CuO-modified LaNi0.4Al0.6O3−δ with improvement performance in MSR at low temperature

The novel CuO/LaNi_0.4Al_0.6O_3−δ catalyst was synthesized by the impregnation method and characterized by X-ray diffraction (XRD), TEM, BET, and X-ray photoelectron spectroscopy (XPS) techniques. The effects of CuO loading amount on the microstructure and the hydrogen production performance from methanol steam reforming (MSR) were investigated. Results demonstrate that the sample with 15 wt% CuO loading has the best hydrogen production performance. Furthermore, compared with the unloaded LaNi_0.4Al_0.6O_3−δ perovskite catalysts, the methanol conversion of 15 wt% CuO/LaNi_0.4Al_0.6O_3−δ was improved, and the catalytic temperature of MSR was reduced. LaNi_0.4Al_0.6O_3−δ as support will form a strong interaction with Cu particles exposed on or around its surface and improve the catalytic performance. The XPS results show that the structure of LaNi_0.4Al_0.6O_3−δ perovskite oxide is not destroyed after reduction treatment, whereas CuO is reduced to elemental Cu, which is consistent with the XRD results. The reduced catalyst has a porous structure, which helps to increase the contact area between the reaction medium and the active components. This improves the efficiency of the reaction. In addition, the optimal catalytic temperature, water–methanol ratio, and liquid hourly space velocity were determined to be 350°C, 2.5:1, and 15 h⁻¹, respectively. Therefore, the CuO/LaNi_0.4Al_0.6O_3−δ developed in this study is a promising catalyst for MSR applications.     

Enhancing the sinterability and electrical properties of BaZr0.1Ce0.7Y0.2O3-δ proton-conducting ceramic electrolyte

A novel strategy was proposed to enhance the sinterability and electrical properties of BaZr_0.1Ce_0.7Y_0.2O_3-δ (BZCY) proton-conducting electrolyte by adding 10 wt.% La_0.9Sr_0.1Ga_0.8Mg_0.2O_3-δ (LSGM) to form a 90 wt.% BZCY–10 wt.% LSGM (BL91) composite electrolyte. XRD patterns showed that no reaction occurred between the BZCY and LSGM electrolytes after sintering at 1400°C, 1450°C, 1500°C, and 1550°C for 10 h. The BL91 composite electrolyte exhibited higher relative densities and Vickers hardness and excellent electrical properties compared with those of the BZCY electrolyte. A combined approach of equivalent circuit model and distribution of relaxation time analysis was used to distinguish the bulk and grain-boundary contributions to the total conductivity and electrode processes. The introduction of 10 wt.% LSGM serves as a grain-boundary pinning phase, which can reduce the mobility of grain boundaries, thereby increasing sintered density and enhancing conductivity in BL91. A solid oxide fuel cell with proton-conducting BL91 and BZCY membranes was tested, in which the former displayed higher power outputs than the latter. Ohmic and interfacial polarization resistances decreased by approximately 20%, thereby revealing the remarkable electrical properties of the BL91 electrolyte. Results demonstrated that BL91 composite is a development prospect proton-conducting electrolyte.     

Application of the cold sintering process to the electrolyte material BaCe0.8Zr0.1Y0.1O3-δ

This paper describes and discusses the application of the original sintering process named cold sintering to the electrolyte material BaCe_0.8Zr_0.1Y_0.1O_3-δ to enhance its densification at a temperature below that needed in a conventional sintering. This new technique enables the acceleration of the densification resulting in a more compacted microstructure with an unexpected high relative density of 83 % at only 180 °C. A subsequent annealing at 1200 °C further enhances the densification which reaches 94 %. The electrochemical performance of CSP sintered ceramics was investigated and optimized by varying different process parameters. The comparison with the conventional sintered material reveals an increase of the total conductivity by mostly increasing the grain boundary one. This result emphasizes the benefits of CSP to not only reduce the sintering temperature but also to enhance the electrochemical properties.     

