Effect of Pt loading on the hydrogen production of CNT/Pt composites functionalized with carboxylic groups

This work reports the morphological and photocatalytic hydrogen generation properties of CNT/Pt composites with and without functionalization by carboxylic/oxygen groups. The composites with and without functionalization were named f-CNT/Pt and CNT/Pt, respectively. Several f-CNT/Pt and CNT/Pt composites with different content of Pt NPs (from 0 to 30 wt%) were synthesized and analyzed by scanning electron microscopy (SEM). Those images revealed that the composites without functionalization presented higher agglomerations of Pt nanoparticles (NPs). Furthermore, the average sizes of the Pt NPs in the named f-CNT/Pt composites (2.3–2.9 nm) were lower than these in the CNT/Pt composites (2.5–3.1 nm). The hydrogen generation rates were also calculated from the decomposition of pure water under UV irradiation (365 nm) and found maximum values of 45.4 and 193.9 μmol·h⁻¹ g⁻¹ for the CNT/Pt and f-CNT/Pt composites (they contained 20 wt% of Pt NPs), respectively. Additional experiments for hydrogen generation were achieved using sodium sulfite as sacrificial agent; in this case, a maximum value of 13850 μmol·h⁻¹ g⁻¹ was obtained for the f-CNT/Pt composite. The f-CNT/Pt composites produced more hydrogen than the CNT/Pt composites because they presented higher content of defects; this was confirmed by the Raman spectra. We also showed that the Pt NPs acted as electron trap centers, which delayed the recombination of the photogenerated electrons and holes, this in turn, enhanced the hydrogen generation rates of the composites (the hydrogen generation was maximized by varying the content of Pt NPs deposited on the CNTs). The CNT/Pt composites presented here were simpler and easier to synthesize than the previous published ternary systems based on TiO₂, CNTs and Pt NPs.     

Design and preparation of highly active carbon nanotube-supported sulfated TiO2 and platinum catalysts for methanol electrooxidation

A novel electrocatalyst structure of carbon nanotube-supported sulfated TiO₂ and Pt (Pt-S-TiO₂/CNT) is reported. The Pt-S-TiO₂/CNT catalysts are prepared by a combination of improved sol-gel and ethylene glycol reduction methods. Transmission electron microscopy and X-ray diffraction show that the sulfated TiO₂ is amorphous and is coated uniformly on the surface of the CNTs. Pt nanoparticles of about 3.6 nm in size are homogenously dispersed on the sulfated TiO₂ surface. Fourier transform infrared spectroscopy analysis proves that the CNT surfaces are modified with sulfated TiO₂ and a high concentration of SO_x, and adsorbed OH species exist on the surface of the sulfated TiO₂. Electrochemical studies are carried out using chronoamperometry, cyclic voltammetry, CO stripping voltammetry and impedance spectroscopy. The results indicate that Pt-S-TiO₂/CNT catalysts have much higher catalytic activity and CO tolerance for methanol electrooxidation than Pt/TiO₂/CNTs, Pt/CNTs and commercial Pt/C.     

Ethanol oxidation reaction activity of highly dispersed Pt/SnO2 double nanoparticles on carbon black

Highly dispersed Pt and SnO₂ double nanoparticles containing different Pt/Sn ratios (denoted as Pt/SnO₂/CB) were prepared on carbon black (CB) by the modified Bönnemann method. The average size of Pt and SnO₂ nanoparticles was 3.1 ± 0.5 nm and 2.5 ± 0.3 nm, respectively, in Pt/SnO₂(3:1)/CB, 3.0 ± 0.5 nm and 2.6 ± 0.3 nm, respectively, in Pt/SnO₂(1:1)/CB, and 2.8 ± 0.5 nm and 2.5 ± 0.3 nm, respectively, in Pt/SnO₂(1:3)/CB. The Pt/SnO₂(3:1)/CB electrode showed the highest specific activity and lowest overpotential for ethanol oxidation reaction (EOR), and was superior to a Pt/CB electrode. Current density for EOR at 0.40 and 0.60 V vs. reversible hydrogen electrode for the Pt/SnO₂(3:1)/CB electrode decayed more slowly than that for the Pt/CB electrode because of a synergistic effect between Pt and SnO₂ nanoparticles. The predominant reaction product was acetic acid, and its current efficiency was about 70%, while that for CO₂ production was about 30%.     

