Highly stable PtRuTiOx/C anode electrocatalyst for direct methanol fuel cells

In the present investigation, PtRuTiO_x/C electrocatalyst was prepared by a modified polyol synthesis method and the as-prepared electrocatalyst was treated under the reductive atmosphere (30 vol% H₂ in Ar) at 500 °C for 2 h (denoted as PtRuTiO_x/C-500) to enhance the interaction between the metal particles and the support. For comparison, the commercial PtRu/C electrocatalyst was also treated by the same procedure as PtRuTiO_x/C (denoted as PtRu/C-500). Transmission electron microscopy results indicated that PtRuTiO_x/C electrocatalyst exhibited not only a uniform dispersion and narrow size distribution with a smaller particle size, but also excellent stability during the thermal treatment. In contrast, the commercial PtRu/C electrocatalyst is not stable during the thermal treatment and the metal particles greatly agglomerated. The results of CO-stripping voltammetry, single direct methanol fuel cell tests and life-time test jointly showed that PtRuTiO_x/C-500 had better durability than commercial PtRu/C while keeping a desirable activity toward methanol electro-oxidation, which may be attributed to the addition of titanium oxide that improved the interaction between noble metal particles and the support.     

Emf Measurements on Nanocrystalline Copper-Doped Ceria

Mixed oxide samples of nanostructured Cu_xCe_1−xO_2−yof various composition were generated by (i) chemical precipitation and ball milling and (ii) inert gas condensation. X-ray diffraction measurements suggested that copper oxide was dissolved in nanostructured cerium oxide up to concentrations ofx=0.15. Solid electrolyte cells of the typeA, Cu₂O/CuBr/Cu_xCe_1−xO_2−y(A=Cu or CuO) showed reversible cell voltages. The ratio of the formal chemical activities of CuO and Cu₂O dissolved in nanostructured cerium oxide were calculated from the cell voltages. The results are discussed in terms of an apparent macroscopic solubility, due to interfacial segregation of copper oxide on nanostructured cerium oxide.     

Effect of the cerium content on the activity of Cu-Ce-Al-O catalysts in the methanol steam reforming reaction in a flow reactor

The Cu_18.5Ce _x Al_{81.5 ? x} (where x = 2, 7.4, and 14) oxide catalysts were synthesized by coprecipitation and tested in the methanol steam reforming reaction in an integral flow reactor at 270°C. It was found that the activity of the catalysts increased with the calcination temperature and catalysts with intermediate cerium contents exhibited the highest activity; these catalysts exhibited the greatest values of S _BET and S _Cu. The phase analysis demonstrated that copper in these samples occurred almost entirely as a CuO-CeO₂ solid solution. The concentration of carbon monoxide at the reactor outlet decreased with the calcination temperature. For the most active sample with a cerium content of 7.4% calcinated at 700°C, the concentration of CO reached a minimum of no higher than 0.3%.     

Electronic Metal-Support Interaction-Modified Structures and Catalytic Activity of CeOx Overlayers in CeOx/Ag Inverse Catalysts

Electronic metal-support interactions (EMSIs) of oxide-supported metal catalysts strongly modifies the electronic structures of the supported metal nanoparticles. The strong influence of EMSIs on the electronic structures of oxide overlayers on metal nanoparticles employing cerium oxides/Ag inverse catalysts is reported herein. Ce₂O₃ overlayers were observed to exclusively form on Ag nanocrystals at low cerium loadings and be resistant to oxidation treatments up to 250 °C, whereas CeO₂ overlayers gradually developed as the cerium loading increased. Ag cubes enclosed by {001} facets with a smaller work function exert a stronger EMSI effect on the CeO_x overlayers than Ag cubes enclosed by {111} facets. Only the CeO₂ overlayers with a fully developed bulk CeO₂ electronic structure significantly promote the catalytic activity of Ag nanocrystals in CO oxidation, whereas cerium oxide overlayers with other electronic structures do not. These results successfully extend the concept of EMSIs from oxide-supported metal catalysts to metal-supported oxide catalysts.     