Enhanced chemical stability and electrochemical performance of BaCe0.8Y0.1Ni0.04Sm0.06O3-δ perovskite electrolytes as proton conductors

Although doped BaCeO₃ electrolytes are proton conductors that undergo the fast conduction processes of inter-mediate temperature solid oxide fuel cells (IT-SOFCs), their wide application is impeded by their poor chemical stability under water vapour or CO₂ conditions. In this work, we selected the metallic cations with suitable electronegativity to improve the perovskite crystal structures of BaCeO₃ to enhance the chemical stability and electrochemical performance. We utilized Ni and Sm cations to improve the chemical stability of BaCeO₃ electrolytes in water vapour and CO₂ via a novel synthesis method, and the results revealed that the BaCe_0.8Y_0.1Ni_0.04Sm_0.06O_3-δ electrolyte, -with high electrochemical performance and chemical stability-, is a promising electrolyte material for conduction in IT-SOFCs. The optimum result offers new insights into synthesizing the membrane of IT-SOFCs for their application.     

Flexural strength and flaw distributions of SrFe0.2Co0.4Mo0.4O3−δ ceramic-supports for SOFCs at operating conditions

Solid-oxide fuel cells (SOFCs) have the potential to increase electricity generation efficiency, but traditional SOFCs supported by nickel cermets suffer from reliability challenges due to weaker mechanical strength caused by cracking after redox cycling. To solve this problem, a new ceramic anode material, SrFe_0.2Co_0.4Mo_0.4O_3−δ (SFCM) combined with Ce_0.9Gd_0.1O₂ (GDC), was evaluated for conductivity and mechanical strength at SOFC operating conditions and after redox cycling. Fracture toughness of SFCM was determined to be (0.124 ± 0.023) MPa√m at room temperature in air, increasing to (0.286 ± 0.038) MPa√m at 600°C. A mixture of SFCM:GDC showed fracture toughness between the two materials, following SFCM's trend with temperature. The SFCM-GDC anode supported half-cell strength increases by 31% from room temperature to 600°C as intrinsic stresses remaining from sintering are relaxed and thermal expansion pushes existing cracks closed. Exposure to reducing gasses decreases strength by 29% compared to ambient, due to oxygen vacancy formation and microstructural flaw changes. It is found that SFCM-GDC based cells tolerate cycling well because of phase stability but weaken from 34.3 to 22.4 MPa due to uniform growth of critical microstructural flaws.     

Chemical stability and electrical properties of Nb doped BaCe0.9Y0.1O3−δ as a high temperature proton conducting electrolyte for IT-SOFC

BaCe_0.9?xNb_xY_0.1O_3?δ (where x=0, 0.01, 0.03 and 0.05) powders were synthesized by solid-state reaction to investigate the influence of Nb concentration on chemical stability and electrical properties of the sintered samples. The dense electrolyte pellets were formed from the powders after being uniaxially pressed and sintered at 1550 °C. The electrical conductivities determined by impedance measurements in temperature range of 550–750 °C in different atmospheres (dry argon and wet hydrogen) showed a decreasing trend with an increase of Nb content. For all samples higher conductivities were observed in the wet hydrogen than in dry argon atmosphere. The chemical stability was enhanced with increasing of Nb concentration. It was found that BaCe_0.87Nb_0.03Y_0.1O_3?δ is the optimal composition that satisfies the opposite demands for electrical conductivity and chemical stability, reaching 0.8×10^?2 S cm^?1 in wet hydrogen at 650 °C compared to 1.01×10^?2 S cm^?1 for undoped electrolyte.     

