltammetry and chronoamperometry were used to evaluate the electrocatalytic activity of the Pt/carbon aerogel catalyst for methanol oxidation at room temperature. The Pt/carbon aerogel catalyst shows higher electrochemical catalytic activity and stability for methanol oxidation than a commercial Pt/C catalyst of the same Pt loading.     

Preparation and characterization of PtRu nanoparticles supported on nitrogen-doped porous carbon for electrooxidation of methanol

N-doped porous carbon nanospheres (PCNs) were prepared by chemical activation of nonporous carbon nanospheres (CNs), which were obtained via carbonization of polypyrrole nanospheres (PNs). The catalysts, PtRu and Pt nanoparticles supported on PCNs and Vulcan XC-72 carbon black, were prepared by ethylene glycol chemical reduction. Transmission electron microscopy, X-ray diffraction, and energy-dispersive X-ray spectroscopy were employed to characterize samples. It was found that PCNs containing N function groups possess a large number of micropores. Uniform and well-dispersed Pt and PtRu particles with narrow particle size distribution were observed. The electrooxidation of liquid methanol on these catalysts was investigated at room temperature by cyclic voltammetry, chronoamperometry and electrochemical impedance spectroscopy (EIS). The results showed that alloy catalyst (Pt(1)Ru(1)/PCN) possessed the highest catalytic activity and better CO tolerance than the other PtRu and Pt-only catalysts; PtRu nanoparticles supported on PCN showed a higher catalytic activity and more stable sustained current than on carbon black XC-72. Compared to commercial Alfa Aesar PtRu catalyst, Pt(1)Ru(1)/PCN reveals an enhanced and durable catalytic activity in methanol oxidation because of the high dispersion of small PtRu nanoparticles and the presence of N species of support PCNs.     

Electrocatalysts for methanol oxidation based on platinum/carbon nanofibers nanocomposite

New carbon nanomaterials, i.e., carbon nanotubes and nanofibers, with special physico-chemical properties, are recently studied as support for methanol oxidation reaction electrocatalysts replacing the most widely used carbon black. Particularly, carbon fibrous structures with high surface area and available open edges are thought to be promising. Platelet type carbon nanofibers, which have the graphene layers oriented perpendicularly to the fiber axis, exhibit a high ratio of edge to basal atoms. Different types of carbon nanofibers (tubular and platelet) were grown by plasma enhanced chemical vapour deposition on carbon paper substrates. The process was controlled and optimised in term of growth pressure and temperature. Carbon nanofibers were characterised by high resolution scanning electron microscopy and X-ray photoelectron spectroscopy to assess the morphological properties. Then carbon nanofibers of both morphologies were used as substrates for Pt electrodeposition. High resolution scanning electron microscopy images showed that the Pt nanoparticles distribution was well controlled and the particles size went down to few nanometers. Pt/carbon nanofibers nanocomposites were tested as electrocatalysts for methanol oxidation reaction. Cyclic voltammetry in H2SO4 revealed a catalyst with a high surface area. Cyclic voltammetry in presence of methanol indicated a high electrochemical activity for methanol oxidation reaction and a good long time stability compared to a carbon black supported Pt catalyst.     

Effect of ceria on carbon supported platinum catalysts for methanol electrooxidation

Pt–CeO₂/C catalysts were synthesized by a one-step microwave polyol process and compared with Pt/C (E-TEK) catalyst in terms of the electrochemical activity for methanol oxidation using the cyclic voltammetry and chronoamperometry. The results demonstrated that Pt–CeO₂/C catalysts exhibited lower onset potential, higher current peak and better stability for methanol electrooxidation than Pt/C (E-TEK) catalyst. The effect of ceria on the catalytic activity was investigated by electrochemical measurements and the highest electrochemical activity was obtained at the molar ratio of Pt to Ce by 2:1. The preliminary mechanism of the enhanced electrocatalytic performance for methanol oxidation was discussed.     

Convenient immobilization of Pt-Sn bimetallic catalysts on nitrogen-doped carbon nanotubes for direct alcohol electrocatalytic oxidation

Pt-Sn alloy nanoparticles were conveniently immobilized on nitrogen-doped carbon nanotubes (NCNTs) through microwave-assisted ethylene glycol reduction. The nanoparticles have a narrow particle size distribution with the average particle size around 3 nm as measured by transmission electron microscopy and x-ray diffraction. The binding energy of metallic Sn passively shifts due to the charge transfer from Sn to Pt, as revealed by x-ray photoelectron spectroscopy. In comparison with the commercial Pt/C catalyst, Pt/NCNT presents a clear increase in activity for alcohol electro-oxidation due to the improved support, while the bimetallic Pt-Sn/NCNT has even higher activity owing to the alloying of Pt with Sn. Both Pt-Sn/NCNT and Pt/NCNT catalysts exhibit competitive long-term stability to Pt/C catalyst. The low cost, simple preparation and superior electrocatalytic performance indicate the great potential of Pt-Sn/NCNT in direct alcohol fuel cells.     

