A facile method for preparation of high performance Pt catalyst supported on multi-wall carbon nanotubes for methanol electrooxidation

Due to the inherent inertness of multi-wall carbon nanotubes (MWCNTs), complicated procedures are involved in the preparation of MWCNT-supported catalysts. In this paper, a facile and effective method is introduced to prepare Pt nanoparticles dispersed on the surface of purified MWCNTs. In this method, sodium phthalate (SP) is used as a special additive to function as an effective cross linker between MWCNTs and Pt ions, and ethylene glycol (EG) aqueous solution is used as an effective solvent. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) analyses reveal that the prepared face-centered cubic Pt nanoparticles with the average diameter of 2.2 nm are well dispersed on the surface of the MWCNTs. Cyclic voltammetry and chronoamperometry tests demonstrate that the Pt/MWCNTs catalyst obtained from typical experiment exhibits better catalytic activity and stability for methanol electrooxidation than the Pt catalyst supported on conventional acid-treated MWCNTs (AO-MWCNTs) and JM commercial 20% Pt/C catalyst.     

Deposition of platinum nanoparticles on organic functionalized carbon nanotubes grown in situ on carbon paper for fuel cells

Deposition of small Pt nanoparticles of the order of 2-2.5?nm on carbon nanotubes (CNTs) grown directly on carbon paper is demonstrated in this work. Sulfonic acid functionalization of CNTs is used as a means to facilitate the uniform deposition of Pt on the CNT surface. The organic molecules attached covalently to the CNT surface via electrochemical reduction of corresponding diazonium salts are treated with concentrated sulfuric acid and the sulfonic acid sites thus attached are used as molecular sites for Pt ion adsorption, which are subsequently reduced to yield the small Pt nanoparticles. Cyclic voltammograms reveal that, after removal of the organic groups during high temperature reduction, these Pt nanoparticles are in electrical contact with the carbon paper backing. A typical Pt loading of 0.09?mg?cm(-2) is achieved, that shows higher specific surface area of Pt than an E-TEK electrode with Pt loading of 0.075?mg?cm(-2). A membrane and electrode assembly (MEA) is prepared with a Pt/CNT electrode as cathode and an E-TEK electrode as anode, and it offers better performance than a conventional E-TEK MEA.     

Catalytic performance of acid-treated multi-walled carbon nanotube-supported platinum catalyst for PEM fuel cells

Effects of the surface functional groups of multi-walled carbon nanotubes (MWCNTs) as catalyst support for the durability of polymer electrolyte membrane fuel cells (PEMFCs) were examined at high Pt loading conditions. The amount of oxygen functional groups on the MWCNTs surface was increased as the acid treatment time and temperature increased. We found that more functional groups in MWCNTs improved initial Pt dispersion but deteriorated durability due to the reduced carbon corrosion resistance. The experimental results also showed that despite the surface oxidation, Pt/MWCNT catalysts showed highly improved durability than Pt/C catalysts due to the graphitic nature of MWCNTs. Membrane electrode assembly (MEA) fabricated by 4 h acid treated MWCNTs at 25 °C showed 4 times better durability than commercial Pt/C based MEA at the reverse potential operation generated by fuel starvation conditions. We believe that MWCNTs can be effectively used for PEMFCs even at high loading due to their excellent anti-corrosion properties.     

Deposition of silver nanoparticles on dendrimer functionalized multiwalled carbon nanotubes: synthesis, characterization and antimicrobial activity

