Partial internal short circuit resulting from the Ce4+/Ce3+ redox reaction is currently one of the most critical issues that hinder the practical application of solid oxide fuel cells (SOFCs) with doped ceria electrolytes. In this work, a new strategy utilizing a Sr diffusion induced in situ solid-state reaction to generate a blocking layer to prevent Ce0.8Sm0.2O1.9 (SDC) from reduction is proposed for the first time. As a proof of concept, Ni-SrCe0.95Yb0.05O3−δ is deployed as a Sr source for the electron-blocking interlayer and was evaluated as an anode for SDC-based SOFCs. A thin interlayer composed of SrCe1−x(Sm,Yb)xO3−δ and SDC is formed in situ during the sintering process of the half cell due to the interdiffusion of metal cations, and the interlayer thickness is highly dependent on the sintering temperature. The high-resolution TEM results indicate that the SrCe1−x(Sm,Yb)xO3−δ perovskite phase is generated and coated on the SDC grains, forming an SDC@SrCe1−x(Sm,Yb)xO3−δ core–shell structure. The SrCe1−x(Sm,Yb)xO3−δ phase effectively suppresses the Ce4+/Ce3+ redox reaction and hence eliminates electronic conduction through the electrolyte membrane. Consequently, the OCVs of the fuel cell are significantly improved after incorporating the electron-blocking interlayer and increase with increasing the interlayer thickness. The OCVs of the cell sintered at 1250 °C reach 0.962, 0.989, 1.017, and 1.039 V at 650, 600, 550, and 500 °C, respectively. The present results demonstrate that Ni-SrCeO3-based composites are promising alternative anodes for CeO2-based SOFCs towards enhanced working efficiency at high operating voltages.

•BCS-SDC composite electrolytes were synthesized by in-situ solid-state reaction.•The SDC nanoparticles are partly coated by a thin layer of BaCe1-xSmxO3-δ.•The effect of BCS content in composites on cell performances was investigated.•Introduction a small amount of BCS into SDC is beneficial to cell performances.A series of composites with nominal compositions of BaCe0.8Sm0.2O3-δ (BCS)-Ce0.8Sm0.2 O1.9 (SDC) (20:80, 35:65, 50:50, 65:35 wt.%) are synthesized by a modified citric acid-nitrate sol-gel combustion method and evaluated as the electrolytes for low-temperature solid oxide fuel cells (SOFCs). The TEM results show that doped BaCeO3 decorated SDC particles are formed after calcining at 1000 °C for 3 h. X-ray diffraction results reveal that the composites are only composed of BaCeO3-based and SDC phases without any other impurity phases. Besides, BaCeO3-based phase is uniformly distributed in the sintered electrolytes according to EDS element mapping. The open cell voltages (OCVs) of the single cells increase gradually with increasing the proportion of BaCeO3-based phase, and are higher than those for bare SDC-based cells. Besides, the power performances of the cells are superior to SDC-based cells when BaCeO3-based phase is lower than 35 wt.%. Electrochemical impedance spectroscopy analysis indicates that, in addition to blocking electronic current leakage, BaCeO3-based phase would induce higher ohmic and polarization resistance, which is detrimental to power performance. Further specific effort should be focused on synthesizing uniform SDC@BCS core-shell electrolyte powders and minimizing the proportion of BCS phase towards high-performance SOFCs with high OCVs.

Developing highly efficient ceria-based solid oxide fuel cells with high power density is still a big concern for commercial applications. In this work, a novel structured Ce0.8Sm0.2O2−δ (SDC)-based fuel cell with a bilayered anode consisting of Ni-SDC and Ni-BaZr0.1Ce0.7Y0.2O3-δ (Ni-BZCY) was designed. In addition to the catalysis function, the Ni-BZCY anode “functional” layer also provides Ba source for generating an electron-blocking layer in situ at the anode/electrolyte interface during sintering. The Ni-BZCY thickness significantly influences the quality of the electron-blocking layer and electrochemical performances of the cell. The cell with a 50 μm thick Ni-BZCY layer exhibits the best performance in terms of open circuit voltage (OCV) and peak power density (1068 mW cm–2 at 650 °C). The results demonstrate that this cell with an optimal structure has a distinct advantage of delivering high power performance with a high efficiency at reduced temperatures.Keywords: doped ceria; electron-blocking layer; internal short circuit; open circuit voltage; solid oxide fuel cells

•A novel composite cathode ESB-PBM is developed for HPLT-SOFCs.•ESB-PBM achieved an encouraging performance based on the SNDC|ESB bilayer film.•The cell with ESB-PBM cathode has the power output of 994 mW cm−2 at 650 °C.•The ESB-PBM cathode layer has a uniform porous nanostructure.A novel composite cathode consisting of A-site disordered Pr0.5Ba0.5MnO3−δ (PBM) and Er0.4Bi1.6O3 (ESB) is developed for solid oxide fuel cells (SOFCs) with ceria-bismuth bilayer electrolyte. Based on Sm0.075Nd0.075Ce0.85O2−δ|ESB (SNDC|ESB) bilayer structured film, the single cell NiO-SNDC|SNDC|ESB|ESB-PBM achieves an encouraging performance with the maximum power density (MPD) of 994 mW cm−2 and an interfacial polarization resistance (Rp) of 0.027 Ω cm2 at 650 °C. Although a possible reaction between ESB and PBM has been identified in the cathode, the ascendant electrochemical performance including the very high fuel cell performance and Rp obtained here can demonstrate that the novel cobalt-free composite cathode ESB-PBM is a preferable alternative for ceria-bismuth bilayer electrolyte high performance low temperature SOFCs (HPLT-SOFCs) and the interfacial reaction in the cathode seems not to be detrimental to the electrochemical performance.

