Polyvinyl alcohol-modified graphene oxide as a support for bimetallic Pt–Pd electrocatalysts to enhance the efficiency of formic acid oxidation

The aim of this research was to study the efficiency of polyvinyl alcohol (PVA)-modified graphene oxide (GO) as a supporting material for catalysts that oxidize formic acid. The active metal catalysts (e.g., Pt and Pd) were electrodeposited on PVA/GO surfaces. The morphologies of the prepared catalysts were characterized by scanning electron microscopy and transmission electron microscopy, while their chemical compositions were identified by X-ray diffraction and X-ray photoelectron spectroscopy. The results show that compared with the other catalysts on GO, the prepared active PtPd alloy catalyst nanoparticles with 11.49–20.73 nm sizes were well dispersed on the PVA/GO surfaces. Electrochemical results indicate that the activities of the catalysts with PVA provided a higher current density than that of the catalysts without PVA. The bimetallic 3Pt3Pd/PVA/GO catalyst showed the greatest catalytic activity, stability, and CO oxidation when compared to those of other catalysts. The electronic, morphological, and structural properties promote the mass-charge transfer through the interaction. These results indicate that the PVA-modified GO provides a suitable site for active bimetallic catalyst surfaces, resulting in excellent formic acid oxidation and high CO elimination. The 3Pt3Pd/PVA/GO electrocatalyst is promising for enhancing formic acid oxidation.     

Hydrogen oxidation reaction: Evidences of different electrocatalytic activity between α and β Pd–H

The hydrogen oxidation reaction (hor) was studied in steady state conditions on a palladium thin film electrode supported on a gold rotating disc. The electrode surface was characterized by cyclic voltammetry and SEM observation. The hydrogen absorption process was analysed by open circuit potential decay in an acid solution saturated with hydrogen and the kinetic measurements were carried out potentiostatically in the same solution. The results obtained show a marked change on the dependence of the current density on overpotential due to the transition between the α and β phases of the Pd–H system. These results were correlated with appropriate kinetic expressions and the corresponding electrocatalytic activity of both phases was estimated.     

Electrocatalytic activity of supported gold nanoparticles toward CO oxidation: The perimeter effect of gold–support interface

The gold nanoparticles (AuNPs) sputtered on indium tin oxide (ITO) were used to investigate the origin of the high catalytic activity of AuNPs toward electrooxidation of CO in alkali media. We demonstrated that the catalytic activity is closely related to the gold–ITO perimeter, which represents only a very small percentage of the total surface area of AuNPs. Increasing the perimeter-to-surface ratio of the ITO-supported AuNPs leads to an increase of catalytic activity. This work provides a potential strategy to further promote the catalytic activity of AuNPs in the electrochemical system.     

The catalytic activity of bimetallic Pt—Pd polymer nanocomposites in formic acid oxidation

The platinum-palladium/Nafion metal—polymer nanocomposites were synthesized by chemical reduction of metal ions in water—organic reverse microemulsion solutions. The catalytic activity of the synthesized polymer composites with bimetallic Pt—Pd nanoparticles was estimated in the oxidation of hydrogen and formic acid.     

Liquid-phase oxidation of propylene to propylene glycol acetates over Pd/C and Pt?Pd/C: Effect of platinum on catalyst activity and metal dispersity

Kinetics of oxidation of propylene to propylene glycol and its acetates in acetic acid solutions of lithium nitrate over Pd/C and Pd–Pt/C catalysts has been studied. Catalysts were investigated using X-ray phase analysis and electron microscopy. Platinum introduction into catalyst increases the metal dispersity and the catalyst stability but produces no effect on the nature of surface sites active in propylene oxidation.

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Pd/C Pd–Pt/C. . , , , .

     

Preparation of carbon supported Pd–Pb hollow nanospheres and their electrocatalytic activities for formic acid oxidation

Pd–Pb hollow nanospheres dispersed on carbon black were developed by a galvanic replacement reaction between sacrificial cobalt nanoparticles and Pd²⁺, Pb²⁺ ions. The as-prepared catalysts were characterized by transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX), and X-ray diffraction (XRD). The electrochemical measurements show that the as-prepared catalysts have excellent catalytic activity for formic acid electrooxidation, which is attributed to the large surface area caused by the hollow structure and the lead doping effect which might modify the electronic structure of the catalysts.     

Oscillatory kinetics of the permanganate oxidation of oxalic acid?

The oxidation of oxalic acid by permanganate satisfies the mechanistic criteria of the oscillatory kinetics. However, the oscillatory changes in the absorbancy eventually found are due to formation of colloidal and coagulated MnO₂ and not to the chemical events.

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. , , MnO₂, .

