Properties of Interface between Platinum Sponge and Solid Electrolyte Na5TbSi4O12in an Oxygen Atmosphere at Moderate Temperatures: Effect of the Platinum Grain Size

The behavior of electrochemical cells Pt(sponge)/Na₅TbSi₄₁₂/Na_0.65Co₂(cell I) and Pt(sponge)/Na₅TbSi₄₁₂/Pt(sponge) (cell II) is studied by, respectively, potentiometric and impedance methods in oxygen and argon atmospheres at 50–300°C. Dependence of potential of cell I on the oxygen concentration is affected by the grain size of platinum sponge and the temperature. At 50–200°C the coarse-grained platinum electrode in contact with solid electrolyte Na₅TbSi₄₁₂ exhibits an oxygen function characterized by the potential-determining reaction ₂(g) + ₂ + 2 = ^– ₂ + ^–. An impedance method shows the triple-phase boundary ₂, Pt(sponge)/Na₅TbSi₄₁₂ to be reversible with respect to oxygen. The reversibility is realized by minority charge carriers in the solid electrolyte, i.e. by oxygen ions.     

Polyaniline‐Modified Silver and Binary Silver‐Cobalt Catalysts for Oxygen Reduction Reaction

Novel dendrite‐like silver particles were electrodeposited on Ti substrates from a supporting electrolyte‐free 30 mmol L^?1 Ag(NH₃)₂⁺ solution, to synthesize the den‐Ag/Ti electrode. Binary Ag_xCo_y/Ti electrodes with different Ag:Co atomic ratios were further obtained by electrodeposition of Co particles on the den‐Ag/Ti electrode. Polyaniline (PANI) modified den‐Ag/Ti and Ag_xCo_y/Ti electrodes, PANI(n)‐den‐Ag/Ti and PANI(n)‐Ag_xCo_y/Ti, were also obtained by cyclic voltammetry at different numbers of cycles (n) in acidic and alkaline solutions containing aniline, respectively. All these electrodes exhibit high electroactivity for oxygen reduction reaction (ORR) in alkaline solution and their electroactivities follow the order: PANI(15)‐Ag₃₁Co₆₉/Ti>Ag₃₁Co₆₉/Ti>PANI(20)‐den‐Ag/Ti>den‐Ag/Ti. Among them, PANI(15)‐Ag₃₁Co₆₉/Ti displays the highest electrocatalytic activity for ORR with a much positive onset potential of 0 V (vs. Ag/AgCl) and a high ORR current density of 1.2 mA cm^?2 at ?0.12 V (vs. Ag/AgCl). The electrocatalysts are electrochemically insensitive to methanol and ethanol oxidation, and, as cathode electrocatalysts of direct alcohol fuel cells, can resist poisoning by the possible alcohol crossover from the anode.     

Phase Equilibria and Crystal Structure of Complex Oxides in the La–Sr–Co–Ni– System

Phase equilibria in the La–Sr–Co–Ni–O system were studied in air at 1100°. The samples for the study were synthesized by the standard ceramic and citrate processes. The limiting solubility and structure of La_1-xSr_xCo_1-yNi_yO_3- and (La_1-xSr_x)₂Co_1-yNi_yO₄ solid solutions were determined by Xray powder diffraction analysis. La_1-xSr_xCo_1-yNi_yO₃- solid solutions with 0 x 0.5 have a distorted rhombohedral perovskitelike structure (R c space group). An increase in the strontium concentration reduces the rhombohedral distortions, and the compounds with x < 0.5 have an ideal cubic structure (Pm3m space group). (La_1-xSr_x)₂Co_1-yNi_yO₄ crystals have a tetragonal K₂NiF₄ type unit cell (I4/mmm space group). The relationships between unit cell parameters and compositions were obtained for singlephase La_1-xSr_xCo_1-yNi_yO_3- and (La_1-xSr_x)₂Co_1-yNi_yO₄ samples. The existence regions of La_1-xSr_xCo_1-yNi_yO₃- and La_1-xSr_x)₂Co_1-yNi_yO₄ solid solutions were distinguished on P–T phase diagrams.     

