Wet Air Atmosphere Research Articles

Catalytic Decomposition of n-C7 Asphaltenes Using Tungsten Oxides–Functionalized SiO2 Nanoparticles in Steam/Air Atmospheres

A wide range of technologies are being developed to increase oil recovery, reserves, and perform in situ upgrading of heavy crude oils. In this study, supported tungsten oxide nanoparticles were synthesized, characterized, and evaluated for adsorption and catalytic performance during wet in situ combustion (6% of steam in the air, in volumetric fraction) of n-C7 asphaltenes. Silica nanoparticles of 30 nm in diameter were synthesized using a sol–gel methodology and functionalized with tungsten oxides, using three different concentrations and calcination temperatures: 1%, 3%, 5% (mass fraction), and 350 °C, 450 °C, and 650 °C, respectively. Equilibrium batch adsorption experiments were carried out at 25 ℃ with model solutions of n-C7 asphaltenes diluted in toluene at concentrations from 100 mg·L−1 to 2000 mg·L−1, and catalytic wet in situ combustion of adsorbed heavy fractions was carried out by thermogravimetric analysis coupled to FT-IR. The results showed improvements of asphaltenes decomposition by the action of the tungsten oxide nanoparticles due to the reduction in the decomposition temperature of the asphaltenes up to 120 °C in comparison with the system in the absence of WOX nanoparticles. Those synthesis parameters, such as temperature and impregnation dosage, play an important role in the adsorptive and catalytic activity of the materials, due to the different WOX–support interactions as were found through XPS. The mixture released during the catalyzed asphaltene decomposition in the wet air atmosphere reveals an increase in light hydrocarbons, methane, and hydrogen content. Hydrogen production was prioritized between 300 and 400 °C where, similarly, the reduction of CO, CH4, and the increase in CO2 content, associated with water–gas shift, and methane reforming reactions occur, respectively. The results show that these catalysts can be used either for in situ upgrading of crude oil, or any application where heavy fractions must be transformed.

Effects of Ambience on Thermal-Diffusion Type Ga-doping Process for ZnO Nanoparticles

Various annealing atmospheres were employed during our unique thermal-diffusion type Ga-doping process to investigate the surface, structural, optical, and electrical properties of Ga-doped zinc oxide (ZnO) nanoparticle (NP) layers. ZnO NPs were synthesized using an arc-discharge-mediated gas evaporation method, followed by Ga-doping under open-air, N2, O2, wet, and dry air atmospheric conditions at 800 °C to obtain the low resistive spray-coated NP layers. The I–V results revealed that the Ga-doped ZnO NP layer successfully reduced the sheet resistance in the open air (8.0 × 102 Ω/sq) and wet air atmosphere (8.8 × 102 Ω/sq) compared with un-doped ZnO (4.6 × 106 Ω/sq). Humidity plays a key role in the successful improvement of sheet resistance during Ga-doping. X-ray diffraction patterns demonstrated hexagonal wurtzite structures with increased crystallite sizes of 103 nm and 88 nm after doping in open air and wet air atmospheres, respectively. The red-shift of UV intensity indicates successful Ga-doping, and the atmospheric effects were confirmed through the analysis of the defect spectrum. Improved electrical conductivity was also confirmed using the thin-film-transistor-based structure. The current controllability by applying the gate electric-field was also confirmed, indicating the possibility of transistor channel application using the obtained ZnO NP layers.

Hole transport free flexible perovskite solar cells with cost-effective carbon electrodes

Low temperature derived carbon electrodes are employed to fabricate low cost hole transport layer free perovskite solar cells, in which perovskite films annealed in glovebox and ambient air are used as the absorbers, respectively. Results suggest that the air annealed sample has bigger crystal grains and higher crystallinity, and the existence of a small amount of lead iodide which passivates grain boundaries contributes to a lower trap density. As a result, a maximum power conversion efficiency (PCE) of 13.07% was obtained on the air annealed device, which is higher than those of devices annealed in glovebox (11.25%). Furthermore, the stability of unencapsulated devices stored in wet (with humidity around 90% ± 5%) air atmosphere are investigated and the results prove that our devices exhibit good stability. In addition to rigid devices, flexible perovskite solar cells are also fabricated using the same procedure. The highest PCE of 11.53% is demonstrated on the champion flexible device, and 69% of its initial PCE can be maintained even after 2000 bending cycles with a bending radius of 2 mm. Our work provides a promising and simple rout for low-cost, air-stable, high-efficiency carbon perovskite solar cells for both large area production and flexible electronic devices industry.

