Carbon oxidation with platinum supported catalysts

The effect of the support oxide, Pt precursor and reactant gas composition on the catalysis of soot oxidation was investigated using carbon black as a model soot and simulated exhaust gases. The Pt precursors used were Pt(NH₃)₄(OH)₂, H₂PtCl₆·6H₂O, Pt(NH₃)₄(NO₃)₂, and Pt(NH₃)₄Cl₂. The support metal oxides used were SiO₂, Al₂O₃, and ZrO₂. Pt/SiO₂ prepared from Pt(NH₃)₄(OH)₂ showed the highest carbon oxidation activity. It had much higher activity in the condition of N₂+O₂+H₂O+NO+SO₂ than without NO and SO₂.     

Atomic layer deposition of TiO2 on carbon-nanotubes membrane for capacitive deionization removal of chromium from water

Chromium (Cr) is a common heavy metal that has severe impacts on the ecosystem and human health. Capacitive deionization (CDI) is an environment-friendly and energy-efficient electrochemical purification technology to remove Cr from polluted water. The performance of CDI systems relies primarily on the properties of electrodes. Carbon-nanotubes (CNTs) membranes are promising candidates in creating advanced CDI electrodes and processes. However, the low electrosorption capacity and high hydrophobicity of CNTs greatly impede their applications in water systems. In this study, we employ atomic layer deposition (ALD) to deposit TiO₂ nanoparticulates on CNTs membranes for preparing electrodes with hydrophilicity. The TiO₂-deposited CNTs membranes display preferable electrosorption performance and reusability in CDI processes after only 20 ALD cycles deposition. The total Cr and Cr(VI) removal efficiencies are significantly improved to 92.1% and 93.3%, respectively. This work demonstrates that ALD is a highly controllable and simple method to produce advanced CDI electrodes, and broadens the application of metal oxide/carbon composites in the electrochemical processes.     

Highly dispersed Pt nanoparticles by pentagon defects introduced in bamboo-shaped carbon nanotube support and their enhanced catalytic activity on methanol oxidation

Bamboo-shaped carbon nanotubes (BCNTs), which were synthesized through chemical vapor deposition by using cresol as the carbon source, were explored as Pt catalyst support in comparison with conventional carbon nanotubes (CNTs) and Vulcan XC carbon blacks. The pyrolysis of cresol produced a large amount of pentagon defects introduced in the walls of BCNTs, which could possess higher chemical activity and stronger interaction with metal particles. After a mild purification, the BCNTs exhibited more oxygen-containing functional groups than CNTs, as shown by Fourier transform infrared spectra and cyclic voltammetry. The formed oxygen-containing functional groups as well as the pentagon defects could act as uniform active sites for metal particle loading. By ethylene glycol reduction, highly dispersed Pt nanoparticles with a narrow size distribution of 2-3 nm were easily supported on BCNTs, as shown by transmission electron microscope. The Pt/BCNT catalyst showed higher electro-catalytic activity on the methanol oxidation than the Pt/CNT and Pt/Vulcan XC catalyst, which could be largely ascribed to the highly dispersed Pt nanoparticles due to the introduced pentagon defects in the tube-walls (comparing with Pt/CNT) and the graphitic nanotube network that could provide good electron conduction (comparing with Pt/Vulcan XC).     

Microemulsions in the preparation of highly active combustion catalysts

Catalytic activity in combustion of toluene in toluene–air mixtures and physical–chemical properties of platinum catalysts prepared from reverse microemulsions (water-in-oil) and by classical impregnation from water solutions of H₂PtCl₆ were studied. Microemulsion catalysts were more active than those prepared classically from water solutions. Size of Pt in classically impregnated catalysts was three times higher than that of catalysts prepared from microemulsions. In case of microemulsion preparation method, platinum is located near the pellet surface or its position in the pellet can be optimised. The effect of oil used in microemulsion system seems to be negligible for the activity of the catalysts with 0.1 wt.% Pt.     