Oxide cathodes for electrochemical devices made with the use of a nanostructured composition material

The possibility of using the LnO _x mischmetal (Ln = Ce, La, Nd, Pr, Sm) for preparation of cathodes for solid-oxide fuel cells with the supported YSZ electrolyte is studied. The electrical and electrochemical characteristics of Ln-Mn-O electrodes with the ratio of all lanthanides contained in the mischmetal except for cerium to manganese Ln: Mn = 1: 1 and also of a material comprised of Ln-Mn-O and La_0.8Sr_0.2MnO₃ are studied. The latter electrode material that contains 35?C40 wt % of Ln-Mn-O and was sintered at 1200°C has the specific ohmic resistance of 0.1 ?? cm at 800°C. The polarization conductivity is compared for electrodes made of 100% Ln-Mn-O, 40 wt % Ln-Mn-O + 60 wt % La_0.8Sr_0.2MnO₃, and 100% La_0.8Sr_0.2MnO₃ in the initial state and after their modification through the introduction of an electrocatalyst (PrO_{2 ? x} ). The highest polarization conductivity is typical of Ln-Mn-O + (La, Sr)MnO₃ electrodes containing 40 wt % Ln-Mn-O and PrO_{2 ? x} . The polarization conductivity of these electrodes is found to be 25 S/cm² at 800°C.     

A Molecular Approach to Self‐Supported Cobalt‐Substituted ZnO Materials as Remarkably Stable Electrocatalysts for Water Oxidation

In regard to earth‐abundant cobalt water oxidation catalysts, very recent findings show the reorganization of the materials to amorphous active phases under catalytic conditions. To further understand this concept, a unique cobalt‐substituted crystalline zinc oxide (Co:ZnO) precatalyst has been synthesized by low‐temperature solvolysis of molecular heterobimetallic Co_4?xZn_xO₄ (x=1–3) precursors in benzylamine. Its electrophoretic deposition onto fluorinated tin oxide electrodes leads after oxidative conditioning to an amorphous self‐supported water‐oxidation electrocatalyst, which was observed by HR‐TEM on FIB lamellas of the EPD layers. The Co‐rich hydroxide‐oxidic electrocatalyst performs at very low overpotentials (512 mV at pH 7; 330 mV at pH 12), while chronoamperometry shows a stable catalytic current over several hours.     

The physicochemical and catalytic properties of the Pt-CeO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> system

The properties of the Pt-CeO _x system prepared by the oxidation of the Pt₂Ce intermetallic compound were studied. The sample was characterized by X-ray diffraction in situ, thermogravimetry, scanning electron microscopy (with an accessory for energy dispersion analysis), transmission electron microscopy, and temperature-programmed reduction with hydrogen. The catalytic properties of the sample were studied in the model reaction of toluene hydrogenation. The oxidation of the intermetallic compound caused the appearance of metallic platinum and cerium oxide phases and high-dispersity platinum particles encapsulated in cerium oxide. Metallic platinum on the surface of the catalyst experienced rapid deactivation in the presence of hydrogen sulfide; high-dispersity platinum particles encapsulated in cerium oxide exhibited enhanced stability toward sulfur compounds.     

Preparation of rare earth oxyfluorides and their properties as a material for fuel cell

The formation of rare earth oxyfluorides and their properties as an electrocatalyst and/or a solid electrolyte using for fuel cell were studied by means of x-ray and electrochemical methods.By a high temperature solid reaction between rare earth fluorides and rare earth or zirconium oxides not only the simple oxyfluoride such as NdOF, SmOF, CeOF and YOF but also the binary one written by Nd_1?xLn_xOF, (NdOF)_1?x(MO)_x and (ZrO₂)_1?x(LnF₃)_x were obtained, where Ln; Y, La, Nd, Sm and Yb, MO; alkaline earth oxide and Nb₂O₅. On the solid reaction process, it was found that the exchange reaction of anion, that is F? and O^2?, took place at first between the rare earth fluoride and the oxide. LnF₃ could form the solid solution with ZrO₂ at above 1200°C taking the fluorite structure in the composition range of below 30 mol%-LnF₃, so-called the stabilized zirconia.The crystal type of these oxyfluorides was any one of the rhombohedral, the cubic and the tetragonal. The cubic phase oxyfluorides contained Nd showed high electrocatalytic activity for both the hydrogen oxidation and the oxygen reduction. Then (NdOF.)_0.9(Nb₂O₅)_0.1 and (ZrO₂)_1?x(LnF₃)_x were found to act as the oxide ion conducting solid electrolyte.     