Exploring MnCr2O4–Gd0.1Ce0.9O2-δ as a composite electrode material for solid oxide fuel cell

Symmetrical solid oxide fuel cell (SOFC) adopting the same material at both electrodes is potentially capable of promoting thermomechanical compatibility between near components and lowering stack costs. In this paper, MnCr2O4–Gd0.1Ce0.9O2-δ (MCO-GDC) composite electrodes prepared by co-infiltration method for symmetrical electrolyte supported and anode supported solid oxide fuel cells are evaluated at a temperature range of 650–800 °C in wet (3% H2O) hydrogen and air atmospheres. Without any alkaline earth elements and cobalt, the co-infiltrated MCO-GDC composite electrode shows excellent activity for oxygen reduction reaction but mediocre activity for hydrogen oxidation reaction. With MCO-GDC as the cathode, the Ni-YSZ (Y2O3 stabilized ZrO2) anode supported asymmetrical cell demonstrates a peak power density of 665 mW cm−2 at 800 °C. The above results suggest MCO-GDC is a promising candidate cathode material for solid oxide fuel cells.

Aluminum dual doping and oxygen transport pathway in novel Sr11Mo4−xAlxO23 oxide-ion solid electrolytes

Three new electrolytes of composition Sr11Mo4-xAlxO23-δ (x = 0.5, 1.0 and 1.5) were synthesized by wet-chemistry procedures (citrate method) as polycrystalline samples. They were crystallographically studied from synchrotron and neutron diffraction techniques. They derive from the Sr11Mo4O23 complex perovskite, which can be rewritten as Sr1.75□0.25SrMoO5.75, highlighting the relationship with double perovskites A2B′B″O6. From these analyses via Rietveld refinement, a dual doping was found from synchrotron data, where the aluminum is equally allocated at both Sr (B′) and Mo (B″) sites. A detailed analysis of the neutron data from Difference Fourier Maps (DFM) unveiled the oxygen delocalization around the Mo site. From the refined crystal structures at room and high temperatures, a Bond Valence Sum Map (BVSM) analysis was useful to find the oxygen pathway in the crystal structure, and the minimum density to allow connections among oxygen atoms. The structural characterization was complemented with thermogravimetric and thermodilatometric analysis. The ionic conductivity was measured from electrochemical impedance spectroscopy (EIS) in wet and dry air and nitrogen atmospheres.

Fabrication of integrated BZY electrolyte matrices for protonic ceramic membrane fuel cells by tape-casting and solid-state reactive sintering

Integrated porous/dense/porous tri-layer BaZr0.8Y0.2O3-δ (BZY) electrolyte asymmetrical matrices were designed for protonic ceramic membrane fuel cells (PCMFCs) and fabricated by multilayer tape-casting and solid-state reactive sintering. The effects of pore-former, sintering aid and sintering program on the microstructure of integrated electrolyte matrices (IEMs) were studied. Graphite and NiO were appropriate pore-former and sintering aid, respectively, and an accelerated heating program was more desirable. The conductivities of the IEM with designed microstructure in different atmospheres were measured by AC impedance spectroscopy at 400–600 °C. The highest conductivity of 6.9 × 10−3 S cm−1 at 600 °C was obtained in wet air atmosphere, and the corresponding activation energy was 0.602 eV. Gas-tightness of the IEM was confirmed by a stable open circuit voltage (OCV) of 0.97 V at 600 °C from a button fuel cell with impregnated NiO anode and BaCo0.4Fe0.4Zr0.1Y0.1O3-δ (BCFZY) cathode. These indicate that the fabricated BZY-based IEM has great potential for PCMFC application.