Kinetics of mixed-controlled oxygen reduction at nafion-impregnated Pt-alloy-dispersed carbon electrode by analysis of cathodic current transients

The effects of Co alloying to Pt catalyst and Nafion pretreatment by NaClO₄ solution on the rate-determining step (RDS) of oxygen reduction at Nafion-impregnated Pt-dispersed carbon (Pt/C) electrode were investigated as a function of the potential step ΔE employing potentiostatic current transient (PCT) technique. For this purpose, the cathodic PCTs were measured on the pure Nafion-impregnated and partially Na⁺-doped Nafion-impregnated Pt/C and PtCo/C electrodes in an oxygen-saturated 1 M H₂SO₄ solution and analyzed. From the shape of the cathodic PCTs and the dependence of the instantaneous current on the value of ΔE, it was confirmed that oxygen reduction at the pure Nafion-impregnated electrodes is controlled by charge transfer at the electrode surface mixed with oxygen diffusion in the solution below the transition potential step |ΔE _tr| in absolute value, whereas oxygen reduction is purely governed by oxygen diffusion above |ΔE _tr|. On the other hand, the RDS of oxygen reduction at the partially Na⁺-doped Nafion-impregnated electrodes below |ΔE _tr| is charge transfer coupled with proton migration, whereas above |ΔE _tr|, it becomes proton migration in the Nafion electrolyte instead of oxygen diffusion. Consequently, it is expected in real fuel cell system that the cell performance is improved by Co alloying since the electrode reaches the maximum diffusion (migration) current even at small value of |ΔE|, whereas the cell performance is aggravated by Nafion pretreatment due to the decrease in the maximum diffusion (migration) current.     

Catalysis of Multi‐walled Carbon Nanotubes Supported PdxCoy Nanoparticles Prepared by a Pyrolysis Method Using Ionic Liquids as the Solvent toward Ethanol Oxidation Reaction

Multi‐walled carbon nanotubes (MWCNTs) decorated with Pd_xCo_y (the nominal atomic ratios of Pd to Co were 3:1, 3:1.5, 3:2, 3:3, respectively) nanoparticles (denoted as Pd_xCo_y/MWCNTs ) were fabricated by a simple pyrolysis process, in which room temperature ionic liquids (RTILs) of butyl‐3‐methylimidazolium hexafluorophosphate (denoted as [BMIM]PF₆) was used as the solvent. X‐ray diffraction (XRD) and transmission electron microscopy (TEM) were all used to characterize the Pd_xCo_y/MWCNTs catalysts, showing that the Pd_xCo_y particles were dispersed on the surface of the MWCNTs with an average particle size of ～25.0 nm. The electro‐catalytic activity of the Pd_xCo_y/MWCNTs catalysts toward ethanol oxidation reaction (EOR) was examined by cyclic voltammetry (CV). It was revealed that the onset potential was ～90 mV lower and the peak current was about four times higher for ethanol oxidation for Pd₃Co_1.5/MWCNTs compared to those of Pd₃Co₁/MWCNTs. The possible catalysis mechanisms of the Pd₃Co_1.5/MWCNTs toward EOR were also discussed.     

Effect of the electrode material on the oxygen reduction at the nonstoichiometric lanthanum fluoride/electrode interface

The voltammetry method with a linear potential scan is used for investigating the effect the electrode material (Ni, Co, electrodes on the basis of cobalt oxides modified with carbon) exerts on the reduction of gaseous oxygen at interfaces solid fluoride-conducting electrode LaF₃:Eu²⁺/electrode, O₂, and conjugated processes. Properties of the modified electrodes are characterized by the impedance spectroscopy, scanning electron microscopy, and x-ray photoelectron spectroscopy methods. The oxygen reaction is irreversible at the LaF₃:Eu²⁺|Ni (or Co) interfaces. At the interface of LaF₃:Eu²⁺ with modified electrodes Co (C n at %), where n = 5 and 9, mobile forms of oxygen are reversible and the reduction of gaseous and chemisorbed oxygen is controlled by diffusion with different effective kinetic parameters.     

