Spectrum and Electrochemical Properties of Nanosized Ce_(1-x)Bi_xO_(2-δ) Solid Solutions

Ce1-xBixO2-δ(x = 0.00, 0.03, 0.05, 0.07, 0.10, 0.15, 0.30) solid solutions were synthesized via a hydrothermal method. The structure, spectra and electrochemical transport properties of the samples were characterized systematically. The powder X-ray diffraction analysis showed that all of the doped samples exhibited single phase fluorite structure. The particle sizes decreased from 18 to 9 nm and the lattice parameters increased gradually with the dopant content increasing from x = 0.03 to x = 0.30. The Bi3+ doping also induced the F2 g Raman peak to shift from 463 to 455 cm-1, and caused a red shift of the band gap energies calculated from UV-Vis spectra. The impedance plots at different temperature demonstrated that the boundary resistance was much larger than the grain resistance, and two activation energy values were obtained in different temperature range.     

Sol-gel synthesis and electrical properties of ceria-based solid electrolytes

A series of solid electrolytes (Ce_(0.8)RE_(0.2))_(1-x)M_xO_(2-δ)(RE: Rare earth, M: Alkali earth) were prepared by sol-gel methods. XRD indicated that a pure fluorite phase was formed at 800℃. The synthesis temperature by the sol-gel methods was about 700℃ lower than by the traditional ceramic method. The electrical conductivity and impedance spectra were measured. XPS showed that the oxygen vacancy increased obviously by doping MO, thus, resulting in the increase of the oxygen ionic transport number and conductivity. The performance of ceria-based solid electrolyte was improved. The effects of RE_2O_3 and MO on the electrical properties were discussed. The conductivity and the oxygen ionic transport number of (Ce_(0.8)Sm_(0.2))_(1-0.05)Ca_(0.05)O_(2(?)δ) is 0.126 S·cm~(-1) and 0.99 at 800℃, respectively.     

Energy Transfer and Green Emitting Properties of Solid Solution PbGd_(1-x)Tb_xB_7O_(13)(x = 0～1)

A series of Tb-doped solid solutions PbGd_(1-x)Tb_xB_7O_(13)(x = 0~1) were synthesized by high-temperature solid state reaction method. The luminescence properties were investigated under UV(274 nm) and near-UV(372 nm) excitation. The emission spectrum by 274 nm exciting reveals a charge-transfer between Gd~(3+) and Tb~(3+) ions. Under near-UV light(372 nm) excitation, PbGd_(1-x)Tb_xB_7O_(13):x Tb~(~(3+)) exhibits intense green emission centered at 543 nm due to the ~5D_4→~7F_5 transition of Tb~(3+) activator. The optimum doping concentrations were found to be x = 0.8 with the quantum efficiency of 35%. One may expect that PbGd_(1-x)Tb_xB_7O_(13) has the potential to be used as a green phosphor activated by near near-UV light.     

Enhancing cathode performance for CO_2 electrolysis with Ce_(0.9)M_(0.1)O_(2-δ)(M=Fe,Co, Ni) catalysts in solid oxide electrolysis cell

Electrochemical conversion with solid oxide electrolysis cells is a promising technology for CO_2 utilization and simultaneously store renewable energy. In this work, Ce_(0.9)M_(0.1)O_(2-δ)(CeM, M=Fe, Co, Ni) catalysts are infiltrated into La_(0.6) Sr_(0.4) Cr_(0.5_ Fe_(0.5) O_(3-δ)–Gd_(0.2) Ce_(0.8) O_(2-δ)(LSCr Fe-GDC) cathode to enhance the electrochemical performance for CO2 electrolysis. Ce Co-LSCr Fe-GDC cell obtains the best performance with a current density of 0.652 A cm-2, followed by Ce Fe-LSCr Fe-GDC and Ce Ni-LSCr Fe-GDC cells with the value of 0.603 and 0.535 A cm~(-2), respectively, about 2.44, 2.26 and 2.01 times higher than that of the LSCr Fe-GDC cell at1.5 V and 800 °C. Electrochemical impedance spectra combined with distributions of relaxed times analysis shows that both CO_2 adsorption process and the dissociation of CO_2 at triple phase boundaries are accelerated by Ce M catalysts, while the latter is the key rate-determining step.     