This report describes the facile solvothermal synthesis of highly monodispersed nickel microspheres with surfaces uniformly covered by nickel dots. Synthesis parameters including reaction times and reagent concentrations significantly influence the microspheric particle characteristics. The novelty of the synthetic method in this work is twofold: first, the controlled synthesis of Ni metallic microspheres using ethylene glycol as the precursor of a reductant and urea as the origin of OH− has never been reported. Second, there are few studies on the construction of Ni microspheres covered by uniform Ni dots using a one-step solvothermal method. Importantly, the as-prepared Ni microspheres show an improved ability to remove Cd2+ ions even at high concentrations in water and a unique adsorption isotherm having an increasing adsorption capacity for Cd2+ ions. The presence of Ni dots was considered to play an important role in the onset of the adsorption process. We believe that this work opens up new and possibly exciting opportunities in the field of adsorption of heavy metal ions.

Two types of proton-blocking composites, La2NiO4+δ–LaNi0.6Fe0.4O3−δ (LNO–LNF) and Sm0.2Ce0.8O2−δ–LaNi0.6Fe0.4O3−δ (SDC–LNF), were evaluated as cathode materials for proton-conducting solid oxide fuel cells (H-SOFCs) based on the BaZr0.1Ce0.7Y0.2O3−δ (BZCY) electrolyte, in order to compare and investigate the influence of two different oxygen transfer mechanism on the performance of the cathode for H-SOFCs. The X-ray diffraction (XRD) results showed that the chemical compatibility of the components in both compounds was excellent up to 1000 °C. Electrochemical studies revealed that LNO–LNF showed lower area specific polarization resistances in symmetrical cells and better electrochemical performance in single cell tests. The single cell with LNO–LNF cathode generated remarkable higher maximum power densities (MPDs) and lower interfacial polarization resistances (Rp) than that with SDC–LNF cathode. Correspondingly, the MPDs of the single cell with the LNO–LNF cathode were 490, 364, 266, 180 mW cm−2 and the Rp were 0.103, 0.279, 0.587, 1.367 Ω cm2 at 700, 650, 600 and 550 °C, respectively. Moreover, after the single cell with LNO–LNF cathode optimized with an anode functional layer (AFL) between the anode and electrolyte, the power outputs reached 708 mW cm−2 at 700 °C. These results demonstrate that the LNO–LNF composite cathode with the interstitial oxygen transfer mechanism is a more preferable alternative for H-SOFCs than SDC–LNF composite cathode with the oxygen vacancy transfer mechanism.

A Sm0.075Nd0.075Ce0.85O2−δ–Er0.4Bi1.6O3 bilayer structured film, which showed an encouraging performance in LT-SOFCs, was successfully fabricated by a simple low cost technique combining one-step co-pressing with drop-coating.

•Bilayered electrolyte membranes composed of BZCY and SDC were evaluated for SOFCs with high OCVs.•The electron-blocking ability of BZCY layer depends on its exact location in the fuel cell.•BZCY located at the anode side could protect SDC from reduction and eliminate internal short circuit.•A thin BZCY layer is critical for achieving high power performance.Bilayered electrolyte membranes composed of BaZr0.1Ce0.7Y0.2O3−δ (BZCY) and Ce0.8Sm0.2O2−δ (SDC) were evaluated for solid oxide fuel cells (SOFCs), and the influence of the membrane architecture on the cell performance was investigated. The electrochemical testing results showed that the electron-blocking ability of BZCY layer depends on its exact location in the fuel cell. The partial internal short circuit was nearly totally eliminated for the cell with BZCY layer located at the anode side, and the corresponding cell exhibited a high open circuit voltage (OCV) of 1.0 V at 700 °C. In contrast, the cell with BZCY layer located at the cathode side still exhibited significant internal short-circuit behavior. The different electron-blocking ability can be ascribed to the atmosphere-dependent charge transport behavior of BZCY. The present results demonstrate that the bilayered BZCY/SDC membrane with BZCY layer located at the anode side is a promising electrolyte for highly efficient low-temperature SOFCs. Besides, the BZCY layer should be as thin as possible to achieve desirable power performance for the fuel cell.

•Two kind DCO–SBO bilayer film cells were evaluated comparably.•The SNDC|ESB bilayer film cell showed superior electrochemical performance.•The cell with SNDC|ESB bilayer film output the MPD of 271 mW cm−2 at 500 °C.•A plausible mechanism explaining the wondrous conductivity of DCO–SBO was proposed.Two types of ceria–bismuth bilayer films Gd0.1Ce0.9O2−δ|Er0.4Bi1.6O3 (GDC|ESB) and Sm0.075Nd0.075Ce0.85O2−δ|ESB (SNDC|ESB) assembled with ESB–La0.74Bi0.1Sr0.16MnO3−δ (ESB–LBSM) cathode are evaluated based on anode supported single cells, in order to compare and investigate the influence of different ceria-based materials GDC and SNDC with different ionic conductivity on the performance of the ceria–bismuth bilayer electrolyte films for high performance low temperature solid oxide fuel cells (HPLT-SOFCs). The single cell with GDC|ESB bilayer film outputs the maximum power density (MPD) of 895 mW cm−2 with interfacial polarization resistance (Rp) of 0.079 Ω cm2 at 650 °C. When SNDC is used, which has a much higher ionic conductivity with respect to GDC, the cell with SNDC|ESB bilayer film achieves the MPD of 930 mW cm−2 and the Rp of 0.035 Ω cm2 at the same conditions which shows better electrochemical performance. Furthermore, the SNDC|ESB bilayer film cell shows higher power output in the entire operation temperature range compared with GDC|ESB-based cell and has the MPD of 271 mW cm−2 at 500 °C which demonstrate the superiority of SNDC|ESB bilayer structure cell in LT-SOFC operations.