Preparation and properties of plasma sprayed NiAl10 and NiAl40 coatings on AZ91 substrate

Magnesium alloys are, due to high specific strength and stiffness, materials suitable for lightweight applications in automotive and aeronautical industries. Very poor corrosion resistance of magnesium and magnesium alloys significantly limits their wide utilization. Magnesium alloys are very susceptible to galvanic corrosion that can result in serious pitting corrosion, particularly in wet and salty environment. Magnesium and its alloys can be protected by formation of protective surface layers which can be achieved by plasma spraying capable of preparing metal and/or ceramic coatings. In this work, plasma coatings of NiAl10 and NiAl40 on AZ91 magnesium alloy substrate were prepared by the hybrid plasma spraying system WSP®-H 500. Present results show a significant effect of the preheat temperature of the AZ91 substrate during plasma spraying on development of a diffusion bonding due to the formation of sub-layer composed of Mg3AlNi2, Al12Mg17 phases and of Mg and Al solid solutions. The plasma sprayed coatings were observed by scanning electron microscope with elements point analysis and by X-ray phase analysis. The mechanical properties of prepared coatings were evaluated by adhesion tests. The corrosion resistance of prepared coatings was evaluated using the method of potentiodynamic measurements performed in the 0.5mol·l−1 NaCl solution while the long-term corrosion resistance was assessed in condensation chamber in wet air atmosphere at the temperature of 35°C. Both the tests showed significant effect of present sub-layers on resulting corrosion resistance.

Improved ceramic and electrical properties of CaZrO3-based proton-conducting materials prepared by a new convenient combustion synthesis method

The present work emphasizes the features of a new combustion synthesis method suitable for easy synthesis and sintering of CaZrO3-based materials as promising proton-conducting electrolytes for electrochemical applications in solid oxide electrochemical devices. Sc- and In-doped CaZrO3 compounds are selected to be the objects of investigation and their crystal structure properties as well as microstructural, thermal and electrical characteristics are studied by the means of X-ray diffraction analysis, high-temperature dilatometry, scanning electron spectroscopy, impedance and 4-probe DC conductivity techniques. The established properties are critically compared with previously obtained data to confirm the prospects of the proposed method synthesis for the preparation of Zr-based proton-conducting ceramic materials. It is found that CaZr0.95Sc0.05O3–δ exhibits predominantly protonic conductivity under wet air atmospheres below 700°C; while, CaZr0.9In0.1O3–δ demonstrates a certain value of electronic conductivity along with ionic one.

Characterization of Proton-Conducting Y(CrO4)1-X (PO4) x As a Cathode Material of Proton-Conducting Ceramic Fuel Cells

It has been reported that proton conducting oxide such as BaCeO3 and BaZrO3 have high proton conductivity at intermediate temperatures, IT, around 400-600°C. Therefore, proton-conducting ceramic fuel cells (PCFC) attract much attention as IT-operating fuel cell system (IT-FC). Nonetheless, the current PCFC performance lags far behind the SOFC performance even at the ITrange of 400-600°C. One of the reasons for the deteriorated performance of PCFC is the lack of suitable cathode materials. Generally, oxide ion-electron mixed conductors such as La0.6Sr0.4Co0.8Fe0.2O3- δ(LSCF) are used for the PCFC cathode, but these reveal large overpotential since forming the limited reaction zone due to the mismatch of ionic carriers with electrolyte. Accordingly, there is motivation to develop the proton-electron mixed conductors which can be used in cathode conditions of fuel cells. Previously, we found that Y(CrO4)1-x (PO4) x solid solution (YCP) have proton-electron mixed conductivity in wet air atmosphere. Hence, it is motivated to use YCP as additives of cathode materials of PCFC in order to extend the reaction zone. In this work, we examined the fuel cells using composite cathode of YCP and LSCF. BaCe0.7Zr0.1Y0.2O3- δ(BZCY) was used as proton conducting electrolyte. Bulk electrolyte cell were constructed with a BZCY disc which were prepared by solid state reactive sintering (SSRS) method. The electrolyte precursor powder was prepared by mixing proper amount of BaCO3, CeO2, ZrO2, and Y2O3 according to the desired stoichiometry with the addition of 2.0wt.% NiO as a sintering aid. This mixture was ball-milled for 48 h and uniaxially pressed under 20 MPa for 1 min and then cold-isostatic-pressed under 100 MPa for 1 min. Finally, the green pellets were calcined at 1400°C for 18 h so as to obtain bulk electrolyte disc (2 mmd, 9 mmf). YCP powders were synthesized by pyrolysis of the mixed Y-Cr-P hydroxide precursor at 700°C for 3h in O2. The hydroxide precursors were prepared by coprecipitation method with (NH3)H2PO4, Cr(NO3)3 and Y(NO3)3. YCP powders dispersed in a-Terpineol were mixed with LSCF paste (NexTek) in the volume ratio of YCP:LSCF = 1:1. YCP-LSCF mixed pastes were screen printed on the side of BZCY electrolyte as a cathode and Pt paste as anode was applied to the opposite faces so as to form Pt|BZCY|YCP5/LSCF cell. Au wire was attached along the side of BZCY disc as a reference electrode by using Au paste. To investigate cathode polarization characteristics, the complex impedance measurements were carried out with the three-electrode cell. The XRD pattern indicated that a single orthorhombic perovskite phase of BZCY was prepared by the SSRS method. The density of the sintered pellets was about 90%. The bulk electrolyte cell with the YCP5/LSCF cathode gives OCV over 1.0 V and maximum power density about 40 mW cm-2 at 600°C. The complex impedance measurements indicate that the cells reveal two impedance arcs according to cathodic polarization in Nyquist plots. The semicircle appearing in high frequency region (104-102 Hz), SH, can be assigned to the charge transfer reaction between the electrolyte and the cathode and one in low frequency region (102-10-1 Hz), SL, can be attributed to the dissociative oxygen adsorption reaction. SH of the cell with YCP-LSCF composite cathode was smaller than that of the cell with LSCF cathode. On the other hand, the SL of the composite cathode cells was larger than that of the LSCF cathode cells. These results indicate that the interfacial charge transfer reaction is promoted by adding proton-conducting YCP because of the extension of the electrode-electrolyte-air three phase boundary.