High performance and stability of double perovskite-type oxide NdBa_(0.5)Ca_(0.5)Co_(1.5)Fe_(0.5)O_(5+δ) as an oxygen electrode for reversible solid oxide electrochemical cell

In this study,we successfully synthesized double perovskite-type oxide NdBa_(0.5)Ca_(0.5)Co_(1.5)Fe_(0.5)O_(5+δ)(NBCCF) using a conventional wet chemical method as the oxygen electrode for reversible solid oxide electrochemical cells (RSOCs).The polarization resistance (R_p) of the composite electrode NBCCFGd_(0.1)Ce_(0.9)O_2 (GDC) is only 0.079Ωcm~2 at 800℃under air.The single cell based on NBCCF-GDC electrode displays a peak power density of 0.941 W/cm~2 in fuel cell mode and a low R_p value of 0.134Ωcm~2.In electrolysis cell mode,the cell displays an outstanding oxygen evolution reaction (OER) activity and shows current density as high as 0.92 A/cm~2 with 50 vol%AH (Absolute Humidity) at 800℃and applied voltage of 1.3 V.Most importantly,the cell exhibits admirable durability of 60 h both in electrolysis mode and fuel cell mode with distinguished reversibility.All these results suggest that NBCCF is a promising candidate electrode for RSOC.     

Electrochemical ageing study of mixed lanthanum/praseodymium nickelates La2-xPrxNiO4+δ as oxygen electrodes for solid oxide fuel or electrolysis cells

The chemical and electrochemical stability of lanthanide nickelates La2 NiO4+δ(LNO),Pr2 NiO4+δ(PNO)and their mixed compounds La(2-x)PrxNiO4+δ(LPNOs)with x=0.5,1 or 1.5 is reported.The aim is to promote these materials as efficient electrodes for solid oxide fuel cell(SOFC)and/or solid oxide electrolysis cell(SOEC).La2 NiO4+δand La1.5Pr0.5NiO4+δcompounds are chemically very stable as powders over one month in the temperature range 600-800℃,while the other materials rich in praseodymium progressively decompose into various perovskite-deriving components with additional Pr6 O11.Despite their uneven properties,all these materials are quite efficient and sustainable as electrodes on top of gadolinium doped ceria(GDCBL)//yttrium doped zirconia(8 YSZ)electrolyte,for one month at 700℃without polarization.Under polarization(300 mA·cm-2),the electrochemical performances of LNO,PNO and La1.5Pr0.5NiO4+δ(LP5 NO)quickly degrade in SOFC mode,i.e.for the oxygen reduction reaction,while they show durability in SOEC mode,i.e.for the oxide oxidation reaction.     

Studies on electrical properties of system La_(2-x)(Sr_(1-y)Ca_y)_xNiO_4

A new series of solid solutions of composition La_(2-x)(Sr_(2-y)Ca_y)_xNiO_4(0相似文献   

Catalytic properties of Ni/ceria-yttria electrode materials for partial oxidation of methane

The catalytic properties of electrode materials Ni/Ce1-xYxO2-δ (x = 0.05, 0.10, 0.15 and 0.20) were investigated for partial oxidation of methane (POM). The CeO2-Y2O3 solid solutions were prepared by co-precipitaion method. The Ni-based catalysts supported on the solid solutions were obtained using the impregnation method. Structural, surface and redox characteristics of the prepared catalysts were systematically examined by means of X-ray diffraction (XRD), N2 adsorption-desorption (Brunauer-Emmet-Teller BET method), H2 temperature-programmed reduction (H2-TPR) and X-ray photoelectron spectroscopy (XPS) methods. The results indicated that yttria doped in the ceria system, forming a good solid solution, readily induced more defects and oxygen vacancies that favored the improvement of catalytic activity and coking resistance. In the temperature range of 600-850 ℃, Ni/Ce0.90Y0.10O1.95 catalyst exhibited the best catalytic activity among the four tested catalysts, with the CH4 conversion, CO selectivity and H2 selectivity of 78.8%, 90.6% and 89.8%, respectively, at 850 ℃. And the H2/CO molar ratio in products of Ni/Ce0.90Y0.10O1.95 catalyst was closer to the theoretical value of 2.0. The excellent coking resistant behaviors for all catalysts were clearly manifested by Thermal Analysis.     

