Self-assembly of palladium nanoparticles on functional multi-walled carbon nanotubes for formaldehyde oxidation

In this work, we report a concise method to self-assemble Pd nanoparticles onto the surface of MWNTs. Highly dispersed palladium nanoparticles are loaded on the MWNTs functionalized with mercaptobenzene moieties. The structure of the resulting Pd–fMWNT composite were characterized by transmission electron microscopy (TEM), the results show that the chemically synthesized Pd nanoparticles were homogeneously dispersed and well-separated from one another on the functional MWNT surfaces. Cyclic voltammogram (CV) showed that Pd–fMWNT composite materials perform excellent electrocatalytic activity and long-term stability toward formaldehyde oxidation. Electrochemical impedance spectroscopy (EIS) revealed the strong interaction between fMWNTs and Pd facilitates the effective degree of electron dolocalization, and thus enhances the conductivity of the composite. The results imply that the self-organized Pd–fMWNT composite as a promising support material shows the excellent electrocatalytic activity and has a promising application potential in fuel cells and biosensors.     

Temperature-dependent hydrogen storage mechanism in palladium nanoparticles decorated on multi-walled carbon nanotubes

In this study, Palladium (Pd) nanoparticles (NPs) are decorated on the multi-walled carbon nanotubes (MWCNTs) using the chemical reduction method. In situ extended x-ray absorption fine structure (EXAFS) spectroscopy of Pd NPs decorated on MWCNTs is carried out in different temperatures from 77 K up to 540 K to investigate the local structure around the absorber atom Pd, under molecular hydrogen, H₂, pressure, and in a vacuum. The Pd K-edge EXAFS gives a deeper insight into the structural properties of Pd-MWCNT compounds under in-situ H₂ treatment at various temperatures. EXAFS data show three mechanisms of the interaction of H₂ with Pd: the first mechanism involves physical absorption of H₂ at low temperatures from 110 to 190 K, the second mechanism includes the formation of PdH_x compound at 300 K, and the third mechanism is attributed to the decomposition of PdH_x compound at above 400 K. Furthermore, X-ray photoelectron spectroscopy (XPS) results verify the reduction of the palladium oxide after interaction of the sample with molecular hydrogen and the stability of the catalyst under several cycles of annealing and cooling in hydrogen.     

Methanol electro-oxidation on Ni@Pd core-shell nanoparticles supported on multi-walled carbon nanotubes in alkaline media

A novel method to prepare well-dispersed Ni@Pd core-shell nanoparticles on multi-walled carbon nanotubes (Ni@Pd/MWCNTs) is reported. The morphology and crystallinity of the catalyst are characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) analyses, respectively. Binary composite Ni@Pd/MWCNTs have been obtained and investigated for electrocatalysis of methanol oxidation in 0.5 M NaOH. It is observed that Ni@Pd/MWCNTs increases the apparent electrocatalytic activity and stability of the electrode considerably than that of PdNi/MWCNTs and Pd/MWCNTs catalysts. It is implied that Ni@Pd core-shell nanoparticles supported on MWCNTs is very promising for portable applications in DMFC in alkaline solution.     

Development of Pd and Pd-Co catalysts supported on multi-walled carbon nanotubes for formic acid oxidation

Pd-Co and Pd catalysts were prepared by the impregnation synthesis method at low temperature on multi-walled carbon nanotubes (MWCNTs). The nanotubes were synthesized by spray pyrolysis technique. Both catalysts were obtained with high homogeneous distribution and particle size around 4 nm. The morphology, composition and electrocatalytic properties were investigated by transmission electron microscopy, scanning electron microscopy-energy dispersive X-ray analysis, X-ray diffraction and electrochemical measurements, respectively. The electrocatalytic activity of Pd and PdCo/MWCNTs catalysts was investigated in terms of formic acid electrooxidation at low concentration in H₂SO₄ aqueous solution. The results obtained from voltamperometric studies showed that the current density achieved with the PdCo/MWCNTs catalyst is 3 times higher than that reached with the Pd/MWCNTs catalyst. The onset potential for formic acid electrooxidation on PdCo/MWCNTs electrocatalyst showed a negative shift ca. 50 mV compared with Pd/MWCNTs.     