•Ni-LDC asymmetric cermet membrane was prepared by a simple method.•The membrane showed the best permeability among LDC-based membranes.•Hydrogen separation and generation could be realized using the Ni-LDC membrane.•JH2 remained stable whether operating in CO2 condition or dual-function mode.In this work, hydrogen permeation properties of Ni–La0.5Ce0.5O2−δ (LDC) asymmetrical cermet membrane are investigated, including hydrogen fluxes (JH2) under different hydrogen partial pressures, the influence of water vapor on JH2 and the long-term stability of the membrane operating under the containing-CO2 atmosphere. Ni-LDC asymmetrical membrane shows the best hydrogen permeability among LDC-based hydrogen separation membranes, inferior to Ni–BaZr0.1Ce0.7Y0.2O3−δ asymmetrical membrane. The water vapor in feed gas is beneficial to hydrogen transport process, which promote an increase of JH2 from 5.64 × 10−8 to 6.83 × 10−8 mol cm−2 s−1 at 900 °C. Stability testing of hydrogen permeation suggests that Ni-LDC membrane remains stable against CO2. A dual function of combining hydrogen separation and generation can be realized by humidifying the sweep gas and enhance the hydrogen output by 1.0–1.5 times. Ni-LDC membrane exhibits desirable performance and durability in dual-function mode. Morphologies and phase structures of the membrane after tests are also characterized by SEM and XRD.

•Fabricate thin BZPY layer on BCY half-cell with pulsed laser deposition.•The bilayer electrolyte improves chemical stability against CO2 atmosphere.•The bilayer electrolyte cell shows a good electrochemical performance.•The bilayer cell exhibits a good long-term stability under cell testing condition.A thin BaZr0.7Pr0.1Y0.2O3-δ (BZPY) layer (∼3.3 μm) is fabricated on anode-supported BaCe0.8Y0.2O3-δ (BCY) electrolyte layer (∼28 μm) with pulsed laser deposition (PLD) technique. The BZPY/BCY bilayer electrolyte shows better chemical stability against CO2 atmosphere compared with the BCY single electrolyte layer. The open circuit voltages (OCVs) of 0.966, 0.997 and 1.021 V with maximum power densities of 250, 177, 122 mW cm−2 are measured in the bilayer electrolyte cell at 700, 650 and 600 °C, respectively. Besides, the BZPY/BCY bilayer electrolyte cell also exhibits a good long-term stability under the operating condition. BZPY thin film deposited with PLD technique can improve chemical stability with little effect on the electrochemical performance of proton-conducting SOFC.

•PSCF-SDC composite was firstly evaluated as cathode for H-SOFC.•The optimum sintering temperature of PSCF-SDC was 800 °C.•PSCF-SDC cathode is promising for H-SOFC at intermediate temperature.Pr0.6Sr0.4Cu0.2Fe0.8O3−δ-Ce0.8Sm0.2O2−δ (PSCF-SDC) (70:30 wt.%), a new cobalt-free composite cathode, is investigated for BaZr0.3Ce0.5Y0.2O3−δ-based proton-conducting solid oxide fuel cells (H-SOFCs). The influence of firing temperature on cathode microstructure and electrochemical performance of fuel cells is researched and analyzed. These results show that the optimum sintering temperature of PSCF-SDC composite cathode is 800 °C. The low polarization resistance of 0.14 Ω cm2 and the maximum power density of 456 mW cm−2 are achieved at 650 °C. Cell performance is further enhanced when the BaZr0.3Ce0.5Y0.2O3−δ electrolyte is replaced by BaZr0.1Ce0.7Y0.2O3−δ with higher proton conductivity; resulting in an improved maximum power density of 556 mW cm−2 at 650 °C.

One-, two- and three-dimensional nanostructures of copper molybdenum oxide hydroxide were successfully constructed by a simple approach through a pH-dependent dimensional transformation of ammonium copper molybdate. Thin nanoplates of copper molybdate, which were obtained by sintering the two-dimensional nanobelts of copper molybdenum oxide hydroxide, exhibited remarkably high reversible lithium storage capacity, good rate capability and excellent cycling stability.

•Fabricate dense SDC interlayer on YSZ electrolyte with pulsed laser deposition.•Porous SDC interlayer was deposited with dip-coating method.•SDC interlayer with SSC cathode improves the electrochemical performance.Application of Sm0.5Sr0.5CoO3−δ (SSC) cathode in solid oxide fuel cells (SOFCs) has its advantage of reducing polarization loss at intermediate operating temperatures (600–800 °C). However, the SSC cathode cannot be applied directly on yttria stabilized zirconia (YSZ) electrolyte due to the thermal mismatch and chemical reaction. In this work, Ce0.8Sm0.2O2−δ (SDC) thin interlayers are fabricated between YSZ electrolyte layers and Sm0.5Sr0.5CoO3−δ-SDC (SSC–SDC) cathode layers with dip-coating and pulsed laser deposition (PLD) methods. The 1400 °C-sintered SDC interlayer deposited by dip-coating method exhibits a porous microstructure. PLD technique yields a thin and dense SDC layer at a low substrate temperature of 600 °C and no additional peaks of (Zr, Ce)O2-based solid-solution are present. Besides, the electrochemical performance of the YSZ/SDC (electrolyte/interlayer) fuel cell has a great improvement at intermediate operating temperature.

