Highly dispersed Pt nanoparticles supported on poly(ionic liquids) derived hollow carbon spheres for methanol oxidation

Hollow carbon spheres (HCSs) are prepared using poly(ionic liquids) (PILs) as a carbon precursor and monodisperse silica particles as a template for the first time. The ILs form a uniform polymer coating on the template surface after polymerization. Carbonization of the coating and the subsequent removal of the template produces porous carbon spheres with a hollow structure. The HCSs possess a high surface area, good conductivity, and porosity suitable for mass transport, and they can be used as a support for Pt electrocatalysts. Pt nanoparticles with an average size of 2.8 nm are homogeneously distributed onto the HCSs. The high surface area and unique structure facilitates the fine dispersion of Pt nanoparticles. The obtained Pt/HCSs exhibit a significant catalytic activity for the oxidation of methanol.     

Enhanced electro-oxidation of methanol at nanoparticle-based Ru/Pt bimetallic catalyst: Impact of GC substrate pretreatment

This study addresses the facile preparation of electro-active Ru–Pt binary nanocatalyst layer electrodeposited onto glassy carbon (GC) electrodes for efficient methanol electrooxidation reaction (MOR). Unmodified GC and GC electrodes modified with Nafion (Naf/GC) and zeolite (Naf-Zeo/GC) are used as substrates for the electrodeposition of the Ru–Pt binary catalyst. Morphological, compositional, crystallographic and electrochemical characterizations were disclosed using scanning electron microscopy (SEM) coupled with energy dispersive X-ray (EDX) unit, XRD, and cyclic voltammetry (CV), respectively. The electrocatalytic activity of the various modified GC electrodes towards MOR depends markedly on the structure of the catalyst layer and the pretreatment of the underlying GC substrate as well. The highest catalytic activity was obtained at Ru–Pt/Naf-Zeo/GC electrode as demonstrated in highest peak current and favorable negative shift of the onset potential of MOR. The underlying zeolite increases the tolerance of the Ru–Pt catalyst layer against CO poisoning possibly by facilitating its oxidative removal and thus retrieval of Pt active sites.     

Preparation and physical/electrochemical characterization of Pt/poly(vinylferrocenium) electrocatalyst for methanol oxidation

Preparation and characterization of a platinum (Pt)-based catalyst using a redox polymer, poly(vinylferrocenium) (PVF⁺), as the support material was described. Pt was obtained from aqueous solution of K₂PtCl₄ in the complex form. Pt particles were reduced by chemical and electrochemical means. Chemical reduction was performed using aqueous hydrazine solution and electrochemical reduction was carried out in H₂SO₄ solution. The Pt/PVF⁺ catalyst system showed catalytic activity towards methanol oxidation. Cyclic voltammetry was used for the electrochemical characterization of the catalyst system. Scanning electron microscopy (SEM) images and energy dispersive X-ray spectrum (EDS) of the catalyst system were also recorded. The system was tested in a single fuel cell configuration at ambient temperature and atmospheric pressure. The open circuit voltage (OCV) was 680 mV for the system and the maximum power density was 0.31 mW cm⁻² at a current density of 0.63 mA cm⁻². Catalytic activity of Pt/PVF⁺ system towards methanol oxidation was comparable with the related catalysts in the literature.     

The three-dimensional carbon nanosheets as high performance catalyst support for methanol electrooxidation

In this paper, we perform three typical oxidation treatments, such as O₃, HNO₃ and H₂O₂, to modify the surface structure of the novel three dimensional carbon nanosheets (3D CNSs). The different treatment generates kinds of oxygenated functional groups on the surface of support. One of them, the CNSs treated by ozone produces the greatest amount of carboxyl groups and keeps the original morphology, which can be used as the excellent support for the electrochemical oxidation of methanol in acidic medium. Through various characterizations, it is discovered that the PtCo/CNSs-1 shows the excellent lamellar structure, good crystallinity, abundant pore structure and large interlayer spacing, which provide ultrahigh specific surface area, superb electron and ionic conductivity. Furthermore, the superfine PtCo alloy nanoparticles evenly deposits on the 3D CNSs, which reveals superior electrocatalytic performance. More importantly, the capacity of anti-poisoning of which is enhanced obviously.     