The nanohybrids composed of silver nanoparticles and aromatic polyamide functionalized multiwalled carbon nanotubes (MWCNTs) is successfully synthesized and tested for their antibacterial activity against different pathogens. Prior to deposition of silver nanoparticles, acid treated MWCNTs (MWCNTs-COOH) were successively reacted with p-phenylenediamine and methylmethacrylate to form series of NH2-terminated aromatic polyamide dendrimers on the surface of MWCNTs through Michael addition and amidation. Existence of high abundance of amine groups on the surface of functionalized MWCNTs (f-MWCNTs) provided sites for formation of silver nanoparticles by the reduction of aqueous solution of AgNO3. The silver nanoparticles formed in the resulted f-MWCNTs-Ag nanohybrids were determined to be face centered cubic (fcc) symmetry. The structure and nature of f-MWCNTs and f-MWCNTs-Ag nanohybrids were characterized by UV-vis spectroscopy, Fourier transform infrared spectroscopy (FTIR), powder X-ray diffraction analysis (XRD), Raman spectroscopy and thermogravimetric analysis (TGA). The dispersion state of f-MWCNTs and immobilization of silver nanoparticles on the surface of f-MWCNTs were investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Elemental composition of f-MWCNTs-Ag nanohybrids was determined by energy dispersive X-ray spectroscopy (EDS). The antimicrobial activity of f-MWCNTs-Ag nanohybrids were estimated against E. coli, P. aeruginosa and S. aureu and compared with MWCNTs-COOH and f-MWCNTs. The results indicate that functionalization of MWCNTs with aromatic polyamide dendrimers and successive deposition of Ag nanoparticles could play an important role in the enhancement of antimicrobial activity.     

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.     

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.     

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.     

Synthesis and electrocatalytic oxygen reduction properties of truncated octahedral Pt3Ni nanoparticles

Pt₃Ni nanoparticles have been obtained by shape-controlled synthesis and employed as oxygen reduction electrocatalysts for proton exchange membrane fuel cells (PEMFC). The effects of varying the synthesis parameters such as the types of the capping agent and the reducing agent, and the reaction time have been systematically studied. The as-prepared Pt₃Ni nanoparticles were subjected to a butylamine-based surface treatment in order to prepare carbon-supported electrocatalysts. The Pt₃Ni electrocatalysts show an areaspecific activity of 0.76 mA/cm²(Pt) at 0.9 V in an alkaline electrolyte, which is 4.5 times that of a commercial Pt/C catalyst (0.17 mA/cm² (Pt)). The mass activity reached 0.30 A/mg(Pt) at 0.9 V, which is about twice that of the commercial Pt/C catalyst. Our results also show that the area-specific activities of these carbon-supported Pt₃Ni electrocatalysts depend strongly on the (111) surface fraction, which is consistent with the results of a study based on Pt₃Ni extended single-crystal surfaces.     

Design of an Assembly of Poly(benzimidazole), Carbon Nanotubes,and Pt Nanoparticles for a Fuel‐Cell Electrocatalyst with an Ideal Interfacial Nanostructure

A newly designed and fabricated novel nanocomposite composed of multiwalled carbon nanotubes (MWNTs), poly(benzimidazole) (PBI), and Pt nanoparticles. This composite is fabricated by the preparation of PBI‐wrapped MWNTs (MWNT/PBI), followed by Pt loading onto the MWNT/PBI. As a result of the PBI wrapping, the loading efficiency of the Pt nanoparticles onto the MWNTs is dramatically improved up to 58.8% compared to that of the pristine MWNTs (41.0%). The process also allows homogeneous Pt immobilization onto the surface of MWNTs without any strong oxidation process for the MWNTs that is typically used for metal supporting on carbon nanotubes. Far‐IR spectroscopy of the composite shows a peak from the Pt? N bonding, indicating that these improvements are derived from the coordination of the Pt ion with the PBI molecules. Cyclic voltammogram measurements reveal that the Pt nanoparticles deposited on the MWNT/PBI shows higher utilization efficiency (74%) for electrocatalysts compared to that on the pristine MWNT (39%).     

Preparation of a platinum electrocatalyst by coaxial pulse arc plasma deposition

Abstract

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.     

