Kinetics and mechanism of oxygen electroreduction in acidic and neutral solutions on carbon black XC-72R modified by products of pyrolysis of cobalt 5,10,15,20-tetrakis(4-methoxyphenyl)porphyrin

Cathodic oxygen reduction on the XC-72R carbon black modified by the products of pyrolysis of cobalt 5,10,15,20-tetrakis(4-methoxyphenyl)porphyrin (CoTMPP) (XC-72M) was studied in acidic and neutral electrolytes. Formation of new active centers on XC-72M is confirmed by voltammetric curves (specific charge density grows as compared to the XC-72R carbon black by 2–2.5 times) using the methods of rotating disk electrode (a shift in half-wave potential E _1/2 by 600 mV) and rotating ring-disk electrode (the fraction of the direct reaction increases to 70%). Herewith, the $\frac{{\partial E_{1/2} }} {{\partial pH}}$\frac{{\partial E_{1/2} }} {{\partial pH}} value in the range of pH 0.3–8.5 is −60 mV. It is shown that proton necessarily participates in the slow stage of the first electron transfer for the further occurrence of the direct reaction to water. At a transition from acidic solutions to neutral ones, the polarization curves converge for XC-72M and XC-72R, which is due to a decrease in the concentration of proton in the solution and variation of the mechanism of the oxygen reduction slow stage.     

Kinetics and mechanism of oxygen electroreduction in alkaline solutions on xc-72r carbon black modified by products of pyrolysis of cobalt 5,10,15,20-tetrakis(4-methoxyphenyl)porphyrin

Cathodic oxygen reduction on XC-72R carbon black modified by products of pyrolysis of cobalt 5,10,15,20-tetrakis(4-methoxyphenyl)porphyrin (CoTMPP) (XC-72M) was studied. When XC-72R carbon black is modified, new active centers (ACs) are formed on the surface of the carbon support, on which the direct reaction to OH^- occurs, as shown using the rotating ring-disk electrode technique. The process of oxygen reduction on nonmodified carbon black occurs via the serial path. At low polarizations, the dependence of potential on pH corresponds to the slope of ??30 mV both for the carbon material and modified carbon black. This value is close to the coefficient in the Nernst equation for H₂/HO ₂ ^? . The slow stage of oxygen reduction is the transfer of the first or second electron to the adsorbed molecule. Herewith, the difference in the kinetics and mechanism of oxygen reduction on XC-72R and XC-72M is related to a stronger adsorption interaction of oxygen and ACs on XC-72M. The {ie1113-1} value in the pH range of 12?C14.6 is ?15 to ?20 mV both for XC-72R and XC-72M. In the case of the second halfwave potential on XC-72R, it is ?50 to ?60 mV. The observed effects are explained by a change in the surface state of catalysts at an increase in adsorption of OH^? ions at an increase in pH.     

Electrocatalytic oxidation of methanol on Pt-Pd nanoparticles supported on honeycomb-like porous carbons in alkaline media

Honeycomb-like porous carbons (PCs) were synthesized using a facile self-assembly method with phenolic resin as the carbon source and tetraethyl orthosilicate (TEOS) as the silica source. The PCs were found to have a large BET surface area of 458 m² g^?1 and a partially graphitized structure. The obtained PCs were used as a support for various Pt-Pd bimetallic alloy catalysts employed for methanol oxidation in alkaline media. Compared with Pt supported on commercial Vulcan XC-72R carbon (Pt/C) and with the other Pt-Pd bimetallic alloy catalysts on PCs, Pt₃Pd₁ on PCs displayed the most negative onset potential for methanol oxidation and the highest steady-state current (2.04 mA cm^?2). This may be because the Pt₃Pd₁/PCs catalyst has the largest electrochemical active surface area (ESA), and because adding Pd to the catalyst improves the ability of the intermediate species to tolerate oxidation. The results show that the prepared Pt-Pd/PCs is a potential candidate for application as a catalyst in alkaline direct methanol fuel cells.     