Nitrogen-doped graphite encapsulated Fe/Fe_3C nanoparticles and carbon black for enhanced performance towards oxygen reduction

Non-noble metal(NNM) catalysts have recently attracted intensive interest for their high catalytic performance towards oxygen reduction reaction(ORR) at low cost.Herein,a novel NNM catalyst was synthesized by the simple pyrolysis of carbon black,urea and a Fe-containing precursor,which exhibits excellent ORR catalytic activity,superior durability and methanol tolerance versus the Pt/C catalyst in both alkaline and acidic solutions.Scanning electron microscopy(SEM),transmission electron microscopy(TEM) and X-ray diffraction(XRD) characterizations demonstrate that the product is a nitrogen-doped hybrid of graphite encapsulated Fe/Fe_3C nanoparticles and carbon black.X-ray photoelectron spectrum(XPS) and electrochemical analyses indicate that the catalytic performance and chemical stability correlate closely with a nitrogen-rich layer on the Fe/Fe_3C nanoparticle after pyrolysis with presence of urea,leading to the same four-electron pathway towards ORR as the Pt/C catalyst.The hybrid is prospective to be an efficient ORR electrocatalyst for direct methanol fuel cells with high catalytic performance at low cost.     

A Prussian blue route to nitrogen-doped graphene aerogels as efficient electrocatalysts for oxygen reduction with enhanced active site accessibility

Developing high-performance nonpredous-metal electrocatalysts for the oxygen reduction reaction (ORR) is crudal for a variety of renewable energy conversion and storage systems.Toward that end,rational catalyst design principles that lead to highly active catalytic centers and enhanced active site accessibility are undoubtedly of paramount importance.Here,we used Prussian blue nanoparticles to anchor Fe/Fe3C species to nitrogen-doped reduced graphene oxide aerogels as ORR catalysts.The strong interaction between nanosized Fe3C and the graphitic carbon shell led to synergistic effects in the ORR,and the protection of the carbon shell guaranteed stability of the catalyst.As a result,the aerogel electrocatalyst displayed outstanding activity in the ORR on par with the state-of-the-art Pt/C catalyst at the same mass loading in alkaline media,good performance in acidic media,and excellent stability and crossover tolerance that rivaled that of the best nonprecious-metal ORR electrocatalysts reported to date.     

2D Porous Carbons prepared from Layered Organic–Inorganic Hybrids and their Use as Oxygen‐Reduction Electrocatalysts

2D porous carbon nanomaterials have attracted tremendous attention in different disciplines especially for electrochemical catalysis. The significant advantage of such 2D materials is that nearly all their surfaces are exposed to the electrolyte and can take part in the electrochemical reaction. Here, a versatile active‐salt‐templating strategy to efficiently synthesize 2D porous carbon nanosheets from layered organic–inorganic hybrids is presented. The resulting heteroatom‐doped carbon nanosheets (NFe/CNs) exhibit exceptional performance for the oxygen‐reduction reaction and in Zn–air battery electrodes. The activity of the best catalyst within a series of NFe/CNs exceeds the performance of conventional carbon‐supported Pt catalysts in terms of onset potential (0.930 vs 0.915 V of Pt/C), half‐wave potential (0.859 vs 0.816 V of Pt/C), long‐time stability, and methanol tolerance. Also, when applied as a cathode catalyst in a zinc–air battery the NFe/CNs presented here outperform commercial Pt/C catalysts.     