Atomic layer deposition assisted Pt-SnO2 hybrid catalysts on nitrogen-doped CNTs with enhanced electrocatalytic activities for low temperature fuel cells

Nitrogen doped carbon nanotubes (CN_x) of a high nitrogen concentration were synthesized directly on carbon paper as the skeleton of a 3D composite electrode. Ultra-fine SnO₂ nanoparticles about 1.5 nm were deposited on CN_x with atomic layer deposition (ALD) technique. Pt nanoparticles from 1.5 to 4 nm were deposited on CN_x/carbon paper and SnO₂/CN_x/carbon paper with ethylene glycol reduction method. Three dimensional Pt/CN_x/carbon paper and Pt-SnO₂/CN_x/carbon paper composite electrodes were obtained, respectively. They were characterized over oxygen reduction reaction (ORR) and methanol oxidation reaction (MOR) for low temperature fuel cells. With similar sizes of Pt nanoparticles, the electrochemical surface area (ECSA) of Pt-SnO₂/CN_x/carbon paper is larger than that of Pt/CN_x/carbon paper. Pre-deposited SnO₂ nanoparticles promote the electrocatalytic activity of Pt toward ORR, carbon monoxide (CO) stripping and MOR. The underlying mechanisms for the enhanced activities are discussed.     

Thin layer vs. nanoparticles: Effect of SnO2 addition to PtRhNi nanoframes for ethanol oxidation reaction

When designing catalysts for direct ethanol fuel cell applications (DEFC), four main parameters must be considered: shape, structure, size, and chemical composition. According to this knowledge, it is assumed that polyhedral hollow Pt-based nanoframes, with the addition of Rh and SnO₂ with a size below 50 nm, could be a promising nanocatalysts for the anode of DEFC. In this work, two different PtRhNi/SnO₂ nanoframes-based catalysts are obtained. First consists of PtRhNi nanoframes covered with small, about 3 nm, SnO₂ nanoparticles (PtRhNi/SnO₂ NPs); and second is the PtRhNi nanoframes covered with a thin and incomplete SnO₂ layer (PtRhNi/SnO₂ TL). Both nanocatalysts were tested toward ethanol oxidation reaction (EOR) and show higher activity in comparison to PtRhNi nanoframes without SnO₂ (PtRhNi NFs) addition and commercially used Pt nanoparticles. Especially, the electrochemical durability and stability of obtained nanocatalysts were tested. It was shown that both PtRhNi/SnO₂ nanoframes-based catalysts develop similar mass and specific activity, as well as nearly the same onset potential, but their stability is significantly different. It turns out, that catalyst based on PtRhNi nanoframes covered with a thin SnO₂ layer is susceptible to degradation, while the catalyst consisting of PtRhNi nanoframes covered with SnO₂ nanoparticles is much more durable and could be used as an efficient catalyst toward EOR.     

Synthesis and characterization of Pt nanoparticles on sulfur-modified carbon nanotubes for methanol oxidation

Pt nanoparticles supported on carbon nanotubes (Pt/CNTs) have been synthesized from sulfur-modified CNTs impregnated with H₂PtCl₆ as Pt precursor. The dispersion and size of Pt nanoparticles in the synthesized Pt/CNT nanocomposites are remarkably affected by the amount of sulfur modifier (S/CNT ratio). The results of X-ray diffraction and transmission electron microscopy indicate that an S/CNT ratio of 0.3 affords well dispersed Pt nanoparticles on CNTs with an average particle size of less than 3 nm and a narrow size distribution. Among different catalysts, the Pt/CNT nanocomposite synthesized at S/CNT ratio of 0.3 showed highest electrochemically active surface area (88.4 m² g⁻¹) and highest catalytic activity for methanol oxidation reaction. The mass-normalized methanol oxidation peak current observed for this catalyst (862.8 A g⁻¹) was ∼ 6.5 folds of that for Pt deposited on pristine CNTs (133.2 A g⁻¹) and ∼ 2.3 folds of a commercial Pt/C (381.2 A g⁻¹). The results clearly demonstrate the effectiveness of a relatively simple route for preparation of sulfur-modified CNTs as a precursor for the synthesis of Pt/CNTs, without the need for tedious pretreatment procedures to modify CNTs or complex equipments to achieve high dispersion of Pt nanoparticles on the support.     