Hodrogen Oxidation Reaction Mechanisms in Mixed Ionic and Electronic Conducting Oxide Anode for Solid Oxide Fuel Cells

Ceramics anode offers certain advantages in terms of impurity tolerance and other properties, as compared to conventional Ni/YSZ anode for solid oxide fuel cells (SOFC). However, ceramic anodes typically have much lower electrochemical performance, and there is very few studies on the hydrogen oxidation reaction (HOR) mechanisms and kinetics in ceramic anodes. In this research, using Doped YCrO3 as baseline material, we systematically investigated the HOR mechanisms in mixed ionic and electronic conducting (MIEC) ceramic anodes, with the focus on the effect of electronic conductivity, electro-catalytic activity, triple-phase-boundary (3PB), and electrolyte, on the HOR kinetics. It is found that both electrical conductivity and electrode performance of yttrium chromites have been enhanced after Co and Ni doping. Electrochemical impedance spectroscopy (EIS) results indicate that charge transfer process at high frequency and surface adsorption/diffusion processes at low frequency domain can be the dominant anode reaction steps. Ni doping accelerates the surface processes by reducing the related activation energy from 1.2 to 0.5 eV. It also substantially improves the charge transfer process probably by increasing the amount of adsorbed H on electrode surface. The resistance of high frequency is found to be dependent on H2 content. The observed reaction order is 1/4 for Co doped and 1/3 ~ 1/2 for Ni doped yttrium chromites. A model of H2oxidation reaction is proposed, revealing this dependence stems from the reaction between adsorbed H and the lattice oxygen. The influence of electrolyte to electrode performance was investigated by replacing YSZ electrolyte with scandium stabilized zirconium (SSZ). Smaller polarization resistances are observed on each electrode in both wet H2 and air atmospheres. Replacement of electrolyte can alter not only the rate of charge transfer process but also in some cases other surface processes not related to the electrolyte directly. It is proposed that the impact of the electrolyte on each electrode process is passed down as in a chain and the charge transfer step functions as the first ring in the chain.