The improvement of methanol oxidation using nano-electrocatalysts

ABSTRACT

In this study, a nano-scale perovskite LaMnO₃ (LaMnO₃NPs) was synthesised by a rapid microwave-assisted co-precipitation method and characterised by X-ray powder diffraction, Fourier transform infrared, scanning electron microscopy and energy dispersive X-ray techniques. A modified glassy carbon electrode with Pt nanoparticles (PtNPs), functionalised multi-walled carbon nanotubes (CNTs) and LaMnO₃NPs as multifunctional catalyst was prepared and furthermore, its catalytic activity toward methanol oxidation was investigated. Based on the electrochemical studies, the PtNPs–CNTs–LaMnO₃NPs nanocomposite showed considerable activity for methanol oxidation in comparison to PtNPs, PtNPs–CNTs and PtNPs–LaMnO₃NPs. The results displayed the adding of CNTs and LaMnO₃NPs into PtNPs catalyst and the use of a more porous matrix of chitosan can improve the anode performance for methanol oxidation. The transition metals presence at catalyst structure caused to catalyse the methanol dehydrogenation. The decreasing the poisoning rate of the PtNPs with intermediates and by-products of anodic reaction was observed due to the bi-functional effect electrical and oxygen ion conductive perovskite. Direct methanol fuel cell (DMFC) was designed, assembled and tested with suggested PtNPs–CNTs–LaMnO₃NPs nanocomposites as anodic catalyst at variety conditions. The effect of experimental factors such as temperature and methanol concentration on DMFC performances was investigated and optimised.     

Ethylene glycol oxidation on Pt and Pt-Ru nanoparticle decorated polythiophene/multiwalled carbon nanotube composites for fuel cell applications

A novel supporting material containing polythiophene (PTh) and multiwalled carbon nanotubes (MWCNTs) (PTh-CNTs) is prepared by in?situ polymerization of thiophene on carbon nanotubes using FeCl(3) as oxidizing agent under sonication. The prepared polythiophene/CNT composites are further decorated with Pt and Pt-Ru nanoparticles by chemical reduction of the corresponding metal salts using HCHO as reducing agent at pH = 11 (Pt/PTh-CNT and Pt-Ru/PTh-CNT). The fabricated composite films decorated with nanoparticles were investigated towards the electrochemical oxidation of ethylene glycol (EG). The presence of carbon nanotubes in conjugation with a conducting polymer produces a good catalytic effect, which might be due to the higher electrochemically accessible surface areas, electronic conductivity and easier charge-transfer at polymer/electrolyte interfaces, which allows higher dispersion of Pt and Pt-Ru nanoparticles. Such nanoparticle modified PTh-CNT electrodes exhibit better catalytic behavior towards ethylene glycol oxidation. Results show that Pt/PTh-CNT and Pt-Ru/PTh-CNT modified electrodes show enhanced electrocatalytic activity and stability towards the electro-oxidation of ethylene glycol than the Pt/PTh electrodes, which shows that the composite film is more promising for applications in fuel cells.     

Facile design of Au@Pt core-shell nanostructures: Formation of Pt submonolayers with tunable coverage and their applications in electrocatalysis

A facile design of Pt nanostructures from submonolayer to monolayer has been realized by ion adsorption-in situ electrochemical reduction on Au nanoparticles supported on multiwall carbon nanotubes （CNTs）. The as prepared Au@Pt/CNTs catalysts display coverage-specific electrocatalysis. Au@Pt/CNTs with low Pt coverage is inactive towards methanol oxidation whereas it oxidizes formic acid effectively through a direct pathway with mass specific activity 90 times that of a commercial Pt/C catalyst. Due to its inertness to methanol, it shows high performance in the oxygen reduction reaction （ORR） with high methanol tolerance. In contrast, simply increasing the Pt coverage to above 40% switches the formic acid oxidation process to both direct and indirect catalytic pathways, and also results in high methanol oxidation activity.     

Electrocatalytic activity of Pt nanoparticles supported on novel functionalized reduced graphene oxide-chitosan for methanol electrooxidation

Here, graphene oxide (GO) was synthesized by a modified Hummers’ method and was functionalized with 1,1′-dimethyl-4,4′-bipyridinium dichloride (MV) accompanied by chitosan (CH) to prepare a novel MV-RGO-CH support. Pt/MV-RGO-CH catalyst was prepared by immobilization of the Pt nanoparticles on MV-RGO-CH support. The microstructure and morphology of the prepared catalyst was characterized by transmission electron microscopy and X-ray powder diffraction analysis. The electrocatalytic activity of Pt/MV-RGO-CH catalyst was investigated for methanol electrooxidation through cyclic voltammetry (CV), CO_ads stripping voltammetry, chronoamperometry, and electrochemical impedance spectroscopy (EIS) techniques. The effects of some experimental factors for methanol electrooxidation such as methanol concentration, scan rate and temperature were studied at the prepared catalyst. Durability of the catalyst was also investigated. Comparing the catalytic activity of the Pt/MV-RGO-CH nanocatalyst with Pt/CH and Pt/MV-RGO catalysts indicated that Pt/MV-RGO-CH has a very good catalytic activity for methanol electrooxidation.     

