Catalytic activity,stability and impedance behavior of PtRu/C,PtPd/C and PtSn/C bimetallic catalysts toward methanol and formic acid oxidation

PtRu, PtPd and PtSn with weight ratios of (2:1) on carbon black (Vulcan XC-72) supported bimetallic catalysts were prepared by using microwave method via chemically reduction of H₂PtCl₆·6H₂O, RuCl₃, PdCl₂ and SnCl₂·2H₂O precursors with ethylene glycol (EG). These prepared catalysts were systematically investigated and obtained results were compared with commercial Pt black, PtRu black catalysts and with each other. The catalysts were characterized with XRD, ICP-MS, EDS and TEM. The electrocatalytic activities, stability and impedance of the catalysts were investigated in sulfuric acid/methanol and sulfuric acid/formic acid mixtures using electrochemical measurements. The results showed that PtSn/C catalyst showed comparable activity and durability with commercial Pt/C catalyst toward methanol oxidation. The synthesized PtRu/C catalyst was found to completely oxidize methanol and it showed more catalytic activity than commercial PtRu catalyst. Bimetallic PtPd/C catalyst gave better activity than both commercial Pt black and synthesized Pt/C catalyst for oxidation of formic acid. Higher electrochemical active surface areas were obtained with supported bimetallic catalysts.     

Synthesis and characterization of polypyrrole/carbon composite as a catalyst support for fuel cell applications

Polypyrrole (PPy)/Carbon composites were synthesized by in situ chemical oxidative polymerization of pyrrole monomer on carbon black. Effects of polymerization temperature (either 0 °C or 25 °C) and different dopants including p-toluenesulfonic acid (p-TSA) and sodium dodecyl sulfate (SDS) on the properties of the composites were investigated. The synthesized composites were characterized by XRD, FTIR and TGA. Electrical conductivities of the composites were determined by using four-point probe technique. Electrochemical oxidation characteristics of the synthesized PPy/Carbon composites were investigated by cyclic voltammetry via potential holding experiments. The PPy/Carbon composites synthesized at 0 °C and with p-TSA as dopant showed the best oxidation resistance than carbon and other composites.     

Silicotungstic acid stabilized Pt–Ru nanoparticles supported on carbon nanofibers electrodes for methanol oxidation

Silicotungstic acid stabilized Pt–Ru nanoparticles supported on Functionalized Carbon Nanofibers have been prepared by a microwave-assisted polyol process. The samples were characterized by XRD, SEM and TEM analysis. The electro-catalytic activities of the prepared composites (20% Pt–Ru/STA–CNF) were examined by using Cyclic Voltammetry (CV) for oxidation of methanol. The electro-catalytic activity of the carbon nanofiber based composite (20% Pt–Ru/STA–CNF) electrode for methanol oxidation showed better performance than that of commercially available Johnson Mathey 20% Pt–Ru/C and 20% Pt–Ru/STA–C catalyst. The results imply that carbon nanofiber based STA composite electrodes are excellent potential candidates for application in direct methanol fuel cells.     

Preparation of PEDOT-modified double-layered hollow carbon spheres as Pt catalyst support for methanol oxidation

In this paper, Pt nanoparticles (Pt NPs) deposited hybrid carbon support is prepared by modifying double-layered hollow carbon spheres（DLHCs）with poly(3,4-ethylenedioxythiophene) (PEDOT) and used as anode catalyst of methanol oxidation. The structure of nanocomposites is characterized by SEM, TEM, FT-IR, XRD and XPS, confirming the greatly enhanced synergistic effect between the PEDOT and DLHCs, and illustrating the uniform distribution of Pt NPs on the PEDOT/DLHCs composite surface with a small particle size (~2.63 nm). Cyclic voltammetry, chronoamperometry and impedance spectroscopy applied to determine the electrocatalytic activity of catalysts, it is found that the synthesized PEDOT/DLHCs/Pt possesses excellent characteristics such as large electrochemically active surface area and high mass activity of 59.45 m² g⁻¹ and 807 mA mg⁻¹ in 0.5 M H₂SO₄ containing 1 M methanol solution, which is almost 1.24 and 2.8 times greater than those of commercial Pt/C, and the catalyst exhibits superior stability after 500 durability cycles. The enhanced electrocatalytic behavior can be ascribed to the excellent electronic conductivity of PEDOT-modified DLHCs and the strong binding of PEDOT/DLHCs to Pt NPs, suggesting that the PEDOT/DLHCs/Pt is a promising electrocatalyst for direct methanol fuel cell.     