Solvent effect in the synthesis of nanostructured Pt–Sn/CNT as electrocatalysts for the electrooxidation of ethanol

Pt and Pt–Sn nanoparticles were synthesized and supported onto carbon nanotubes (CNT), the electrocatalytic activity towards the ethanol oxidation reaction was analyzed. The effect of the solvent employed for the synthesis was evaluated. Metal nanoparticles synthesis was made using water (Pt–Sn/CNT-W) or ethanol (Pt–Sn/CNT-E) as a solvent. Pt–Sn/CNT-W material presented only Pt–Sn alloy nanoparticles homogeneously distributed on the carbon nanotubes support. Pt–Sn/CNT-E sample showed non well-dispersed nanoparticles forming agglomerates along the CNTs surface with predominantly Sn⁴⁺ superficial species (SnO₂) as show the XPS, FTIR and electrochemical results. These surface arrangements had important effects on the electrocatalytic properties. Pt–Sn/CNT-W shows higher ethanol electrooxidation activity than the Pt–Sn/CNT-E, which is attributed to: a) the double catalytic effect and the intrinsic electronic mechanism favored by the presence of Sn; b) the good particle dispersion of the bimetallic active phase on the CNT and; c) the absence of SnO₂ species.     

Enhanced activity of Pt nanoparticle catalysts supported on manganese oxide-carbon nanotubes for ethanol oxidation

Pt nanoparticles deposited on manganese oxide-carbon nanotubes (Pt/MnO_x-CNTs) are prepared by a microwave-assisted polyol method. Their structure characterizations are carried out by Fourier transform infrared spectrometry (FTIR), thermogravimetric analysis (TGA), X-ray diffraction (XRD), transmission electron microscope (TEM) and X-ray photoelectron spectroscopy (XPS) measurements, indicating that MnO_x nanoparticles cover the surface of CNTs and then Pt nanoparticles are uniformly dispersed on MnO_x-CNTs with the average particle size of about 2.2 nm. Ethanol oxidation peak current on Pt/MnO_x-CNTs (1141.4 mA mg⁻¹ Pt) is 1.82 times higher than that on Pt/CNTs (626.4 mA mg⁻¹ Pt) and 1.28 times higher than that on PtRu/C (JM) (888.6 mA mg⁻¹ Pt). The Pt/MnO_x-CNT catalyst presents not only excellent electrocatalytic activity and very high stability for ethanol oxidation, but also high tolerance to the poisonous carbonaceous intermediates generated during ethanol oxidation compared to Pt/CNT catalyst. This is attributed to the excellent proton conductivity of MnO_x and the synergistic effect between Pt and MnO_x. The optimum mass ratio of MnO_x to CNTs is 1:1 in the Pt/MnO_x-CNT catalysts.     

Nitrogen doped carbon layer coated platinum electrocatalyst supported on carbon nanotubes with enhanced stability