Studies of Nano－sized Co304 as Anode Materials for Lithium－ion Batteries

The structural evolution of the Co₃O₄ fine powders prepared by rheological phase reaction and pyrolysis method upon different temperature has been investigated using X‐ray diffraction (XRD) topography. The electrochemical performance of Co₃O₄ electrode materials for Li‐ion batteries is studied in the form of Li/Co₃O₄ cells. The reversible capacity as high as 930 mAh/g for the Co₃O₄ sample heat‐treated at 600 °C is achieved and sustained over 30 times charge‐discharge cycles at room temperature. The detailed information concerning the reaction mechanism of Co₃O₄ active material together with lithium ion is obtained through ex‐situ XRD topography, X‐ray photoelectron spectroscopy (XPS) analysis and cyclic voltammetry (CV) technique. And it is revealed that a “two‐step” reaction is involved in the charge and discharge of the Li/Co₃O₄ cells, in which Co₃O₄ active material is reversibly reduced into xCoO(3 ‐ x)CoO and then into metallic Co.     

The Mechanism of Methane Reforming with Carbon Dioxide: Comparison of Supported Pt and Ni (Co) Catalysts

The interaction of the catalyst 5.16 wt % Pt/-Al₂O₃ with ₄, ₂, ₂, and ₄ + ₂ pulses is studied using a setup involving the differential scanning calorimeter DSC–111 and a system for chromatographic analysis. Comparison of the results obtained with analogous data on Ni/Al₂O₃ and Co/Al₂O₃ suggests that methane activation occurs via a common pathway via dissociative chemisorption on the metal surface with the formation of ₂ and carbon on all the catalysts studied. Carbon dioxide activation on Pt/Al₂O₃ differs from its activation on Ni()/Al₂O₃. It follows from the enthalpy of formation that carbon on Pt/Al₂O₃ is graphite-like in contrast to carbide carbon on Ni(Co)/Al₂O₃. This graphite carbon is more stable and less reactive.     

Mild hydrothermal synthesis, crystal structure, spectroscopic and magnetic properties of the [M=Fe, x=2.08, y=1.58; M=Co, Ni, x=2.5, y=2] compounds

The [M=Fe (1), x=2.08, y=1.58; M=Co (2), x=2.5, y=2; Ni (3), x=2.5, y=2] compounds have been synthesized using mild hydrothermal conditions at 170 °C during five days. Single-crystals of (1) and (2), and polycrystalline sample of (3) were obtained. These isostructural compounds crystallize in the orthorhombic system, space group Aba2, with a=9.9598(2), b=18.8149(4) and c=8.5751(2) Å for (1), a=9.9142(7), b=18.570(1) and c=8.4920(5) Å for (2) and a=9.8038(2), b=18.2453(2) and c=8.4106(1) Å for (3), with Z=8 in the three phases. An X-ray diffraction study reveals that the crystal structure is composed of a three-dimensional skeleton formed by [MO₅F] and [MO₄F₂] (M=Fe, Co and Ni) octahedra and [HPO₃] tetrahedra, partially substituted by [PO₄] tetrahedra in phase (1). The IR spectra show the vibrational modes of the water molecules and those of the (HPO₃)²⁻ tetrahedral oxoanions. The thermal study indicates that the limit of thermal stability of these phases is 195 °C for (1) and 315 °C for (2) and (3). The electronic absorption spectroscopy shows the characteristic bands of the Fe(II), Co(II) and Ni(II) high-spin cations in slightly distorted octahedral geometry. Magnetic measurements indicate the existence of global antiferromagnetic interactions between the metallic centers with a ferromagnetic transition in the three compounds at 28, 14 and 21 K for (1), (2) and (3), respectively. Compound (1) exhibits a hysteresis loop with remnant magnetization and coercive field values of 0.72 emu/mol and 880 Oe, respectively.     