A comparative investigation on protonic ceramic fuel cell electrolytes BaZr0.8Y0.2O3-δ and BaZr0.1Ce0.7Y0.2O3-δ with NiO as sintering aid

Solid oxide fuel cells based on proton-conducting ceramic electrolytes, i.e., protonic ceramic fuel cells (PCFCs), are promising in operating at intermediate to low temperature. BaZr_0.8Y_0.2O_3-δ (BZY) and BaZr_0.1Ce_0.7Y_0.2O_3-δ (BZCY) are two typical electrolyte materials for PCFCs. However, there is still a lack of basis for making a choice between the two materials. In this paper, we present a comparison investigation on practical BZY and BZCY electrolytes with NiO of 2 mol.% as sintering aid. Their crystal structure, sinterability, microstructure, and electrical conductivity in humid air and hydrogen (3% H₂O) are measured and analyzed. Anode-supported PCFCs based on the two electrolyte materials are prepared and their electrochemical performances are tested and analyzed in association with an examination on their microstructure. The results show that both materials can be densified after sintered with NiO aid at 1400 °C for 6h. Ni is doped into the interstitial of BZY while it occupies the B site of perovskite lattice of BZCY. The sintered BZY has small grains and many grain boundaries while BZCY has large grains and much fewer grain boundaries, resulting in lower conductivity of BZY than that of BZCY. A PCFC with BZY electrolyte gives a peak power density of 360 mW cm^?2 at 700 °C, while this value for a PCFC with BZCY is 855 mW cm^?2. Although the performances of BZCY seems much better than those of BZY, a stability test in 10% CO₂-containing Ar at 650 °C shows BZY is stable while BZCY reacts with CO₂ to form BaCO₃ and CeO₂.     

Characterization and optimization of highly active and Ba-deficient BaCo0.4Fe0.4Zr0.1Y0.1O3-δ-based cathode materials for protonic ceramics fuel cells

Highly active triple-conducting (proton-, oxygen-ion-, and electron-conducting) perovskite oxide BaCo_0.4Fe_0.4Zr_0.1Y_0.1O_3-δ need to further optimize the electrochemical performance and chemical stability in carbon dioxide and water containing atmospheres, greatly limiting its widespread use in protonic ceramics fuel cells (PCFCs). Here, Ba-site deficient Ba_0.9Co_0.4Fe_0.4Zr_0.1Y_0.1O_3-δ (B9CFZY) was synthesized and investigated as a promising candidate concerning the chemical and structural stability, electrical conductivity and electrochemical performance. Anode-supported button cells with the prevalent BaZr_0.1Ce_0.7Y_0.2O_3-δ (BZCY) as electrolyte using B9CFZY and B9CFZY-BZCY cathodes, respectively, were fabricated and then measured at 700-550 °C. The maximum power density of the cells with B9CFZY-based cathodes increase from 452 mW cm⁻² to 537 mW cm⁻² at 700 °C, however, the corresponding polarization loss decreases from 0.30 to 0.15 Ω cm² by adding proton-conducting BZCY. Importantly, to better explore the reasons for the improved electrochemical performance, the distribution function of relaxation time (DRT) is used to distinguish different electrode polarization processes of both cells. The results indicate the polarization peaks (P3) of cells with composite cathode resulting from oxygen gas adsorption and dissociation can be greatly accelerated as well as the polarization peaks (P2) resulting from oxygen species diffusion to three phase boundaries or active sites in the cathode. The dramatic improvements demonstrate Ba deficient B9CFZY-BZCY material can be a very competitive cathode material for PCFCs.     

Structural,morphological, and electrochemical behavior of titanium-doped SrFe1-xTixO3-δ (x = 0.1–0.5) perovskite as a cobalt-free solid oxide fuel cell cathode