Layer-by-layer assemblies of chitosan/multi-wall carbon nanotubes and glucose oxidase for amperometric glucose biosensor applications

A novel amperometric glucose biosensor based on multilayer films containing chitosan, multi-wall carbon nanotubes (MWCNTs) and glucose oxidase (GOD) was developed. MWCNTs were solubilized in chitosan (Chit-MWCNTs) used to interact with GOD. Poly (allylamine) (PAA) and polyvinylsulfuric acid potassium salt (PVS) were alternately deposited on the cleaned Pt electrode surface ((PVS/PAA)₃/Pt). The (PVS/PAA)₃/Pt electrode was alternately immersed in Chit-MWCNTs and GOD to assemble different layers of multilayer films. PBS washing was applied at the end of each assembly deposition for dissociating the weak adsorption. Micrographs of MWCNTs were obtained by scanning electron microscope, and properties of the resulting biosensors were measured by electrochemical measurements. Among the resulting biosensors, the biosensor based on eight layers of multilayer films was best. The resulting biosensor was able to efficiently monitor glucose, with the response time within 8 s, a detection limit of 21 μM estimated at a signal-to-noise ratio of 3, a linear range of 1–10 mM, the sensitivity of 0.45 μA/mM, and well stability. The study can provide a feasible simple approach on developing a new immobilization matrix for biosensors and surface functionalization.     

Decoration of single-walled carbon nanotubes with Pt nanoparticles from an organometallic precursor

Carbon nanotubes (CNTs) are nanomaterials of high interest due to their unique structural, electrical, and mechanical properties. Carbon materials have been widely employed to support metallic nanoparticles for catalysis and electrochemical applications. In this work, we investigated the synthesis of platinum nanoparticles generated from the complex Pt₂(dba)₃ (tris(dibenzylideneacetone) diplatinum) and stabilized with a long alkyl chain amine, hexadecylamine (HDA) and supported on functionalized single-walled carbon nanotubes (SWCNTs). High resolution transmission electron microscopy (HRTEM) studies revealed isolated Pt nanoparticles (2?C3 nm) on SWCNTs. Powder X-ray diffraction (XRD) was used to assess the structure of Pt nanoparticles dispersed on SWCNTs assigned to Pt face-centered cubic (fcc). Additionally, infrared Fourier transform spectroscopy confirmed the presence of the stabilizer at the surface of the Pt nanoparticles even after the purification step and functional groups at the surface of pre-treated SWCNTs. This synthetic method may be an alternative route to prepare small size Pt nanoparticles supported on functionalized SWCNTs.     

Synthesis of Pt/PEI-MWCNT composite materials on polyethyleneimine-functionalized MWNTs as supports

Composite materials with highly dispersed platinum (Pt) nanoparticles on multiwalled carbon nanotubes (MWCNTs), functionalized with polyethyleneimine (PEI) by a noncovalent method were prepared. The PEI-functionalization provided high density homogeneous functional groups on the MWCNTs’ sidewalls for binding Pt nanoparticles. Cationic PEI leads to homogeneous dispersion in solutions such as water and organic solvents. The effects of a reducing agent on the Pt nanoparticles that form on the surfaces of the MWCNT were studied by varying the molar ratio of NaOH to H₂PtCl₆. These composite materials were characterized with transmission electron micrograph (TEM), X-ray diffractometer (XRD) and X-ray photoelectron spectroscopy (XPS). The Pt/PEI-MWCNT catalyst exhibits excellent electrocatalytic activity and compared with Pt/PVP-MWCNT catalysts obtained with polyvinylpyrrolidone (PVP). Finally, the cyclic voltammogram of methanol electrooxidation for Pt/PEI-MWCNT shows better tolerance to CO and methanol oxidation to CO₂ than of Pt/PVP-MWCNT.     