胶体溶液制备碳纳米管负载钌纳米颗粒的电催化合成氨性能

利用胶体溶液制备Ru纳米颗粒。将Ru纳米颗粒负载在碳纳米管上得到用于电化学合成氨的催化剂Ruc/CNT。通过调节Ru胶体溶液的加入量可调整Ruc/CNT上Ru的负载量。借助X射线衍射(XRD)仪、X射线光电子能谱(XPS)、透射电子显微镜(TEM)、接触角测量仪和电化学技术对催化剂进行表征测试。结果表明,通过胶体溶液制备的Ruc/CNT上的钌纳米颗粒缩小至1～5 nm,相比于Ru/CNT上的钌颗粒具有更好的分散性。钌的负载量为2.5%的0.025-Ruc/CNT实现了最高10.98μg/(h·mgcat.)的氨产率及2.18%的法拉第效率,而直接在碳纳米管上回流还原制备的Ru/CNT催化剂仅有5.19μg/(h·mgcat.)的氨产率及0.05%的法拉第效率。通过对照实验对氨的来源进行验证,结果证明氨来源于电化学催化氮气还原过程,钌是催化剂的主要活性位点。钌催化剂颗粒粒径的减小可促进载体与钌纳米颗粒间的电荷转移,削弱反应过程中高能的N≡N三键,提高钌对氮气电化学合成氨的选择性,同时碳纳米管载体的应用为0.025-Ruc/CNT提供足够多的负载位点,分散性更好的钌纳米颗粒能够暴露更多的活...     

Highly dispersed Pd nanoparticles supported on 1,10-phenanthroline-functionalized multi-walled carbon nanotubes for electrooxidation of formic acid

Functionalization step is generally prerequisite to immobilize metal nanoparticles on multi-walled carbon nanotubes (MWCNTs) for production of a high efficient electrocatalyst. We herein report a novel method to functionalize MWCNTs with 1,10-phenanthroline (phen-MWCNTs) as a catalyst support for Pd nanoparticles. Raman spectroscopic analysis results reveal that this phen functionalization method can preserve the integrity and electronic structure of MWCNTs and provide the highly effective functional groups on the surface for Pd nanoparticles. According to the transmission electron microscopy (TEM) measurements, the as-prepared Pd nanop articles are evenly deposited on the surface of the phen-MWCNTs without obvious agglomeration, and the average particle size of the Pd nanoparticles is 2.3 nm. Electrochemical measurements demonstrate that the as-prepared Pd/phen-MWCNTs catalyst has a better electrocatalytic activity and stability for the oxidation of formic acid than Pd catalyst on acid-treated MWCNTs. It is concluded that the as-prepared Pd/phen-MWCNTs would be a potential candidate as an anode electrocatalyst in direct formic acid fuel cell (DFAFC).     

Pd nanoparticles supported on functionalized multi-walled carbon nanotubes (MWCNTs) and electrooxidation for formic acid

To improve the utilization and activity of anodic catalysts for formic acid electrooxidation, palladium (Pd) particles were loaded on the MWCNTs, which were functionalized in a mixture of 96% sulfuric acid and 4-aminobenzenesulfonic acid, using sodium nitrite to produce intermediate diazonium salts from substituted anilines. The composition, particle size, and crystallinity of the Pd/f-MWCNTs catalysts were characterized by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM) and energy dispersive spectroscopy (EDS) measurements. The electrocatalytic properties of the Pd/f-MWCNTs catalysts for formic acid oxidation were investigated by cyclic voltammetry (CV) and linear sweep voltammetry (LSV) in 0.5 mol L⁻¹ H₂SO₄ solution. The results demonstrated that the catalytic activity was greatly enhanced due to the improved water-solubility and dispersion of the f-MWCNTs, which were facile to make the small particle size (3.8 nm) and uniform dispersion of Pd particles loading on the surface of the MWCNTs. In addition, the functionalized MWCNTs with benzenesulfonic group can provide benzenesulfonic anions in aqueous solution, which may combine with hydrogen cation and then promote the oxidation of formic acid reactive intermediates. So the Pd/f-MWCNTs composites showed excellent electrocatalytic activity for formic acid oxidation.     

