Effect Of A-site Deficiency Research Articles

Boosting electrochemical CO2 directly electrolysis by tuning the surface oxygen defect of perovskite

The insufficient CO2 adsorption ability on the cathode hinders the development of solid oxide electrolysis cells (SOECs). Regulating the surface oxygen defect of the cathode is an efficient strategy to enhance the electrochemical performance of CO2 electrolysis. Herein, we design oxygen-defect perovskite (La0.5Sr0.5)1-xFe0.9Mn0.1O3-δ oxide by introducing A-site cation deficiency. The effect of A-site deficiency on surface oxygen vacancy and electrocatalytic activity for CO2 reduction is systematically investigated. The relaxation time distribution (DRT) results demonstrate that the enhanced surface oxygen vacancy concentration significantly improves the CO2 adsorption ability, leading to high electrochemical performance for CO2 electrolysis. The single cell with (La0.5Sr0.5)0.9Fe0.9Mn0.1O3-δ cathode attains a current density of 1.1 A cm−2 at 1.6 V and 800 °C. The polarization resistance decreases from 0.6 for (La0.5Sr0.5) Fe0.9Mn0.1O3-δ to 0.25 Ω cm2 for (La0.5Sr0.5)0.9Fe0.9Mn0.1O3-δ cathode at 1.2 V. This work shows that oxygen-defect (La0.5Sr0.5)0.9Fe0.9Mn0.1O3-δ is a potential cathode material for CO2 directly electrolysis.

Effect of A-site deficiency on perovskite-type Mn4+-activated La5/3MgTaO6 red phosphor and green luminescence of the Mn2+ occupied six-coordinate site in Mg2LaTaO6

White light LEDs have a long life and high energy efficiency; however, their application is limited owing to the lack of red components. Herein, we use the solid-state reaction method to fabricate a new Mn-activated perovskite-type La5/3MgTaO6 phosphor that exhibits red emission under UV excitation at 365 ​nm. A-site deficiency in the perovskite-type structure plays a crucial role in the emission of Mn4+ in La5/3MgTaO6 because Mn4+—which is located in the non-inversion symmetry site—is activated for such an emission. In addition, the newly Mn-activated pyrochlore-type Mg2LaTaO6 phosphor exhibited green emission under UV excitation at 254 ​nm owing to the oxide ion deficiency of Mg2LaTaO6. Based on the features of the oxide-deficient pyrochlore-type structure, we infer that Mn2+ may be present in the six-coordinate octahedral site with high distortion in pyrochlore-type Mg2LaTaO6.

Stable, efficient and cost-competitive Ni-substituted Sr(Ti,Fe)O3 cathode for solid oxide fuel cell: Effect of A-site deficiency

In this work, a cost-competitive oxide system of Ni-substituted Sr1-xTi0.3Fe0.6Ni0.1O3-δ (STFN, x = 0, 0.02, 0.05), is evaluated as Solid Oxide Fuel Cell cathode. All STFN oxides present cubic perovskite structure with maximum conductivities over 22 S/cm in air. The introduction of Sr deficiency yields higher oxygen vacancy and lower thermal expansion coefficient. As a result, the cathode polarization resistance of 0.107 Ω cm2 is obtained for Sr0.95Ti0.3Fe0.6Ni0.1O3-δ (STFN-95) at 750 °C and pO2=0.21atm, with weak oxygen partial pressure dependence. Specially, STFN-95 presents higher stability with slower Rp increasing rate in lower oxygen partial pressure of 0.14 atm than in 0.21 atm, which greatly facilitates the cathode practical application in SOFC stack under high air utilization condition. Finally, a stable operation of 400 h is achieved using STFN-95 cathode on anode supported single cell at 750 °C, without showing Sr and other elements diffusions.

Synthesis and Electrochemical Performance of Ni Substituted SrTi0.3Fe0.7O3-δ Cathode: Effect of A-Site Deficiency

Herein, we present the synthesis and electrochemical properties of Ni substituted Sr1-xTi0.3Fe0.6Ni0.1O3-δ (STFN, x=0; STFN-5, x=0.05) as solid oxide fuel cell cathodes. First, the results suggest a Ni solubility limit in SrTi0.3Fe0.7O3-δ, lower than ~14 at% in B-site. Second, the conductivities increase first with temperature increasing and then decrease; STFN shows a maximum conductivity of 23.9 S/cm at 700 oC, while STFN-5 shows similar peak value but at much lower temperature of ~600-650 oC. Third, the electrochemical impedance spectroscopy tests are conducted in a wide range of oxygen partial pressures below 0.21 atm, using symmetrical cells. The A-site deficient STFN-5 cathode shows smaller polarization resistance values compared with A-site stoichiometric composition. The polarization resistance of STFN-5 is ~0.11 Ω·cm2 at 750 oC in oxygen partial pressure of 0.21 atm and shows a relative stable operation during long term test in air.