Partial internal electronic short circuit continues to be a main problem for ceria-based oxide-ion conductors. A novel composite anode composed of BaZr0.45Ce0.45Gd0.1O3−δ and nickel (Ni–BZCG) is proposed to avoid partial reduction from Ce4+ to Ce3+ in Gd0.1Ce0.9O2−δ (GDC) electrolyte by forming a functional electron-blocking interlayer in situ at Ni–BZCG|GDC interface. Open circuit voltages (OCVs) above 1.0 V at 650 °C can be achieved for cells with Ba-containing anodes, which are much higher than the value obtained with Ni–GDC anode (lower than 0.8 V) under the same conditions. The enhanced OCVs are attributed to the formation of a new electron-blocking layer with GDC@Ba(Ce,Zr)1−xGdxO3−δ core/shell structure. The interrelations between the structural interlayer and the OCVs for improved cells are also studied. Furthermore, based on the microstructure of the new structured interlayers in the fuel cells, the high polarization resistance can be mainly attributed to the insulative BaNiO3−δ phase reducing reaction zone at anode.

Acceptor-doped barium cerate is considered as one of the state-of-the-art high temperature proton conductors (HTPCs), and the proton conductivity of such HTPCs is heavily dependent on the dopant. In this work, a codoping strategy is employed to improve the electrical conductivity and sinterability of BaCeO3-based HTPC. BaCe0.8SmxY0.2–xO3−δ (0 ≤ x ≤ 0.2) powders are synthesized by a typical citrate–nitrate combustion method. The XRD and Raman spectra reveal all the compounds have an orthorhombic perovskite structure. The effects of Sm and/or Y doping on the sinterability and electrical conductivity under different atmospheres are carefully investigated. The SEM results of the sintered BaCe0.8SmxY0.2–xO3−δ pellets indicate a significant sintering enhancement with increasing Sm concentration. BaCe0.8Sm0.1Y0.1O3−δ exhibits the highest electrical conductivity in hydrogen among the BaCe0.8SmxY0.2–xO3−δ pellets. Anode-supported BaCe0.8Sm0.1Y0.1O3−δ electrolyte membranes are also fabricated via a drop-coating process, and the corresponding single cell exhibits desirable power performance and durability at low temperatures. The results demonstrate that BaCe0.8Sm0.1Y0.1O3−δ is a promising proton conductor with high conductivity and sufficient sinterability for proton-conducting solid oxide fuel cells operating at reduced temperatures.Keywords: barium cerate; electrical conductivity; high temperature proton conductors; sinterability; solid oxide fuel cells;

•Series of LNO–LNF composites were firstly evaluated as cathodes for H-SOFC.•The electrical conductivity of LNO–LNF73 reaches 99.2 S cm−1 at 650 °C.•LNO–LNF73 is the most optimized combination among all composite cathodes.•At 700 °C, the cell with LNO–LNF73 showed the highest MPD of 590 mW cm−2.Series of proton-blocking La2NiO4+δ (LNO)–LaNi0.6Fe0.4O3−δ (LNF) (1:0, 7:3, 5:5, 3:7, 0:1 wt.%) composites were evaluated as cathodes for BaZr0.1Ce0.7Y0.2O3−δ (BZCY)-based proton-conducting solid oxide fuel cell (H-SOFC). The X-ray diffraction (XRD) results show a good chemical compatibility for each composition below 1100 °C. Electrochemical studies reveal that LNO–LNF73 shows the lowest area specific polarization resistance in symmetrical cells and the best electrochemical performance in single cell tests with the highest maximum power density (MPD) and the lowest interfacial polarization resistance (Rp). These results corroborate the electrical conductivity analysis. The single cell with LNO–LNF73 as cathode outputs the MPD of 590 mW cm−2 and the Rp of 0.091 Ω cm2 at 700 °C. This work confirms that LNO–LNF73 composite material could be a promising cathode for H-SOFC.

•BaZr0.3Ce0.5Y0.2−xYbxO3−δ powders were synthesized via a combustion method.•The phase structure and electrical conductivity of BaZr0.3Ce0.5Y0.2−xYbxO3−δ were investigated.•BaZr0.3Ce0.5Y0.2O3−δ exhibits the highest conductivity.•BaZr0.3Ce0.5Y0.2O3−δ-based single cells achieved excellent performance at intermediate/low temperatures.The acceptor-doped BaCeO3–BaZrO3 solid solution shows a good compromise between conductivity and chemical stability. Y and/or Yb doped BaCeO3–BaZrO3 solid solution BaZr0.3Ce0.5Y0.2−xYbxO3−δ (x = 0, 0.05, 0.1, 0.15, 0.2) powders are synthesized via a typical citrate–nitrate combustion method in this work. The crystal structure and electrical conductivity of BaZr0.3Ce0.5Y0.2−xYbxO3−δ are investigated. The XRD results reveal all the powders possess orthorhombic perovskite structure. The electrical conductivity decreases monotonously with increasing the proportion of Yb, and BaZr0.3Ce0.5Y0.2O3−δ exhibits the highest electrical conductivity. Single cells with BaZr0.3Ce0.5Y0.2O3−δ as the electrolyte are fabricated and tested, and the cell outputs excellent power density and stability. The peak power density of the cell reaches as high as 513 and 396 mW cm−2 at 650 and 600 °C, suggesting that BaZr0.3Ce0.5Y0.2O3−δ-based fuel cells are promising solid oxide fuel cells (SOFCs) working at low temperatures.