Enhancement in durability of electrocatalyst is still one of the most important issues in polymer electrolyte fuel cells (PEFCs). Here, we report a structurally coated electrocatalyst supported on carbon nanotubes (CNT), in which platinum (Pt) nanoparticles are coated by nitrogen doped carbon (NC) layers. CNT/NC/Pt/NC shows comparable electrochemical surface area (ECSA) and oxygen reduction reaction (ORR) activity to the non-coated electrocatalyst (CNT/NC/Pt), indicating that NC layer on Pt nanoparticles almost negligibly affects the activities of electrocatalyst; while, CNT/NC/Pt/NC exhibits a higher Pt stability due to the unique structure, in which the Pt nanoparticles are stabilized by the NC layers and Pt aggregation is decelerated proved by TEM measurement. Maximum power density of CNT/NC/Pt/NC reached 604 mW cm^?2 with Pt loading of 0.1 mg_Pt cm^?2, which only decreases by 7% compared to CNT/NC/Pt (650 mW cm^?2). The electrochemical analysis and fuel cell test illustrate that NC layer on Pt nanoparticles enhances the durability without serious deterioration of fuel cell performance.     

Photodeposition of Pt nanoparticles onto TiO2@CNT as high-performance electrocatalyst for oxygen reduction reaction

The commonly used Pt/C catalyst has low durability for oxygen reduction reaction (ORR). In this work, CNT-supported TiO₂ nanoparticles, which synergistically combines the merits of TiO₂ (high stability and strong interactions with the supported Pt nanoparticles) and CNT (high specific surface area and large electrical conductivity), are prepared by a sol-gel process coupled with an annealing process and used as the support for Pt nanoparticles, which are anchored around TiO₂ nanoparticles by a photodeposition technique. The as-synthesized Pt/TiO₂@CNT catalyst exhibits a mass activity 5.3 times as large as that of the commercial Pt/C catalyst (0.358 A mg_Pt⁻¹ vs. 0.067 A mg_Pt⁻¹ at 0.9 V) and an excellent stability (no activity loss after 10000 potential cycles) for ORR, which can be mainly attributed to the lower oxygen adsorption energy of Pt, resulting from the strong metal-support interaction induced by the deposition of Pt nanoparticles around the well-dispersed TiO₂ nanoparticles on CNT.     

Investigation of the effect of graphitized carbon nanotube catalyst support for high temperature PEM fuel cells

In this study, it is aimed to investigate the graphitization effect on the performance of the multi walled carbon nanotube catalyst support for high temperature proton exchange membrane fuel cell (HT-PEMFC) application. Microwave synthesis method was selected to load Pt nanoparticles on both CNT materials. Prepared catalyst was analyzed thermal analysis (TGA), Transmission Electron Microscopy (TEM) and corrosion tests. TEM analysis proved that a distribution of Pt nanoparticles with a size range of 2.8–3.1 nm was loaded on the Pt/CNT and Pt/GCNT catalysts. Gas diffusion electrodes (GDE) were manufactured by an ultrasonic spray method with synthesized catalyst. Polybenzimidazole (PBI) membrane based Membrane Electrode Assembly (MEA) was prepared for observe the performance of the prepared catalysts. The synthesized catalysts were also tested in a HT-PEMFC environment with a 5 cm² active area at 160 °C without humidification. This study demonstrates the feasibility of using the microwave synthesis method as a fast and effective method for preparing high performance Pt/CNT and Pt/GCNT catalyst for HT-PEMFC. The HT-PEMFC performance evaluation shows current densities of 0.36 A/cm²0.30 A/cm² and 0.20 A/cm² for the MEAs prepared with Pt/GCNT, Pt/CNT and Pt/C catalysts @ 0.6 V operating voltage, respectively. AST (Accelerated Stress Test) analyzes of MEAs prepared with Pt/GCNT and Pt/CNT catalysts were also performed and compared with Pt/C catalyst. According to current density @ 0.6 V after 10,000 potential cycles, Pt/GCNT, Pt/CNT and Pt/C catalysts can retain 61%, 67% and 60% of their performance, respectively.     