Electrocatalytic oxidation of methanol on Pt modified single-walled carbon nanotubes

Platinum nanoparticles on modified single-walled carbon nanotubes (SWNT) were investigated by a completely new electrochemical method. A Pt(IV) complex was formed on the SWNT surface through coordination to the oxygen atom of an oxide functional group on the SWNT surface and then converted to platinum nanoparticles by a potential pulse method. The structure and chemical nature of Pt nanoparticles on SWNTs have been investigated by transmission electron microscopy and X-ray diffraction, the mean diameter of Pt nanoparticles was 5–8 nm. The electrocatalytic properties of the Pt/SWNT electrode for methanol oxidation and its kinetic characterization were investigated by cyclic voltammetry (CV) and excellent electrocatalytic activity was observed.     

Hydrogenation of carbon monoxide over cobalt nanoparticles supported on carbon nanotubes

This paper describes a catalytic reaction of hydrogen and carbon monoxide (Fischer-Tropsch synthesis (FTS)) over carbon nanotubes (CNTs) supported cobalt nanoparticles. We have investigated the effect of calcination of the catalysts on FTS performance using X-ray diffraction (XRD), H₂ chemisorption, temperature programmed reduction (TPR), temperature programmed oxidation (TPO), and transmission electron microscopy (TEM) techniques. With the increase of outer diameter of CNTs, specific surface area of the catalyst decreases while Co particle size increased accompanying with a decrease in CO conversion. The FTS performance is similar for samples calcined in N₂ or air at temperature below 550 °C. Over 550 °C, the results are much different in that the Co/CNTs can keep its activity due to the unchanged CNTs structure in N₂ while the Co/CNTs almost lose activity owing to the loss of CNTs structure and sintering of cobalt oxide clusters in air.     

Electrocatalytic oxidation of formic acid and formaldehyde on platinum nanoparticles decorated carbon-ceramic substrate

Electrochemical characteristics of formic acid (FM) and formaldehyde (FM) oxidation on a potent catalyst, platinum nanoparticles supported on carbon-ceramic substrate (CC/Pt), were investigated via cyclic voltammetric and chronoamperometric analysis in mixed 0.75 M FM (or 0.75 M FM) and 0.1 M H₂SO₄ solutions. The results were compared to those at a polycrystalline platinum electrode and platinum particles deposited on platinum and glassy carbon electrodes. It was found that CC/Pt was catalytically more active than smooth platinum and platinum particles supported on platinum and glassy carbon electrodes. On the other hand, such nanoparticles on CC substrate exhibit better catalytic behavior towards FA and FM than the corresponding platinum and glassy carbon electrodes, which is raised form high porosity of CC substrate for better distribution of platinum particles and to produce of platinum particles in nano size. The effect of some experimental factors was studied and optimum conditions were suggested. Finally, the long-term stability of the modified electrode has also been investigated. These results indicate that the system studied in the present work is the most promising system for use in fuel cells.     

Radiation induced synthesis of Pt nanoparticles supported on carbon nanotubes

Pt nanoparticles supported on multi-walled carbon nanotubes (MWNTs) were obtained by γ-irradiation induced synthesis and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The Pt nanoparticles, which were uniform in shape and size and well dispersed on the carbon nanotubes, were 2.5–4.0 nm in diameter. Test runs on a single stack proton exchange membrane fuel cell (PEMFC) showed that these electrocatalysts are very promising for fuel cell applications.     

MnO2 modified multi-walled carbon nanotubes supported Pd nanoparticles for methanol electro-oxidation in alkaline media

A novel method to prepare MnO₂ modified multi-walled carbon nanotubes (MnO₂/MWCNTs) supported Pd (Pd-MnO₂/MWCNTs) electrocatalyst is reported. The morphology, component and crystallinity of the catalyst were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), respectively. The activity of Pd-MnO₂/MWCNTs was tested using methanol electro-oxidation in alkaline media. The results showed that the Pd-MnO₂/MWCNTs exhibited higher electrocatalytic activity and stability than Pd/MWCNTs and Pd/Vulcan (Pd/commercial Vulcan XC-72 carbon black).     

