Radiolysis route to Pt nanodendrites with enhanced comprehensive electrocatalytic performances for methanol oxidation

Unique Pt nanodendrites with controlled size were prepared by a rapid radiolysis route. The Pt nanodendrites display drastically enhanced electrochemical catalytic performances toward methanol oxidation. They exhibit a better CO tolerance for methanol oxidation compared with commercial catalysts and other nanodendritic Pt-based catalysts.     

Graphene growth on nanodiamond as a support for a Pt electrocatalyst in methanol electro-oxidation

A core/shell structure nanodiamond/graphene (ND/G) was prepared by annealing ND in a vacuum at the temperatures of 1200 and 1500 °C. ND/G with a controllable few-layer graphene covering on the ND surface was achieved. The prepared ND/G was used as a support for a platinum (Pt) electrocatalyst in direct methanol fuel cells. A higher dispersion of Pt nanoparticles was observed on ND/G compared to pristine NDs and the material showed better catalytic activity and greater stability for methanol electro-oxidation than Pt/ND.     

Enhanced electrochemical activity of Pt nanowire network electrocatalysts for methanol oxidation reaction of fuel cells

In this work, Pt nanowire networks supported on high surface area carbon (Pt NWNs/C) are synthesized as electrocatalysts for direct methanol fuel cells (DMFCs). The electrocatalytic behavior of Pt NWNs/C catalysts for the methanol and adlayer CO oxidation reactions is investigated and the results are compared with the Pt nanoparticles (NPs) supported on carbon (Pt NPs/C). The results indicate that Pt NWNs are characterized by interconnected nanoparticles with large number of grain boundaries, downshifted d-band center and reduced oxophilicity, which results in the enhanced surface mobility of oxygen-containing species such as CO_ads and OH_ads. The enhanced surface mobility of CO_ads and OH_ads in turn facilitates the removal of intermediate CO species during the methanol oxidation. The activity of the Pt NWNs/C electrocatalyst for the methanol oxidation reaction and electrooxidation of adsorbed CO is also evaluated by cyclic voltammetry, CO stripping, and kinetic analysis. The results show that Pt NWNs/C catalysts have a significantly higher electrocatalytic activity for the methanol oxidation reaction as compared to Pt NPs/C catalysts. The enhanced electrocatalytic activity of Pt NWNs/C catalysts is mainly due to the existence of large number of the grain boundaries of the interconnected nanoparticles of the unique Pt NWN structure.     

Electrochemical activation of nanostructured carbon-supported PtRuMo electrocatalyst for methanol oxidation

The factors controlling the behavior and the stability of electrocatalysts based on Pt, Ru and Mo nanoparticles during exhaustive electrochemical treatment are examined. Along this treatment, it has been observed that in the case of ternary catalysts there are pronounced changes in the structure of their surface resulting in electrode activation for methanol and CO electrooxidation, whereas the activity of binary PtRu/C and PtMo/C catalysts decreases. Therefore, the role of both Ru and Mo is crucial for the electrochemical activation of the catalyst, though metal losses do occur during electrochemical process. For the first time a detailed study of this phenomenon is presented, including characterization by HRTEM, TXRF, XRD, electrochemical measurements and in situ Fourier transform infrared spectroscopy (FTIR). In order to get a deeper insight into the surface structure, chemical state, and stability of the electrocatalyst under reaction conditions, a combination of cyclic voltammetry, chronoamperometry and X-ray photoelectron spectroscopy (XPS) has been used. By comparing bulk and surface composition, our results point out to the key role of the geometric effect enhanced by previous reduction of the nanoparticles. At the end of the electrochemical treatment, Mo-PtRu/C catalysts surface was restructured with substantial enrichment in Pt and a less pronounced Mo surface enrichment, while Ru is incorporated into the Pt-Mo overlayer. These results underline the possibility of further optimization of the surface structure and composition producing PtRuMo nanoparticles with high methanol and CO oxidation activity.     