Y and In-doped BaCeO3-BaZrO3 solid solutions: Chemically stable and easily sinterable proton conducting oxides

BaCeO3 and BaZrO3 based perovskites display good protonic conductivity. However, the former suffers from low chemical stability while the latter exhibits good stability but lower conductivity and sinterability. Hence, a combination or solid solution of these two systems can be a good approach to maintain both conductivity and chemical stability. In this study, Ba(Ce, Zr)O3 solid solution was doped with yttrium and indium and the effect of various levels of In-doping, BaCe0.4Zr0.3In0.3−xYxO3−δ (x = 0, 0.1, 0.2), on the sinterability, chemical stability and conductivity was studied. The pellets of In-containing samples could be sintered easily at a much lower temperature (1450 °C) yielding sintered density ≥94% of the theoretical density. The density was found to increase with increasing In content and a relative sintered density as high as 99% was achieved in the BaCe0.4Zr0.3In0.3O3−δ composition. The chemical stability against CO2 and water atmospheres also improved with In addition. The perovskite phase in the composition without In (BaCe0.5Zr0.3Y0.2O3−δ) was stable till 500 °C in CO2 but reacted beyond that (>500 °C) forming the undesirable BaCO3 phase. The In-doped compositions, especially x = 0 and 0.1(In = 0.3 and 0.2), were fully stable even after a long term exposure of 12 h at 700 °C in CO2. A similar trend was observed in H2O atmosphere as well i.e. In-containing compositions showing fully stable behavior. The In-doped compositions showed lower conductivity compared to the In-free composition due to higher defect association in dry air and lower mobility of the protonic carrier in wet air atmosphere. However, the conductivity was still higher than many reported values for similar materials.

Effects of Pt-Based Electrode Compositions on CO Sensing Properties of NASICON-Based Solid Electrolyte Gas Sensors

We have reported recently the potential of planar-type NASICON-based solid electrolyte gas sensors equipped with Pt mixed with Bi2O3as a sensing electrode and pristine Pt as a reference electrode [1]. This type of sensors could be operated at room temperature with sufficiently high CO response and selectivity. The present study was directed to investigating the effects of the addition of various kinds of metal oxides to both the Pt sensing and reference electrodes on the CO sensing properties. Pt paste (Tanaka Corp., TR-7907) mixed with an appropriate amount (n wt%) of a metal oxide (MO), which is denoted as Pt(nMO), and just Pt paste or another kind of Pt(nM’O) were applied on the same surface of the NASICON disc as a sensing and a counter electrode, respectively, and then were fired at 700ºC for 30 min in air. The sensor thus fabricated was denoted as Pt(nMO)/Pt or Pt(nMO)/Pt(nM’O). The metal oxides tested were Bi2O3, La2O3, In2O3, V2O5, WO3 and CeO2. The magnitude of gas response was defined as the difference in EMF (ΔEMF) measured between in a sample gas and in base air. CO response properties of the sensors equipped with the pristine Pt reference electrode were found to depend on the kind of metal oxides added to the Pt sensing electrode. CO response with a EMF change to a positive direction was observed with a Pt(15Bi2O3)/Pt sensor, whereas a Pt(15CeO2)/Pt sensor showed a EMF change to a negative direction, as shown in Fig. 1. The operating temperature dependence of the CO response of sensors was also affected by the kind of the metal oxides added (see Fig. 2). By referring such CO response properties of these Pt(15MO)/Pt sensors, a Pt(15Bi2O3)/Pt(15CeO2) sensor was fabricated and then its CO response properties were further investigated in detail. The CO sensing performance of the Pt(15Bi2O3)/Pt(15CeO2) sensor in both dry and wet air atmosphere, including interferences from 300 ppm CO2, CH4, C3H6 and H2, will be reported in the presentation. Reference [1] H. Takeda, T. Ueda, T. Hyodo, Y. Shimizu, of the 10th Asian Conference on Chemical Sensors, Chiang Mai, Thailand, Nov. 11-14, p. 110 (2013). Figure 1

Ionic conduction of Ti0.95Mg0.05P2O7 at intermediate temperatures

In this study, intermediate temperature ionic conducting Ti0.95Mg0.05P2O7 sample was prepared by solid state reaction. The variation of conductivities as a function of atmosphere, temperatures (100–300°C) and the pO2 pressures were studied. The highest conductivities of Ti0.95Mg0.05P2O7 are observed in dry air atmosphere to be 1.4×10−2Scm−1 at 225°C and in wet air atmosphere (pH2O=3.2×103Pa) to be 2.0×10−2Scm−1 at 200°C, respectively. The logσ–log(pO2) plot result indicates that Ti0.95Mg0.05P2O7 is almost a pure ionic conductor under high oxygen partial pressure and a mixed conductor of ion and electron under low oxygen partial pressure. The result of water vapor concentration cells indicate that the sample has a few existence of oxide ionic conduction under wet H2 atmosphere and mainly protonic conduction under wet O2 atmosphere.