Titanium, Ti-doped SrFe_1-xTi_xO_3-δ (x = 0.1–0.5) perovskite-structured ceramics were synthesized via solution combustion. The structural, morphological, and electrochemical behaviors of the as-synthesized materials were investigated to determine the applicability of SrFe_1-xTi_xO_3-δ as a cobalt-free cathode material for intermediate-temperature solid oxide fuel cells. X-ray diffraction analysis confirmed the formation of a single-phase cubic perovskite structure. The unit volume of this perovskite structure increased as the amount of Ti dopant increased. Morphological analysis revealed that the porosity of the SrFe_1-xTi_xO_3-δ perovskite cathode film was inversely proportional to the amount of Ti dopant. The cathode SrFe_0·9Ti_0·1O_3-δ film exhibited a high porosity of 24.74 ± 0.52%, a low but acceptable hardness value of 0.70 ± 0.01 GPa and an area specific resistance of 0.57 Ω cm². These results suggested that cobalt-free SrFe_1-xTi_xO_3-δ cathode was still not good enough to be compared with the existing cobalt-containing cathode such as lanthanum strontium cobalt ferrite. But, the results obtained from this work can be considered as a major turning point as the literature works on SrFe_1-xTi_xO_3-δ cathode showed excellence electrochemical performance. The contradict result between the present and past studies proved that the use of SrFe_1-xTi_xO_3-δ cathode is worthy of being studied into details to confirm its capability.     

Creep behavior of porous La0.6Sr0.4Co0.2Fe0.8O3-δ substrate material for oxygen separation application

Advanced oxygen transport membrane designs consist of a thin functional layer supported by a porous substrate material that carries mechanical loads. Creep deformation behavior is to be assessed to warrant a long-term reliable operation at elevated temperatures. Aiming towards an asymmetric composite, the current study reports and compares the creep behavior of La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δ (LSCF) perovskite porous substrate material with different porosity and pore structures in air for a temperature range of 800–1000?°C. A porosity and pore structure independent average stress exponent and activation energy are derived from the deformation data, both being representative for the LSCF material. To investigate the structural stability of the dense layer in an asymmetric membrane, sandwich samples of Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3-δ (BSCF) and La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δ (LSCF) with porous substrate and dense layers on both side were tested by three-point bending with respect to creep rupture behavior of the dense layer. Creep rupture cracks were observed in the tensile surface of BSCF, but not in the case of LSCF.     

Structural and mechanical properties of La0.6Sr0.4M0.1Fe0.9O3-δ (M: Co,Ni and Cu) perovskites

La_0.6Sr_0.4M_0.1Fe_0.9O_3-δ (M: Co, Ni and Cu) perovskite nanostructures were synthesized using low frequency ultrasound assisted synthesis technique and effect of substitution of Fe by Co, Ni and Cu on crystal structure and mechanical properties in La_0.6Sr_0.4FeO_3-δ perovskite was studied. The HRTEM and Rietveld refinement analyses revealed the uniform equi-axial shape of the obtained nanostructures with the existence of La_0.6Sr_0.4M_0.1Fe_0.9O_3−δ with mixed rhombohedral and orthorhombic structures. Substitution by Cu decreases the melting point of La_0.6Sr_0.4FeO_3-δ. The results of mechanical characterizations show that La_0.6Sr_0.4Co_0.1Fe_0.9O_3−δ and La_0.6Sr_0.4Ni_0.1Fe_0.9O_3−δ have ferroelastic behavior and comparable elastic moduli, however, substitution by Ni shows higher hardness and lower fracture toughness than Co in B-site doping.     

Effect of CuO on self-lubricating properties of ZrO2(Y2O3)–Mo composites at high temperatures

In this paper, ZrO₂ matrix high-temperature self-lubricating composites with addition of CuO as lubricant were prepared using a hot-pressing method by tailoring the content of CuO. The wear and friction behaviour of the composites were investigated from 700 °C to 1000 °C. The composites sliding against an Al₂O₃ ceramic ball exhibited excellent self-lubricating and anti-wear properties at high temperatures. The low friction and wear mechanisms were investigated in detail.     