Direct Synthesis of Ultrathin Pt Nanowire Arrays as Catalysts for Methanol Oxidation

High‐performance electrocatalysts are of critical importance for fuel cells. Morphological modulation of the catalyst materials is a rare but feasible strategy to improve their performance. In this work, Pt nanowire arrays are directly synthesized with a template‐less wet chemical method. The effects of surface functionalization and the reduction kinetics are revealed to be vital to the nanowire growth. The growth mechanism of the Pt nanowires is studied. By adjusting the concentration of the organic ligands, Pt nanowire arrays with tunable surface roughness can be obtained on various substrate surfaces. Such arrays avoid the contact resistance of randomly packed particles and allow open diffusion channels for reactants and products alike, making them excellent electrocatalysts for the methanol oxidation reaction. In particular, Pt nanowire arrays with rough surface have a mass activity of 1.24 A mg_Pt^?1 at 1.12 V (vs Ag/AgCl), 3.18‐fold higher than that of the commercial Pt/C catalysts. It also shows more resistant against poisoning, as indicated by the higher I_f/I_b ratio (2.06), in comparison to the Pt/C catalysts (1.30).     

Pt Single Atoms on CrN Nanoparticles Deliver Outstanding Activity and CO Tolerance in the Hydrogen Oxidation Reaction

The large-scale application of proton exchange membrane fuel cells is currently hampered by high cost of commercial Pt catalysts and their susceptibility to poisoning by CO impurities in H₂ feed. In this context, the development of CO-tolerant electrocatalysts with high Pt atom utilization efficiency for hydrogen oxidation reaction (HOR) is of critical importance. Herein, Pt single atoms are successfully immobilized on chromium nitride nanoparticles by atomic layer deposition method, denoted as Pt SACs/CrN. Electrochemical tests establish Pt SACs/CrN to be a very efficient HOR catalyst, with a mass activity that is 5.7 times higher than commercial PtRu/C. Strikingly, the excellent performance of Pt SACs/CrN is maintained after introducing 1000 ppm of CO in H₂ feed. The excellent CO-tolerance of Pt SACs/CrN is related to weaker CO adsorption on Pt single atoms. This work provides guidelines for the design and construction of active and CO-tolerant catalysts for HOR.     

碳纳米管载体改性条件对Pt纳米粒子电催化氧化性能的影响

利用紫外光照射诱导亚甲基蓝改性碳纳米管(MWCNTs), 是一种工艺简单、绿色无毒的改性催化剂碳载体的新方法。本研究以光照改性时间、改性剂(亚甲基蓝)用量和紫外光波长为主要影响因素, 系统研究了不同因素对MWCNTs改性的影响及其对催化剂催化性能的影响。利用透射电子显微镜(TEM)对不同条件下的催化剂形貌进行了表征, 采用循环伏安法(CV)和时间电流法(i-t)等电化学测试手段对催化剂在碱性介质中催化氧化甲醇的催化活性和催化稳定性分别进行了测试, 研究结果表明: 光照时间为6 h、亚甲基蓝用量为10 mg、紫外光波长采用254 nm时, MWCNTs的改性效果最佳, Pt纳米粒子在改性最佳的MWCNTs表面的负载均匀性最好, 所得催化剂的催化性能也最优, 其催化活性是商业Pt/C催化剂的2倍多, 这种改性方式为高活性、低成本燃料电池阳极催化剂的研究提供了新方法。     

Polyaniline/Pt Hybrid Nanofibers: High‐Efficiency Nanoelectrocatalysts for Electrochemical Devices

A simple and facile procedure to synthesize a novel hybrid nanoelectrocatalyst based on polyaniline (PANI) nanofiber‐supported supra‐high density Pt nanoparticles (NPs) or Pt/Pd hybrid NPs without prior PANI nanofiber functionalization at room temperature is demonstrated. This represents a new type of 1D hybrid nanoelectrocatalyst with several important benefits. First, the procedure is very simple and can be performed at room temperature using commercially available reagents without the need for templates and surfactants. Second, ultra‐high density small “bare” Pt NPs or Pt/Pd hybrid NPs are grown directly onto the surface of the PANI nanofiber, without using any additional linker. Most importantly, the present PANI nanofiber‐supported supra‐high density Pt NPs or Pt/Pd hybrid NPs can be used as a signal enhancement element for constructing electrochemical devices with high performance.     