Highly dispersed Pt nanoparticles on nitrogen-doped magnetic carbon nanoparticles and their enhanced activity for methanol oxidation

Pt nanoparticles dispersed nitrogen-doped magnetic carbon nanoparticles (N-MCNPs) were prepared by chemical method, conventional sodium borohydride reduction. Then, those probable applications were evaluated for a support material comparing with Vulcan XC-72 for polymer electrolyte membrane fuel cell. N-MCNPs-supported Pt nanoparticles show a better activity of methanol oxidation reaction compared to Vulcan XC-72-supported one in terms of both mass and electrochemical surface area (ESA) normalized current density. In particular, Pt/N-MCNPs show more enhanced activity based on the mass normalized specific activity rather than ESA normalized activity. For investigation of physical characterizations of Pt/N-MCNPs, and Pt/Vulcan XC-72, X-ray diffraction (XRD), high resolution-transmission electron microscopy (HR-TEM), and X-ray photoelectron spectroscopy (XPS) likes various experiments were performed. Especially, to identify the role of nitrogen in the N-MCNPs for Pt nanoparticles dispersion, specific investigation of N 1s XP spectra with peak deconvolution were performed on N-MCNPs support material of the before and after chemical reduction of Pt nanoparticles.     

Nitrogen-containing graphitized carbon support for methanol oxidation Pt catalyst

Graphitized carbon (GrC) with a relatively uniform pore size was synthesized using polyvinylpyrrolidone as a nitrogen-containing carbon source. Ni was employed as both a graphitization catalyst and a pore structure template. The polyol method was applied to load Pt nanoparticles with a narrow distribution of sizes on the synthesized GrC. The Pt catalyst supported on GrC showed higher electrocatalytic activity than that supported on heat-treated Vulcan XC-72R carbon despite the small specific surface area of GrC. Mass- and area-normalized current densities of Pt/GrC were 2.2 and 3.0 times greater than those for Pt catalyst supported on the commercial carbon, respectively. The better performance of the Pt/GrC could be due to high electric conductivity and interaction between GrC and Pt nanoparticles resulting from the presence of nitrogen in the prepared GrC.     

酸性环境中甲醇电氧化催化剂的研究进展

甲醇的电催化氧化是直接甲醇燃料电池的核心反应,高效、长寿命的阳极催化剂的开发是直接甲醇燃料电池研究的一个重要方向。本文总结了近年来酸性环境中直接甲醇燃料电池阳极催化剂的研究进展,包括甲醇电催化反应机理、催化剂的设计合成及其应用。重点介绍了铂基催化剂纳米材料活性和稳定性的增强策略,如组分调控、形貌调控、非金属掺杂以及氧化物的协同催化、载体材料的选用等。最后,对阳极催化剂目前仍存在的制备成本高、催化剂耐久性不足、表征技术有限等问题进行了分析讨论,并对阳极催化剂未来的发展方向进行了展望。     

High performance self-supporting 3D nanoporous PdNi alloy foam for methanol oxidation electrocatalysis

Journal of Porous Materials - Low-cost and high-activity electrocatalyst is crucial to the development of fuel cells. In this work, methanol oxidation electrocatalysis for self-supporting...     

Carbon paste electrodes modified by Pt and Pt-Ni microparticles dispersed in polyindole film for electrocatalytic oxidation of methanol

Electrocatalytic activity of the Pt microparticles dispersed into polyindole (PIn) films obtained by electropolymerization on carbon paste electrodes (CPE) towards methanol oxidation in perchloric acid medium has been demonstrated and investigated using cyclic voltammetry, potentiodynamic polarization, chronoamperometry and impedance spectroscopic techniques. The results show that PIn films obtained on these electrodes serve as good host matrices for the dispersion of Pt microparticles and exhibit good catalytic activity towards the electrooxidation of methanol compared to bulk Pt and CPE modified with Pt. The morphology and composition of the modified and unmodified films were obtained using SEM and EDX techniques. The effect of scan rate, amount of Pt and concentration of methanol, on the activity of the electrode has been tested. The effect of alloying Pt with different amounts of Ni was studied and it was found that when the metals are deposited from a solution containing the metal salts in 1:1 ratio the activity towards methanol oxidation was significantly enhanced.     