Activity evaluation of carbon paste electrodes loaded with pt nanoparticles prepared in different radiolytic conditions

Three Pt-based catalysts prepared in different radiolytic conditions and supported on graphite powder were packed into a carbon paste electrode configuration. They were compared to each other, to the commercial (Pt) deposited on activated carbon powder (Johnson Matthey) and to pure Vulcan XC-72 for their respective abilities toward the hydrogen evolution reaction (HER). The Tafel parameters were determined for all these electrodes. From the I–V curves and their quantitative treatment, the following order of activity emerged unambiguously and reads: (PtCO)₂ (fcc structure) > (PtCO)₁ (Chini cluster) > (Pt)_neat > (Pt)_JM (Johnson Matthey) ≫ (Vulcan XC-72). As expected, all the Pt-loaded electrodes were more efficient than Vulcan XC-72. The classification appears to be linked with the mean nanoparticle size, and for comparable sizes, with the surface morphology of the materials. The results and the stability of the electrodes suggest that the small particle sizes and the good dispersity on the carbon support were maintained during the HER.     

Preparation and characterization of anion-cation surfactants modified montmorillonite

The low-temperature molar heat capacities of CoPc and CoTMPP were measured by temperature modulated differential scanning calorimetry (TMDSC) over the temperature range from 223 to 413 K for the first time. No phase transition or thermal anomaly was observed in the experimental temperature range for CoPc. However, a structural change was found to be nonreversible for CoTMPP in the temperature range of 368–403 K, which was further validated by the results of IR and XRD. The molar enthalpy ΔH _m and entropy ΔS _m of phase transition of the CoTMPP were determined to be 3.301 kJ mol⁻¹ and 8.596 J K⁻¹ mol⁻¹, respectively. The thermodynamic parameters of CoPc and CoTMPP such as entropy and enthalpy relative to reference temperature 298.15 K were derived based on the above molar heat capacity data. Moreover, the thermal stability of these two compounds was further investigated through TG measurements. Three steps of mass loss were observed in the TG curve for CoPc and five steps for CoTMPP.     

Metal Oxide Promoted Electrocatalysts for Methanol Oxidation

An important research target in DMFCs is to find better catalyst materials that are cheaper, less-prone to poisoning and more catalytically active. In this context, metal oxides with good catalytic properties and stronger interaction with Pt nanoparticles can generate active interfacial regions for electrocatalysis. Pt catalysts promoted by certain metal oxides show enhanced methanol electro-oxidation activity and CO tolerance behavior. In this paper we summarize the recent progress from our laboratory which explored the possibility of developing Pt–MoO₃/C and Pt–Nb₂O₅/C electrocatalysts in acidic media, and Pt–V₂O₅/C electrocatalyst in alkaline media for direct electro-oxidation of methanol. The oxide electrocatalysts have been prepared by a fast and efficient method of loading the metal oxide on carbon black (Vulcan XC-72) employing an intermittent microwave heating (IMH) method. These materials are found to achieve higher activity and stability towards methanol electro-oxidation.     

Low Temperature WGS Catalysts for Hydrogen Station and Fuel Processor Applications

Generally, water gas shift (WGS) reaction is a very important step in the industrial production of hydrogen, ammonia and other bulk chemicals utilizing synthesis gases. In this paper, we are reporting WGS reaction carried out in our research group for the application of hydrogen station and fuel processor. We prepared various Mo₂C, Pt–Ni-based and Cu-based catalysts for low temperature WGS reaction. The characteristics of the prepared catalyst were analyzed by N₂ physisorption, CO chemisorptions, XRD, SEM and TEM technologies, and compared with that of commercial Cu-Zn/Al₂O₃ catalyst. It was found that prepared catalysts displayed reasonably good activity and thermal cycling stability than commercial LTS (Cu–Zn/Al₂O₃) catalyst. It was found that the deactivation of commercial LTS catalyst during the thermal cycling run at 250 °C was caused by the sintering of active metal even though it shows high activity at less than 250 °C. The deactivation of Mo₂C catalyst during the thermal cycling run was caused by the transition of Mo^δ+, Mo^IV and Mo₂C on the surface of Mo₂C catalyst to Mo^VI(MoO₃) with the reaction of H₂O in reactants. However, they showed higher stability than the commercial LTS catalyst during thermal cycling test. The Pt–Ni/CeO₂ catalyst after the thermal cycling shows slightly deactivation due to the sintering of Ni metal. Among Cu-based catalysts, it was found that Cu–Mo/Ce_0.5Zr_0.5O₂ catalyst has higher WGS activity and stability over commercial LTS catalyst. The results suggested that Pt–Ni/CeO₂ and Cu–Mo/Ce_0.5Zr_0.5O₂ catalysts are desirable candidates for application in hydrogen station and fuel processor system even though all other catalysts deactivated slowly during the thermal cycling run.     