Low-temperature synthesis of Mn(3)O(4) nanoparticles loaded on multi-walled carbon nanotubes and their application in electrochemical capacitors

A low-temperature, efficient and one-step deposition method, in which Mn(CH(3)COO)(2)·4H(2)O serves as precursor and O(2) as oxidant, was employed to deposit Mn(3)O(4) nanoparticles on multi-walled carbon nanotubes (MWCNTs) in ethanol solution at 150 and 200?°C. The resulting Mn(3)O(4)/MWCNT composites were characterized by means of different techniques including x-ray diffraction, x-ray photoelectron spectroscopy and transmission electron microscopy. It was indicated that the Mn(3)O(4) nanoparticles were attached uniformly on MWCNTs with sizes less than 10?nm, and the loading amount of Mn(3)O(4) could be tuned by changing the initial weight ratio of Mn(CH(3)COO)(2)·4H(2)O/MWCNT. The electrochemical behavior of the Mn(3)O(4)/MWCNT composites was examined by cyclic voltammetry, and the result indicated the specific capacitance of the composite electrode was 330?F?g(-1), nearly 18 times higher than that of the pure MWCNT electrode. The good performance of the as-prepared composites as electrode material may be attributed to the synergistic effects of the Mn(3)O(4) nanoparticles and the MWCNTs.     

Synthesis of platinum nanoparticles by aerosol assisted deposition method

An atmospheric pressure aerosol assisted deposition method has been developed to grow highly oriented nanoparticles and thin continuous films of platinum on a variety of substrates for applications such as catalysts including their use in proton exchange membrane fuel cells. Pt nanoparticles with sizes ranging from 4 nm to 78 nm were synthesized on Si, silicon dioxide coated Si substrates and carbon nanotubes. The size and density of the nanoparticles was found to depend strongly on the precursor carrier gas flow rate and deposition time. The particles showed preferential orientation of (111) that was independent of substrate used. The resulting nanoparticles were characterized by Scanning Electron Microscopy, X-ray Diffraction Spectroscopy and X-ray Photoelectron Spectroscopy in order to obtain information about their morphology, crystallinity and composition. The method developed can deposit uniform coatings of highly oriented, pure Pt nanoparticles without the need of any substrate pretreatment such as surface functionalization, deposition of seed layer for electrodeposition on insulating or semiconducting substrates, and without the use of expensive vacuum equipment.     

Synthesis,characterization and comparison of polythiophene–carbon nanocomposite materials as Pt electrocatalyst supports for fuel cell applications

A novel polymer–carbon (PTh–C) nanocomposites containing different percentages of polythiophene (10, 20 and 50% (w/w)) and carbon (Vulcan XC-72) was prepared by a facile solution dispersion method and used to support platinum nanoparticles. The effect of using different percentages of polythiophene in nanocomposites and subsequently prepared electrocatalysts was investigated. The resultant electrocatalysts were extensively characterized by physical (X-ray diffraction (XRD) and transmission electron microscopy (TEM)) and electrochemical (cyclic voltammetry (CV)) techniques. The TEM results showed that the fine Pt nanoparticles prepared by ethylene glycol (EG) method were distributed on the surface of the 50% PTh–C nanocomposites successfully. From the XRD patterns, the average size of dispersed Pt nanoparticles with the face-centered cubic (fcc) structure on 50% PTh–C, 20% PTh–C, 10% PTh–C and carbon were about 4.9, 5.2, 5.4 and 6.1 nm, respectively. The conductivity of PTh–C with different percentages of pure PTh was compared with the conductivity of the corresponding support of pure PTh. It is observed that the conductivity of 50% PTh–C nanocomposites is about 600 times higher than that of pure PTh. Finally, CV measurements of hydrogen and methanol oxidations indicated that Pt/50% PTh–C had a higher electrochemical surface area and higher catalytic activity for methanol oxidation reaction compared to other electrocatalysts. These measurements showed that the Pt/50% PTh–C electrocatalyst by the value of 3.85 had higher \(I_{\mathrm{f}}/I_{\mathrm{b}}\) ratio with respect to Pt/10% PTh–C and Pt/20% PTh–C by the values of 2.66 and 2.0, respectively.