Pt-CeO2/C anode catalyst for direct methanol fuel cells

In order to develop a cheaper and durable catalyst for methanol electrooxidation reaction, ceria (CeO₂) as a co-catalytic material with Pt on carbon was investigated with an aim of replacing Ru in PtRu/C which is considered as prominent anode catalyst till date. A series of Pt-CeO₂/C catalysts with various compositions of ceria, viz. 40 wt% Pt-3–12 wt% CeO₂/C and PtRu/C were synthesized by wet impregnation method. Electrocatalytic activities of these catalysts for methanol oxidation were examined by cyclic voltammetry and chronoamperometry techniques and it is found that 40 wt% Pt-9 wt% CeO₂/C catalyst exhibited a better activity and stability than did the unmodified Pt/C catalyst. Hence, we explore the possibility of employing Pt-CeO₂ as an electrocatalyst for methanol oxidation. The physicochemical characterizations of the catalysts were carried out by using Brunauer Emmett Teller (BET) surface area and pore size distribution (PSD) measurements, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) techniques. A tentative mechanism is proposed for a possible role of ceria as a co-catalyst in Pt/C system for methanol electrooxidation.     

Anodic catalysts for polymer electrolyte fuel cells: the catalytic activity of Pt/C,Ru/C and Pt-Ru/C in oxidation of CO by O2

The catalytic activity for oxidation of CO by O₂ was investigated on commercial Pt/C, Pt-Ru/C (Pt/Ru atomic ratio = 20, 3, 1, 1/3) and Ru/C. All samples contained 20 wt.% metal. Assuming equal surface and bulk composition, the number of surface Pt and Ru atoms was calculated from the average size of the supported metal particle as determined by TEM. On Pt-Ru/C alloys, the turnover frequency per Ru atom, N_Ru/molecules s⁻¹ Ru-atom⁻¹, was independent of chemical composition. This finding suggests that the active site in these alloys is Ru. In the temperature range 300–400 K, the turnover frequency per active metal atom was 50–300 times higher on Pt-Ru/C than on Pt/C. The turnover frequency was 400 times higher on Ru/C than on Pt/C at 313 K and 90 times higher at 353 K. Addition of water vapor to the reactant mixture left the catalytic activity of Ru/C unchanged but slightly increased the activity of Pt/C. On both catalysts the activation energy and reaction orders were nearly the same as in dry atmosphere. Conversely, the addition of water markedly decreased the activation energy for Pt-Ru(1 : 1)/C alloy (from 19 to 11 kcal mol⁻¹). These findings suggest that fuel cells equipped with Pt-Ru/C anodes perform better than cells with Pt/C anodes. They do so because Ru effectively oxidizes the carbon monoxide present as an impurity in the H₂-reformed fuel.     

Stabilization and dispersion of PtRu and Pt nanoparticles on multiwalled carbon nanotubes using phosphomolybdic acid,and the use of the resulting materials in a direct methanol fuel cell

PtRu and Pt nanoparticles were deposited on the surface of multiwalled carbon nanotubes (MWCNTs) with the assistance of phosphomolybdic acid (PMo) by a one-pot hydrothermal reduction strategy. Transmission electron microscopy shows a high-density PtRu (or Pt) nanoparticles uniformly dispersed on the surface of the MWCNTs with an average diameter of 1.8 nm for PtRu nanoparticles and 2.4 nm for Pt nanoparticles. Moreover, the as-prepared PMo/PtRu/MWCNT and PMo/Pt/MWCNT electrocatalysts are highly electroactive for the electrochemical oxidation of methanol. Cyclic voltammograms show a high electrochemical surface area (ESA) and a large current density for methanol oxidation at the modified electrode by PMo/PtRu/MWCNT and PMo/Pt/MWCNT electrocatalysts. Electrochemical impedance spectroscopy reveals a high CO tolerance for PMo/PtRu/MWCNT and PMo/Pt/MWCNT electrocatalysts in the electrochemical catalysis of methanol oxidation. For comparison, PtRu/MWCNT and Pt/MWCNT electrocatalysts were prepared in control experiments without PMo. The results demonstrate that PtRu and Pt nanoparticles deposited on MWCNTs in the presence of PMo were superior to those on MWCNTs without PMo in several respects including: (1) a smaller size and a higher dispersion; (2) a higher ESA; (3) a larger current density for methanol oxidation; (4) a higher tolerance for CO poisoning.     