Thermally Prepared Ti/RhO x Electrodes: Hydrogen Evolution in Alkaline Solution

Ti/RhO _x electrodes were prepared at 400–600° by thermal decomposition of RhCl₃. Oxide layers were characterized by cyclic voltammetry in H₂SO₄ as well as in KOH solution. The voltammetric charge exhibited a maximum at 470°C in both cases. ₂ evolution from KOH solution was studied by steady-state polarization curves. Only one Tafel slope close to 40 mV was observed over the explored current range. The reaction order with respect to ^– was negative and fractional. A mechanism is proposed for H₂ evolution on RhO _x in KOH solution. The stability of the electrodes was tested by comparing the voltammetric charge before and after the ₂ evolution experiments. Stability was observed to increase with increasing calcination temperature. The same is the case for the electrocatalytic activity normalized to unit surface charge.     

CNx-modified Fe3O4 as Pt nanoparticle support for the oxygen reduction reaction

A novel electrocatalyst support material, nitrogen-doped carbon (CN_x)-modified Fe₃O₄ (Fe₃O₄-CN_x), was synthesized through carbonizing a polypyrrole-Fe₃O₄ hybridized precursor. Subsequently, Fe₃O₄-CN_x-supported Pt (Pt/Fe₃O₄-CN_x) nanocomposites were prepared by reducing Pt precursor in ethylene glycol solution and evaluated for the oxygen reduction reaction (ORR). The Pt/Fe₃O₄-CN_x catalysts were characterized by X-ray diffraction, Raman spectra, X-ray photoelectron spectroscopy, scanning electron microscopy, and transmission electron microscopy. The electrocatalytic activity and stability of the as-prepared electrocatalysts toward ORR were studied by cyclic voltammetry and steady-state polarization measurements. The results showed that Pt/Fe₃O₄-CN_x catalysts exhibited superior catalytic performance for ORR to the conventional Pt/C and Pt/C-CN_x catalysts.     

Structure and electrical conductivity of cobalt-doped Bi<Subscript>26</Subscript>Mo<Subscript>10</Subscript>O<Subscript>69</Subscript>

The existence boundaries, structures, and transport parameters of Bi_{1 ? x} Co _x [Bi₁₂O₁₄]Mo₅O_{20 ± δ} and Bi[Bi₁₂O₁₄]Mo_{5 ? y} Co _y O_{20 ± δ} solid solutions, which have a unique columnar structure, were studied. Electrical conductivity in these solid solutions was studied by impedance spectroscopy.     

Solid state reaction synthesis of filled skutterudite compounds (Ce or Y)yFexCo4-xSb12 and the effect of filling atoms Ce or Y on lattice thermal conductivity

The synthesis of filled skutterudite compounds (Ce or Y)yFexCo₄-xSb12, through a solid state reaction using chloride of Ce or Y, high purity powder of Co, Fe, and Sb as starting materials, was investigated. (Ce or Y)yFexCo₄-xSb12 (x = 0 1.0,y = 0 0.15) compounds were obtained at 850 1 123 K. The results of Rietveld analysis demonstrate that (Ce or Y)yFexCo₄-xSb12 synthesized by a solid state reaction possesses a filled skutterudite structure. The filling fraction of Ce or Y obtained by Rietveld analysis agrees well with the composition obtained by chemical analysis. The lattice constant of CeyFexCo₄-xSb12 increases with increasing substitution of Fe at Co sites, and with an increasing Ce filling fraction in the Sb-dodecahedron voids. The lattice thermal conductivity of (Ce or Y)yFexCo₄-xSb12 decreases significantly with an increasing Ce or Y filling fraction in the voids and with substitution of Fe at Co sites.     