     

Electrochemical-reduced graphene oxide-modified carbon fiber as Pt–Au nanoparticle support and its high efficient electrocatalytic activity for formic acid oxidation

A simple electrochemical approach is developed to prepare reduced graphene oxide (RGO)-wrapped carbon fiber (CF) as a novel support for Pt–Au nanocatalysts. The obtained composite electrodes have been characterized by scanning electron microscopy (SEM), X-ray energy dispersive spectroscopy (EDX), thermal gravimetric analysis (TGA), and electrochemical methods. SEM images reveal that the Pt–Au nanoparticles deposited on RGO-wrapped CF (RGO/CF) electrode display smaller particle size and more uniform dispersion than those on the bare CF electrode. Cyclic voltammetry, linear sweep voltammetry, chronoamperometry, chronopotentiometry, Tafel plots, and electrochemical impedance spectroscopy (EIS) analyses demonstrate that the introduced RGO on CF electrode surface is beneficial to the dispersion of Pt–Au nanoparticles, as a consequence, to the enhancement of the electrocatalytic activity and the antipoisoning ability of Pt–Au towards formic acid electrooxidation.     

Electrocatalytic oxidation of formic acid on functional MWCNTs supported nanostructured Pd–Au catalyst

In this work, PdAu nanocatalysts with different weight ratio of Pd and Au supported on functional multi-walled carbon nanotubes (f-MWCNTs) were prepared, and their electrocatalytic activity for the oxidation of formic acid was also studied. The electrocatalysts were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The electrochemical results showed that the 4Pd1Au/f-MWCNTs (by weight) catalyst, exhibited distinctly higher activity and better stability in formic acid electrooxidation than the Pd/f-MWCNTs catalyst. The Nano-Au improves potentially the performance of Pd-based electrocatalysts for the direct formic acid fuel cells (DFAFCs).     

Electrodeposited nanostructured Pt–Ru co-catalyst on graphene for the electrocatalytic oxidation of formaldehyde

The electrochemical oxidation of formaldehyde over graphene surfaces modified with Pt–Ru co-catalyst is presented. Graphene was chemically converted from graphite and Pt–Ru co-catalyst was electrochemically deposited using cyclic voltammetry. The hybrid surface is prepared using “green approaches” and displayed electrocatalytic activity towards formaldehyde in the form of current oscillations. The current oscillations that were mainly due to adsorption/desorption of carbonaceous oxidative products are a factor of several parameters such as the concentrations of both formaldehyde and supporting electrolyte in solution, the amount of catalyst loading, scan rate of potential, upper potential limit, and the temperature change. CCG/Pt–Ru exhibited higher electrocatalytic activity toward formaldehyde electro-oxidation, and intense electrochemical current oscillations were obtained at relatively low HCHO concentrations compared to other work mentioned in literature for CCG/Pt–Pd.     

A study of the electrocatalytic oxidation of methanol on a nickel–salophen-modified glassy carbon electrode

Nickel–salophen-modified glassy carbon electrodes prepared by transferring one drop of Ni–salophen complex solution on the electrode surface. This modified electrode has been used for the electrocatalytic oxidation of methanol in alkaline solutions with various methods such as cyclic voltammetry, chronoamperometry, and electrochemical impedance spectroscopy. The electrooxidation was observed as large anodic peaks, and early stages of the cathodic direction of potential sweep around 20 mV vs. Ag|AgCl|KCl_sat. A mechanism based on the electrochemical generation of Ni (Ш) active sites and their subsequent consumptions by methanol have been discussed. EIS studies were employed to unveil the charge transfer rate as well as the electrical characteristics of the catalytic surface. For the electrochemical oxidation of methanol at 5.0 M concentration, charge transfer resistance of nearly 0.936 kΩ was obtained, while the resistance of the electrocatalyst layer was about 111.6 Ω.     

Why does silane enhance the protective properties of epoxy films?

Using neutron reflectivity, the protection mechanisms of a novel one-step epoxy-silane coating system were investigated in terms of coating structure and water response behavior. By comparing pure epoxy and epoxy-silane mixtures in various aqueous environments, the effects of the addition of silane were determined. Specifically, a bridged bis-silane coupling agent with six alkoxy moieties and a polysulfur bridge was investigated. The key mechanisms of silane-enhanced protection are (1) the silane is enriched at the substrate-coating interface, forming a hydrophobic dense interfacial layer and good adhesion to the substrate, and (2) the silane serves as a cross-linker, resulting in a denser and less hydrophilic bulk film compared to the neat epoxy. The hydrophobic nature of bis-sulfur silane also increases the overall hydrophobicity of the mixed film.     