Sulfur and carbon tolerance of BaCeO3–BaZrO3 proton-conducting materials

In the present work, BaCe0.8−xZrxY0.2O3−δ-based ceramic samples (BCZYx) are prepared and their chemical stability in corrosive atmospheres containing high concentrations of H2O, CO2 and H2S is investigated. Based on both the fresh (not exposed) and the treated (exposed to corrosive atmospheres) samples, the estimation of the tolerance degree is obtained by determining the: i) phase structures, ii) unit cell parameters, iii) surface microstructures, and iv) electrical conductivities. Fresh ceramics is found to be single-phased in the whole range of x. It is also found that all the treated materials exhibit good chemical stability in the water vapor atmosphere, whereas the samples with 0 ≤ x ≤ 0.2 and 0 ≤ x ≤ 0.3 are not single-phased in pure CO2 and 10% H2S/Ar, respectively. The analysis of crystal structure and transport characteristics of the treated BCZY0.3 samples is shown a weak deviation of unit cell parameters and no degradation in electrical conductivity. For fresh BCZY0.3 the transport nature in various atmospheres is evaluated. At 600 °C the BCZY0.3 exhibits conductivity of 2.7, 4.0, 1.7 and 3.7 mS cm−1 in air, wet air, hydrogen and wet hydrogen atmospheres, respectively. Based on the obtained results, BCZY0.3 can be considered as a perspective proton-conducting material having reasonable transport and tolerance properties.

Electrical conduction of CeP2O7 and Ce0.95Yb0.05P2O7 at intermediate temperatures

Abstract Intermediate temperature proton conducting Ce0.95Yb0.05P2O7 and CeP2O7 samples are prepared and the conduction behaviors are investigated from 100 to 300 °C. The variation of conductivity with the pH2O or time is also studied. The highest conductivity of Ce0.95Yb0.05P2O7 is observed in dry air atmosphere at 300 °C to be 9.6 × 10− 5 S·cm− 1 and in wet air atmosphere (pH2O = 3.2 × 103 Pa) at 150 °C to be 3.3 × 10− 3 S·cm− 1. The log σ ~ log (pH2O) plot result shows that the conductivities increase linearly with increasing pH2O and reach 3.4 × 10− 3 S·cm− 1 with pH2O = 1.2 × 104 Pa in air at 100 °C.

Electrical properties of an intermediate temperature ionic conductor, Ti0.95Al0.05P2O7

In this study, intermediate temperature ionic conducting Ti0.95Al0.05P2O7 sample was prepared by a solid state reaction. The variation of conductivity as a function of atmosphere, temperature (100–300°C) and the pO2 pressure were studied. The highest conductivities of Ti0.95Al0.05P2O7 sample are observed in dry air atmosphere to be 1.2×10−3Scm−1 at 175°C and in wet air atmosphere (pH2O=3.2×103Pa) to be 4.7×10−3Scm−1 at 150°C, respectively. The log σ~log (pO2) plot result indicates that Ti0.95Al0.05P2O7 is almost a pure ionic conductor under oxidizing conditions and a mixed conductor of ion and electron under reducing conditions.

Studies on Ionic Conduction in Ce0.95Eu0.05P2O7at Intermediate Temperatures

In this study, an intermediate temperature ionic conductor, <TEX>$Ce_{0.95}Eu_{0.05}P_2O_7$</TEX>, was prepared by solid state reaction. The variation of conductivities with the pressure <TEX>$pH_2O$</TEX> or time were studied. The highest conductivity of <TEX>$Ce_{0.95}Eu_{0.05}P_2O_7$</TEX> sample was observed in dry air atmosphere at <TEX>$300^{\circ}C$</TEX> to be <TEX>$1.1{\times}10^{-4}S{\cdot}cm^{-1}$</TEX> and in wet air atmosphere (<TEX>$pH_2O=7.4{\times}10^3Pa$</TEX>) at <TEX>$100^{\circ}C$</TEX> to be <TEX>$1.4{\times}10^{-3}S{\cdot}cm^{-1}$</TEX>, respectively. The log <TEX>${\sigma}$</TEX> ~ log (<TEX>$pO_2$</TEX>) plot result indicated that <TEX>$Ce_{0.95}Eu_{0.05}P_2O_7$</TEX> was almost a pure ionic conductor under high oxygen partial pressure and a mixed conductor of ion and electron under low oxygen partial pressure.