Transitional Area of Ce~(4+) to Ce~(3+) in Sm_xCa_yCe_(1-x-y)O_(2-δ) with Various Doping and Oxygen Vacancy Concentrations: A GGA + U Study

In this work,we perform DFT+U periodic calculations to study geometrical and electronic structures and oxygen vacancy formation energies of Sm_xCa_yCe_(1-x-y)O_(2-δ)systems(x=0.0312,0.0625,0.125 and 0.250;y=0.0312,0.0625,0.125 and 0.250;δ=0.0312,0.0625,0.125,0.250 and 0.50)with different oxygen vacancy and doping concentrations.The calculated results show that the V_1-Sm~(3+)-V_2 structures where there is a position relationship of the face diagonal between V_1 and V_2 both nearest to Sm~(3+)have the lowest energy configurations.The study on electronic structures of the Sm_xCa_yCe_(1-x-y)O_(2-δ)systems finds that excess electrons arise from oxygen vacancies and are localized on f-level traps of their neighbor Ce,and Ca~(2+)and Sm~(3+)co-doping effectively restrains the reduction of Ce~(4+).In order to avoid the existence of Ce~(3+),x and y must be both larger than 0.0625 asδ=0.125 orδmust be smaller than 0.125 as x=y=0.0625.The Ce~(3+)/Ce~(4+)change ratio k has an obvious monotonous increase with increasing the vacancy oxygen concentration.The introduction of Sm~(3+)decreases k.In addition,the doped Sm~(3+)can restrain the reduction of Ce~(4+)when the V_1-Sm~(3+)-V_2 structure with a face diagonal position relationship in lower reduced atmosphere exists.It need be pointed out that the Sm_(0.25)Ce_(0.75)O_(1.5) system should be thought of as a Sm-doped Ce_2O_3 one.     

Hydrothermal Synthesis and Characterization of Ce_(1-x)Mn_xO_(2-δ) Solid Solutions

Nanocrystals of Ce1-xMnxO2-δ(x=0.00,0.05,0.10,0.15,and 0.20) were synthesized by a hydrothermal reaction route.The solid solutions crystallized in a cubic fluorite structure with a particle size in the range of 11～15 nm.The incorporation of Mn ions in CeO2 resulted in a lattice volume reduction.Mn ions showed a mixed valence state of +2,+3 and +4 in CeO2 lattice.An obvious red-shift of the absorption threshold edge was observed from the UV-visible spectrum.Compared with the bulk CeO2,Ce1-xMnxO2-δ nanocrystals exhibited a lower releasing oxygen temperature as indicated by TPR technique.     

Direct synthesis of La-Mg-Ni-Co type hydrogen storage alloys from oxide mixtures

(La_(1-x)Mg_x)_2(Ni_(0.8)Co_(0.2))_7(x = 0.125, 0.25, 0.5) alloys were synthesized from the sintered mixture of La_2O_3+ Ni O + Co O + Mg O in the molten CaCl_2 electrolyte at 750 °C and the electrochemical hydrogen storage capacities of the synthesized alloys were measured. Non-hygroscopic LaNiO_3 phase formed during sintering(at 1200 °C for 2 h) as a result of the reaction of hygroscopic La_2O_3 with NiO. Another sinter product was Mg_(0.4)Ni_(0.6)O phase. Both mixed oxide sinter products facilitated the La-Ni and Mg-Ni phase formations. X-ray diffraction peaks indicated that the first stable phase appeared in the alloy structure was LaNi_5 which formed upon reduction of La_2NiO_4 phase. Increase in Mg content caused formation of La_(1.5)Mg_(0.5)Ni_7 phase in the alloy structure and the presence of this phase improved the hydrogen storage performance of the electrodes. It was observed that(La_(1-x)Mg_x)_2(Ni_(0.8)Co_(0.2))_7(x = 0.125, 0.25, 0.5) alloys have promising discharge capacities change between 319 m Ah/g and 379 m Ah/g depending on the alloy Mg content.     

Effect of dopant valence on the oxygen desorption and oxygen permeability of SrCo0.4Fe0.5M0.1O3-δ （M -Ni,Al and Zr） mixed-conducting oxides

The effect of dopant valence on oxygen desorption and oxygen permeability of SrCo0.4Fe0.5M0.1O3-δ （M = Ni, Al and Zr） mixed-conducting oxides were investigated in detail by O2-TPD and oxygen permeation measurement. The SrCo0.4Fe0.5M0.1O3-δ for M = Fe, Ni, Al and Zr were denoted as SCF, SCFN, SCFA and SCFZ, respectively. O2-TPD analysis revealed that the amount of α oxygen desorption decreased with increasing the valance of doped metal elements （SCFN 〉 SCFA SCF 〉 SCFZ）. The oxygen permeation flux at the temperature ≈igher than 1148 K decreased in the order of SCFN 〉 SCF 〉 SCFZ 〉 SCFA. Single activation for oxygen permeation was observed for SCFZ oxide and the activation energies of SCF and SCFA change at around 1073 K, while the change temoerature of SCFN was about 1173 K.     