Effects of dopant concentration and aging on the electrical properties of Y-doped ceria electrolytes

High purity cerium oxide and yttrium oxide were used to form ceria-based solid solution (Ce_1−xY_xO_2−δ, 0.05x0.4) via a conventional mixed-oxide method. All the samples used were aged at 1000 °C in air for 8 days. Crystal structure and microstructure were characterized by means of X-ray diffraction (XRD) and scanning electron microscopy (SEM). The ionic conductivity (i.e., grain interior (GI) grain boundary (GB) and total conductivities) in this system were systematically studied as a function of dopant content over the temperature range of 250–850 °C in air using an impedance spectroscopy. The lattice parameter decreased with increasing the Y content, but it did not obey Vegard's law. The Y doping had no significant effect on densification behavior and final sintered density, but leading to a significant decrease in grain size as compared to the undoped ceria. The composition x0.1 had a maximum GI conductivity, while a maximum total conductivity was observed at x0.15. A significant high-temperature aging effect was also found for the samples with higher Y doping levels. 10% and 15% decreases in the GI and GB conductivities, respectively, were detected in the aged Ce_0.7Y_0.3O_2−δ ceramic.     

Dispersed platinum supported by hydrogen molybdenum bronze-modified carbon as electrocatalyst for methanol oxidation

A new electrocatalyst, Pt/H_xMoO₃-C, for methanol oxidation, was prepared by dispersing platinum nano-particles on Vulcan XC-72 modified by hydrogen molybdenum bronze (H_xMoO₃, 0 ≤ x ≤ 2). The modification of Vulcan XC-72 with H_xMoO₃ on was accomplished by reducing the adsorbed molybdic acid and the platinum nano-particles were dispersed on the modified carbon by reducing chloroplatinic acid, with formaldehyde as the reductant. The prepared Pt/H_xMoO₃-C was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersion spectrometer, cyclic voltammetry (CV), chronoamperometry (CA), and single-cell test, with a comparison of the electrocatalyst, carbon-supported platinum (Pt/C) prepared under the same condition but without the modification. The results obtained from XRD and SEM showed that the modification of Vulcan XC-72 with H_xMoO₃ reduced the platinum particle size and improved distribution uniformity of platinum on carbon. The results, obtained from CV, CA, and the single-cell test, showed that Pt/H_xMoO₃-C exhibited better electrocatalytic activity toward methanol oxidation than Pt/C.     

Oxygen exchange properties in the new pyrochlore solid solution Ce2Sn2O7-Ce2Sn2O8

The phase-pure cerium stannate pyrochlore (Ce₂Sn₂O₇) has been prepared for the first time. The structure and oxidation states of both cations were carefully reviewed, and the compound was unambiguously replaced within the rare-earth stannate series. As a consequence of the low stability of trivalent cerium in oxide phases, one oxygen per formula unit could be intercalated by calcination under O₂ at 400 °C, leading to the new Ce₂Sn₂O₈ pyrochlore. This latter phase is subject to oxygen under-stoichiometry from 400 to 700 °C. However, oxygen deintercalation seems to be in competition with cerium oxide segregation at high temperature, leading to the formation of cerium deficient pyrochlore phases.     

Visualization of Heterogeneous Oxygen Storage Behavior in Platinum‐Supported Cerium‐Zirconium Oxide Three‐Way Catalyst Particles by Hard X‐ray Spectro‐Ptychography

The cerium density and valence in micrometer‐size platinum‐supported cerium–zirconium oxide Pt/Ce₂Zr₂O_x (x=7–8) three‐way catalyst particles were successfully mapped by hard X‐ray spectro‐ptychography (ptychographic‐X‐ray absorption fine structure, XAFS). The analysis of correlation between the Ce density and valence in ptychographic‐XAFS images suggested the existence of several oxidation behaviors in the oxygen storage process in the Ce₂Zr₂O_x particles. Ptychographic‐XAFS will open up the nanoscale chemical imaging and structural analysis of heterogeneous catalysts.     