Well dispersed Pt nanoparticles on commercial carbon black oxidized by ozone possess significantly high electro-catalytic activity for methanol oxidation

In this paper, the electro-catalytic methanol oxidation on the commercial carbon black treated with ozone at different temperatures to support platinum (Pt) nanoparticles was investigated. The necessary techniques like transmission electron microscopy (TEM), Raman spectroscopy, nitrogen adsorption-desorption techniques, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) have been used to discovery the composition, morphology and structure of the catalysts. The electro-catalytic methanol oxidation activity and durability of the catalysts was estimated by the cyclic voltammetry and chronoamperometric techniques. The results indicated that the platinum nanoparticles with average sizes of 2.04 nm can be uniformly dispersed on the surfaces of carbon black oxidized by ozone at 140 °C. In the meanwhile it has significantly high electro-catalytic activity for methanol oxidation. This phenomenon is attributed to the fact that ozone oxidation increase the content of oxygen-containing groups on the carbon black, which is helpful for improving the dispersion and decreasing the size of platinum nanoparticles. Oxygen-containing groups play a critical role in enhancing the performance of methanol electro-oxidation.     

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.     

Electrochemical degradation of Nafion ionomer to functionalize carbon support for methanol electro-oxidation

An effective electrochemical route to produce functional groups on carbon surface is demonstrated. Cyclic voltammetric (CV) sweeps are performed in 0.5 M H₂SO₄ electrolyte on electrodes containing carbon cloth, Vulcan XC72R, and Nafion ionomer. With supply of ambient oxygen, the generation of hydroxyl radicals from the oxygen reduction reaction during CV cycles initiates the decomposition of Nafion ionomer that leads to formation of oxygenated functional groups on the carbon surface. Ion chromatography confirms the dissolution of sulfate anions upon CV scans. Raman analysis suggests a minor alteration for the carbon structure. However, X-ray photoelectron spectroscopy indicates a significant increase of oxygenated functional groups in conjunction with notable reduction in the fluorine content. The amount of the oxygenated functional groups is determined by curve fitting of C 1s spectra with known constituents. These functional groups can also be found by immersing the as-prepared electrode in a solution containing concentrated residues from Nafion ionomer decomposition. The functionalized electrode allows a 170% increment of Pt ion adsorption as compared to the reference sample. After electrochemical reductions, the functionalized electrode reveals significant improvements in electrocatalytic abilities for methanol oxidation, which is attributed to the oxygenated functional groups that facilitates the oxidation of CO on Pt.     

Impact of dehydrogenation on the methanol oxidation reaction occurring on carbon nanotubes supported Pt catalyst with low Pt loading

The electro-catalytic methanol oxidation reaction (MOR) has received considerable research attention due to its importance in the development of direct methanol fuel cells. In this study, the dehydrogenation step in MOR was investigated using low levels of platinum (Pt) which supported on carbon nanotubes as a catalyst. The concentration of H⁺ had a significant effect on the MOR activity of Pt catalysts supported by carbon nanotubes (Pt/CNTs), indicating that the dehydrogenation process was a critical step in MOR for Pt/CNTs with low Pt loading. Furthermore, the effects of Pt particle size and the distance between the Pt particles were investigated. We suggested a hypothesis: for the Pt catalyst with large particle size, only a few particles were needed for dehydrogenation to proceed; for the Pt catalyst with small particle size, many Pt particles were needed to form a network for the dehydrogenation reaction, but when the Pt particles were close enough, only a few Pt particles were needed. Our study provided insight into the electro-catalytic activity of Pt/CNTs from a mechanistic perspective.     