Synthesis, phase stability and conduction behavior of rare earth and transition elements doped barium cerates

BaCeO3 exhibits high protonic conductivity, however, it suffers from low chemical stability. In this study, BaCeO3 was doped with erbia (BCE) and BCE was co-doped with ytterbia (Yb-BCE) and scandia (Sc-BCE) with a view to improve the chemical stability. The undoped sample (BaCeO3) disintegrated into BaCO3 and CeO2 on exposure to CO2 while doped (BCE) and co-doped compositions (Yb-BCE and Sc-BCE) remained almost unaffected indicating effectiveness of the dopant Er3+ and the co-dopants (Yb3+, Sc3+) in improving the chemical stability. The Sc-BCE composition showed better stability. Exposure to water atmosphere led to formation of Ba(OH)2 in BCE and Yb-BCE samples while the Sc-BCE sample exhibited much better stability against water vapor as well. A modified solution combustion synthesis was found to be better for phase formation by calcinations at comparatively lower temperatures. The conduction mode was found to be ionic in dry air and mixed protonic–ionic in wet air atmosphere. In wet Argon–Hydrogen mix (AHM), the conduction mode was primarily protonic. The co-doped compositions, Yb-BCE and Sc-BCE showed higher conductivity compared to BCE and Yb-BCE exhibited the best conductivity in wet AHM.

Studies on ionic conductivity of dense 6 mol% Sc3+-doped SnP2O7–SnO2 composite ceramic at intermediate temperatures

A dense 6mol% Sc3+-doped SnP2O7–SnO2 composite ceramic was prepared by low-temperature sintering (at 600°C). The XRD result confirmed that an SnP2O7 phase grows on the internal surface of the SnO2 substrate. The SEM result showed that the composite ceramic was sufficiently dense. The highest conductivities were observed to be 2.9×10−2Scm−1 in wet air atmosphere and 5.0×10−2Scm−1 in wet H2 atmosphere at 325°C. The lgσ–lg(pO2) plot result indicated that the composite ceramic was almost a pure ionic conductor under high oxygen partial pressure and the protonic conduction became dominant under low oxygen partial pressure.

Characterization of Doped Yttrium Chromites as Electrodes for Solid Oxide Fuel Cell by Impedance Method

Redox-stable ceramic electrodes, Co and Ni doped yttrium chromites, for solid oxide fuel cell (SOFC) are characterized by electrochemical impedance spectroscopy (EIS) in various PO2 and PH2 atmosphere. The polarization resistances for Y0.8Ca0.2Cr0.8Co0.2O3-δ (YCCC) and Y0.8Ca0.2Cr0.9Ni0.1O3-δ (YCCN) on yttrium stabilized zirconia (YSZ) electrolyte are 0.96 and 8.4 Ωcm2 in wet H2, 1.2 and 36.7 Ωcm2 in air at 850°C, respectively. For the anode application, the rate-limiting steps (RDS) are identified as charge transfer and surface diffusion for both YCCC and YCCN. The primary active zone in YCCN is three-phase boundary (3PB) but extends to a small portion of the electrode bulk in the YCCC anode. For the cathode application, O2 dissociative adsorption or diffusion is one of the RDS for both electrodes, and the active zone is limited to the 3PB area. The influence of electrolyte to electrode performance is investigated by replacing YSZ electrolyte with scandium stabilized zirconium (SSZ). Smaller polarization resistances are observed on each electrode in both wet H2 and air atmospheres. Replacement of electrolyte can alter not only the rate of charge transfer process but also in some cases other surface processes not related to the electrolyte directly. It is proposed that the impact of the electrolyte on each electrode process is passed down as in a chain and the charge transfer step functions as the first ring in the chain. The best performance is obtained with the YCCC/SSZ combination, 0.49 and 1 Ωcm2 in wet H2 and air at 850°C, respectively, making YCCC a promising electrode.