Electrocatalysts and membrane for direct ethanol-oxygen fuel cell with alkaline electrolyte

Results of studies of anodic (RuNi/C) and cathodic (PtCo/C; CoN₄/C) catalysts, polybenzimidazole membrane, and membrane-electrode assemblies on their basis for alkaline ethanol-oxygen fuel cell are presented. It is shown that the anodic catalyst RuNi/C optimized in its composition (Ru: Ni = 68: 32 in atomic percent) and the metal mass on carbonaceous support (15–20%) is sufficiently effective with respect to ethanol oxidation; it is well superior to commercial Pt/C- and RuPt/C-catalysts when calculated per unit mass of the precious metal. The effect of electrolyte composition, electrode potential, and temperature on the CO₂ yield is studied by chromatographic analysis of the ethanol oxidation products. It is shown that the highest CO₂ yield (the process involves the C-C bond break) is achieved at low electrolysis overvoltage and elevated temperature. The mean number of electrons given up by C₂H₅OH molecule approaches 10 at temperatures over 60°C. The studied cathodic catalysts form the following series of their specific activity in the oxygen reduction reaction: (20 wt % Pt) E-TEK ≥ (7.3 wt % Pt) PtCo/C > CoN₄/C; however, in the presence of alcohol the activity series is reversed. On this reason fuel cell cathodes were prepared by using synthesized CoN₄/C-catalyst. For the alkali-doped polybenzimidazole membrane the conductivity and ethanol crossover were determined. A membrane-electrode assembly for platinum-free alkaline ethanol-oxygen fuel cell is designed. It comprised anodic (RuNi/C) and cathodic (CoN₄/C) catalysts and polybenzimidazole membrane. The period of service of the fuel cell exceeded 100 h at a voltage of 0.5 V and current of 100 mA/cm².     

Preparation and electrocatalytic performance of Fe–N–C for electroreduction of H2O2

Fe–N–C catalysts were prepared through metal-assisted polymerization method. Effects of carbon treatment, Fe loading, nitrogen source, and calcination temperature on the catalytic performance of the Fe–N–C for H₂O₂ electroreduction were measured by voltammetry and chronoamperometry. The Fe–N–C catalyst shows optimal performance when prepared with pretreated active carbon, 0.2 wt.% Fe, paranitroaniline (4-NA) and one-time calcination. The Fe–N–C catalyst displayed good performance and stability for electroreduction of H₂O₂ in alkaline solution. An Al–H₂O₂ semi-fuel cell was set up with Fe–N–C catalyst as cathode and Al as anode. The cell exhibits an open-circuit voltage of 1.3 V and its power density reached 51.4 mW cm⁻² at 65 mA cm⁻².     

Titania-supported mixed HPMoV polyoxometallates as precursors of hydrodesulfurization catalysts

HDS catalysts were prepared by loading H₃PMo₁₂O₄₀ or H₄PMo₁₁V₁O₄₀ polyoxometallates on TiO₂ (0.5 and 1.0 mmol (Mo+V)). Activity of the catalysts was tested in the HDS of thiophene. The activity of catalysts of low concentration was 2–3 times higher than the activity of those of high concentration. Temperature programmed reduction (TPR) and IR spectroscopy were used to determine the properties of the catalyst. TPR measurements proved that vanadium promotes and stabilizes HDS activity due to an increase in the Mo⁵⁺/Mo⁴⁺ ratio.     