Synthesis of ordered macroporous Pt/Ru nanocomposites for the electrooxidation of methanol

Highly catalytic PtRu catalysts with different molar ratios of Pt to Ru have been synthesized by using the inverted colloidal crystals template technique. Three-dimensional ordered Pt/Ru alloys with pore size of 320 nm could be conveniently obtained by electrochemical codeposition of metal precursors inside the voids of the template. The structural and chemical properties of the macroporous catalysts were studied by using SEM, XPS and XRD methods. The decomposition and oxidation of methanol on the macroporous catalyst surfaces with different Pt and Ru molar ratios (Pt100Ru0, Pt90Ru10, Pt80Ru20, Pt70Ru30 and Pt56Ru44) were systemically discussed. Potentiostatic experiments showed that the special structure characteristics (e.g., interconnected pore framework and the flexible curvature) lead to enhanced methanol oxidation efficiency on the macroporous materials as compared to the directly deposited catalyst. These results demonstrate that the three-dimensional ordered porous bimetallic catalysts are promising alternatives for developing high performance DMFC anodic catalysts, especially for the fabrication of microfuel cells.     

Mass-produced multi-walled carbon nanotubes as catalyst supports for direct methanol fuel cells

Commercially mass-produced multi-walled carbon nanotubes, i.e., VGNF (Showa Denko Co.), were applied to support materials for platinum-ruthenium (PtRu) nanoparticles as anode catalysts for direct methanol fuel cells. The original VGNFs are composed of high-crystalline graphitic shells, which hinder the favorable surface deposition of the PtRu nanoparticles that are formed via borohydride reduction. The chemical treatment of VGNFs with potassium hydroxide (KOH), however, enables highly dispersed and dense deposition of PtRu nanoparticles on the VGNF surface. This capability becomes more remarkable depending on the KOH amount. The electrochemical evaluation of the PtRu-deposited VGNF catalysts showed enhanced active surface areas and methanol oxidation, due to the high dispersion and dense deposition of the PtRu nanoparticles. The improvement of the surface deposition states of the PtRu nanoparticles was significantly due to the high surface area and mesorporous surface structure of the KOH-activated VGNFs.     

Preparation of a platinum electrocatalyst by coaxial pulse arc plasma deposition

We have developed a new method of preparing Pt electrocatalysts through a dry process. By coaxial pulse arc plasma deposition (CAPD), highly ionized metal plasma can be generated from a target rod without any discharged gases, and Pt nanoparticles can be deposited on a carbon support. The small-sized Pt nanoparticles are distributed over the entire carbon surface. From transmission electron microscopy (TEM), the average size of the deposited Pt nanoparticles is estimated to be 2.5 nm, and their size distribution is narrow. Our electrocatalyst shows considerably improved catalytic activity and stability toward methanol oxidation reaction (MOR) compared with commercially available Pt catalysts such as Pt black and Pt/carbon (PtC). Inspired by its very high efficiency toward MOR, we also measured the catalytic performance for oxygen reduction reaction (ORR). Our PtC catalyst shows a better performance with half-wave potential of 0.87 V, which is higher than those of commercially available Pt catalysts. The higher performance is also supported by a right-shifted onset potential. Our preparation is simple and could be applied to other metallic nanocrystals as a novel platform in catalysis, fuel cells and biosensors.     

Electrochemical characterization of nano-sized Pd-based catalysts as cathode materials in direct methanol fuel cells

To improve the catalytic activity of palladium (Pd) as a cathode catalyst in direct methanol fuel cells (DMFCs), we prepared palladium-titanium oxide (Pd-TiO2) catalysts which the Pd and TiO2 nanoparticles were simultaneously impregnated on carbon. We selected Pd and TiO2 as catalytic materials because of their electrochemical stability in acid solution. The crystal structure and the loading amount of Pd and TiO2 on carbon were characterized by X-ray diffraction (XRD) and energy dispersive X-ray microanalysis (EDX). The electrochemical characterization of Pd-TiO2/C catalysts for the oxygen reduction reaction was carried out in half and single cell systems. The catalytic activities of the Pd-TiO2 catalysts were strongly influenced by the TiO2 content. In the single cell test, the Pd-TiO2 catalysts showed very comparable performance to the Pt catalyst.