•Fabricate thin BZY layer on BCY half-cell with pulsed laser deposition.•The bilayer electrolyte proves a good chemical stability against CO2 atmosphere.•The bilayer cell exhibits a good long-term stability under cell testing condition.•The bilayer electrolyte cell shows a comparable electrochemical performance.BaZr0.8Y0.2O3−δ (BZY) layers with various thicknesses (∼0.7, ∼1.7, ∼2.4 and ∼3.6 μm) are fabricated using the pulsed laser deposition (PLD) technique on anode-supported BaCe0.8Y0.2O3−δ (BCY) electrolyte films. Sm0.5Sr0.5CoO3−δ-SDC (SSC-SDC, 70:30 wt.%) cathode is applied onto the BZY/BCY bilayer electrolyte to form a single cell. The chemical stability of the BZY/BCY bilayer electrolytes improves with increasing BZY layer thickness. The BZY (∼3.6 μm)/BCY bilayer electrolyte shows an excellent chemical stability after treated in 100% CO2 atmosphere at 900 °C. The maximum power densities of 447, 370, 276, 218 and 163 mW cm−2 are measured with the BZY layer thicknesses of 0, 0.7, 1.7, 2.4 and 3.6 μm at 700 °C, respectively. In general, the BZY/BCY bilayer electrolyte cell with an optimum BZY layer thickness can improve chemical stability without great influence on the electrochemical performance for intermediate temperature solid oxide fuel cells.

•Fabricate thin LSGM layer on SDC half-cell with pulsed laser deposition.•The thin LSGM layer blocks electronic current in SDC layer.•The bilayer cell retains the chemical, mechanical and structural integrity.•The electrochemical performance and OCVs of the cell have been improved.A dense La0.9Sr0.1Ga0.8Mg0.2O3−δ (LSGM) film is fabricated using the pulsed laser deposition (PLD) technique on a Ce0.8Sm0.2O2−δ (SDC) electrolyte which is prepared using a co-pressing process on a NiO–SDC anode substrate. The LSGM/SDC bilayer electrolyte cell with Sm0.5Sr0.5CoO3−δ–Ce0.8Sm0.2O2−δ (SSC–SDC, 70:30 wt.%) cathode achieves significantly enhanced cell performance, yielding open circuit voltage (OCV) value of 0.89 V and maximum power density of 758 mW cm−2 at 700 °C. The electrical current leakage in the SDC single layer cell caused by the reduction of Ce4+ to Ce3+ in reducing environment has been eliminated by depositing the LSGM thin film as a blocking layer; besides, the reaction between NiO and LSGM can be prevented due to the dense SDC electrolyte layer. The influence of oxygen pressure and post-annealing temperature on the crystallinity, microstructure and surface roughness of the LSGM films are studied for obtaining a high quality film. Characterization analysis of the cell shows that the bilayer electrolyte deposited by the PLD technique have retained the chemical, mechanical and structural integrity of the cell.

•Hydrogen permeation properties of Ni-BZPY membranes were investigated systematically.•Bulk diffusion step controlled hydrogen permeation process.•The membrane showed good stability against water vapor and carbon dioxide.In order to obtain chemically stable hydrogen-permeable cermet membranes against CO2 and H2O, the composite membranes consisting of Ni and Ba(Zr0.7Pr0.1Y0.2)O3−δ (BZPY) are fabricated by the dry-press technique and reducing atmosphere sintering process. SEM results show that the cermet membrane is extremely dense and metal nickel is randomly distributed in BZPY oxide matrix. Hydrogen permeation properties of the Ni-BZPY membranes are systemically studied including the influence of the operating temperature, H2 concentration in feed stream, humidification degree and membrane thickness. The Ni-BZPY membrane presents good chemical stability in humid condition or CO2-containing environments and is potential candidates for hydrogen separation.

•Chemically stable BaZr0.8Y0.2O3−δ–Ni was successfully demonstrated as an anode for a highly efficient Ce0.8Sm0.2O2−δ-based SOFC.•A thin electron-blocking layer composed of Ce0.8Sm0.2O2−δ@Ba(Ce, Zr)1−x(Sm, Y)xO3−δ core/shell-like grains was formed in situ at the anode/electrolyte interface.•The electron-blocking layer substantially eliminated electronic conduction through electrolyte film.•The new structured cell output high open circuit voltages, promising power densities as well as good operating durability.Chemically stable composite BaZr0.8Y0.2O3−δ–Ni (BZY–Ni) was proposed and evaluated as the anode for solid oxide fuel cells (SOFCs) based on Ce0.8Sm0.2O2−δ (SDC) electrolyte. A thin electron-blocking interlayer was formed in situ at the anode/electrolyte interface when the anode-supported half cell was prepared via a high-temperature sintering process. Raman spectra and high-resolution TEM (HRTEM) results revealed that the electron-blocking interlayer consisted of Ce0.8Sm0.2O2−δ@Ba(Ce, Zr)1−x(Sm, Y)xO3−δ core/shell-like grains. The Ba(Ce, Zr)1−x(Sm, Y)xO3−δ shell protected SDC grains from reduction and consequently the electronic conduction through the SDC electrolyte film was nearly completely eliminated in the new structured fuel cell. The fuel cell exhibited significantly improved open circuit voltages (OCVs), high power densities as well as good operating durability, demonstrating that BZY–Ni is a promising anode for CeO2-based SOFCs operating at a higher efficiency. These findings also imply that doped CeO2@doped Ba(Ce, Zr)O3 core/shell composite is a promising electrolyte with high ionic transport number, which directs a new strategy to design novel electrolyte materials for SOFCs.