CoSe nanoparticles prepared by the microwave-assisted polyol method as an alcohol and formic acid tolerant oxygen reduction catalyst

CoSe catalyst supported on nanoporous carbon was synthesized by microwave heating of glycerol solutions of Co(II) acetate and sodium selenite. The electrocatalytic behavior of the CoSe/C for oxygen reduction reaction (ORR) and its tolerance to several alcohols and formic acid were investigated by rotating disk electrode voltammetry and the results were compared with those of Pt/C. The results indicate that CoSe/C is a highly selective electrocatalyst towards ORR and shows a very high degree of tolerance to the presence of formic acid, methanol, ethanol, 2-propanol and ethylene glycol in acid medium. For a 20 wt.% CoSe/C, the onset potential and the magnitude of the current for ORR were almost the same with or without the presence of these fuels. In contrast, the Pt/C catalyst exhibited a mixed potential due to the simultaneous oxidation of the fuels and reduction of oxygen, which in turn caused the onset potential for the ORR to shift cathodically by ca. 500 mV in the presence of these fuels. Electrochemical measurements showed that the synthesized CoSe/C catalyst had a four-electron transfer mechanism for ORR. It is expected that this low cost electrocatalyst with its almost full tolerance and multi-fuel capability can find application in conventional and mixed-reactant fuel cells fueled with low molecular weight alcohols or formic acid.     

Hydrogen production by partial oxidation of ethanol over Pt/CNT catalysts

The platinum‐supported catalysts have been prepared by ethylene glycol reduction method, and the catalysts were applied to the partial oxidation of ethanol (POE) for hydrogen production. Four types of support, including CNTs, Al₂O₃, ZrO₂, and CeO₂, were used on POE catalytic performance test. Prior to catalyst preparation, the influence of acidic pretreatment on CNTs purity, surface morphology, and pore structure were investigated. The acid‐treated CNTs and prepared catalysts were characterized with N₂ physisorption, Raman, thermogravimetric, and transmission electron microscopy analysis. The experimental results show that the particle size and metal dispersion of platinum on CNTs, as well as POE activity, depend on pH value of reducing agent and reduction temperature in the stage of catalyst preparation. In the condition pH value of 10 and temperature at 120 °C for catalyst 5 wt% Pt/CNTs preparation, 2 nm platinum clusters were obtained. Using the as‐prepared catalyst to study the effects of POE reaction conditions on the ethanol conversion, hydrogen selectivity, and hydrogen production rate under constant gas hourly space velocity, the corresponding values at the optimum reaction temperature 400 °C and O₂/C₂H₅OH molar ratio of 0.5 were 98.2%, 97.5%, and 202.3 mmol s^?1 kg^?1, respectively. Copyright © 2013 John Wiley & Sons, Ltd.     

Facile synthesis of reduced graphene oxide supported PtAg nanoflowers and their enhanced electrocatalytic activity

In this work, a simple and facile method is developed in the synthesis of well-dispersed PtAg nanoflowers on reduced graphene oxide nanosheets (PtAg/RGOs) under solvothermal conditions, using ethylene glycol as a reducing agent and hexadecyl trimethyl ammonium bromide (CTAB) as capping and stabilizing agents. The as-prepared nanocomposites show a superior electrocatalytic activity, good tolerance, and better stability toward the oxidation of formic acid and ethylene glycol in alkaline media, compared with the commercial Pt/C (10 wt%) catalyst. For the oxidation of formic acid, the PtAg nanoflowers own thirty times higher of the catalytic currents than those of the commercial Pt/C catalyst. Meanwhile, for the oxidation of ethylene glycol, the ratio of forward current (j_F) to reverse current (j_R) is high up to 8.4, which is almost four times higher than that of the commercial Pt/C catalyst. This strategy provides a promising platform for direct formic acid and ethylene glycol fuel cells.     