Effect of transition metals (Ni,Sn and Mo) in Pt5Ru4M alloy ternary electrocatalyst on methanol electro-oxidation

Pure Pt, PtRu and Pt₅Ru₄M (M = Ni, Sn and Mo) electrocatalysts were prepared using a NaBH₄ reduction method. The alloy formation and particle size of the electrocatalysts were determined by X-ray diffraction (XRD) and transmission electron microscopy (TEM), respectively. The formation of crystalline Pt was confirmed regardless of the addition of Ru and transition metals. The average particle size was found to be about 2.5–3.5 nm.The electrochemical properties of the electrocatalysts were analyzed by methanol electro-oxidation and CO stripping in the half cell. The mass activity and specific activity were obtained through these experiments. Methanol electro-oxidation and the specific activity of the PtRuNi electrocatalyst were much higher than that of PtRu electrocatalyst. The specific activity of methanol electro-oxidation based on EAS for the PtRuSn and PtRuMo electrocatalysts was higher than that of the PtRu, although their mass activity of methanol electro-oxidation was lower.     

Studies of physical and chemical properties of styrene-based plasma polymer films deposited by radiofrequency Ar/styrene glow discharge

Styrene-based plasma polymer (SPP) films having thickness in the range of 900–1800 nm are deposited from radiofrequency (RF) Ar/styrene glow discharge. Depositions of the SPP films are carried out at working pressure of 1.2 × 10^?1 mbar and in the RF power range of 40–130 W. The physical and chemical properties of the SPP films are investigated as a function of RF power. Optical emission spectroscopy (OES) studies on Ar/styrene glow discharge reveal that the relative concentrations of active plasma species are strongly dependent on the variation of RF power. Fourier transform infrared (FT-IR) and X-ray photoelectron spectroscopy (XPS) are used to analyze the internal chemical structures of the films. It is revealed that the SPP film with highest carbon content exhibits enhanced scratch and corrosion resistance behavior along with stable thermal properties. The thermogravimetric (TGA) and gel permeation chromatography (GPC) results suggest the presence of both aliphatic and aromatic units in the SPP films. Attempts are made to correlate the results obtained from OES, FT-IR and XPS analyses with the deposited films properties. The possibility of using SPP films as protective coatings is also explored.     

Investigation of the corrosion protection behavior of natural montmorillonite clay/bitumen nanocomposite coatings

The influence of clay particles on the corrosion properties of bituminous coating was studied. Different percentages of natural montmorillonite clay (Cloisite Na⁺) were added to emulsified bitumen in water to make 2 wt.%, 3 wt.% and 4 wt.% of clay/bitumen nanocomposite coatings. The coatings were applied on steel 37. Optical microscopy and transmission electron microscopy (TEM) were employed to study the structure of nanocomposite. To investigate the anti-corrosion properties of the coated panels, electrochemical impedance spectroscopy (EIS) was used. The findings indicated that the addition of clay nanolayers improved corrosion resistance of the coatings. Moreover, increasing clay loading up to 4 wt.%, increased the corrosion resistance.     