Preparation of Pt nanoparticles on carbon support using modified polyol reduction for low-temperature fuel cells

Highly dispersed Pt nanoparticles supported on Vulcan XC-72R were prepared by a modified polyol reduction for low-temperature fuel cells. The modified polyol reduction was controlled with various concentrations of reducing agent and reduction times at 90 °C. The 20 wt% Pt/C catalyst prepared under an optimum reduction condition (reduction temperature = 90 °C, ethylene glycol/H₂O volume ratio = 1, and reduction time = 10 h) exhibited the highest electrochemical active surface area (EAS) and methanol oxidation activity due to the small Pt nanoparticles (1.2 nm) with quite a narrow size distribution between 0.5 and 2 nm. The 40 wt% Pt/C catalyst was prepared using the optimum condition to confirm the applicability of the preparation method. The synthesized 40 wt% Pt/C catalyst had smaller-sized Pt nanoparticles (1.3 nm) and a higher EAS than that of a commercial 40 wt% Pt/C catalyst. With pure H₂ (anode) and air (cathode), a PEMFC using the synthesized 40 wt% Pt/C catalyst as a cathode had higher single-cell performance than that of the commercial catalyst.     

Effective monitoring and classification of hydrogen and ammonia gases with a bilayer Pt/SnO2 thin film sensor

The monitoring and classification of different gases, such as H₂ and NH₃ using a low-cost resistive semiconductor sensor is preferred in practical applications in hydrogen energy, breath analysis, air pollution monitoring, industrial control, and etc. Herein, porous bi-layer Pt/SnO₂ thin film sensors were fabricated to enhance H₂ and NH₃ sensing performance for effective monitoring and classification. Different Pt film thicknesses of 2, 5, 10, and 20 nm were deposited on 150 nm SnO₂ film-based sensors by sputtering method to optimize the response to H₂ and NH₃ gases. Gas sensing results showed that the fabricated Pt/SnO₂ films significantly improved the sensor response to NH₃ and H₂ compared to pure SnO₂ thin film. The sensors based on 5 and 10 nm Pt catalyst layers presented the highest responses to H₂ and NH₃, respectively. The optimal working temperature for NH₃ was in the range from 250 °C to 350 °C, and that for H₂ gas is less than 200 °C. The response of Pt/SnO₂ sensors to CH₄, CO, H₂S, and liquefied petroleum gas was much lower than that to NH₃ and H₂ supporting the high selectivity. On the basis of sensing results at different working temperatures or Pt thicknesses, we applied a radar plot and linear discriminant analysis methods to distinguish NH₃ and H₂. The results showed that H₂ and NH₃ could be classified without any confusion with different Pt layer thicknesses at a working temperature of 250 °C.     

Electrochemical activity and stability of Pt catalysts on carbon nanotube/carbon paper composite electrodes

This article reports a facile microwave-assisted approach to synthesize Pt catalysts on carbon nanotube (CNT)/carbon paper (CP) composite through catalytic chemical vapor deposition. The Pt deposits, with an average size of 3–5 nm were uniformly coated over the surface of oxidized CNTs. The electrochemical activity and stability of the Pt–CNT/CP electrode were investigated in 1 M H₂SO₄ using cyclic voltammetry (CV) and ac electrochemical impedance spectroscopy. The Pt catalysts showed not only fairly good electrochemical activity (electrochemically active surface area) but also durability after a potential cycling of >1000 cycles. The analysis of ac impedance spectra associated with equivalent circuit revealed that the presence of CNTs significantly reduced both connect and charge transfer resistances, leading to a low equivalent series resistance ˜0.22 Ω. With the aid of CNTs, well-dispersed Pt catalysts enable the reversibly rapid redox kinetic since electron transport efficiently passes through a one-dimensional pathway. Thus, the CNTs do not only serve as carbon support, they also charge transfer media between the Pt catalysts and the gas diffusion layer. The results shed some light on the use of CNT/CP composite, offering a promising tool for evaluating high-performance gas diffusion electrodes.     