The effect of ferric ions on the conductivity of various types of polymer cation exchange membranes

Recently, rejuvenated interest to fuel cells has posed a number of problems regarding the polymer electrolyte membrane properties and their behaviour in different electrolyte solutions. This work was dedicated to study the conductivity of H⁺-, Fe³⁺- and mixed H⁺/Fe³⁺-forms of cation exchange membranes Neosepta CMS, Nafion 112, 115 and 117 and Selemion HSF under conditions similar to these in the Fe³⁺/Fe²⁺–H₂/H⁺ fuel cell in the range of current densities 0–90 mA/cm². It was found that the conductivities of these membranes in 1.09 M H₂SO₄ solution decrease in the following order: Selemion HSF › Nafion 117 ≈ Nafion 115 ≈ Neosepta CMS › Nafion 112. Conductivities of perfluorinated membranes were discussed in terms of Hsu and Gierke percolation theory [20]. The Fe³⁺-forms of Nafion membranes studied displayed a monotonous decline in the resistance when current increased, which is a manifestation of gradual conversion of the Fe³⁺-form into H⁺-form of these membranes. Unlike the Nafion membranes, the Fe³⁺-forms of Neosepta CMS and Selemion HSF membranes exhibited a sharp jump of resistance at relatively high current densities (more than 70 mA/cm²) that is most probably a result of concentration polarization.     

Improved electrochemical performance of Ca2Fe1.4Co0.6O5–Ce0.9Gd0.1O1.95 composite cathodes for intermediate-temperature solid oxide fuel cells

The performance of Ca₂Fe_1.4Co_0.6O₅–Ce_0.9Gd_0.1O_1.95 (CFC–CGO) composite cathode has been investigated for potential application in intermediate-temperature solid oxide fuel cells (IT-SOFCs). The composite cathodes are prepared and characterized by XRD and SEM, respectively. The electrochemical properties of the composite cathodes are investigated using AC impedance and DC polarization methods from 500 to 700 °C under different oxygen partial pressures. The polarization resistance (R _p) decreases with the increase of CGO content in the composite electrode. The addition of 40 wt.% CGO in CFC results in the lowest R _p of 0.48 Ω cm² at 700 °C in air. Oxygen partial pressure dependence study indicates that the charge-transfer process is the rate limiting step for oxygen reduction reaction. CFC-40CGO composite cathode exhibits the lowest overpotential of about 67 mV at a current density of 85 mA cm⁻² at 700 °C in air.     

Influence of alkaline earth oxides on thermal stability of oxyfluoride glass

A new type of glass from the Na₂O–MeO–Al₂O₃–SiO₂–LaF₃ system where MeO = MgO, CaO, BaO and SrO has been studied. The aim of the investigation was to determine, by means of thermal techniques (DTA and DSC), the influence of alkaline earth ions additions on its thermal stability and the ability of LaF₃ phase to crystallization. The effect of LaF₃ crystallization was analyzed in connection with glass composition expressed by the Al₂O₃/(MeO + Na₂O + 3La₂F₆) ratio varying from 0.4 to 0.8 for the alkaline earth admixtures. The compositions of the glasses have been designed so as to make it possible to define the effect of the charge of the ion modifiers (Na⁺, Me²⁺, La³⁺) on the alumina position in the framework of the glass. Two series of glasses were obtained with a different F⁻ content. The formation of LaF₃ depends directly on the strength of the network and can be control by the Al₂O₃/modifiers ratio as well as the content of fluorine ions. Generally, it can be stated that transparent glass-ceramic with nanocrystallization of LaF₃ can be obtained for Al₂O₃/(Na₂O + MeO + 3La₂F₆) ≤0.6 in the examined glasses. The more the ionicity of the alkaline earth ions the greater the tendency for the crystallization of Me₂LaF₇ and MeF₂. In the glass structure the substitution of oxygen ions by F⁻ ions facilitated the crystallization of LaF₃. Simultaneously, it influenced the thermal stability of the aluminosilicate network and induced the crystallization of appropriate silicates during the heat treatment.     