Highly dispersed ultrafine Pt nanoparticles on nickel-cobalt layered double hydroxide nanoarray for enhanced electrocatalytic methanol oxidation

Highly dispersed ultrafine Pt nanoparticles (NPs) were loaded on a nickel-cobalt layered double hydroxide (NiCo-LDH) nanoarray that was grown on Ni foam (NF) via an in situ redox reaction without any external agent between Co²⁺ (Co(OH)₂) in NiCo-LDH and PtCl₆^2-. The obtained Pt/NiCoLDH/NF composite was used as a catalyst for methanol oxidation in alkaline media, showing much higher electrocatalytic activity and better anti-poisoning ability and stability for methanol oxidation than commercial Pt/C, mainly because of the uniform dispersion of ultrafine Pt NPs, the synergistic effect and stable support of NiCoLDH. The NiCoLDH nanoarray effectively increased the specific surface area and location sites for supporting Pt NPs and enhanced the catalytic performance and tolerance to intermediate species. This enhancement was probably due to the synergistic effect between Pt and the NiCo-LDH nanosheets, in which the LDH can provide adequate OH^?_ads species for accelerating the methanol oxidation reaction (MOR).     

CeO2 nanowires stretch-embedded in reduced graphite oxide nanocomposite support for Pt nanoparticles as potential electrocatalyst for methanol oxidation reaction

A novel hybrid composite RGO-CeO_{2 NWS} with the nanowire-sheet structure was synthesized by a facile hydrothermal process using ethanol/water as the solvent without any organic additives. The graphene oxide proceeds to reduce to graphene and chemical bonds form between graphene oxide and CeO_{2 NWS}. Pt-based catalysts with the RGO-CeO_{2 NWS} composite as the support were then prepared by a microwave-assisted polyol process. The resultant catalysts were characterized by X-ray diffraction, Raman spectroscopy, Scanning tunneling microscopy, X-ray photoelectron spectroscopy, High resolution transmission electron microscopy and electrochemical tests. The results show that the hybrid Pt/RGO₄-CeO_{2 NWS} exhibits the best catalytic activity and the increased catalytic efficiency of Pt in the hybrid catalysts is evidence that CeO_{2 NWS} are anchored onto the chemical defects in the wrinkles and edges of the graphene surface. This avoids the restacking of graphene oxide, thus hindering the Pt nanoparticles embedded in folding and increasing the exposed active sites. The changed valence state from Ce⁴⁺ to Ce³⁺ in CeO_{2 NWS} will introduce oxygen vacancies and thus promote the tolerance of intermediate species in 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.     

Coverage-dependent electro-catalytic activity of Pt sub-monolayer/Au bi-metallic catalyst toward methanol oxidation

The coverage-dependent catalytic properties of a Pt nanofilm formed on a Au substrate were investigated for the electro-oxidation of methanol. The coverage of Pt nanofilm was precisely fabricated by the formation of coverage-controlled under potential deposition of Cu adlayer and followed by the surface limited redox replacement reaction with different Pt complex ions. The STM images exhibit the formation of Pt nano-film on Au substrate with different coverage. It was clearly shown that the activity of Pt nanofilm deposited on Au substrate toward the methanol electro-oxidation was highly sensitive to its surface coverage. Pt–Au bimetallic catalyst was found to become active at the Pt surface coverage near 0.2 and reached its maximum around 0.6. The electro-catalytic activity as well as CO tolerance on Pt–Au bimetallic system was found higher than those on a Pt electrode.     

Pt incorporated hollow core mesoporous shell carbon nanocomposite catalyst for proton exchange membrane fuel cells

In the present study, various commercial carbon black materials like Vulcan XC72, Black Pearl 2000, and Regal 330 were used as supporting material for polymer electrolyte membrane fuel cell (PEMFC) electrocatalysts. A promising carbon material exhibiting hollow core mesoporous shell (HCMS) structure was synthesized by the template replication of the silica spheres with solid core and mesoporous shell structure. Two carbon supports with similar pore texture were prepared by the injection of two different carbon precursors. 20 wt% Pt/C electrocatalysts were synthesized by microwave irradiation method as the cathode electrode for PEMFC. Ex situ characterization of the electrocatalysts was performed by N₂ adsorption analysis, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), and transmission electron microscopy (TEM). Electrochemical characterization of the electrocatalysts was conducted by cyclic voltammetry (CV) analysis. Effect of different carbon supports on the cathode performance was investigated in a single cell H₂/O₂ PEMFC. Fuel cell performance tests and additional ex situ characterizations showed that HCMS carbons exhibit good support characteristics with improved single cell performance. For the cathode electrode kinetics, promising fuel cell performance results were obtained as compared to the commercial carbon blacks.     