Meso-macroporous Co3O4 electrode prepared by polystyrene spheres and carbowax templates for supercapacitors

Meso-macroporous Co₃O₄ electrode is synthesized by drop coating with a mixed solution containing Co(OH)₂ colloid, polystyrene spheres, and carbowax (namely polyethylene glycol), followed by calcining at 400?°C to remove polystyrene spheres and carbowax. For comparison, nonporous Co₃O₄ and mesoporous Co₃O₄ electrodes are prepared by drop coating with Co(OH)₂ colloid and with a mixed solution containing Co(OH)₂ colloid and carbowax under the same condition, respectively. Capacitive property of these electrodes is measured by cyclic voltammetry, potentiometry and electrochemical impedance spectroscopy. The results show that meso-macroporous Co₃O₄ electrode exhibits larger specific capacitance than those of nonporous Co₃O₄ electrode and mesoporous Co₃O₄ electrode at various current densities. The specific capacitance of meso-macroporous Co₃O₄ electrode at the current density of 0.2?A?g^?1 is 453?F?g^?1. Meanwhile, meso-macroporous Co₃O₄ electrode possesses the highest specific capacitance retention ratio at the current density ranging from 0.2 to 1.0?A?g^?1, indicating that meso-macroporous Co₃O₄ electrode suits to high-rate charge?Cdischarge.     

Convenient and Mild Epoxidation of Alkenes Using Heterogeneous Cobalt Oxide Catalysts

A general epoxidation of aromatic and aliphatic olefins has been developed under mild conditions using heterogeneous Co_xO_y–N/C (x=1,3; y=1,4) catalysts and tert‐butyl hydroperoxide as the terminal oxidant. Various stilbenes and aliphatic alkenes, including renewable olefins, and vitamin and cholesterol derivatives, were successfully transformed into the corresponding epoxides with high selectivity and often good yields. The cobalt oxide catalyst can be recycled up to five times without significant loss of activity or change in structure. Characterization of the catalyst by XRD, TEM, XPS, and EPR analysis revealed the formation of cobalt oxide nanoparticles with varying size (Co₃O₄ with some CoO) and very few large particles with a metallic Co core and an oxidic shell. During the pyrolysis process the nitrogen ligand forms graphene‐type layers, in which selected carbon atoms are substituted by nitrogen.     

Effects of Metal Electrode Support on the Catalytic Activity of Fe(oxy)hydroxide for the Oxygen Evolution Reaction in Alkaline Media

FeO_xH_y and Fe-containing Ni/Co oxyhydroxides are the most-active catalysts for the oxygen evolution reaction (OER) in alkaline media. However, the activity of Fe sites appears strongly dependent on the electrode-substrate material and/or the elemental composition of the matrix in which it is embedded. A fundamental understanding of these interactions that modulate the OER activity of FeO_xH_y is lacking. We report the use of cyclic voltammetry and chronopotentiometry to assess the substrate-dependent activity of FeO_xH_y on a number of commonly used electrode substrates, including Au, Pt, Pd, Cu, and C. We also evaluate the OER activity and Tafel behavior of these metallic substrates in 1 M KOH aqueous solution with Fe³⁺ and other electrolyte impurities. We find that the OER activity of FeO_xH_y varies by substrate in the order Au>Pd≈Pt≈Cu>C. The trend may be caused by differences in the adsorption strength of the Fe oxo ion on the substrate, where a stronger adhesion results in more adsorbed Fe at the interface during steady-state OER and possibly a decreased charge-transfer resistance at the FeO_xH_y-substrate interface. These results suggest that the local atomic and electronic structure of [FeO₆] units play an important role in catalysis of the OER as the activity can be tuned substantially by substrate interactions.     