The effect of the Pt deposition method and the support on Pt dispersion on carbon nanotubes

Carbon nanotube supported platinum (Pt/CNTs) catalysts prepared by different Pt deposition methods and on different CNT supports were studied. Colloidal based methods were demonstrated to be more effective than other wet chemistry deposition methods (e.g., impregnation and precipitation) for the preparation of highly dispersed Pt/CNTs. Pt catalyst supported on CNTs with a dispersion uniformity comparable to that supported on carbon powder was achieved using a zwitterionic surfactant 3-(N,N-dimethyldodecylammonio) propanesulfonate (SB12) as stabilizer in a monitored pH environment. It was experimentally observed that oxygen-containing surface functionalities on CNTs can greatly affect the catalyst particle dispersion by manipulating Pt anchoring and/or nucleating sites. Furthermore, it was revealed that the performance of Pt/CNTs based fuel cell is strongly dependent on the electrode fabrication method.     

In situ grown carbon nanotubes on carbon paper as integrated gas diffusion and catalyst layer for proton exchange membrane fuel cells

In situ grown carbon nanotubes (CNTs) on carbon paper as an integrated gas diffusion layer (GDL) and catalyst layer (CL) were developed for proton exchange membrane fuel cell (PEMFC) applications. The effect of their structure and morphology on cell performance was investigated under real PEMFC conditions. The in situ grown CNT layers on carbon paper showed a tunable structure under different growth processes. Scanning electron microscopy (SEM) and Brunauer–Emmett–Teller (BET) demonstrated that the CNT layers are able to provide extremely high surface area and porosity to serve as both the GDL and the CL simultaneously. This in situ grown CNT support layer can provide enhanced Pt utilization compared with the carbon black and free-standing CNT support layers. An optimum maximum power density of 670 mW cm⁻² was obtained from the CNT layer grown under 20 cm³ min⁻¹ C₂H₄ flow with 0.04 mg cm⁻² Pt sputter-deposited at the cathode. Furthermore, electrochemical impedance spectroscopy (EIS) results confirmed that the in situ grown CNT layer can provide both enhanced charge transfer and mass transport properties for the Pt/CNT-based electrode as an integrated GDL and CL, in comparison with previously reported Pt/CNT-based electrodes with a VXC72R-based GDL and a Pt/CNT-based CL. Therefore, this in situ grown CNT layer shows a great potential for the improvement of electrode structure and configuration for PEMFC applications.     

微乳液法制备Pt/Al2O3催化剂及其催化氯代硝基苯选择加氢活性

采用十六烷基三甲基溴化铵（CTAB）/正丁醇/环己烷/H₂PtCl₆溶液的微乳体系,以N₂H₄·H₂O为还原剂,Al₂O₃为载体制备Pt/Al₂O₃催化剂。以邻氯硝基苯（o-CNB）选择加氢反应为探针,考察微乳液组成对Pt/Al₂O₃催化剂选择加氢活性的影响。运用XRD、XPS、IR、TEM和EDS对载体和催化剂进行表征。结果表明,微乳体系中CTAB∶正丁醇∶环己烷质量比9∶21∶70,3.6% H₂PtCl₆溶液中制备的Pt/Al₂O₃催化剂的o-CNB选择加氢活性最高。Pt粒子粒径5 nm左右,与载体之间没有明显的电子效应。对于取代位置不同的间、对氯硝基苯（m-CNB、p-CNB）加氢,Pt/Al₂O₃催化剂也表现出较高的催化活性。     

Electrochemical deposition of Pt nanoparticles on CNTs for fuel cell electrode

In order to increase the performance of fuel cell electrode, carbon nanotubes (CNTs) were used as support instead of conventional carbon black, and the Pt catalyst was synthesized by using electrochemical deposition (ECD) method which has recently been adopted as a synthetic tool of metal nanoparticles. CNTs used in this paper were grown directly on carbon paper by chemical vapor deposition (CVD) of acetylene. Highly dispersed and nano-sized Pt particles were electrochemically deposited on CNTs surface, which would simplify the manufacturing process of membrane-electrode-assembly (MEA). Pt particles on CNTs were investigated by SEM and TEM. The particle size of Pt is less than 2 nm, which is relatively small compared to that of conventional wet impregnated catalyst (2–8 nm). CO chemisorption results show that the amounts of catalytic sites are about three times larger in Pt/CNT prepared by ECD than those in conventional wet-impregnated one. The mass activity of the former catalyst for oxygen reduction is more than three times higher compared to that of the latter one. This paper was presented at the 11th Korea-Japan Symposium on Catatysis held at Seoul, Korea, May 21–24, 2007.     