Two Ternary Europium Chalcogenides Eu_(1-x)Ga_2Te_4(x≈0.19) and EuY_2Se_4, Experimental and Theoretical Investigations

Two ternary europium chalcogenides, Eu_(1-x)Ga_2Te_4(x ≈ 0.19)(1) and EuY_2Se_4(2), have been synthesized by a facile solid-state route using boron as the reducing reagent. Eu_(1-x)Ga_2Te_4 crystallizes in the tetragonal space group I4/mcm with a = 8.2880(9), c = 6.7439(12) ?, V = 463.24(13) ?~3, and Z = 2. EuY_2Se_4 crystallizes in the orthorhombic space group Pnma with a = 12.4726(16), b = 4.1204(6), c = 14.849(2) ?, V = 763.11(19) ?~3, and Z = 4. Eu_(1-x)Ga_2Te_4 belongs to the Tl Se-type 3D closed structure, while EuY_2Se_4 adopts the CaFe_2O_4-type 3D channel structure. The optical band gap of Eu_(1-x)Ga_2Te_4 is determined to be 0.48 eV. Electronic structures of 1 and 2 are calculated using TB-LMTO software.     

Phase Evolution and Magnetic Properties of Sn_(1-2x)Fe_xNb_xO_2(0.45≤x≤0.50)

Sn1-2xFexNbxO2(0.45≤x≤0.50) samples were prepared at 1000 ℃ via a simple chemical co-precipitation method.The effects of the concentrations of Sn doped on the structures and magnetic properties of the samples have been investigated.A systematic variation from monoclinic to orthorhombic FeNbO4 structure was observed with increasing Sn content.The phase evolutions were observed from monoclinic structure with x=0.50 to the coexistence of monoclinic and orthorhombic structures with x=0.48,0.47,0.46,and then to orthorhombic structure with x=0.45.Antiferromagnetic behavior was observed for all the samples,and the magnetic ordering temperatures decrease with increasing Sn concentration,which further indicated the sequence of phase transitions.The results suggest that the incorporation of Sn can stabilize the orthorhombic FeNbO4.     

Efficient CO_2 Electrolysis with Fluorite Structure Nanoparticles Modified Perovskite Structure La_(0.75)Sr_(0.25)Cr_(0.5)Mn_(0.5)O_(3-δ) Cathode

Perovskite structure La_(0.75)Sr_(0.25)Cr_(0.5)Mn_(0.5)O_(3-δ)(LSCM) cathode with unique structure can electrolyze CO_2 to CO in solid oxide electrolysers(SOEs).However,the cell performance is restricted by its electro-catalysis activity.In this work,fluorite structure nanoparticles(CeO_(2-δ)) are impregnated on LSCM cathode to improve the electro-catalysis activity.X-ray diffraction(XRD),scanning electron microscope(SEM) and X-ray photoelectron spectroscopy(XPS) together approve that the fluorite structure nanoparticles are uniformly distributed on the perovskite structure LSCM scaffold.Electrochemical measurements illustrate that direct CO_2 electrolysis with 10%mol CeO_(2-δ) impregnated LSCM cathode exhibits excellent performance for current density(0.5 A×cm~(-2)) and current efficiency(～95%) at 800 ℃ under 1.6 V.It is believed that the enhanced performance of directed CO_2 electrolysis may be due to the synergetic effect of fluorite structure CeO_(2-δ) nanoparticles and perovskite structure LSCM ceramic electrode.     