The Interaction of Iodide Film with Platinum Microparticles on Different Electrode Materials for Various Electrocatalytic Reactions

The electrochemical depositions of Pt microparticles and KI film were successfully carried out on glassy carbon electrodes (GCE), gold electrodes (GE), and indium tin oxide electrodes (ITO). The electrochemical studies of Pt micro/KI film on GCE show that the film was stable, active at pH 1.5 electrolyte solutions. The Pt microparticle/KI film modified ITO electrodes were examined by using scanning electron microscopy (SEM) and atomic force microscopy (AFM) techniques. The SEM and AFM results show that the Pt particle sizes were in the range of 120 nm–1.4 μm, respectively. The proposed film on GCE shows efficient electrocatalysis for oxygen, Cr₂O reduction by using cyclic voltammetry. Further the electrochemical oxidation of sodium meta‐arsenite (As(III)), H₂O₂ were successfully carried out and the detection of H₂O₂ in real samples has been validated.     

A Flame‐Reaction Method for the Large‐Scale Synthesis of High‐Performance SmxCoy Nanomagnets

We report a flame‐reaction method to synthesize high‐performance Sm_xCo_y (x=1, y=5; x=2, y=17) particles on a multigram scale. This flame reaction allows the controlled decomposition of Sm(NO₃)₃ and Co(NO₃)₂ to 320 nm SmCo‐O (SmCoO₃ + Co₃O₄) particles. A 5.8 g sample of SmCo_3.8‐O particles was coated with CaO and then reduced at 900 °C by Ca to give 4.2 g of 260 nm SmCo₅ particles. The SmCo₅ particles are strongly ferromagnetic and the aligned particles in epoxy resin exhibit a large room‐temperature coercivity (H_c) of 41.8 kOe and giant (BH)_max (maximum magnetic energy product) of 19.6 MGOe, the highest value ever reported for SmCo₅ made by chemical methods. This synthesis can be extended to synthesize Sm₂Co₁₇ particles, providing a general approach to scaling up the synthesis of high‐performance Sm_xCo_y nanomagnets for permanent magnet applications.     

NixCo3-xO4表面修饰对CdSe/TiO2纳米管阵列光电化学氧化水活性的影响

利用氨挥发诱导法在CdSe/TiO2纳米管阵列表面负载一层NixCo3-xO4。采用SEM、XRD、XPS、UV-Vis对样品进行表征,通过线性扫描伏安法测定光阳极的释氧电势来评价其光电水氧化活性。结果表明:表面NixCo3-xO4是尖晶石结构;相对于CdSe/TiO2纳米管阵列光阳极,NixCo3-xO4/CdSe/TiO2光阳极能将光电氧化水的过电势降低430 mV。Ni离子的引入使得NixCo3-xO4表面富含三价阳离子(Ni3+,Co3+),从而促进CdSe/TiO2光阳极光电水氧化的进行。     

Theoretical and Experimental Studies of the Nature of the Catalytic Activity of VO x /TiO2 Systems

The states of supported vanadium and the nature of activation of ammonia adsorbed on vanadium sites of V _x /Ti₂ catalysts are studied by ⁵¹V NMR spectroscopy and diffuse-reflectance IR Fourier-transform (DRIFT) spectroscopy using cluster quantum chemical calculations of N₃ adsorption. We employ the V _x /Ti₂ catalyst of two types: the monolayer catalyst in which vanadium is located on the surface of well-crystallized anatase and the catalyst in which vanadium embedded in the anatase lattice at a rather great depth. It is shown that ammonia is predominantly adsorbed on Lewis acid sites of the monolayer catalyst, whereas most of N₃ adsorbed on the catalyst containing bulk vanadium is in the form of ammonium ions. Analysis of experimental and calculated data suggests that, in the monolayer catalyst, N₃ molecules in the selective reduction of nitrogen oxides are activated on Lewis acid sites. Ammonia activation involves the dissociation of the N–H bond in a coordinated molecule, which results in the formation of the amide V–N₂ group and a water molecule coordinated by a V⁵⁺ ion. It is likely that, in the case of the catalyst containing bulk vanadium, this reaction occurs with the predominant participation of ammonium ions.