Spatially electrodeposited platinum in polyaniline doped with poly(styrene sulfonic acid) for methanol oxidation

Polyaniline (PANI) can be doped with poly(styrene sulfonic acid) (PSS) via doping–dedoping–redoping process. The specific characteristics of PANI doped with PSS (PANI-PSS) were checked by UV–vis spectroscopy, cyclic voltammetry, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). PANI-PSS was found to have spatial structure with minimum degradation products. Platinum can be potentiostatically deposited in a spatial layer of the PANI-PSS as evidenced by electron dispersive element analysis (EDS) and Auger electron spectroscopy (AES). The electrochemical measurements demonstrated that PANI-PSS-Pt exhibited a much higher electrocatalytic activity for methanol oxidation than PANI-Pt.     

The short-channel function of hollow carbon nanoparticles as support in the dehydrogenation of cyclohexane

The structure function of hollow carbon nanoparticles (HCNP) as support of Pt particles in the dehydrogenation of cyclohexane was studied. The catalysts and supports were characterized by the XRD, TEM, TG-MS and N₂ adsorption/desorption technologies. The results indicated that the short-channel of HCNP can improve the activity and stability of Pt/HCNP, which was confirmed and explained by the temperature programmed desorption (TPD) experiments. The extent of coke deposited on HCNP was much less than that on MCNT, which can be attributed to fast diffusion and quick removal of benzene from active sites through the short path of HCNP. The HCNP with short channel is very important for improving catalyst performance in the storage system of liquid organic hydrides.     

PtCo/N-doped carbon sheets derived from a simple pyrolysis of graphene oxide/ZIF-67/H2PtCl6 composites as an efficient catalyst for methanol electro-oxidation

Many alloy catalysts have been developed for methanol electro-oxidation, but most synthetic methods are complicated. Herein, PtCo alloy catalysts supported on N-doped carbon sheets (PtCo/NCS) are successfully prepared by a simple pyrolysis of graphene oxide/ZIF-67/H₂PtCl₆ composites at different temperatures (700, 800, 900 °C) under a gas flow of H₂/Ar, in which ZIF-67 is served as Co and N sources. SEM, TEM, XRD, XPS and electrochemical characterization are employed to study as-prepared catalysts. In acidic methanol solution, the area-specific activity (1.25 mA cm⁻² Pt) of PtCo alloy catalyst obtained at 800 °C (PtCo/NCS-800) is 2.6 times of commercial Pt/C (0.48 mA cm⁻² Pt), and the area-specific activity of PtCo/NCS-800 is 3.5 times of Pt/C after 1000 cycles. Furthermore, an improved CO-tolerance of Pt is confirmed. The electronic effect and synergistic effect of metallic elements are responsible for outstanding performance of as-prepared catalysts. This work provides a simple approach to obtain high performance alloy catalysts.     

Highly efficient,large surface area and spherically shaped Pt particles deposited electrolytically synthesized graphene for methanol oxidation with impedance spectroscopy

Graphene was synthesized via electrochemical exfoliation technique of graphite rod in Poly (sodium 4-styrenesulfonate) solution. Laser Raman and X-ray Diffraction Spectroscopies were used to confirm the defects and crystal nature of graphene. The surface wettability studies based on water contact angle, further differentiates the affinity of as-prepared graphene and pristine graphite towards water. Modified Glassy carbon (GC) electrodes were prepared by electro-deposition of Platinum (Pt) on bare and graphene coated GC, denoted as GC/Pt and graphene/Pt modified GC respectively. The morphology and chemical composition of the thus synthesized graphene and graphene/Pt modified electrodes were investigated by High resolution transmission electron microscopy, Scanning electron microscopy and Energy dispersive spectroscopy. The electrochemically active surface area of the electro-deposited spherically shaped Pt particles was calculated to be 63.96 m² g^?1 and 25.10 m² g^?1 on graphene/Pt and GC/Pt, respectively. The electro-catalytic performance of modified electrodes for methanol oxidation was envisaged by cyclic voltammetry, linear sweep voltammetry and chronoamperometry. Graphene/Pt modified GC electrode showed higher oxidation peak current (42.90 mA cm^?2) than GC/Pt modified electrode (16.24 mA cm^?2) in forward scan of methanol oxidation because of the uniform distribution of spherically shaped Pt particles on graphene. The reaction path for methanol oxidation at different potentials was elucidated by means of Electrochemical Impedance Spectroscopy.     