Electrochemical oxidation of small organic molecules on hydrothermal synthesized Pt and PtCo/ordered mesoporous carbon

Ordered mesoporous carbon (OMC) supported nanosized Pt and PtCo alloy electrocatalysts were synthesized by ethylene glycol hydrothermal reduction route and their electrochemical oxidation activity toward several typical small organic molecules (SOMs) was investigated. Structural characterization revealed that Pt and PtCo nanoparticles with mean diameter of 3-4 nm were well dispersed on OMC (BET specific surface of 2220 cm²/g). Electrochemical measurements confirmed that electrochemical oxidation behaviors of SOMs on synthesized Pt/OMC and PtCo/OMC catalysts were complicated and the carbon chain length of SOMs and the intermediates, especially CO_ads oxidation behaviors on Pt active sites are two main factors which affect the SOMs oxidation.     

Supported gold nanoparticles as anode catalyst for anion-exchange membrane-direct glycerol fuel cell (AEM-DGFC)

The carbon supported Au nanoparticles (Au-NPs) catalyst with a small average size (3.5 nm) and narrow size distribution (2–6 nm) was synthesized by a solution phase-based nanocapsule method. The reactivity of glycerol oxidation on Au/C is much higher than that of methanol and ethylene glycol oxidations in alkaline electrolyte. The anion-exchange membrane-direct glycerol fuel cell (AEM-DGFC) with the Au/C anode catalyst and a Fe-based cathode catalyst shows high performances with both high-purity glycerol and crude glycerol fuel: the open circuit voltages (OCVs) are 0.67 and 0.66 V, and peak power densities are 57.9 and 30.7 mW cm⁻² at 80 °C, respectively. Fed with crude glycerol, the Au/C anode catalyst-based AEM-DGFC also demonstrates high performance stability at 80 °C. The product analysis shows that the electrooxidation of glycerol on the Au/C anode catalyst in AEM-DGFCs favors production of deeper-oxidized chemicals: tartronic acid, mesoxalic acid and oxalic acid, which leads to higher fuel cell's Faradic efficiency.     

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.     

Study of core-shell platinum-based catalyst for methanol and ethylene glycol oxidation

A Ru_core-Pt_shell, XC72-supported catalyst was synthesized in a two-step process: first, by deposition of Ru on XC72 by the polyol process and then by deposition of Pt on the XC72-supported Ru, with NaBH₄ as reducing agent. The structure and composition of this core-shell catalyst were determined by EDS, XPS, TEM and XRD. Electrochemical characterization was determined with the use of cyclic voltammetry and chronoamperometry. The methanol and ethylene glycol oxidation activities of the core-shell catalyst were studied at 80 °C and compared to those of a commercial catalyst. It was found to be significantly better (in terms of A g⁻¹ of Pt) in the case of methanol oxidation and worse in the case of ethylene glycol oxidation. Possible reasons for the lower ethylene glycol oxidation activity of the core-shell catalyst are discussed.     

Glycerol electrooxidation on highly active Pd supported carbide/C aerogel composites catalysts

The nanosized carbide supported on carbon aerogel composites have been synthesized by polycondensation of resorcinol and formaldehyde (RF) method in the presence of sodium tungstate and sodium molybdate. The materials are characterized by X-ray diffraction, transmission electron microscopy, energy dispersive X-ray spectroscopy (EDS), and cyclic voltammetry. The Pd nanoparticles supported on binary-carbide and carbon aerogel composites (Pd@WC-Mo₂C/C) for glycerol oxidation are investigated for the first time. The Pd@WC-Mo₂C/C as electrocatalyst shows a superior activity toward the glycerol oxidation in terms of the peak current density, which is almost two times higher than that of Pd/C and show better poison-resistant ability. The binary transition-metal carbide will be the potential catalyst support for the direct alcohol fuel cells.     