A novel CO2-stable and reduction-tolerant Ce0.8Sm0.2O2−δ–La0.9Sr0.1FeO3−δ (SDC–LSF) dense dual-phase oxygen-permeable membrane was designed and evaluated in this work. Homogeneous SDC–LSF composite powders for membrane fabrication were synthesized via a one-pot combustion method. The chemical compatibility and ion interdiffusion behavior between the fluorite phase SDC and perovskite phase LSF during the synthesis process was studied. The oxygen permeation flux through the dense dual-phase composite membranes was evaluated and found to be highly dependent on the volume ratio of SDC and LSF. The SDC–LSF membrane with a volume ratio of 7:3 (SDC70–LSF30) possessed the highest permeation flux, achieving 6.42 × 10-7 mol·cm–2·s–1 under an air/CO gradient at 900 °C for a 1.1-mm-thick membrane. Especially, the membrane performance showed excellent durability and operated stably without any degradation at 900 °C for 450 h with helium, CO2, or CO as the sweep gas. The present results demonstrate that a SDC70–LSF30 dual-phase membrane is a promising chemically stable device for oxygen production and CO2 capture with sufficiently high oxygen permeation flux.Keywords: CO2-stable membrane; dual-phase membrane; oxygen permeation; reduction-tolerant membrane; stability;

•A model for asymmetric Ni–BZCY hydrogen separation membrane was proposed.•Model results were in accord with experiment.•Involved processes in asymmetric membrane were considered.•Influence of each process in asymmetric membrane was recognized.Hydrogen separation membrane of Ni–BaCe0.7Zr0.1Y0.2O3−δ cermet with an asymmetric structure was simulated by considering several involved processes, such as mass transportation in porous support, bulk diffusion in dense layer, interfacial exchange on both sides of the membrane, and hydrogen permeation through nickel phase. The model was compared with experimental results and could match them in general. Equivalent resistances of each step in asymmetric membrane were introduced to determine their influence on the performance and recognize the rate-determining step. Advice on further capacity improvement was given based on the simulation results. This model could be used to analyze and predict the performance of this kind of asymmetric hydrogen separation membrane.

Barium zirconate-based high-temperature proton conductors (HTPCs) exhibit excellent chemical stability in atmospheres containing CO2 or water vapor. However, such HPTCs haven't been widely used as electrolyte materials for solid oxide fuel cells (SOFCs) due to their poor sintering activity. In this work, indium is selected as a dopant to improve the sintering activity of barium zirconate. BaZr0.8In0.2O3−δ (BZI) powders with a pure cubic perovskite structure are synthesized via a typical citric acid–nitrate gel combustion process. The SEM results show that BZI exhibits improved sintering activity compared to the state-of-the-art proton conductor BaZr0.8Y0.2O3−δ (BZY), and fully dense BZI pellets with increased grain size are obtained after sintered at 1600 °C in air. Moreover, BZI also keeps sufficiently high chemical stability as BZY. The electrical conductivity of BZI under various atmospheres is investigated by electrochemical impedance spectroscopy (EIS) in detail. The total conductivity achieves 1.0 × 10−3 S cm−1 at 700 °C in wet H2 (3% H2O). Dense BZI electrolyte films are successfully fabricated on the anode substrates by a dry-pressing method after sintered at 1400 °C for 5 h in air. Single cells with dense BZI electrolyte films are also assembled and tested to further evaluate the feasibility of BZI as an electrolyte material for proton-conducting SOFCs.Highlights► BaZr0.8In0.2O3−δ (BZI) powders were synthesized via the gel combustion process. ► BZI shows good sintering activity and high chemical stability. ► The electrical conductivity of dense BZI pellet was investigated in detail. ► A single cell with a dense BZI electrolyte film was fabricated and tested.

Bilayer electrolytes composed of an yttria stabilized zirconia (YSZ) layer (∼2 μm) and a samaria doped ceria (SDC) layer (∼6 μm) have been successfully fabricated by pulsed laser deposition (PLD) technique at 600 °C for thin film solid oxide fuel cells (SOFCs). A NiO-YSZ (60:40 wt.% with 10 wt.% starch) anode supported YSZ/SDC bilayer electrolytes cell with Sm0.5Sr0.5CoO3−δ-Ce0.8Sm0.2O2−δ (SSC-SDC, 70:30 wt.%) cathode was tested, yielding open circuit voltage (OCV) value of 0.843 V and maximum power density of 0.87 W cm−2 at 700 °C. With a NiO-YSZ anode functional layer (50:50 wt.%) introduced into anode/electrolyte interface, significantly enhanced cell performance was achieved, i.e., the cell OCV of 0.959 V and 0.98 V with maximum power density of 1.19 W cm−2 and 1.08 W cm−2 at 750 °C and 700 °C, respectively. The electrical current leakage in the SDC single layer cell caused by the reduction of Ce4+ to Ce3+ in reducing environment has been eliminated by depositing the YSZ thin film as a blocking layer. Characterization analysis of the cell showed that the bilayer electrolyte deposited by PLD technique have retained the chemical, mechanical and structural integrity of the cell.Highlights► Fabricate thin film YSZ/SDC bilayer electrolytes SOFCs by pulsed laser deposition. ► The thin YSZ layer blocks electronic current in SDC layer. ► The bilayer cell retains the chemical, mechanical and structural integrity. ► The electrochemical performance and OCVs of the cell have been improved.

A yttria stabilized zirconia (YSZ) layer (∼2 μm) is fabricated by pulsed laser deposition (PLD) technique on an Ce0.8Sm0.2O2−δ (SDC) electrolyte film which is prepared by a co-pressing process on a NiO-SDC anode substrate. La0.8Sr02MnO3−δ-YSZ (LSM-YSZ, 70:30 wt.%) cathode is applied onto the SDC/YSZ bilayer electrolytes to form a single cell. The open circuit voltages of the cell increase significantly compared with that of the SDC single electrolyte cell. Preparation of an SDC buffer layer (∼500 nm) on the bilayer electrolytes by PLD method is also studied for reducing the cathode polarization losses with a Sm0.5Sr0.5CoO3−δ-SDC (SSC-SDC, 70:30 wt.%) cathode and preventing the interfacial chemical reaction between YSZ and SSC. The YSZ thin film blocks electrical current leakage in the SDC layer, whereas the SDC buffer layer with the SSC-SDC cathode decreases the cathode polarization losses, which results in the overall enhanced performance.Highlights► Fabricate thin YSZ layer on SDC half-cell with pulsed laser deposition. ► The thin YSZ layer blocks electronic current in SDC layer. ► Preparation of an SDC layer with a nanoscale thickness as a buffer layer. ► SDC buffer layer with SSC cathode improves the electrochemical performance.