Characterization and evaluation of Pt-Ru catalyst supported on multi-walled carbon nanotubes by electrochemical impedance

In this work the authors present the results of a systematic characterization and evaluation of the carbon nanotube supported Pt-Ru (Pt-Ru/CNT) for its use as methanol oxidation catalyst. Its activity was compared with that of Pt and Pt-Ru catalysts supported on Vulcan and synthesized from carbonyl precursors, and another commercial Pt-Ru catalyst. The cyclic voltammetry, CO stripping and electrochemical impedance techniques were employed to determine the electrocatalytic activity of the catalysts. The electrochemical studies were performed in 0.5 M H₂SO₄ containing different concentrations of methanol (0.05–1 M). The results showed a noticeable influence of the catalyst support (CNT) on the performance of the catalyst for CO oxidation. The electrochemical impedance studies allowed us to separate the different steps in the methanol oxidation reaction and to control these steps or reactions by varying the applied potential and the methanol concentration. At low methanol concentration and potentials the de-hydrogenation of methanol predominated. But, at high potential and methanol concentrations, the CO oxidation predominated. These results allowed us to clearly describe at what potential and concentration ranges the bi-functional effect of Ru becomes evident. Our results indicated that the CO oxidation occurs both on Pt and Ru. Compared to other catalysts, Pt-Ru supported on carbon nanotubes showed superior catalytic activity for CO and methanol oxidation.     

Tuning surface composition of multiwalled carbon nanotubes supported Pt-Co bimetallic nanoparticles for boosting methanol oxidation catalysis

Developing catalysts with high performance and low cost for methanol oxidation reaction (MOR) is the key to promoting the industrialization of direct methanol fuel cells (DMFCs). In this work, multiwalled carbon nanotubes (MWCNTs) supported PtCo alloys catalysts with improved MOR properties and anti-CO poisoning ability are successfully prepared by integrating low temperature adsorption and high temperature reduction method. The Pt₁Co₃@NC/MWCNTs sample with moderate Co²⁺ feeding content (0.81 mA/ug_Pt) achieves a factor of 1.93 enhancement in MOR mass activity compared to the commercial Pt/C catalyst (0.42 mA/ug_Pt). In addition, the Pt₁Co₃@NC/MWCNTs sample displays a lower CO oxidation onset potential respect to pristine Pt/C catalyst (0.74 V vs. 0.82 V). Scuh improvement of MOR activity, durability and anti-CO poisoning ability of the Pt₁Co₃@NC/MWCNTs catalyst is ascribed to the moderate surface compositions, optimal electronic interaction between PtCo alloys and MWCNTs, and the protection of N-doped carbon (NC) shells. This study provides a new direction to decrease the utilization of platinum and improve the MOR activity, stability and anti-CO poisoning ability of electrocatalysts which will be potential in design and fabrication of the highly efficient electrocatalysts for DMFCs applications.     

Effect of multi-wall carbon nanotubes supported palladium addition on hydrogen storage properties of magnesium hydride

To improve the hydrogen storage performance of magnesium hydride, multi-wall carbon nanotubes supported palladium (Pd/MWCNTs) was introduced to the magnesium-based materials. Pd/MWCNTs catalysts with different amounts of Pd (20 wt.%, 40 wt.%, 60 wt.%, 80 wt.%) were synthesized by a solution chemical reduction method. Afterwards, Mg₉₅–Pd_m/MWCNTs_5−m (m = 0, 1, 2, 3, 4, 5) were prepared for the first time by hydriding combustion synthesis (HCS) and mechanical milling (MM). It is determined by X-ray diffraction (XRD) analysis that Pd/MWCNTs can significantly increase the hydrogenation degree of magnesium during the HCS process. The microstructures of the composites obtained by transmission electron microscope (TEM) and field emission scanning electronic microscopy (FESEM) analyses show that Pd nanoparticles are well supported on the surface of carbon nanotubes and the Pd/MWCNTs are dispersed uniformly on the surface of MgH₂ particles. Moreover, it is revealed that there is a synergistic effect of MWCNTs and Pd on the hydrogen storage properties of the composites. The Mg₉₅–Pd₃/MWCNTs₂ shows the optimal hydriding/dehydriding properties, requiring only 100 s to reach its saturated hydrogen absorption capacity of 6.67 wt.% at 473 K, and desorbing 6.66 wt.% hydrogen within 1200 s at 573 K. Additionally, the dehydrogenation activation energy of MgH₂ in this system is decreased to 78.6 kJ/mol H₂, much lower than that of as-received MgH₂.     