The use of nitrogen-doped graphene supporting Pt nanoparticles as a catalyst for methanol electrocatalytic oxidation

Nitrogen-doped graphene (N-G) was prepared by thermal annealing of graphene oxide in ammonia at different temperatures. The resultant N-G was used as a conductive support for Pt nanoparticles (Pt/N-G) and the electrocatalytic activity of the Pt/N-G catalysts towards methanol oxidation was examined. To investigate the microstructure and morphology of the synthesized catalysts, X-ray diffraction, scanning and transmission electron microscopy and X-ray photoelectron spectroscopy were used. The catalytic activity of the catalysts towards the oxidation of methanol was evaluated by cyclic voltammetry. Compared to a control catalyst of Pt loaded on undoped graphene, the Pt/N-G materials show higher electrochemical activity towards methanol oxidation. The excellent electrochemical performance of Pt/N-G is mainly attributed to the nitrogen doping and the uniform distribution of Pt particles on the doped graphene support. These results indicate that N-doped graphene has great potential as a high-performance catalyst support for fuel cell electrocatalysis.     

In situ microscope FTIR studies of methanol adsorption and oxidation on an individually addressable array of nanostructured Pt microelectrodes

An individually addressable array of nanostructured Pt microelectrodes was designed and prepared according to the concept of combinatorial electrochemistry. Different nanostructures on the array were obtained systematically by electrochemical deposition under cyclic voltammetric conditions. The surface structure and electrochemical behavior of the array were investigated, respectively using scanning tunneling microscopy (STM) and cyclic voltammetry (CV), and electrocatalytic properties of the array towards methanol oxidation were studied by CV and in situ microscope Fourier transform infrared reflection spectroscopy (MFTIRS). The results revealed the higher electrocatalytic activity of nanostructured Pt surfaces, and demonstrated that the combination of an individually addressable array with in situ MFTIRS is an efficient combinatorial approach in studies of electrocatalytic reaction processes at molecular level.     

Probing the electronic structure of an active catalyst surface under high-pressure reaction conditions: the oxidation of methanol over copper

The active phase of a bulk metallic copper catalyst is investigated by surface sensitive X-ray absorption spectroscopy at the oxygen K-edge and the Cu L-edges in the total electron yield mode under practical steady state flow-through conditions. The active catalyst surface contains oxygen atoms revealing significant spectral differences compared to those of known copper oxides. The partial oxidation of methanol to formaldehyde is correlated to the abundance of this copper suboxide. These oxygen atoms probe defects of the copper lattice, which represent catalytically active sites. The suboxide is undetectable under UHV conditions. The total oxidation of methanol is catalysed by a conventional copper(I) oxide species and the abundance of carbon dioxide in the gas phase is increasing with decreasing integrated intensity of the oxide species. This revised version was published online in July 2006 with corrections to the Cover Date.     

Green synthesis of a Pt nanoparticle/polyoxometalate/carbon nanotube tri-component hybrid and its activity in the electrocatalysis of methanol oxidation

The easy, room temperature and environmentally friendly synthesis of Pt nanoparticle-decorated carbon nanotubes (CNTs) is reported. Polyoxometalates (POMs) were used to serve as both reducing and bridging molecules. Characterization using transmission electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction analysis, etc. was performed and verified the structure of the prepared nanohybrid of Pt@POM/CNT. The nanohybrid showed a higher electrocatalytic activity towards methanol oxidation reaction than did a traditional Pt–C catalyst and the other reported Pt/CNT systems. The POM also serves as a co-catalyst in the nanohybrid, which plays a key role in improving the electrocatalytic activities of the catalyst.     

Platinum-alloy nanostructured thin film catalysts for the oxygen reduction reaction

In an effort to study advanced catalytic materials for the oxygen reduction reaction (ORR), a number of metallic alloy nanostructured thin film (NSTF) catalysts have been characterized by rotating disk electrode (RDE). Optimal loadings for the ORR and activity enhancement compared to conventional carbon supported nanoparticles (Pt/C) were established. The most efficient catalyst was found to be PtNi alloy with 55 wt% of Pt. The enhancement in specific activity is more than one order of magnitude, while the improvement factor in mass activity is 2.5 compared to Pt/C. Further lowering of the platinum to nickel ratio in NSTF catalysts did not lead to increased mass activity values.     