Preparation of carbon supported Pd–P catalyst with high content of element phosphorus and its electrocatalytic performance for formic acid oxidation

The carbon supported Pd–P (Pd–P/C) anodic catalyst in direct formic acid fuel cell (DFAFC) was prepared with a novel phosphorus reduction method. The Pd–P/C catalyst obtained possesses the high content of P⁰ in the alloying state. Because alloying P⁰ could decrease the 3d electron density of Pd and the adsorption affinity of CO and H on Pd, alloying P⁰ would promote the formic acid (FA) oxidation through the direct pathway. Therefore, the electrocatalytic performance of the Pd–P/C catalyst for the FA oxidation is much better than that of the Pd/C catalyst.     

Anticorrosion activity of aniline–aniline-2-sulfonic acid copolymers on the steel surface

The structure and barrier properties of layers formed on the interface of steel with aniline–orthanilic acid copolymers of different compositions were determined. The structure of the protective system ensuring the best anticorrosion properties was found.     

Oxidation of phenol on RuO2–TiO2/Ti anodes

The oxidation of phenol on the RuO₂–TiO₂/Ti electrode has been studied by cyclic voltammetry, polarization measurements, electrochemical impedance spectroscopy and potentiostatic transients in H₂SO₄ and NaCl aqueous solutions. A reaction path with polymerization as the main reaction and side reactions after the initial step, similar to the reaction path on other electrode materials, is suggested. The formation of a phenoxy radical in a diffusion-controlled irreversible process is the initial step. The polymerization of phenoxy radicals leads to the formation of porous polyoxyphenylene film, strongly adherent to the electrode surface. The cyclic voltammetry measurements indicate side products, which could be, according to the literature, of quinone-like structure. Polyoxyphenylene film inhibits further oxidation of phenol, although complete electrode passivation was not observed. The presence of polyoxyphenylene film does not influence the pseudocapacitive behaviour of the electrode to a great extent, since the polyoxyphenylene film covers dominantly the coating surface, while active sites placed within coating cracks remain uncovered. The film seems to be permeable for hydrogen ions and water molecules.     

Effect of the metal−support interaction in Ag/CeO<Subscript>2</Subscript> catalysts on their activity in ethanol oxidation

The interaction of silver with the surface of CeO₂ in the Ag/CeO₂ catalysts prepared by coprecipitation and impregnation techniques was studied by temperature-programmed reduction, X-ray diffraction, and high-resolution transmission electron microscopy. It was shown that coprecipitation technique led to formation of strong silver–support interaction and the epitaxy of silver particles (d ₁₁₁ = 2.35 Å) on the surface of CeO₂ (d ₁₁₁ = 3.1 Å). This provided incresed catalytic activity in the oxidative dehydrogenation of ethanol at relatively low temperatures (a 15% conversion of ethanol with 100% selectivity for the formation of acetaldehyde was reached at 85°C). Above 130°C, the deep oxidation of ethanol to CO₂ becomes the predominant direction of a catalytic reaction, and the Ag/CеО₂ catalyst obtained by impregnation technique was most active in this region as a consequence of the weaker metal–support interaction.     

Further study on the synthesis of F-containing porphyrins and their catalytic activity on oxidation of cyclohexene

Reaction of tetrakis(p-allyloxyphenyl)porphyrin and perfluoroalkanesulfonyl bromides givestetrakis(p-polyfluoroalkoxylphenyl)substituted porphyrins.The yields are over 90%.The synthesis ofthe metal ion complexes of these F-containing porphyrins is also reported.Preliminary results on thestudy of the catalytic activity of the manganese(Ⅲ)complexes of various fluorinated porphyrins onoxidation of cyclohexene indicate that the introduction of R_F group into porphyrin contributes to thestability of the catalysts.     

Electrocatalytic oxidation of alcohols on carbon electrodes modified by functionalized polypyrrole–RuO2 films

The electrocatalytic activity of several types of polypyrrole films bearing cationic pendant group [tris(bipyridyl)ruthenium(II) complexes, viologen, ammonium] and containing dispersed microparticles of RuO₂ towards the oxidation of alcohols to aldehydes or ketones has been investigated. Best results are obtained with polypyrrole films substituted by a tris(bipyridyl)ruthenium(II) complex, the latter acting as an electron relay for the electrogeneration of the strong oxidizing species RuO₄²⁻. The influence of several parameters such as base, supporting electrolyte, electrolysis potential and catalyst amount on the efficiency of the electrocatalysis has been examined. Under optimum conditions a maximum turnover of 10 900 was reached. In all cases the lifetime of these electrode materials was limited by the slow release of the RuO₄²⁻ species.     

The promotional effect of SO42− on N2 selectivity for selective catalytic oxidation of ammonia over RuO2/ZrO2 catalyst

Research on Chemical Intermediates - The promoting effects of SO42? on N2 selectivity for selective catalytic oxidation (SCO) of ammonia to nitrogen over RuO2/ZrO2 catalyst were...