Hollow carbon hemispheres supported palladium electrocatalyst at improved performance for alcohol oxidation

The synthesis procedure of the hollow carbon hemispheres (HCHs) using glucose as carbon source and polystyrene spheres (PSs) as templates and the formation mechanism of the HCHs have been presented. The HCHs have regular morphology and high BET surface area of 702.7 m² g⁻¹. The advantage of the HCHs compared to the hollow carbon spheres is that the HCHs can provide similar surface area at reduced volume. The electrocatalytic activity of ethanol oxidation on Pd supported on HCHs electrocatalyst (Pd/HCH) is 2.8 times higher than that of Pd supported on commercial Vulcan XC-72 carbon (Pd/C) electrocatalyst at the same Pd loadings. The high surface area is beneficial for the dispersion of the precious metal nanoparticles to increase their utilization. The hemispherical structure with hollow shell results in the improvement in the mass transfer and therefore more concentrated ethanol solution can be used to increase the energy density.     

Highly dispersed palladium nanoparticles anchored on polyethylenimine-modified carbon nanotubes for dehydrogenation of formic acid

Formic acid has been recognized as an excellent liquid hydrogen storage material. The development of catalysts with high performance for the dehydrogenation of formic acid is significant. Herein, we employed polyethylenimine-modified carbon nanotubes as a carrier for Pd nanoparticles to synthesize a novel catalyst by a wet chemical reduction method. It was found that the amino polymers on polyethylenimine-modified carbon nanotubes have great effects on reducing the size of Pd nanoparticles, changing the electronic state of Pd, and enhancing the hydrophilicity of catalyst. Therefore, the as-synthesized Pd/CNTs-A-PEI₁₈₀₀ catalyst showed superior activity for FA dehydrogenation in the absence of additives with an initial TOF value of 1506 h^?1 and a 100% selectivity of hydrogen.     

Enhanced electrocatalytic performance for methanol oxidation of Pt nanoparticles on Mn3O4-modified multi-walled carbon nanotubes

We report the preparation of well-dispersed Pt nanoparticles depositing on Mn₃O₄-modified multi-walled carbon nanotubes (Mn₃O₄-MWCNTs) that can be taken as high performance catalyst in methanol electro-oxidation. Various spectrometry techniques such as FT-IR, Raman, XRD, TEM and XPS measurements were performed, revealing that the Pt nanoparticles were highly dispersed on the surface of Mn₃O₄-modified MWCNTs with a narrow size distribution between 1.7 nm and 3.9 nm. Compared the Pt/MWCNT catalyst without Mn₃O₄ modification, the Pt/Mn₃O₄-MWCNT composite catalyst not only shows relative large electrochemical active surface area (EAS), high catalyzing activity toward methanol electro-oxidation, but also exhibits very high stability with apparent anti-poisoning tolerance to the incomplete oxidized species during methanol oxidation.     

Platinum nanoparticles supported on activated carbon fiber as catalyst for methanol oxidation

Activated carbon fiber (ACF) with high specific surface area has been used as support in the preparation of Pt nanoparticles electrocatalyst (Pt/ACF) for direct alcohol fuel cells. It is found that the Pt nanoparticles on ACF are highly and homogeneously dispersed with a narrow size distribution in the range of 1.5–3.5 nm with an average size of 2.4 nm. In comparison with the commercial E-TEK Pt/C catalyst, the Pt/ACF catalyst exhibits much higher catalytic activity for methanol, ethanol and isopropanol oxidation, which are about 2.4 times as high as that of the former. The Pt/ACF catalyst is observed to be significantly more stable during the constant current density polarization and continuous cyclic voltammetry in comparison with Pt/C catalyst. Both the uniform dispersion of Pt nanoparticles and strong interactions between Pt nanoparticles and ACF are of benefit to achieve the performance improvement of Pt/ACF catalyst.     

Aerogel sheet of carbon nanotubes decorated with palladium nanoparticles for hydrogen gas sensing

In the development of hydrogen sensors, it is required to meet the demands of both high sensor performance as well as the ease of fabrication for mass production. For this purpose we proposed a chemiresistive hydrogen sensors based on an aerogel sheet of carbon nanotubes decorated with palladium nanoparticles (CNT/Pd sheet). The fabrication process is straightforward that a dry-spun CNT aerogel sheet is suspended between concentric electrodes followed by depositing Pd nanoparticles on CNT sheets by thermal evaporation. The present CNT/Pd sheet sensors can detect hydrogen at concentrations as low as 2 ppm at room temperature with a detection range from 2 to 1000 ppm. The aerogel nature of CNT/Pd sheet contributes to low detection limit and broad detection range of the CNT/Pd sensor. Relations between hydrogen concentration and sensor response and response time, and the effects of temperature on sensor performance were investigated.