As a promising candidate of a proton conductor under reducing atmosphere, La2Ce2O7 has attracted considerable research interest. However, the thermodynamically stable structure of bulk La2Ce2O7 has remained rather unclear. In this paper, first-principles calculations are carried out to resolve this issue. It is found that the lattice of La2Ce2O7 is substantially stabilized by the formation of anion Frenkel defects, i.e., oxygen atoms displaced from their original sites to interstitial regions. Consequently, the bulk La2Ce2O7 favors disordered fluorite configurations over pyrochlore structure. Our calculation results are consistent with the previously reported neutron diffraction patterns. In addition, partial disordering of cations is also likely under experimental conditions. We then explore the possible proton transfer pathways inside bulk La2Ce2O7. It is revealed that the partial disordering in La2Ce2O7 increases the energy barriers of proton transfer pathways.

A model for symmetric cermets hydrogen permeation membrane is developed, which makes it possible to correlate permeation performance directly to measurable variables, such as experimental conditions and geometric parameters of membrane. The model is successfully applied in Ni–BaCe1−x−yZryYx O3−δ cermets membranes, with the usage of percolation theory to describe the effective properties of the binary composite. The resistances from both interfacial exchange and bulk diffusion, which provide a possible approach to the identification of the rate limiting steps, are discussed. The flux through nickel phase is also considered to decide the conditions under which this flux is remarkable or neglectable. Besides, bulk diffusion coefficient, which is difficult to measure in experiment, can be estimated by simply fitting hydrogen permeation rate using this model. The general trends are in good agreement with experimental results, showing the potential utilization of this model in the analysis of hydrogen separation membrane.Highlights▸ A model of Ni–BZCY composite membrane for hydrogen separation is generated. ▸ Rate limiting step between surface exchange and bulk diffusion is determined. ▸ Hydrogen flux originating from nickel phase is considered in composite membrane. ▸ Bulk diffusion coefficient of doped proton conductor can be simply estimated. ▸ The model exhibits good agreement with the experiment.

Cobalt-free Sm0.6Sr0.4FeO3−δ–Ce0.8Sm0.2O2−δ (SSF–SDC) composite powders are prepared by a newly one-step synthesis method, co-synthesis method. Powders XRD analysis shows that the composite powders exhibit the consistent phase structure with powders derived from traditional method, which demonstrate that the SSF is compatible with SDC. Dry-mixing method, a traditional composite cathode preparation method, is used to obtain SSF–SDC composite cathode as a comparison. The two cathodic composites of microstructures, electrical conductivities and symmetric electrochemical cells are characterized under the same condition. As a result, powders from new method show superior microstructure, high electrical conductivity and good electrochemical properties. Finally, cathode preparing from new method is evaluated by an anode-supported SDC-electrolyte single cell testing. To further study SSF–SDC cathode, the thermal expansion coefficient and thermal cycling performance are measured. The all results imply that co-synthesis method is a facile and practical way to improve the cathode properties and SSF–SDC is a promising cathode for intermediate temperature SOFCs.Highlights► SSF–SDC cathode powders were prepared by two different routes. ► SSF–SDC samples derived from new method showed high electrical conductivity and good catalytic activity. ► The ASRs of SSF–SDC is comparable to those of other cobalt-free cathode. ► The SSF–SDC cathode owns good thermal cycle stability.

A novel solid oxide fuel cell (SOFC) is designed and investigated in this work. Barium-containing anode is employed for Ce0.8Sm0.2O2−δ (SDC)-based SOFC. SEM and EDX results show that barium diffuses from the anode to the electrolyte and a thin BaO–CeO2–Sm2O3 ternary composite interlayer is formed in situ at elevated temperatures. The interlayer is electron-blocking, and eliminates the well-known internal short circuit in the SDC electrolyte membrane completely. Consequently, the open circuit voltages (OCVs) of the cell are improved significantly and achieve as high as 1.04, 1.06, 1.07, and 1.08 V at 700, 650, 600, and 550 °C, respectively, for the cell co-fired at 1350 °C. Notably, the new cell still outputs 221 mW cm−2 at a voltage of 0.9 V at 600 °C, while the traditional ceria-based cell cannot output any performance at all at such a high voltage. The results demonstrate that this novel structured cell exhibits great potential working at low temperatures at high efficiency.Graphical abstractHighlights► A novel ceria-based solid oxide fuel cell (SOFC) was designed employing barium-containing anode. ► A thin electron-blocking layer was formed in situ at the anode/electrolyte interface. ► The electron-blocking layer eliminated the internal short circuit of ceria-based SOFC effectively. ► The new cell can output excellent power performances at low temperatures at high efficiency.

In this work, highly doped ceria with lanthanum, La0.5Ce0.5O2−δ (LDC), are developed as hydrogen separation membrane material. LDC presents a mixed electronic and protonic conductivity in reducing atmosphere and good stability in moist CO2 environment. LDC separation membranes with asymmetrical structure are fabricated by a cost-saving co-pressing method, using NiO + LDC + corn starch mixture as substrate and LDC as top membrane layer. Hydrogen permeation properties are systemically studied, including the influence of operating temperature, hydrogen partial pressure in feed stream and water vapor in both sides of the membrane on hydrogen permeating fluxes. Hydrogen permeability increases as the increasing of temperature and hydrogen partial pressure in feed gas. Using 20% H2/N2 (with 3% of H2O) as feed gas and dry high purity argon as sweep gas, an acceptable flux of 2.6 × 10−8 mol cm−2 s−1 is achieved at 900 °C. The existing of water in both sides of membrane has significant effect on hydrogen permeation and the corresponding reasons are analyzed and discussed.Highlights► La0.5Ce0.5O2−δ is developed as hydrogen separation membrane material. ► A 30 μm-thick asymmetrical membrane was fabricated. ► Hydrogen permeation flux achieved to 2.6 × 10−8 mol cm−2 s−1. ► The influence of H2O on hydrogen permeation was characterized and discussed.