Polyaniline/carbon black composite as Pt electrocatalyst supports for methanol oxidation: Synthesis and characterization

Core/shell composites of polyaniline (PANI) and Vulcan XC‐72 Carbon (VC), in which the carbon represents the core and PANI forms the shell, were synthesized by in situ chemical oxidation polymerization. Platinum (Pt) particles were then deposited on the PANI/VC composites by chemical reduction method. The highest conductivity is obtained when a mass ratio of PANI/VC equals to 0.28, as proved by Fourier transform infrared spectra. And it is also proved that there are some reactions happened between PANI and VC. Scanning electron microscope, transmission electron microscope, and X‐ray diffraction measurements were performed to analyze their structure and surface morphology. It has been observed that the Pt particles are smaller in size and more uniformly distributed on these composite supports than on pure VC supports, considered as a reference. Methanol oxidation performed on the electrode modified by such a composite catalyst has been measured by cyclic voltammogram focusing on the attenuation of methanol oxidation current after 200 cycles. The attenuation degree for the composite catalyst is only one‐third of the one measured for a simple Pt/VC catalyst. It is proved that the composite catalyst better resist carbon monoxide poisoning in comparison with the Pt/VC catalyst, which may be due to the synergetic effects between the composite support and the Pt catalyst. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Preparation and characterization of Pt nanowire by electrospinning method for methanol oxidation

Pt nanowires are prepared by treating electrospun polyvinyl pyrrolidone (PVP)-Pt composite fibers at high temperatures in an air atmosphere and their activities toward a methanol oxidation reaction (MOR) are investigated. Thermogravimetric analysis (TGA) and inductively coupled plasma-atomic emission spectroscopy (ICP-AES) results indicate that the electrospun PVP-Pt composite fibers thermally decompose at 250 °C, which leads to the removal of 98 wt% of the PVP polymer and the simultaneous reduction of the Pt precursor to a Pt nanowire. The physical and electrochemical properties of Pt nanowires are found to be affected by the heat treatment conditions such as heating rate, time, temperature, and atmosphere. Furthermore, polymer fibers subjected to a pyrolization process in nitrogen followed by exposure to an air atmosphere enhance the surface area of the Pt nanowires, leading to high electrochemical activity toward a MOR. The detailed physical and electrochemical properties of the Pt nanowires are characterized by various spectroscopic and electrochemical techniques, and the possibilities of using them as electrocatalysts in a fuel cell are explored.     

The characterization of Pt/Sn catalyst for the electrochemical oxidation of methanol

Pt/Sn electrodeposited catalysts have been prepared, characterized and tested for the electro-oxidation of methanol. Catalyst activities were measured in 3 M H₂SO₄ electrolyte between ambient temperature and 95°C. Enhancement in specific activity by a factor of about 50 was found over electrodeposited platinum black. This behaviour is in contrast to that of alloys of platinum and tin which were found to have very low activities compared with platinum catalysts and to be readily corroded in H₂SO₄ electrolyte.ESCA (electron spectroscopy for chemical analysis) studies and Mössbauer spectroscopy showed the majority of the tin in the deposit to be present in an oxidized form. A small amount (17%) was present as a dilute alloy of tin in platinum. Surface area measurements and X-ray powder diffraction indicated that the increase in activity over platinum black was not attributable to smaller platinum particle size. It seems that the combination of platinum and tin results in a decrease in the poisoning effect by strongly adsorbed organic residues. Whether this arises from the operation of a cyclic Sn(II)/Sn(IV) redox system or from modification of the platinum surface remains unresolved.     

Ultra-long Pt nanolawns supported on TiO2-coated carbon fibers as 3D hybrid catalyst for methanol oxidation

In this study, TiO₂ thin film photocatalyst on carbon fibers was used to synthesize ultra-long single crystalline Pt nanowires via a simple photoreduction route (thermally activated photoreduction). It also acted as a co-catalytic material with Pt. Taking advantage of the high-aspect ratio of the Pt nanostructure as well as the excellent catalytic activity of TiO₂, this hybrid structure has the great potential as the active anode in direct methanol fuel cells. The electrochemical results indicate that TiO₂ is capable of transforming CO-like poisoning species on the Pt surface during methanol oxidation and contributes to a high CO tolerance of this Pt nanowire/TiO₂ hybrid structure.