Dehalogenative oligomerization of dichlorodifluoromethane catalyzed by activated carbon-supported Pt–Cu catalysts: effect of Cu to Pt atomic ratio

Activated carbon-supported Pt–Cu catalysts with a Cu to Pt atomic ratio in the range of 2–18 catalyze the formation of oligomerization hydrocarbon products from an equimolar mixture of CF₂Cl₂ and H₂ at 523 K. The steady-state selectivity toward C₂₊ products is 42% for the Pt1Cu2/C and increases to more than 70% when the Cu/Pt atomic ratio reaches 18:1. All catalysts deactivate with time on stream. The results of the TEM investigation are consistent with the suggestion that deactivation is attributed to carbon deposition and not to particle sintering. All of the catalysts have approximately the same average size of Pt-containing particles, independent of Cu/Pt atomic ratio, and the average size is essentially the same for the freshly reduced and used Pt–Cu catalysts. As the Cu to Pt atomic ratio is increased, a larger fraction of Cu is unalloyed with Pt. The performance of the catalysts in the CF₂Cl₂+H₂ reaction is discussed in terms of the different active sites, which catalyze different elementary reaction steps.     

Preparation of Pt-based catalyst by reverse microemulsion and its selective hydrogenation performance

采用反相（W/O）微乳液法制备负载型Pt基催化剂,以间氯硝基苯（m-CNB）选择加氢反应为探针,考察微乳液组成、助表面活性剂和油相种类、还原剂用量及载体种类等制备参数对催化剂活性的影响,并对Pt粒子及催化剂进行TEM表征。结果表明：选择十六烷基三甲基溴化胺（CTAB）/正丁醇/环己烷/H₂PtCl₆溶液的W/O微乳体系,m(CTAB)∶m(正丁醇)=3∶7,m(CTAB+正丁醇)∶m(环己烷)=3∶7,H₂PtCl₆溶液含量3.6%,N₂H₄·H₂O用量100 μL时制备的Pt/γ-Al₂O₃催化剂对m-CNB选择加氢活性最高。TEM分析表明催化剂中Pt粒子均匀分散在载体上。     

Synergistic effects of hybrid carbon nanomaterials in room‐temperature‐vulcanized silicone rubber

This work examines nanocomposites based on nanofillers and room‐temperature‐vulcanized silicone rubber. The carbon nanofillers used were conductive carbon black (CB), carbon nanotubes (CNTs) and graphene (GE). Vulcanizates for CB, GE, CNTs as the only filler and hybrid fillers using CNTs, CB and GE were prepared by solution mixing. The elastic modulus for CNT hybrid with CB at 15 phr (4.65 MPa) was higher than for CB hybrid with GE (3.13 MPa) and CNTs/CB/GE as the only filler. Similarly, the resistance for CNT hybrid with CB at 10 phr (0.41 kΩ) was lower than for CB (0.84 kΩ) at 20 phr and CNTs as the only filler. These improvements result from efficient filler networking, a synergistic effect among the carbon nanomaterials, the high aspect ratio of CNTs and the improved filler dispersion in the rubber matrix. © 2016 Society of Chemical Industry     

Synthesis of high surface area supported Pt/SiO2 catalysts from H2PtCl6·6H2O by the sol-gel method

A new method has been used to prepare highly dispersed Pt/SiO₂ catalysts. The method is based on the use of metal alcoxides together with the appropriate metal precursor. In particular, H₂PtCl₆·6H₂O and tetraethoxysilane were used to prepare supported Pt/SiO₂ catalysts with a BET surface area in excess of 1000 m²/g. Catalysts prepared by this method were observed to resist deactivation by sintering and coke formation and were observed to have a high selectivity in the hydrogenation of phenylacetylene to styrene.     

A novel high-performance counter electrode for dye-sensitized solar cells

A novel Pt counter electrode for dye-sensitized solar cells (DSC) was prepared by thermal decomposition of H₂PtCl₆ on NiP-plated glass substrate. The charge-transfer kinetic properties of the platinized NiP-plated glass electrode (Pt/NiP electrode) for triiodide reduction were studied by electrochemical impedance spectroscopy. Pt/NiP electrode has the advantage over the platinized FTO conducting glass electrode (Pt/FTO electrode) in increasing the light reflectance and reducing the sheet resistance leading to improve the light harvest efficiency and the fill factor of the dye-sensitized solar cells effectively. The photon-to-current efficiency and the overall conversion efficiency of DSC using Pt/NiP counter electrode is increased by 20% and 33%, respectively, compared to that of using Pt/FTO counter electrode. Examination of the anodic dissolution and the long-term test on the variation of charge-transfer resistance indicates the good stability of the Pt/NiP electrode in the electrolyte containing iodide/triiodide.     