Methanol oxidation efficiencies on carbon-nanotube-supported platinum and platinum-ruthenium nanoparticles prepared by pulsed electrodeposition

Dense carbon nanotubes (CNTs, 30-50 nm in diameter, 6-8 μm in length) were grown via a thermal chemical vapor deposition process on titanium treated carbon cloths. Catalysts in the form of either nano-scale platinum (Pt) or platinum-ruthenium (Pt-Ru) particles were then deposited on the CNT surfaces by pulse-mode potentiostatic electrodeposition. Surface morphologies of the prepared electrodes were examined by scanning electron microscopy and transmission electron microscopy. Well dispersed catalysts, Pt alone (particle sizes of 7-8 nm) or Pt-Ru (particle sizes of 3-4 nm) nanoparticles, were successfully electrodeposited on the CNT surfaces in citric acid aqueous solutions. In addition, electrochemical characteristics of the specimens were investigated by cyclic voltammetry in argon saturated sulfuric acid aqueous solutions and in mixed sulfuric acid and methanol aqueous solutions. The catalytic activity of the Pt-Ru/CNTs electrode for methanol oxidation was 1038.25 A g⁻¹_Pt in a mixed solution containing 0.5 M sulfuric acid and 1.0 M methanol.     

Thermal synthesis of Pt nanoparticles on carbon paper supports

A thermal method of synthesis and fixation of Pt nanoparticles (Pt NPs) on carbon paper is proposed in this paper. Carbon paper was coated with H₂PtCl₆ by simple immersion in an ethanol solution containing the Pt precursor. Thereafter, H₂PtCl₆ was decomposed in inert atmosphere into Pt NPs by applying a temperature of 600 °C. Formed Pt NPs were able to oxidize the surrounding carbon fiber surface. This local thermal oxidation of carbon promoted the generation of nano-roughness and Pt NPs were embedded in the carbon fiber, thus favoring their fixation on carbon paper. Pt load can be easily controlled by the number of coating processes applied. The proposed method combines the advantage of achieving small size nanoparticles (5–10 nm) with enhanced fixation of Pt NPs when compared with electrochemical synthesis. The optimal number of coatings applied was three, which produced a complete coverage of carbon paper surface (with a Pt load of 0.18 mg cm^?2).     

Ammonia electro-oxidation on alloyed PtIr nanoparticles of well-defined size

Carbon-supported PtIr nanoparticles with the nominal atomic ratio of 70 to 30 % in the 3 nm scale are investigated for the ammonia oxidation reaction (AOR) in 1 M KOH. The morphological and surface properties of alloyed PtIr electrocatalysts synthesized at pH 7 and 8.5 are characterized by TEM, XRD, SAXS and XPS. According to SAXS, nanoparticles prepared at lower pH (PtIr (1)) are mono-dispersed with particle size of 2.9 nm, whereas nano-sized catalyst PtIr (2) synthesized at higher pH has bi-modal size distribution with modes at 1.8 and 3.4 nm. XPS revealed that Pt on the surface of PtIr (1) is present in metallic state contrary to PtIr (2) where platinum surface species of higher oxidation state are identified. Iridium on the surface of both samples is present in Ir⁰, Ir³⁺ and Ir⁴⁺ form. From the electrochemical characterizations, the onset potential of PtIr for ammonia oxidation is more negative (−1.07 V vs. MSE) compared to the monometallic Pt nanoparticles of 3.0 nm in size (−0.94 V vs. MSE). Long term electrolysis (12 h) demonstrated a 33% higher degradation rate of ammonia on PtIr (1) than on Pt with N₂ as the main product, in addition to some traces of NO₃ and NO₂. Higher catalytic activity, stability and activity recovery of PtIr nanoparticles is attributed to the electronic effect generated between Pt and Ir atoms in alloy. The surface of alloyed PtIr nanoparticles displays a complex of physicochemical and electrocatalytic properties, thus the maximum electrocatalytic activity towards AOR is highly correlated with the narrow size distribution and lower amount of surface oxygenated species.     