Preparation of nickel catalysts supported on CaO.2Al2O3 for methane reforming with carbon dioxide

Nanocrystalline calcium aluminate (CaO.2Al₂O₃) was prepared by a simple co-precipitation method using Poly (ethylene glycol)-block-poly(propylene glycol)-block poly(ethylene glycol) (PEG-PPG-PEG, MW:5800) as surfactant and employed as catalyst support for nickel catalysts in methane reforming with carbon dioxide. The prepared samples were characterized by X-ray diffraction (XRD), N₂ adsorption (BET), Temperature programmed reduction and oxidation (TPR-TPO) and Scanning electron microscopy (SEM) techniques. The results showed that the prepared support has a high potential as support for nickel catalysts in methane reforming with carbon dioxide. The results showed high catalytic activity and stability for the prepared catalysts. Among the prepared catalysts 15% Ni/CaO.2Al₂O₃ was the most active catalyst and showed the highest affinity for carbon formation. In addition, 7% Ni/CaO.2Al₂O₃ possessed high catalytic stability during 50 h time on stream. The TPO analysis revealed that increasing in nickel content increased the amount of deposited carbon over the spent catalysts. SEM results detected only whisker type of carbon for all spent catalysts.     

Pt-Ru electrocatalysts supported on ordered mesoporous carbon for direct methanol fuel cell

Pt-Ru electrocatalysts supported on ordered mesoporous carbon (CMK-3) were prepared by the formic acid method. Catalysts were characterized applying energy dispersive X-ray analyses (EDX) and X-ray diffraction (XRD). Methanol and carbon monoxide oxidation was studied electrochemically by cyclic voltammetry, and current-time curves were recorded in a methanol solution in order to establish the activity towards this reaction under potentiostatic conditions. The physicochemical and electrochemical properties of the Pt-Ru catalysts supported on CMK-3 carbon were compared with those of electrocatalysts supported on Vulcan XC-72 and commercial catalyst from E-TEK. Additionally, in order to complete this study, Pt electrocatalysts supported on CMK-3 and Vulcan XC-72 were prepared by the same method and were used as reference. Results showed that the Pt-Ru/CMK-3 catalyst presented the best electrocatalytic activity towards the CO oxidation and, therefore, good perspectives to its application in DMFC anodes. On the other hand, the activity of the Pt-Ru/CMK-3 catalyst towards methanol oxidation was higher than that of the commercial Pt-Ru/C (E-TEK) catalyst on all examined potentials, confirming the potential of the bimetallic catalysts supported on mesoporous carbons.     

Platinum-antimony doped tin oxide nanoparticles supported on carbon black as anode catalysts for direct methanol fuel cells

Antimony doped tin oxide supported on carbon black (ATO/C) has been synthesized using an in situ co-precipitation method, and platinum-ATO/C nanoparticles have been prepared using a consecutive polyol process to enhance the catalyst activity for the methanol oxidation reaction. The Pt-ATO/C electrocatalyst is characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microcopy (SEM), energy dispersive X-ray spectroscopy (EDS) and cyclic voltammetry. The Pt-ATO/C catalyst exhibits a relatively high activity for the methanol oxidation reaction compared to Pt-SnO₂/C or commercial Pt/C catalyst. This activity can be attributed to the high electrical conductivities of the Sb-doped SnO₂, which induces the electronic effects with Pt catalysts. Pt-ATO/C is a promising methanol oxidation catalyst with high activity for the reaction in direct methanol fuel cells.     

Single atom iron carbons supported Pd–Ni–P nanoalloy as a multifunctional electrocatalyst for alcohol oxidation

Exploring high-performance and multifunctional electrocatalysts for alcohols oxidation is the key to develop alkaline fuel cells. Herein, we prepared a novel palladium-nickel-phosphorus catalyst supported on single atom iron carbons (SAICs) with different diameter sizes (1000 nm, 200 nm, 100 nm, 50 nm, and 20 nm), which were synthesized by direct carbonization of Fe-doped Zeolitic Imidazolate Framework-8 (ZIF-8). Electrochemical tests reveal that the as-prepared PdNiP/50nmSAIC exhibited excellent electrooxidation activity and stability to the various alcohols (methanol, glycerol, and especially ethylene glycol) electrooxidation in the alkaline solution, which is much higher than that of commercial Pd/C and other advanced Pd-based catalysts. Meanwhile, the rotating disk electrode (RDE) and CO-stripping results proves that PdNiP/50nmSAIC possesses a faster kinetic process of ethylene glycol oxidation and enhanced anti-CO poisoning ability. Our efforts provide a new strategy for the development of MOFs-derived multielement electrocatalyst with excellent activity and stability, and a bright future for alcohol oxidation.     