Cathodes based on (La,Sr)MnO<Subscript>3</Subscript> modified with PrO<Subscript>2 − <Emphasis Type="Italic">x</Emphasis></Subscript>

The electrochemical characteristics of composite cathodes made of (La, Sr) MnO₃-(Zr, Sc)O₂ (LSM-SSZ), modified with PrO_{2 − x} additive, and designed for application in solid oxide fuel cells at moderately high temperatures were studied. The relationship between activity of catalytically modified composite LSM-SSZ cathodes and dispersity of electrocatalyst was revealed. The boundaries of the temperature range with the maximum dispersity of electrocatalyst and electrochemical activity of cathodes were found. The composite LSM-SSZ cathodes modified with PrO_{2 − x} were shown inert with respect to oxidation reactions of hydrocarbon fuel (methane) and highly active electrochemically with respect to oxygen reaction in non-equilibrium gas mixture of CH₄ and O₂. In cells with (Ce, Sm)O₂ (SDC) and (Zr, Y)O₂ (YSZ) electrolytes, their overvoltage is below 80 mV at the current density about 0.5 A/cm² and temperature of 600°C. These electrodes can be used as cathodes in single-chamber fuel cells. Long-term experiments were carried out to study time stability of characteristics of the said composite cathodes. The studied electrodes show parabolic or damped exponential time curves of polarization resistance if contacting with YSZ or SDC electrolyte, respectively. According to the forecast based on the experimental regularities, the polarization resistance of LSM-SSZ cathodes in 10,000 h will not exceed 0.4 or 0.13 Ohm cm², respectively, if YSZ or SDC electrolyte is used.     

Ce掺杂对碳纳米管负载Mn催化剂结构及SCR反应性能的影响

采用等体积浸渍法制备多壁碳纳米管(MWCNTs)负载Ce-Mn的催化剂,考察了Ce掺杂对Mn/MWCNTs催化剂上NH₃选择性催化还原(SCR)NO_x反应活性的影响.并运用透射电镜扫描、N₂吸附-脱附、程序升温还原、X射线光电子能谱、X射线衍射等手段,重点考察了Ce掺杂对Mn/MWCNTs催化剂结构性质的影响.结果表明,Ce掺杂能显著提高催化剂的SCR活性,其活性增量随着Ce含量的增加先增大后减小;当Ce/Mn为0.6时,催化剂活性最佳.表征结果显示,Mn/MWCNTs中添加Ce后,金属氧化物在MWCNTs上的分散程度提高;催化剂的比表面积和孔体积增大,平均孔径减小;氧化能力提高;表面氧含量增加,Mn化合价升高;结晶度降低,Mn主要以无定形或微晶形式存在,Ce主要以CeO₂物相存在.     

A nitrilo-tri-acetic-acid/acetic acid route for the deposition of epitaxial cerium oxide films as high temperature superconductor buffer layers

A water based cerium oxide precursor solution using nitrilo-tri-acetic-acid (NTA) and acetic acid as complexing agents is described in detail. This precursor solution is used for the deposition of epitaxial CeO₂ layers on Ni-5at%W substrates by dip-coating. The influence of the complexation behavior on the formation of transparent, homogeneous solutions and gels has been studied. It is found that ethylenediamine plays an important role in the gelification. The growth conditions for cerium oxide films were Ar-5% gas processing atmosphere, a solution concentration level of 0.25 M, a dwell time of 60 min at 900 °C and 5-30 min at 1050 °C. X-ray diffraction (XRD), scanning electron microscope (SEM), atomic force microscopy (AFM), pole figures and spectroscopic ellipsometry were used to characterize the CeO₂ films with different thicknesses. Attenuated total reflection-Fourier transform infrared (ATR-FTIR) was used to determine the carbon residue level in the surface of the cerium oxide film, which was found to be lower than 0.01%. Textured films with a thickness of 50 nm were obtained.     

Synthesis and Characterization of Indium-borate Glass-ceramics Containing Ho0.01Ce0.74Zr0.25O1.995 Nanorods via Incorporation Method

Glasses in the system 5In₂O₃·94Na₂B₄O₇ were fabricated via melt quenching technique. The amorphous nature of the quenched glasses was confirmed by X‐ray powder diffraction studies, and the infrared spectra of the glasses show no boroxol ring formation in the structure of these glasses. Differential thermal analysis is shown glass transition temperature 696°C and crystallization temperature 1151°C. A cerium‐zirconium mixed oxide Ce_0.75Zr_0.25O₂ and Ho‐doped cerium‐zirconium mixed oxide were obtained by solid‐state method. Then glass powder and Ho‐doped cerium‐zirconium mixed oxide were mixed. The mixture was heated in a crucible. The glass‐ceramic sample was obtained by pouring the melts on stainless steel. Obtained samples were annealed at 450°C for 1 h to remove thermal strain. Differential thermal analysis for glass‐ceramic sample is shown glass transition temperature 668°C and crystallization temperature 1159°C. The scanning electron microscopy study for glass‐ceramic indicates that the crystallized glass consists of rod‐like crystals with average diameter of about 38 nm dispersed in the glassy regions.     