Performance of direct methanol fuel cell using carbon nanotube-supported Pt–Ru anode catalyst with controlled composition

The performance of a single-cell direct methanol fuel cell (DMFC) using carbon nanotube-supported Pt–Ru (Pt–Ru/CNT) as an anode catalyst has been investigated. In this study, the Pt–Ru/CNT electrocatalyst was successfully synthesized using a modified polyol approach with a controlled composition very close to 20 wt.%Pt–10 wt.%Ru, and the anode was prepared by coating Pt–Ru/CNT electrocatalyst on a wet-proof carbon cloth substrate with a metal loading of about 4 mg cm⁻². A commercial gas diffusion electrode (GDE) with a platinum black loading of 4 mg cm⁻² obtained from E-TEK was employed as the cathode. The membrane electrode assembly (MEA) was fabricated using Nafion^® 117 membrane and the single-cell DMFC was assembled with graphite endplates as current collectors. Experiments were carried out at moderate low temperatures using 1 M CH₃OH aqueous solution and pure oxygen as reactants. Excellent cell performance was observed. The tested cell significantly outperformed a comparison cell using a commercial anode coated with carbon-supported Pt–Ru (Pt–Ru/C) electrocatalyst of similar composition and loading. High conductivity of carbon nanotube, good catalyst morphology and suitable catalyst composition of the prepared Pt–Ru/CNT electrocatalyst are considered to be some of the key factors leading to enhanced cell performance.     

Electrocatalytic performance of Nicore@Ptshell/C core–shell nanoparticle with the Pt in nanoshell

The Ni₁@Pt_0.067 core–shell nanoparticles with a thin layer of Pt shell have been prepared by colloidal template method. The structure and composition of the prepared core–shell nanoparticles have been analyzed by using transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). In addition, the electrochemical performance of the prepared nanoparticles has been analyzed by potentiodynamic polarization and cyclic voltammetry (CV), by testing their activity towards oxygen reduction reaction (ORR) and methanol oxidation reaction (MOR). Experimental results indicate that the Ni₁@Pt_0.067 particles are well distributed, with an average particle size of approximately 6 nm and shell thickness of approximately 0.5 nm–2.1 nm. Compared with Pt/C, the Ni₁@Pt_0.067/C nanoparticles prepared in this study show significantly improved catalytic activity towards ORR and MOR. However, with increase in methanol concentration in the electrolyte composed of 0.5 mol L⁻¹ H₂SO₄ + x mol L⁻¹ methanol (where, x = 0, 0.2, 0.5 and 1.0), the limiting current of MOR on Ni₁@Pt_0.067/C increase remarkably, whereas the ORR activity weakens. Based on the experimental data, we analyze the mechanism underlying the impact of methanol concentration on the ORR in Ni₁@Pt_0.067/C and find that the surface of Pt has a variety of activity sites.     

Carbon nanotube-supported Pt-HxMoO3 as electrocatalyst for methanol oxidation

Carbon nanotube (CNT)-supported platinum modified with H_xMoO₃ (Pt-H_xMoO₃/CNT) was prepared and used as an electrocatalyst for methanol oxidation. In the preparation of this electrocatalyst, a platinum precursor was loaded on CNTs and reduced by sodium borohydride in ethylene glycol, resulting in CNT-supported platinum without modification (Pt/CNT), and then the Pt/CNT was modified with H_xMoO₃ that was formed by hydrolysis and subsequent reduction of ammonium molybdate. The surface morphology, structure and composition of Pt-H_xMoO₃/CNT and Pt/CNT as well as their activity toward methanol oxidation were investigated by transmission electron microscopy (TEM), X-ray diffraction (XRD), energy-dispersive spectrometry (EDS), Fourier transform infrared spectroscopy (FTIR), cyclic voltammetry (CV), chronoamperometry (CA), chronopentiometry (CP), and electrochemical impedance spectroscopy (EIS). The results, obtained from TEM, XRD, EDS, and FTIR, indicate that the platinum loaded on CNTs has a face-centered cubic structure with particle sizes of 2–5 nm, and the modification of H_xMoO₃ on platinum with an atom ratio of Pt:Mo = 2:1 has little effect on the particle size, distribution and structure of the platinum. The results, obtained from CV, CA, CP, and EIS, show that the Pt-H_xMoO₃/CNT exhibits higher electrocatalytic activity toward methanol oxidation and better carbon monoxide tolerance than Pt/CNT.