Effect of A-site deficiency on the structural and magnetic properties of La0.8−x□xNa0.2−x□xMnO3 oxides and estimation of the magnetocaloric behavior

The morphological, structural, magnetic and magnetocaloric properties of perovskite manganite oxides La0.8−x□xNa0.2−x□xMnO3 are studied with x = 0 and 0.1. The X-ray diffraction (XRD) data were analyzed by Rietveld refinement technique which reveals that the samples crystallized in a rhombohedral structure with R3¯c space group. As for the magnetic measurements, it is found that the two samples undergo a transition from the ferromagnetic state (FM) to paramagnetic state (PM) with the increase of temperature. The transition temperature, called the Curie temperature (TC), decreases from 324 K for the parent compound (x = 0) to the range of room temperature (304 K) for x = 0.1. Moreover, from magnetization measurements versus magnetic applied field, we studied the magnetocaloric effect (MCE) by the determination of the magnetic entropy change ΔSM. The maximum magnetic entropy changes ΔSMMax increases from 2.91 J/kg.K for x = 0–3.23 J/kg.K for x = 0.1 under an applied magnetic field of 2 T. The Relative Cooling Power (RCP) values were found to reach 76.13 J/K and 70.36 J/K for x = 0 and 0.1, respectively, for the same applied magnetic field (μ0H = 2 T). Thanks to the mentioned values obtained around the Curie temperatures, these materials are suggested to be good candidates as magnetic refrigerants for magnetic refrigeration in the above-room and room temperature range. Besides, a mixture of these two materials may form a composite refrigerant working in a larger temperature range limited by their TC.

Effect of A-site deficiency on investigation of structural, magnetic and magnetocaloric behaviors for (LaSr)-lacunar manganites

We investigated the effect of both lanthanum and strontium deficiencies upon the structural, magnetic and magnetocaloric properties in La0.7Sr0.3MnO3 mixed-valence manganite. Lacunar powder oxides La0.7−x□x Sr0.3MnO3 and La0.7Sr0.3−x□xMnO3 (x = 0, 0.01, 0.02 and 0.05), where □ is a vacancy, were prepared by the sol–gel technique by sintering at 750 °C and 850 °C. Our synthetized samples crystallize in a rhomboedrically distorted perovskite structure with space group R-3C. Both these series of samples are ferromagnets and undergo second order paramagnetic–ferromagnetic transition with decreasing temperature. Magnetization measurements versus magnetic applied field at low temperature confirm the ferromagnetic behavior of our lacunars samples. Curie temperature decrease with increasing vacancy content for strontitum-deficient samples, while, its shows a maximum at about x = 0.01 (TC = 358 K) followed by a minimum for x = 0.03 (TC = 336 K) for lanthanum- deficient compounds. All compounds undergo a large magnetocaloric effect and have consequently potential applications in magnetic refrigeration domain around room temperature.

Effect of A-site deficiency in LaMn0.9Co0.1O3 perovskites on their catalytic performance for soot combustion

The influence of lanthanum stoichiometry in Ag-doped (La1-xAgxMn0.9Co0.1O3) and A-site deficient (La1-xMn0.9Co0.1O3-δ) perovskites with x equal to 10, 20 and 30 at.% has been investigated in catalysts for soot combustion. The catalysts were prepared by the amorphous citrate method and characterized by XRD, nitrogen adsorption, XPS, O2-TPD and TPR. The formation of a rhombohedral excess-oxygen perovskite for Ag-doped and a cubic perovskite structure for an A-site deficient series is confirmed. The efficient catalytic performance of the larger Ag-doped perovskite structure is attributed to the rhombohedral crystalline structure, Ag2O segregated phases and the redox pair Mn4+/Mn3+. A poor catalytic activity for soot combustion was observed with A-site deficient perovskites, despite the increase in the redox pair Mn4+/Mn3+, which is attributed to the cubic crystalline structure.

Electrical Performance of La-Substituted SrTiO3 Anode Material with Different Deficiency in A-Site

Performance of (La0.25Sr0.75)1-xTiO3 (LST) with different deficiency (x) in A-site and the effect of A-site deficiency on the interfacial reaction between LST anode and 1CeO2-10Sc2O3-89ZrO2 (ScSZ) electrolyte were investigated. According to the results of XRD and SEM of LSTs with different deficiency, a maximum value of x (between 0.1 and 0.15) for single phase LST was found to be existed in LST. La2Zr2O7 (LZO) was found to be formed at the interface of ScSZ and stoichiometric LST or LST with little deficiency in A-site. A-site deficiency in LST could suppress the interfacial reaction between LST and ScSZ. The performance of the cells with A-site deficient LST anode was increased as the value of A-site deficiency in LST increased.