Preparation of Pt/NiO-C electrocatalyst and heat-treatment effect on its electrocatalytic performance for methanol oxidation

Pt catalyst supported on Vulcan XC-72R containing 5 wt% NiO (Pt/NiO–C) showed larger electrochemical active surface area and higher electrochemical activity for methanol oxidation than Pt catalyst supported on Vulcan XC-72R using polyol method without NiO addition. Prepared Pt/NiO–C electrocatalyst was heat-treated at four temperatures (200, 400, 600, and 800 °C) in flowing N₂. X-ray diffraction and temperature-programmed desorption results indicated that NiO was reduced to Ni in inert N₂ during heat-treatments at temperatures above or equal to 400 °C, while oxygen from NiO reacted with carbon support due to the catalytic effect of Pt. The reduced Ni formed an alloy with Pt, which, according to the X-ray photoelectron spectroscopy data, resulted in a shift to a lower binding energy of Pt 4f electrons. The Pt/NiO–C electrocatalyst heat-treated at 400 °C showed the best activity in methanol oxidation due to the change in Pt electronic structure by Ni and the minimal aggregation of Pt particles.     

Nitrogen-doped graphene aerogel with an open structure assisted by in-situ hydrothermal restructuring of ZIF-8 as excellent Pt catalyst support for methanol electro-oxidation

We report an innovative strategy to prepare the porous N-doped graphene aerogel with an open structure and abundant defects by hydrothermal self-assembly of zeolitic imidazolate framework (ZIF)-8 and graphene oxide. The in-situ hydrothermal restructuring of ZIF-8 on graphene sheets plays a key role in the synthesis of the open structure and the uniform N-doping. The dissolution and restructuring of ZIF-8 on graphene oxide obviously suppress the stacking and reunion of graphene sheets to obtain the continuous macroporous structure. Moreover, the introduction of N and Zn creates the abundant N-doped sites and microporous structure. Its unique structure and composition improve the accessible surface area, the mass transfer diffusion, the dispersion and electronic structure of Pt nanoparticles, further resulting in the high catalytic performance of Pt-based catalyst for methanol oxidation reaction (MOR). Its MOR activity is about 1.8 times of commercial Pt/C, and its long cycling durability is improved by about 18.7% compared with commercial Pt/C. This work renders a promising method by utilizing ZIF-8 derivatives to synthesize the excellent N-doped carbon materials for electrochemical applications.     

Investigation of Pt/WC/C catalyst for methanol electro-oxidation and oxygen electro-reduction

A Pt/WC/C catalyst is developed to increase the methanol electro-oxidation (MOR) and oxygen electro-reduction (ORR) activities of the Pt/C catalyst. Cyclic voltammetry and CO stripping results show that spill-over of H⁺ occurs in Pt/WC/C, and this is confirmed by comparing the desorption area values for H⁺ and CO. A significant reduction in the potential of the CO electro-oxidation peak from 0.81 V for Pt/C to 0.68 V for Pt/WC/C is observed in CO stripping test results. This indicates that an increase in the activity for CO electro-oxidation is achieved by replacing the carbon support with WC. Preferential deposition of Pt on WC rather than on the carbon support is investigated by complementary analysis of CO stripping, transmission electron microscopy and concentration mapping by energy dispersive spectroscopy. The Pt/WC/C catalyst exhibits a specific activity of 170 mA m⁻² for MOR. This is 42% higher than that for the Pt/C catalyst, viz., 120 mA m⁻². The Pt/WC/C catalyst also exhibits a much higher current density for ORR, i.e., 0.87 mA cm⁻² compared with 0.36 mA cm⁻² for Pt/C at 0.7 V. In the presence of methanol, the Pt/WC/C catalyst still maintains a higher current density than the Pt/C catalyst.