Formation of isoxazole derivatives via nitrile oxide using ammonium cerium nitrate (CAN): a novel one-pot synthesis of 3-acetyl- and 3-benzoylisoxazole derivatives

The reactions of alkenes and alkynes with ammonium cerium(IV) nitrate ((NH₄)₂Ce(NO₃)₆, CAN(IV)) in acetone under reflux gave the corresponding 3-acetyl-4,5-dihydroisoxazole and 3-acetylisoxazole derivatives. In the case of acetophenone, 3-benzoyl-4,5-dihydroisoxazole and 3-benzoylisoxazole derivatives were obtained. Reaction of acetone with CAN(IV) afforded the corresponding furoxan (3,4-diacetyl-1,2,5-oxadiazole 2-oxide) as the dimer of nitrile oxide. Moreover, it was found that yields of isoxazole derivatives were improved using ammonium cerium(III) nitrate tetrahydrate ((NH₄)₂Ce(NO₃)₅·4H₂O, CAN(III))-formic acid. The reaction mechanisms based on nitration and formation of nitrile oxide mediated by CAN(IV) or CAN(III) from acetone or acetophenone are also proposed.     

CoOOH Nanosheets with High Mass Activity for Water Oxidation

Endowing transition‐metal oxide electrocatalysts with high water oxidation activity is greatly desired for production of clean and sustainable chemical fuels. Here, we present an atomically thin cobalt oxyhydroxide (γ‐CoOOH) nanosheet as an efficient electrocatalyst for water oxidation. The 1.4 nm thick γ‐CoOOH nanosheet electrocatalyst can effectively oxidize water with extraordinarily large mass activities of 66.6 A g^?1, 20 times higher than that of γ‐CoOOH bulk and 2.4 times higher than that of the benchmarking IrO₂ electrocatalyst. Experimental characterizations and first‐principles calculations provide solid evidence to the half‐metallic nature of the as‐prepared nanosheets with local structure distortion of the surface CoO_6?x octahedron. This greatly enhances the electrophilicity of H₂O and facilitates the interfacial electron transfer between Co ions and adsorbed ‐OOH species to form O₂, resulting in the high electrocatalytic activity of layered CoOOH for water oxidation.     

Vapor phase reduction of cyclohexanone to cyclohexanol on CexZr1-xO2 solid solutions

Reduction of cyclohexanone to cyclohexanol using propane-2-ol as hydrogen donor has been carried out in vapor phase on Ce_xZr_1-xO₂ solid solutions synthesized by ombustion synthesized at 302°C. The solid solutions around 0.4 mol% cerium content show better catalytic activity compared to pure ZrO₂ and the selectivity to cyclohexanol is 98%. A moderate acid-base and good redox properties of Ce_xZr_1-xO₂ solid solutions are seen to be responsible for the catalytic activity. A possible mechanism of hydride transfer has been proposed with cerium ions as promoters. This revised version was published online in June 2006 with corrections to the Cover Date.     

Low-temperature oxidation of carbon monoxide on Pd(Pt)/CeO2 catalysts prepared from complex salts

Catalysts containing cerium oxide as a support and platinum and palladium as active components for the low-temperature oxidation of carbon monoxide were studied. The catalysts were synthesized in accordance with original procedures with the use of palladium and platinum complex salts. Regardless of preparation procedure, the samples prepared with the use of only platinum precursors did not exhibit activity at a low temperature because only metal and oxide (PtO, PtO₂) nanoparticles were formed on the surface of CeO₂. Unlike platinum, palladium can be dispersed on the surface of CeO₂ to a maximum extent up to an almost an ionic (atomic) state, and it forms mixed surface phases with cerium oxide. In a mixed palladium-platinum catalyst, the ability of platinum to undergo dispersion under the action of palladium also increased; as a result, a combined surface phase with the formula Pd _x Pt _y CeO_{2 ? δ}, which exhibits catalytic activity at low temperatures, was formed.