The performance of Pt nanoparticles supported on Sb2O5.SnO2, on carbon and on physical mixtures of Sb2O5.SnO2 and carbon for ethanol electro-oxidation

Pt nanoparticles were supported on Sb₂O₅.SnO₂ (ATO), on carbon and on physical mixtures of ATO and carbon by an alcohol-reduction process using ethylene glycol as reducing agent. The obtained materials were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Their performance for ethanol oxidation was investigated at room temperature by chronoamperometry and in a direct ethanol fuel cell (DEFC) at 100 °C. Pt nanoparticles supported on a physical mixture of ATO and carbon showed a significant increase of performance for ethanol oxidation compared to Pt nanoparticles supported on ATO or on carbon.     

Mesoporous carbon supported PtRu as anode catalyst for direct methanol fuel cell: Polarization measurements and electrochemical impedance analysis of mass transport

The performance of membrane electrode assembly (MEA) prepared with PtRu nanoparticles supported on a mesoporous carbon as anode catalyst are presented and compared against PtRu synthesized over Vulcan carbon. Polarization and power curves were obtained using 1 M methanol aqueous solution at the anode and O₂ at the cathode. The mesoporous carbon supported catalyst shows peak power of 40 mW cm⁻² and 67 mW cm⁻² at 30 °C and 60 °C respectively, that is, 15–30% higher than the Vulcan supported catalyst, and exhibits a wider range of operating current. Moreover, an improvement in the mass transport is observed for the catalyst supported on mesoporous carbon, yielding a lower voltage drop at high current density. This behavior was confirmed by electrochemical impedance spectroscopy (EIS), where an increases of the Warburg coefficient value by a factor 3–4 for the catalyst supported on mesoporous carbon as compared with that supported on Vulcan, would indicate a more facile diffusion of methanol through the mesoporous carbon.     

Nanostructured polypyrrole/carbon composite as Pt catalyst support for fuel cell applications

A novel catalyst support was synthesized by in situ chemical oxidative polymerization of pyrrole on Vulcan XC-72 carbon in naphthalene sulfonic acid (NSA) solution containing ammonium persulfate as oxidant at room temperature. Pt nanoparticles with 3–4 nm size were deposited on the prepared polypyrrole–carbon composites by chemical reduction method. Scanning electron microscopy and transmission electron microscopy measurements showed that Pt particles were homogeneously dispersed in polypyrrole–carbon composites. The Pt nanoparticles-dispersed catalyst composites were used as anodes of fuel cells for hydrogen and methanol oxidation. Cyclic voltammetry measurements of hydrogen and methanol oxidation showed that Pt nanoparticles deposited on polypyrrole–carbon with NSA as dopant exhibit better catalytic activity than those on plain carbon. This result might be due to the higher electrochemically available surface areas, electronic conductivity and easier charge-transfer at polymer/carbon particle interfaces allowing a high dispersion and utilization of deposited Pt nanoparticles.     

Titanium compounds TiC–C and TiO2–C supported Pd catalysts for formic acid electrooxidation

In this work, Pd nanoparticles supported on TiC–C and TiO₂–C as novel and efficient supports for formic acid electrooxidation are investigated. The Pd/TiC–C and Pd/TiO₂–C catalysts have been synthesized by microwave-assisted polyol process. The Pd nanoparticles in the Pd/TiC–C and Pd/TiO₂–C catalysts are found to disperse more uniformly and have smaller sizes on the TiC–C and TiO₂–C supports than that on carbon support alone. The addition of titanium compounds (TiC and TiO₂) significantly increases catalytic activity and stability of Pd for formic acid electrooxidation because of outstanding oxidation and acid corrosion resistance of titanium compounds (TiC and TiO₂), and metal-support interaction between Pd nanoparticles and titanium compound (TiC or TiO₂). The Pd/TiC–C catalyst displays the best performance among all the samples. The effect of TiC:C mass ratio on the catalytic activity is also investigated. It is found that the maximal catalytic activity and stability for formic acid electrooxidation is observed at the Pd/TiC–C catalyst with TiC:C mass ratio of 1:2.