Study of isothermal decomposition of lanthanide mixed complexes with 2,2,6,6-tetramethyl-3,5-heptanodione and 1,10-phenanthroline

Isothermal decomposition kinetic of three lanthanide mixed complexes with the general formula of Ln(thd)3phen (where Ln=Nd³⁺, Sm³⁺ or Er³⁺, thd=2,2,6,6-tetramethyl-3,5-heptanodione and phen=1,10-phenanthroline) has been studied in this work. The powders were characterized by their melting point, elemental analysis, FTIR spectroscopy and thermogravimetry. The isothermal TG curves have been recorded under the same conditions at 265–285, 265–285 and 250–270°C for Nd(thd)₃phen, Sm(thd)₃phen and Er(thd)₃phen, respectively. The kinetic parameters, i.e. activation energy, reaction order and frequency factor were obtained through the technique of lineal regression using the relation g(α)=kt+g ₀. The analysis was done at decomposed fractions between 0.10–0.90. The values of activation energy were: 114.10, 114.24 and 115.04 kJ mol^–1 for the Nd(thd)₃phen, Sm(thd)₃phen and Er(thd)₃phen complexes, respectively. The kinetic models that best described the isothermal decomposition reaction the complexes were R1 and R2. The values of activation energy suggests the following decreasing order of stability: Nd(thd)₃phen<Sm(thd)₃phen<Er(thd)₃phen.     

Anode performance of Mn-doped ceria–ScSZ for solid oxide fuel cell

The 70 wt.% Mn-doped CeO₂ (MDC)-30 wt.% Scandia-stabilized zirconia (ScSZ) composites are evaluated as anode materials for solid oxide fuel cells (SOFCs) in terms of chemical compatibility, thermal expansion coefficient, electrical conductivity, and fuel cell performance in H₂ and CH₄. The conductivity of MDC10 (10 mol.% Mn-doping), MDC20, and CeO₂ are 4.12, 2.70, and 1.94 S cm⁻¹ in H₂ at 900 °C. With 10 mol.% Mn-doping, the fuel cells performances improve from 166 to 318 mW cm⁻² in H₂ at 900 °C. The cell with MDC10–ScSZ anode exhibits a better performance than the one with MDC20–ScSZ in CH₄, the maximum power density increases from 179 to 262 mW cm⁻². Electrochemical impedance spectra indicate that the Mn doping into CeO₂ can reduce the ohmic and polarization resistance, thus leading to a higher performance. The results demonstrate the potential ability of MDC10–ScSZ composite to be used as SOFCs anode.     

基于能带理论研究非贵过渡金属对Pd基催化剂的影响

采用乙二醇为溶剂和还原剂、谷氨酸为螯合剂、非贵过渡金属为助剂、XC-72为载体的一步溶剂热法制备了3种Pd基催化剂：PdCr/XC-72,PdMn/XC-72和PdHg_3.5/XC-72.实验结果表明,Cr、Mn、Hg 3种非贵过渡金属元素的加入会影响催化剂中活性金属颗粒的粒径和分散度.其中,PdCr/XC-72催化剂具有金属粒径小、分散均匀的特点,其在无溶剂条件下对DL-sec-苯乙醇的转化率为91%,远远高于PdMn/XC-72（53%）和PdHg_3.5/XC-72（32%）.同时,利用基于密度泛函理论的第一性原理,从能带理论和d带空穴的角度出发,进一步从理论上分析了PdCr/XC-72催化剂催化活性较好的原因.     