Electrocatalytic characteristics of Pt–Ru–Co and Pt–Ru–Ni based on covalently cross-linked sulfonated poly(ether ether ketone)/heteropolyacids composite membranes for water electrolysis

Membrane electrode assemblies (MEAs) of covalently cross-linked sulfonated poly(ether ether ketone) (CL-SPEEK)/heteropolyacids (HPAs) composite polymer with platinum-based alloys such as Pt–Ru–Co and Pt–Ru–Ni were prepared and their electrochemical properties for water electrolysis were investigated. The HPAs, which were used in the composite membranes, were tungstophosphoric acid (TPA) (the part of TPA data was permitted by the previous authors), molybdophosphoric acid (MoPA), and tungstosilicic acid (TSiA). The MEAs with Pt–Co, Pt–Ru–Co, and Pt–Ru–Ni in the anode catalyst layer were prepared by means of a non-equilibrium impregnation–reduction (I–R) method. The electrocatalytic properties of composite membranes, such as the cell voltage and coulombic charge in CV, were in the following order: CL-SPEEK/MoPA40 > CL-SPEEK/TPA30 > CL-SPEEK/TSiA40 (wt%). For the optimum cell applications of water electrolysis, the cell voltage of Pt/PEM/Pt–Ru–Co (Electrodeposited (Dep)-MoPA) MEA with a CL-SPEEK/MoPA40 membrane was 1.70 V at 80 °C and 1 A cm^?2, and this voltage carried a value lower than that of 1.81 V of Nafion 117. In addition, the observed activity of Pt–Ru–Co (75:12:13 by EDX) is a little higher than that of Pt–Ru–Ni (79:10:11 by EDX). The mean coulombic charge and activity enhancement of Pt–Ru–Co catalysts, with and without electrodeposition, showed the same CV profiles of the Pt–Ru–Co catalysts and were in the following order: Nafion 117 < CL-SPEEK/TSiA40 < CL-SPEEK/TPA30 < CL-SPEEK/MoPA40. The current density peak of electrodeposited electrodes was a little better than those of inactivated electrodes on the same membranes. The current peak by Pt–Ru–Co with CL-SPEEK/MoPA40 (Dep-MoPA) is more than about three times as high as those of Pt electrodes on the same membranes.     

Sodium borohydride as the hydrogen supplier for proton exchange membrane fuel cell systems

This paper introduces and discusses the latest research on the use of H₂ generated via the NaBH₄ hydrolysis reaction for proton exchange membrane fuel cells (PEMFCs). To realize the NaBH₄–PEMFC system, many hydrolysis catalysts such as Ru/anion-exchange resins, Pt/LiCoO₂, Co powder/Ni foam, PtRu/LiCoO₂ and Ru/carbon have been proposed. Through these efforts, the hydrolysis reaction conversion approached 100%. In addition, the average H₂ generation rate based on most of the reports generally ranged from 0.1 to 2.8 H₂ l min^− 1 g^− 1 (catalyst), which produced a level of PEMFC performance equivalent to 0.1–0.3 kW g^− 1 (catalyst). However, it was also reported that the H₂ generation rate was 28 H₂ l min^− 1 g^− 1 (catalyst) with the catalyst of Pt/carbon (acetylene black).Considering these reports and the advantageous features of NaBH₄ hydrolysis, the NaBH₄–PEMFC system seems to be technologically feasible and would constitute an alternative system of supplying H₂ in fuel cells.However, some challenges remain, such as the deactivation of the catalyst, the treatment of the by-products, and the proper control of the reaction rate. In addition, if the price of NaBH₄ were to be further reduced, this system could become the most powerful competitor in portable application fields of PEMFC.     

Methane dehydroaromatization over modified Mn/H-ZSM-5 zeolite catalysts: Effect of tungsten as a secondary metal

The influence of tungsten (0.5–1.5 wt.%) on the MDA reaction was investigated at 800 °C. Addition of W to a 2Mn/H-ZSM-5 catalyst led to a decrease in methane conversion from 6 to 4%. An aromatic selectivity of 74% was obtained with the unpromoted catalyst but this decreased (i.e. from 41 to 12%) with increase in tungsten loading. Addition of Pt or Ru to a 1.5 W/2Mn/H-ZSM-5 catalyst led to an increase in aromatic selectivity from 12 to 55% (Pt) or 46% (Ru) while the coke selectivity decreased from 78 to 37% (Pt) or 42% (Ru) due to the hydrogenating activity of Pt and Ru.     