Co/Fe oxide and Ce_(0.8)Gd_(0.2)O_(2-δ) composite interlayer for solid oxide electrolysis cell

A composite interlayer comprised of gadolinia doped ceria(GDC) and Co/Fe oxide was prepared and investigated for solid oxide electrolysis cell with yttrium stabilized zirconia(YSZ) electrolyte and La_(0.6)Sr_(0.4)Co_(0.2)Fe_(0.8)O_(3-δ)(LSCF) anode. The interlayer was constructed of a base layer of GDC and a top layer of discrete Co_3O_4/FeCo_2O_4 particles. The presence of the GDC layer drastically alleviated the undesired reactions between LSCF and YSZ, and the presence of Co/Fe oxide led to further performance improvement. At 800 °C and 45% humidity, the cell with 70% Co/Fe-GDC interlayer achieved 0.98 A/cm~2 at 1.18 V, 14% higher than the cell without Co/Fe oxide. Electrochemical impedance spectroscopy(EIS) revealed that with higher Co/Fe content, both the ohmic resistance and the polarization resistance of the cell were reduced. It is suggested that Co/Fe oxide can react with the Sr species segregated from LSCF and Sr_(1-x)(Co,Fe)O_(3-δ), a compound with high catalytic activity and electronic conductivity. The Sr-capturing ability of Co/Fe oxide in combination with the Sr-blocking ability of GDC layer can effectively suppress the undesired reaction between LSCF and YSZ, and consequently improve the cell performance.     

STUDY OF THE MAGNETIC PROPERTIES OF LaGa_(1-x)Fe_xO_3

The dependence of the susceptibitity of LaGA_(1-x)Fe_xO_3(x=0.2,0.5,6.8) on the concentration of Fe~(3+),teperature and magnetic fietdintensity were studied and the change of Neet point was observed.Some regularities were obtained for first time in this paper.     

STUDY OF CATALYTIC BEHAVIOR OF PEROVSKITE-TYPE MIXED OXIDES La_(1-x)Sr_xFeO_(3-λ)(Ⅰ)——RELATIONS OF SOLID STRUCTURE AND DEFECT CHARACTER WITH CATALYTIC BEHAVIOR

According to X-ray structure analysis, it was found that there exist oxygen disordered defects in the crystal lattice of the samples without exception as x was changed from 0 to 1 in La_(1-x)Sr_xFeO_(3-x). With the doping of Sr~(2+), the crystal lattice was distorted extremely, even the crystal type varied. The results of TG showed a large amount of lattice oxygen released under high temperatures as x>0.5 in the samples. After comparison between the experiment results of the three systems La_(1-x)(Ca, Sr)_xMO_(3+x) (M=Mn, Fe and Co), it was concluded that the occurrence of solid defects is affected by the geometric factor and the catalytic activity is related to the concentration and the ordering extent of oxygen defects.     

Effect of Transition Metals (Cu, Co and Fe) on the Autothermal Reforming of Methane over Ni/Ce0.2Zr0.1Al0.7Oδ Catalyst

The transition metals (Cu, Co, and Fe) were applied to modify Ni/Ce0.2Zr0.1 Al0.7Oδcatalyst. The effects of transition metals on the catalytic properties of Ni/Ce0.2Zr0.1 Al0.7Oδautothermal reforming of methane were investigated. The Ni-supported catalysts were characterized by XRD, TPR and XPS. Tests in autothermal reforming of methane to hydrogen showed that the addition of transition metals (Cu and Co) significantly increased the activity of catalyst under the conditions of lower reaction temperature, and Ni/Cu0.05Ce0.2Zr0.1Al0.65Oδwas found to have the highest conversion of CH4 among all catalysts in the operation temperatures ranging from 923 K to 1023 K. TPR, XRD and XPS measurements indicated that the cubic phases of CexZr1-xO2 solid solution were formed in the preparation process of catalysts. Strong interaction was found to exist between NiO and CexZr1-xO2 solid solution. The addition of Cu improved the dispersion of NiO, inhibited the formation of NiAl2O4, and thus significantly promoted the activity of the catalyst Ni/Cu0.05Ce0.2Zr0.1Al0.65Oδ.     

Novel Ba_(0.5)Sr_(0.5)Fe_(0.8)Zn_(0.2)O_(3-δ) membranes for POM

A novel cobalt-free perovskite based on Ba_(0.5)Sr_(0.5)Fe_(0.8)Zn_(0.2)O_(3-δ)(BSFZ)were prepared by EDTA-citric acid method.The lattice constants of the BSFZ perovskite were characterized by in situ high-temperature X-ray diffraction(HTXRD).The thermal expansion coefficient of BSFZ is 10.5×10~(-6)K~(-1),which is lower than that of cobalt-based perovskite materials.The BSFZ membrane was also used to construct reactors for the partial oxidation of methane(POM)to syngas.Results show that the BSFZ membrane...