One- and two-dimensional carbon nanomaterials as counter electrodes for dye-sensitized solar cells

This study examines the dye-sensitized solar cells (DSSCs) equipped with 1-D carbon nanotubes (CNTs) and 2-D graphene nanosheets (GNs) carbon counter electrodes. Imperfect defects were attached to the sidewall or both the ends of the CNTs, and the edges of the GNs were analyzed by X-ray diffraction and Raman spectroscopy. When compared with the GN-based counter electrode, CNT-based counter electrodes showed a better improvement in the incident photon-to-current efficiency and power conversion efficiency of the cells. This enhancement of cell performance can be attributed to the combination of CNT network and spherical graphite bottom layer, favoring dye adsorption, catalytic redox activity, and 1-D charge-transfer path length. Such carbon configuration as counter electrode provides a potential feasibility for replacing metallic Pt counter electrodes.     

Slipping of carbon nanotubes in a rubber matrix

The interactions of carbon nanotubes (CNTs) and carbon black (CB) with rubber matrices are of great interest. Although both belong to the carbon filler family, their interactions are different. In this study the adhesion of CNTs, if any, with natural rubber (NR) was examined. Scanning electron microscopy examinations made on cryogenically fractured surfaces of a crosslinked NR sample containing 7% by weight of CNTs showed that the CNT bundles emerged from the side surface (narrowed by Poisson's ratio) and slowly slid back in when the deformation was removed. The protruded lengths were many times larger than the nanotube bundle diameters. This extensive slipping out of CNTs from the rubber matrix suggests that interfacial interactions between CNTs and NR are quite weak. In contrast, relatively strong interactions were found between CB and rubber, indicated by the large amount of bound rubber formation. Reinforcement of rubber by CNTs is therefore attributed to the large aspect ratio of CNT bundles. Physical entanglement with rubber molecules is then able to generate effective load transfer, replacing the strong adhesion found with CB. Copyright © 2010 Society of Chemical Industry     

Pd–Pt/Al2O3 bimetallic catalysts for the advanced oxidation of reactive dye solutions

The Pd–Pt/Al₂O₃ bimetallic catalysts showed high activities toward the wet oxidation of the reactive dyes in the presence of 1% H₂ together with excess oxygen. Palladium was believed to act as a co-catalyst to spillover the adsorbed H₂ onto the surface of the oxidized Pt surface, and thereby the reducibility of the Pt increased greatly. The organic dye molecule adsorbed on the reduced Pt surface more easily than the oxidized Pt surface under the competition with excess oxygen, which is an essential step for the catalytic wet oxidation (CWO). The Pd–Pt/Al₂O₃ catalysts also produced H₂O₂ from H₂/O₂ mixture, and the hydroxyl radical was formed through the subsequent decomposition of H₂O₂. Additional oxidation of the reactive dyes was obtained with hydroxyl radical. The high activities of the Pd–Pt/Al₂O₃ catalysts were believed to be due to the combined effects of the faster redox cycle resulting from the increased reducibility of Pt surface and the additional oxidation of the reactive dyes with hydroxyl radical.     

Influence of Pyridine‐Polybenzimidazole Film Thickness of Carbon Nanotube Supported Platinum on Fuel Cell Applications

Pyridine‐polybenzimidazole (PyPBI) films of different thickness (∼1.0–2.4 nm) are wrapped on the surfaces of multi‐walled carbon nanotubes (CNTs). To prepare Pt on PyPBI/CNT (Pt‐PyPBI/CNT) catalysts, Pt⁴⁺ ions are immobilized on these PyPBI wrapped CNTs (PyPBI/CNTs) via Lewis acid‐base coordination between Pt⁴⁺ and :N‐ of imidazole groups, followed by reducing Pt⁴⁺ to Pt nanoparticles. The influence of PyPBI film thickness on the Pt particle size, loading and electrochemical surface area, respectively, of Pt‐PyPBI/CNTs is investigated. Fuel cell performances of the PBI/H₃PO₄ based membrane electrode assemblies (MEAs) prepared from these Pt‐PyPBI/CNT catalysts are also evaluated at 160 °C with unhumidified H₂/O₂ gases. Among the catalysts, the Pt‐PyPBI/CNT catalyst with a PyPBI film thickness of ∼1.6 nm (which is around half of the Pt particle size), a Pt loading of ∼44 wt.%, and a Pt particle size of ∼3.3 nm exhibits the best fuel cell performance.     