Enhanced ferroelectric properties of La-substituted BiFeO3 thin films on LaSrCoO3/Pt/TiO2/SiO2/Si (1 0 0) substrates prepared by the soft chemical method

Bi_0.85La_0.15FeO₃ (BLFO015) thin films were deposited by the polymeric precursor solution on La_0.5Sr_0.5CoO₃ substrates. For comparison, the films were also deposited on Pt bottom electrode. X-ray diffraction data confirmed the substitutions of La into the Bi site with the elimination of all secondary phases under a substitution ratio x = 15% at a temperature of 500 °C for 2 h. A substantial increase in the remnant polarization (P_r) with La_0.5Sr_0.5CoO₃ bottom electrode (P_r ≈ 34 μC/cm²) after a drive voltage of 9 V was observed when compared with the same film deposited on Pt substrate. The leakage current behavior at room temperature decreased from 10^?8 (Pt) to 10^?10 A/cm² on (La_0.5Sr_0.5CoO₃) electrode under a voltage of 5 V. The fatigue resistance of the Au/BLFO015/LSCO/Pt/TiO₂/SiO₂/Si (1 0 0) capacitors with a thickness of 280 nm exhibited no degradation after 1 × 10⁸ switching cycles at a frequency of 1 MHz.     

On the intercalation of CO molecules in ultra-high vacuum conditions underneath graphene epitaxially grown on metal substrates

We have studied the interaction of CO with epitaxial graphene on Pt(1 1 1) and Ru(0 0 0 1) by means of high-resolution electron energy loss spectroscopy measurements. Our experiments unambiguously demonstrate that in ultra-high vacuum conditions CO does not intercalate underneath the graphene monolayer supported on Pt(1 1 1) and Ru(0 0 0 1). For submonolayer coverages of graphene on Pt(1 1 1), CO adsorption occurs only in Pt on-top sites while bridge sites, usually populated on the clean Pt(1 1 1) surface, are inhibited. Instead, we find that epitaxial graphene is rather reactive toward water molecules.     

Polypyridyl ruthenium complexes containing anchoring nitrile groups as TiO2 sensitizers for application in solar cells

Ruthenium polypyridyl complexes of general formula [Ru(bpy)_3 − x(Mebpy-CN)_x]^2 + (x = 1,2 and 3, bpy = 2,2′-bipyridine, Mebpy-CN = 4-methyl-2,2′-bipyridine-4′-carbonitrile) can be used as visible dyes in novel solar cells formed with a porous TiO₂ film (1 cm²), Pt counter-electrode and iodine/iodide as the redox mediator electrolyte dissolved in a polymeric matrix. These complexes can be anchored over the surface of nanocrystalline TiO₂ through nitrile groups, as evidenced by Raman spectra of the adsorbed species. Irradiated by a solar simulator (67 mW cm^− 2), the cells assembled with the Ru complexes with x = 2 and 3 as TiO₂ sensitizers exhibit almost identical current–potential curves, with short-circuit photocurrents of 1.25 mA cm^− 2, fill factors of 0.5 and overall efficiencies around 0.44%. The Ru complex with x = 1 and a similar Re complex did not perform as well as sensitizers. These data were consistent with results obtained from quantum efficiency curves and impedance spectra. We conclude that complexes with nitrile groups as anchoring entities are promising candidates for designing efficient DSCCs.     

Facile preparation and unique H2 adsorption behavior of three-dimensional novel Pt–Ru hollow sphere assemblies

Three-dimensional long range ordered hollow Pt–Ru sphere assemblies were prepared using a sacrificial three-dimensionally ordered macroporous (3DOM) carbon template. Metallic salts, such as a mixture of RuCl₃ with H₂PtCl₆ were infiltrated into the carbon template, and a reduced Pt–Ru phase was produced on the surface of the 3DOM carbon template by a borohydride reduction reaction. The sacrificial template was then burnt off in air at 650 °C. The diameter of the hollow Pt–Ru spheres could be tailored using a different pore size 3DOM carbon template. Assemblies with an outer diameter of 550 nm showed high BET surface area of 584.3 m²/g. In addition, a high hydrogen adsorption stoichiometry (>0.5 H/M) was obtained on the Pt–Ru sphere assemblies, which indicated that most of the metal atoms on the surface were exposed.     