Effect of A-site deficiency in BaCe 0.8Sm 0.2O 3-δ on the electrode performance for proton conducting solid oxide fuel cells

The effect of A-site deficiency in BaCe 0.8Sm 0.2O 3-δ on the electrode performance is investigated using Ba 1- x Ce 0.8Sm 0.2O 3-δ ( x = 0.00, 0.02 and 0.05) to constitute composite anode and cathode with NiO and Sm 0.5Sr 0.5CoO 3 (SSC), respectively. Two overlapped arcs are observed in impedance spectra of the cells with those composite electrodes under open circuit conditions. The low frequency resistances reduce first and then increase with the value of A-site deficiency of BaCe 0.8Sm 0.2O 3-δ in both anode and cathode, while the high frequency resistances keep almost stable with activation energy of 0.65 eV. These results suggest that the high frequency resistances are mainly dominated by the conductivity of electrolyte, while the low frequency resistances are more apt to the electrode activity. With Ba 0.98Ce 0.8Sm 0.2O 3-δ substituting for BaCe 0.8Sm 0.2O 3-δ in both anode and cathode, the polarization resistance is 0.339 Ωcm 2 at 650 °C, only 42.1% of that with BaCe 0.8Sm 0.2O 3-δ based electrodes. Meanwhile, maximum power density about 271.0 mWcm − 2 at 650 °C is achieved with the modified electrode compositions.

The effect of A-site deficiency on the performance of La 1− sFe 0.4Ni 0.6O 3− δ cathodes

The effect of lowering the A-site stoichiometry of La–Fe–Ni based perovskite solid oxide fuel cell cathodes was investigated with electrochemical impedance spectroscopy on cone-shaped electrodes using a Ce 0.9Gd 0.1O 1.95 electrolyte. It was shown that a lowering of the A-site stoichiometry lowers the amount of Ni in the perovskite phase, as powder XRD revealed that NiO was expelled from the perovskite lattice when the A-site stoichiometry was decreased. NiO inhibit the reduction of oxygen as the activity of a nominally A-site deficient La 1− s Fe 0.4Ni 0.6O 3− δ perovskite was worse than the activity of the corresponding LaFe 0.4+ s Ni 0.6− s O 3− δ perovskite without NiO. NiO is therefore poison for the reduction of oxygen at the cathode in a solid oxide fuel cell.

Effect of A-site Deficiency on Mixed Conducting Properties of (Ba,Sr)(Co,Fe)O3-δ Electrodes for Solid Oxide Fuel Cell

The effect of A-site deficiency on mixed conducting properties was investigated in (Ba,Sr)(Co,Fe)O3-d (BSCF) perovskite structure cathode material for solid oxide fuel cells (SOFC). For this purpose, BSCF powders with various Sr deficiencies were synthesized via a glycine nitrate process (GNP), followed by calcinations at 1273 K for 10 h. From the structural analyses, the lattice parameter increased with Sr deficiency increased, and the electrode had better sinterability with respect to Sr deficiency. Moreover, from the electrochemical analyses, the electrical conductivity decreased and area specific resistance (ASR) value increased as Sr deficiency increased.

Effect of A-site Deficiency on Mixed Conducting Properties of (Ba,Sr)(Co,Fe)O3-δ Electrodes for Solid Oxide Fuel Cell

not Available.

Effect of A-site deficiency on electrical transport properties of YSZ doped manganites

The electrical transport properties of the composite samples: A-site stoichiometry (1− x)La 2/3Ca 1/3MnO 3+ xYSZ and A-site deficiency (1− x)(La 2/3Ca 1/3) 0.95MnO 3+ xYSZ with different YSZ percentage x were investigated, respectively. The similar metal–insulator transition at different temperature T P was observed in the two types of composite samples: With increasing of the YSZ percentage, the zero-field resistivity of the composite samples increases and T P shifts to the low temperature for the range of x<2%, but zero-field resistivity decreases and T P increases for the range of x>2%. For the same YSZ percentage x, T P of (1− x)La 2/3Ca 1/3MnO 3+ xYSZ is lower than that of (1− x)(La 2/3Ca 1/3) 0.95MnO 3+ xYSZ. The different effects between the two type composites were also observed in the nonlinear current–voltage ( I– V) behaviors. The results suggest that A-site deficiency and YSZ dopant can be used to adjust purposely the metal–insulator transition temperature and resistivity of composites.