Structural and superconducting properties of Y(Ba1-xKx)2Cu3O7-δ ceramics

Y(Ba_1-xK_x)₂Cu₃O_7-δ ceramics (x = 0.00, 0.03, 0.05 and 0.08) were synthesized by thermal treatments of aqueous solution of metals nitrates and polyvinyl pyrrolidone (PVP) that acts as a capping agent. The effects of K-substitution on the crystal structure, microstructure and electrical resistance of samples were investigated. The X-ray diffractions results indicated an improvement of crystallinity and variation of lattice constant, a, b and c of YBa₂Cu₃O_7-δ (Y123) phase with K-substitution. The K-substitution resulted in increasing of orthorhombicity factor compared to pure Y123. Microstructural observation using scanning electron microscopy showed that K-substitution promotes the grain growth of Y123. The superconducting transitions (T_c) of the substituted-samples were higher than that of the pure Y123. The T_c (onset) were 93, 97, 95, 95 K for the samples with x = 0.00, 0.03, 0.05 and 0.08, respectively. Comparing with pure sample, the substituted-samples showed sharper superconducting transition (ΔT_c). The best superconducting properties was observed for sample with x = 0.03.     

The dielectric property and phase transition of Sr-doping effect of Ba1−xSrxTi0.9Mn0.1O3-δ ceramic

In this work, we prepare Ba_1−xSr_xTi_0.9Mn_.01O_3-δ (x = 0.00, 0.01, 0.03, 0.05, and 0.07) ceramics by the mixed oxide method and study the relationship between phase transition and dielectric property of the ceramics. The phase of the samples transformed from a hexagonal phase to mixed phases due to the increase in Sr doping amount. The X-ray diffraction (XRD) profiles and Raman spectra of the samples also show the same phase transformation due to increasing Sr doping amount. The XRD pattern of the undoped sample indicates a single h-BaTiO₃ phase with P6₃/mmc symmetric space group, while the samples with high Sr doping amounts have a mixed phase with t-BaTiO₃ with P₄mm symmetric space group. The scanning electron microscopy images show two types of BaTiO₃ grains, which grew with increasing sintering temperature. With increasing Sr concentration, the K-values (relative dielectric constant) of the ceramics increased, while the Q_xf values (the quality factor multiplied by frequency) decreased, which indicate that the microwave dielectric property is related to phase transformation.     

Mechanical properties of BaCe0.65Zr0.2Y0.15O3-δ proton-conducting material determined using different nanoindentation methods

Proton-conducting membranes have great potential for applications in proton conducting membrane reactors for the production of commodity chemicals or synthetic fuels as well as for use in solid oxide fuel cells. However, to ensure the long-term structural stability under operation relevant conditions, the mechanical properties of the membrane materials need to be characterized. BaCe_0.65Zr_0.2Y_0.15O_3-δ is of particular interest due to its proven functional properties. In this research work, the mechanical properties of BaCe_0.65Zr_0.2Y_0.15O_3-δ were determined on different length scales using different methods including impulse excitation, indentation testing, and micro-pillar splitting. A detailed microstructural analysis of pillars revealed that irregular results are caused by pores causing crack deflection and complex crack patterns.     

Synthesis and electrochemical performance of α-Fe2O3@carbon aerogel composite as an anode material for Li-ion batteries

A α-Fe₂O₃@carbon aerogel (CA) composite material has been successfully synthesized via a simple hydrothermal method in water solution. The microstructure, morphologies, α-Fe₂O₃ loading content in α-Fe₂O₃@CA, porous nanostructure and electrochemical properties of these materials are investigated by X-ray diffraction, scanning electron microscopy, thermal gravimetric analysis, N₂ adsorption-desorption isotherms, constant current charge/discharge tests and cyclic voltammetry tests. The results show that α-Fe₂O₃ is uniformly dispersed on CA with a rugby-like morphology, and the α-Fe₂O₃ active material loading content in α-Fe₂O₃@CA composite is up to 95.72%. The α-Fe₂O₃@CA revealed a high reversible capacity of 581.9 mAh g⁻¹ and stable cyclic retention at 50th cycle. The improvement of reversible capacity and cyclic performance of the α-Fe₂O₃@CA composite is attributed to the unique structure of CA, with high electronic conductivity and three-dimensional porous structures among the interconnected α-Fe₂O₃@CA composite, which could not only effectively load the α-Fe₂O₃ active material, but also could prevent the aggregation of α-Fe₂O₃ nanoparticles and facilitate the transport of electrons and shorten the distance for Li⁺ diffusion. The encouraging experimental results suggest that the novel α-Fe₂O₃@CA composite have great potential for use as an anode material for lithium rechargeable cells.     