Evaluation of corrosion resistance of polypyrrole/functionalized multi-walled carbon nanotubes composite coatings on 60Cu–40Zn brass alloy

Polypyrrole/multi-walled carbon nanotubes (PPy/MWCNT) and its carboxylic functionalized (PPy/MWCNT-COO⁻) composite films were successfully electropolymerized by cyclic voltammetry as protective coating against corrosion on 60Cu–40Zn brass alloy surface. It yielded to strongly adherent and smooth nanocomposite films. Kinetics of the corrosion protection was investigated in 3.5 wt% NaCl solutions by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization tests. The results showed that the presence of MWCNT in PPy coat considerably reduces the corrosion rate of 60Cu–40Zn brass alloy. The enhanced inhibition is most likely due to interaction between MWCNT and PPy. This in turn, improves the alloy passivation improvement and alters the permselectivity of the coating from anionic selectivity to the cationic selectivity. Moreover, PPy/MWCNT-COO⁻ functionalized nanocomposite provided higher corrosion resistance coating than PPy/MWCNT alone.     

Copper/polypyrrole multilayer coating for 7075 aluminum alloy protection

The corrosion behavior of 7075 aluminum (Al), copper modified Al (Al/Cu), polypyrrole modified Al (Al/PPy) and copper (under layer)/polypyrrole (top layer) modified Al (Al/Cu/PPy) samples were investigated in 3.5% NaCl solution. The copper plating on aluminum was carried out from acidic copper sulphate solution by electroless method. Polypyrrole (PPy) was electrochemically synthesized on Al and Al/Cu electrodes from 0.1 M pyrrole containing 0.4 M oxalic acid solution using cyclic voltammetry technique. The films synthesized were characterized by Fourier transform infrared spectroscopy (FT-IR). The thermal stability of PPy films was investigated by thermogravimetric analysis (TGA). The surface morphologies were examined by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The corrosion behavior of samples was investigated by electrochemical impedance spectroscopy (EIS) and anodic polarization curves. The data obtained showed that the synthesis of PPy on top of the Cu layer significantly enhances the corrosion resistance of Al by exhibiting a barrier effect against the attack of corrosive environment.     

Photovoltaic property dependence of dye-sensitized solar cells on sheet resistance of FTO substrate deposited via spray pyrolysis

F-doped SnO₂ (FTO) glass substrate was successfully fabricated via spray-pyrolysis deposition for use as a transparent conducting substrate in dye-sensitized solar cells (DSSCs). To investigate the performance dependence of DSSCs on the sheet resistance of the FTO films, three types of FTO films with sheet resistance values of 2 Ω/□, 4 Ω/□, and 10 Ω/□ were fabricated. Commercial FTO films having a sheet resistance of 15 Ω/□ were prepared for comparison. The structural, electrical, and optical properties of FTO films were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), the four-point probe method, and UV–vis spectrometry. The photocurrent–voltage data show that DSSCs fabricated with a sheet resistance of 2 Ω/□ exhibit the best photoconversion effciency (～5.5%) among the four samples. The performance improvement of DSSCs is due to improved short-circuit current density (～13.7 mA/cm²) and fill factor (～62.3%).     

Ammonia synthesis on magnesia supported ruthenium catalysts with mesoporous structure

Mesoporous Ru/MgO catalysts for ammonia synthesis were prepared by sol–gel method with concurrently decomposing Ru carbonyl complex. The catalytic properties were characterized mainly by means of nitrogen adsorption isotherm, hydrogen chemisorption, X-ray diffraction, and transmission electron microscopy. The detailed observation of decarbonylation behavior on the catalysts prepared under various conditions revealed that the carbonyl complex acted as an effervescent reagent to form a mesoporous structure with radius of 1–9 nm on MgO support. Furthermore, both specific surface area and metal dispersion tended to increase with increasing the Ru carbonyl complex concentration. The best ammonia formation rate was consequently observed on the Ru/MgO catalyst (Ru: 7.1 wt%) with high surface area (290 m²/g) of this series.     