Synthesis of Fe<Superscript>3+</Superscript> doped ordered mesoporous TiO<Subscript>2</Subscript> with enhanced visible light photocatalytic activity and highly crystallized anatase wall

Fe³⁺ doped mesoporous TiO₂ with ordered mesoporous structure were successfully prepared by the solvent evaporation-induced self-assembly process using P123 as soft template. The properties and structure of Fe³⁺ doped mesoporous TiO₂ were characterized by means of XRD, EPR, BET, TEM, and UV–vis absorption spectra. The characteristic results clearly show that the amount of Fe³⁺ dopant affects the mesoporous structure as well as the visible light absorption of the catalysts. The photocatalytic activity of the prepared mesoporous TiO₂ was evaluated from an analysis of the photodegradation of methyl orange under visible light irradiation. The results indicate that the sample of 0.50%Fe–MTiO₂ exhibits the highest visible light photocatalytic activity compared with other catalysts.     

Synthesis,characterization, and catalytic activity in the <Emphasis Type="Italic">n</Emphasis>-heptane conversion over Pt/In–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> sol–gel prepared catalysts

Platinum catalysts supported on indium-doped alumina were prepared by the sol–gel method. The method allows the incorporation of In³⁺ in the alumina network. The indium-doped alumina supports showed narrow pore size distribution (5.4–4.0 nm) and high specific surface areas (258–280 m²/g). The ²⁷Al NMR-MAS spectroscopy identified aluminum in tetrahedral, pentahedral, and octahedral coordination; however, the intensity of the signal assigned to aluminum in pentahedral coordination diminishes with the increase of the content of indium. Total acidity determined by ammonia thermodesorption diminishes strongly in Pt/In–Al₂O₃ catalysts, suggesting a selective deposit of platinum over the acid sites of the support. The effect of the support in the platinum catalytic activity was evaluated in the n-heptane dehydrocyclization reaction. The selectivity patterns for such reaction were modified substantially in the doped Pt/In–Al₂O₃ catalysts, in comparison with the Pt-In/Al₂O₃–I coimpregnated reference catalyst. As an important result, the formation of benzene was suppressed totally over the indium-doped alumina sol–gel supports with a high content (3 wt%) of indium.     

Study of Complex Formation between N-Phenylaza-15-Crown-5 with Mg2+, Ca2+, Ag+ and Cd2+ Metal Cations in Some Binary Mixed Aqueous and Non-aqueous Solvents using the Conductometric Method

The complexation reactions between Mg²⁺, Ca²⁺, Ag⁺ and Cd²⁺ metal cations with N-phenylaza-15-crown-5 (Ph-N15C5) were studied in acetonitrile (AN)–methanol (MeOH), methanol (MeOH)–water (H₂O) and propanol (PrOH)–water (H₂O) binary mixtures at different temperatures using the conductometric method. The conductance data show that the stochiometry of all of the complexes with Mg²⁺, Ca²⁺, Ag⁺ and Cd²⁺ cations is 1:1 (L:M). The stability of the complexes is sensitive to the solvent composition and a non-linear behaviour was observed for variation of log K _f of the complexes versus the composition of the binary mixed solvents. The selectivity order of Ph-N15C5 for the metal cations in neat MeOH is Ag⁺>Cd²⁺>Ca²⁺>Mg²⁺, but in the case of neat AN is Ca²⁺>Cd²⁺>Mg²⁺>Ag⁺. The values of thermodynamic parameters (ΔH _c ^o , ΔS _c ^o ) for formation of Ph-N15C5–Mg²⁺, Ph-N15C5–Ca²⁺, Ph-N15C5–Ag⁺ and Ph-N15C5–Cd²⁺ complexes were obtained from temperature dependence of stability constants and the results show that the thermodynamics of complexation reactions is affected by the nature and composition of the mixed solvents.     

WO3/C hybrid material as a highly active catalyst support for formic acid electrooxidation

The hybrid material based on WO₃ and Vulcan XC-72R carbon has been used as the support of Pd nanocatalysts. The resultant Pd–WO₃/C catalysts in a large range of WO₃ content exhibit excellent catalytic activity and stability for formic acid electrooxidation. The great improvement in the catalytic performance is attributed to the uniform dispersion of Pd with less particle sizes on the WO₃/C support and the hydrogen spillover effect which greatly accelerates the dehydrogenation of HCOOH on Pd.