Mechanical behavior of ferroelastic porous La0.6Sr0.4Co0.2Fe0.8O3−δ prepared with different pore formers

The present work investigated the mechanical behavior of porous La_0.6Sr_0.4Co_0.2 Fe_0.8O_3−δ LSCF under uniaxial compression. The porous (LSCF) samples with the same grain size but different porous structures with 1.5–41% of porosity were prepared using three different pore formers. All the samples had ferroelastic domains and exhibited ferroelastic mechanical behaviors under uniaxial compression. Initial and loading moduli as well as critical stress monotonically decreased and remnant strain increased with increasing the porosity. The initial modulus can be determined by the actual porosity regardless of porous structure or grain size, whereas the other properties were more sensitive to experimental condition such as loading rate and maximum applied stress. Compressive fracture strength could be significantly influenced by porous structure.     

Mechanical properties of BaCe0.65Zr0.2Y0.15O3-δ – Ce0.85Gd0.15O2-δ dual-phase proton-conducting material with emphasis on micro-pillar splitting

BaCe_0.65Zr_0.2Y_0.15O_3-δ – Ce_0.85Gd_0.15O_2-δ (BCZ20Y15-GDC15) dual-phase material revealed potential for H₂ production technologies due to its exceptional H₂ permeation and chemical resistance. In this article, mechanical properties of BCZ20Y15-GDC15 dual-phase material were investigated to evaluate the mechanical behavior and develop strategies to warrant structural stability. Elastic modulus, hardness and fracture toughness values were studied using different indentation-based methods. The fracture experiments at different length-scales both revealed that the introduction of GDC15 makes the material tougher, facilitating the further design of robust and reliable components.     

The characteristics of ZnO–Bi2O3-based varistor ceramics doped with Y2O3 and varying amounts of Sb2O3

ZnO–Bi₂O₃-based varistor samples doped with 0.45 mol% of Y₂O₃ and varying amounts of Sb₂O₃ in the range from 1.8 to 0.0 mol% were fired at 1230 °C. Only in the samples co-doped with Sb₂O₃ did doping with Y₂O₃ resulted in the formation of a fine-grained Bi–Zn–Sb–Y–O phase (the Y₂O₃-containing phase) at the grain boundaries, which very effectively hinders the grain growth. Despite of a decrease in the amount of added Sb₂O₃ from 1.8 to 0.45 mol% and a significant decrease in the amount of spinel phase the samples had a similar ZnO grain size and a threshold voltage of 200 V/mm. The results confirmed that doping with Y₂O₃ is a very promising route for the production of fine-grained high-voltage ZnO–Bi₂O₃-based varistor ceramics, and determining the proper amounts of added Sb₂O₃ and Y₂O₃ is of great importance.     

Effects of mass fraction of La0.9Sr0.1Cr0.5Mn0.5O3-δ and Gd0.1Ce0.9O2-δ composite anodes for nickel free solid oxide fuel cells

The optimal anode mass fraction of La_0.9Sr_0.1Cr_0.5Mn_0.5O_3-δ (LSCM) and Gd_0.1Ce_0.9O_2-δ (GDC) is evaluated in this study. The anodes with GDC share of 30–100 wt.% are investigated. Initial polarization resistance decreased as the GDC share increased. However, anodes with GDC share over 80 wt.% significantly deteriorated in the degradation tests. Nano-scale cracks were observed in the GDC phase at the grain boundaries after the test. These nano-cracks were not observed in composite anodes, from which it is implied that LSCM has stabilization effect on GDC structure. The mass fraction of LSCM : GDC = 30 : 70 wt.% is found to be optimal in terms of initial electrochemical performance and stability. The optimal LSCM-GDC shows lower polarization resistance than conventional Ni-YSZ at low temperatures, which is comparable to Ni-GDC anode.