掺硫碳纳米管作导电添加剂改进磷酸锰铁锂电化学性能

磷酸锰铁锂(LMFP)具有比磷酸铁锂(LFP)更高的能量密度,但因电导率更低,倍率性能较差。本文采用掺硫碳纳米管提升LMFP电极的导电性能,有效提高了LMFP电极的能量密度和功率密度。首先,以亚硫酸钙热解产生的SO₂为掺杂剂,对碳纳米管(CNT)进行气相掺硫处理得到掺硫碳纳米管(SCNT)。与未掺杂CNT相比,SCNT表现出更好的亲水性和导电性。将SCNT水相分散液作为导电添加剂,以水为溶剂制备LMFP电极,分别在室温和-10℃的低温环境下进行倍率性能、循环性能和交流阻抗等测试。结果表明,添加SCNT作导电剂有效提高了LMFP电极的导电性和动力学速率,添加SCNT的LMFP电极在0.2C和5C下可逆容量分别为200 mAh/g和145 mAh/g,显著高于添加了CNT或CB导电剂的LMFP电极。将添加SCNT的LMFP电极与石墨匹配组装全电池,表现出185.0 Wh/kg和665.5 W/kg的超高能量密度和功率密度。     

Influence of chemisorbed carbon monoxide on the impedance of a smooth Pt wire at cathodic polarization in sulfuric acid solution

The ohmic and capacitive components of the impedance of a smooth Pt wire electrode were measured at a cathodic current density of −1 mA cm⁻² at frequencies ν between 10,000 and 25 Hz at different coverages of chemisorbed carbon monoxide in 0.5 M H₂SO₄. The linear dependence upon ω^−1/2, characteristic for predominant H₂ diffusion on clean Pt electrodes, disappears at carbon monoxide coverages above 0.2. The hindrance of the H₂ evolution reaction increases with the coverage of CO_ad in a gradual fashion below 0.7 and rapidly at larger coverages. The hindrance is considerably larger on the Pt wire than on Pt foils, investigated previously. The change of the attenuation factor, caused by the blocking of the free surface, cannot account for the observed effect on the Pt wire electrode. Simple models, based on the Volmer—Tafel or Volmer—Heyrovsky mechanisms for H₂ evolution, cannot describe the experimental frequency dependence of the impedance at coverages above 0.2.     

Electrophoretic deposition of carbon nanotube–ceramic nanocomposites

The purpose of this paper is to present an up-to-date comprehensive overview of current research progress in the development of carbon nanotube (CNT)–ceramic nanocomposites by electrophoretic deposition (EPD). Micron-sized and nanoscale ceramic particles have been combined with CNTs, both multiwalled and single-walled, using EPD for a variety of functional, structural and biomedical applications. Systems reviewed include SiO₂/CNT, TiO₂/CNT, MnO₂/CNT, Fe₃O₄/CNT, hydroxyapatite (HA)/CNT and bioactive glass/CNT. EPD has been shown to be a very convenient method to manipulate and arrange CNTs from well dispersed suspensions onto conductive substrates. CNT–ceramic composite layers of thickness in the range <1–50 μm have been produced. Sequential EPD of layered nanocomposites as well as electrophoretic co-deposition from diphasic suspensions have been investigated. A critical step for the success of EPD is the prior functionalization of CNTs, usually by their treatment in acid solutions, in order to create functional groups on CNT surfaces so that they can be dispersed uniformly in solvents, for example water or organic media. The preparation and characterisation of stable CNT and CNT/ceramic particle suspensions as well as relevant EPD mechanisms are discussed. Key processing stages, including functionalization of CNTs, tailoring zeta potential of CNTs and ceramic particles in suspension as well as specific EPD parameters, such as deposition voltage and time, are discussed in terms of their influence on the quality of the developed CNT/ceramic nanocomposites. The analysis of the literature confirms that EPD is the technique of choice for the development of complex CNT–ceramic nanocomposite layers and coatings of high structural homogeneity and reproducible properties. Potential and realised applications of the resulting CNT–ceramic composite coatings are highlighted, including fuel cell and supercapacitor electrodes, field emission devices, bioelectrodes, photocatalytic films, sensors as well as a wide range of functional, structural and bioactive coatings.