Electrosynthesis of PAni/PPy coatings doped by phosphotungstate on mild steel and their corrosion resistances

Polyaniline/polypyrrole (PAni/PPy), polyaniline-phosphotungstate/polypyrrole (PAni-PW₁₂/PPy) and PAni/PPy-PW₁₂ have been successfully electrodeposited on mild steel (MS) by cyclic voltammetry in aqueous oxalic acid solutions. It was found that the incorporation of PW₁₂ enhanced the corrosion resistance of PAni/PPy coating. Moreover, in comparison to PAni-PW₁₂/PPy, PAni/PPy-PW₁₂ coating exhibited better corrosion resistance for mild steel. After immersion of 36 h in 0.1 M HCl, for instance, the polarization resistance of PAni/PPy-PW₁₂ coating reached 1695 Ω cm², more than those of both PAni/PPy and PAni-PW₁₂/PPy.     

Dissolution of platinum in acidic media

To understand the degradation of the Pt/C cathode for use in polymer electrolyte fuel cells, the solubility and the dissolution mechanism of platinum in acidic media was very important fundamentally. In this study, the platinum solubility has been determined in acidic electrolytes as a function of temperature and pH. The solubility was 3 × 10^?6 mol dm^?3 at 25 °C in 1 mol dm^?3 of H₂SO₄, HClO₄, and CF₃SO₃H under air. It increased at higher temperature and decreased in pH. The apparent enthalpy of the dissolution reaction was ca. 25 kJ mol^?1, and the solubility was proportional to [H⁺] in these acids. The platinum solubility in oxygen was slightly higher than that in air. The detected dissolved Pt species was 4 valent. On the other hand, the solubility of platinum in nitrogen was much lower than the oxygen-containing atmosphere. Based on these results, the platinum solubility in an oxygen-containing atmosphere would mainly be the following acidic dissolution reaction: PtO₂ + H⁺ + H₂O = Pt(OH)₃⁺.     

Studying the effect of organo-modified nanoclay loading on the thermal stability,flame retardant,anti-corrosive and mechanical properties of polyurethane nanocomposite for surface coating

Clay polyurethane nanocomposite (CPN) coating films were fabricated by uniformly dispersing nanoclay, organically modified with 25–30 wt.% octadecylamine in varying concentrations up to 5 wt.%, in a commercial two component, glossy, acrylic aliphatic polyurethane using ultrasonication. Organo-modified nanoclay was characterized by X-ray diffraction (XRD). The dispersion of the nanoclay into the matrix was investigated by scanning electron microscopy (SEM). CPN coating films were characterized by thermogravimetric analysis (TGA), and flame retardant, corrosion resistance and mechanical properties were also investigated. The XRD measurement indicated that, the organo-modified nanoclay particles were mainly constituted of montmorillonite with traces of quartz and calcite also found to be present. The SEM analysis showed that the nanoclay layers were dispersed and intercalated into the polyurethane coating. Thermogravimetric analysis showed that incorporating 5 wt.% organo-nanoclay into polyurethane considerably enhanced the thermal stability and increased the char residue to 14.11 wt.% relative to 4.58 for the sample without organo-nanoclay (blank polyurethane). The limiting oxygen index (LOI) test revealed that incorporation of organo-nanoclay led to a further increase in LOI values, which indicate an improvement in flame retardancy properties. The corrosion resistance also improved and this improvement increases with increase nanoclay wt.%. The mechanical resistance measurements demonstrated that the gloss of the CPN coating films slightly decreased, although hardness, adhesion and impact resistance of the CPN coating films improved with the incorporation of the organo-nanoclay.