Dense BaZr0.8Y0.2O3 − δ (BZY) thin membranes are successfully fabricated on porous NiO-BaZr0.1Ce0.7Y0.2O3 − δ (NiO-BZCY) anode substrates by a dip-coating process after sintered at 1450 °C. The NiO-BZCY anode substrates are prepared by phase inversion method based on in-situ reaction, showing a special asymmetrical structure with a porous finger-like layer and a sponge-like layer. Single cells with Sm0.5Sr0.5CoO3 − δ–Ce0.8Sm0.2O2 − δ (SSC–SDC) as cathodes are assembled and tested. The open circuit voltages (OCVs) of a cell with a 25-μm-thick BZY membrane are 0.95, 0.97, and 1.01 V at 650, 600, and 550 °C, respectively, indicating that the BZY electrolyte membrane is sufficiently dense. Meanwhile, the corresponding maximum power densities of the cell are 70, 55, and 34 mW cm− 2. The results demonstrated that dip-coating process is an effective method for fabricating dense BZY electrolyte membranes.Highlights► Dense BZY electrolyte membrane has been firstly fabricated by a dip-coating process. ► Phase inversion method based on in-situ reaction was used to prepare NiO-BZCY anode. ► NiO-BZCY anode substrates have a novel asymmetric-structure.

In this paper, we reported on the obtention of a series of europium and titanium co-doped BaZrO3 phosphors, which could emit red-orange long afterglow, synthesized by the solid-state reaction method. The structures, morphology and photoluminescent properties of the all samples were characterized and analyzed by X-ray diffraction (XRD), Schottky field-emission scanning electron microscope (FE-SEM), photoluminescence (PL) and decay curves, respectively. The XRD analyses showed that the reflection of all prepared BaZrO3 powders was well indexed to cubic structure. The room-temperature excitation spectra monitored at 594 nm consist of a broad band with the stronger excitation PL peak, which located at 260 nm, and a series of narrow bands. A series of narrow bands from 4f → 4f emission transitions of the 5D0 excited level to the 7FJ (J = 0–4) levels of the Eu3+ ions were observed in the emission spectra excited at 260 nm. The decay curves of samples well coincided with the sum of two exponential functions. Combining experimental results and theoretical analyzis, we proposed a corresponding novel afterglow mechanism, which reasonably explained the afterglow phenomenon of BaZrO3:Eu, Ti. The BaZrO3:Eu, Ti phosphors had stronger afterglow, better monochromaticity and longer decay time compared with BaZrO3:Eu phosphors. It implied that the Ti co-doping was an effectual and practical way to improve afterglow performance of BaZrO3-based phosphors.Graphical abstractThe emission spectra of BaZrO3:Eu0.025, Tix (x = 0, 0.005, 0.015, 0.025, 0.035, 0.045) phosphors (λ = 260 nm) (I) and the relationship point diagram of Ti doping amounts and emission intensity of 594 nm (II). From this Fig. it can be seen that the luminescence intensity caused by the transition of 5D0 → 7F1 of the Eu3+ becomes stronger with the increase of Ti ions concentration when the Ti doping amount is less and the maximum of luminescence intensity is reached when the Ti doping molar fraction is 1.5%. Compared with BaZrO3:Eu0.025 phosphors, the luminescent intensity of BaZrO3:Eu0.025, Ti0.015 is improved six times or so. When x exceeds 0.015, the luminescent intensity of BaZrO3:Eu0.025, Tix weakens, which is probably due to occurring concentration quench by the cross relaxation of neighboring Ti3+ ions. However, the luminescence of the Eu3+ transition of 5D0 → 7F0 becomes weaker with the increase of Ti concentration, this luminescence intensity is barely detectable when Ti molar fraction is up to about 3.5%. Compared with BaZrO3:Eu phosphors, BaZrO3:Eu, Ti phosphors have stronger afterglow, better monochromaticity.Highlights► We prepared new red-orange long-lasting BaZrO3:Eu, Ti phosphors for the first time. ► This phosphor has stronger afterglow, better monochromaticity and longer decay time. ► A series of novel luminescence phenomena of this phosphor were discovered. ► The corresponding afterglow mechanism of this phosphor was proposed and discussed.

The La1.95Ca0.05Ce2O7−δ (LCCO) material is successfully synthesized using the Pechini method. The synthesized powders are exposed to atmospheric CO2 and H2 with 3% H2O at 700 °C. The treated LCCO powders are investigated using X-ray diffraction (XRD) to study the chemical stability. According to the XRD results, LCCO is very stable and shows no reactions with CO2 or H2O. A fuel cell with the LCCO electrolyte is prepared using the suspension spray method and is tested in the range from 600 °C to 700 °C using humidified hydrogen (∼3% H2O) as the fuel and static air as the oxidant. An open-circuit potential of 0.832 V and a maximum power density of 259 mW cm−2 are obtained for a single cell with an interface resistance of 0.23 Ω cm2 at 700 °C.Highlights► We prepare a novel electrolyte La1.95Ca0.05Ce2O7−δ for proton-conducting SOFCs. ► The electrolyte is very stable in CO2 at 700 °C for 100 h. ► The electrolyte is very stable in boiling water for 100 h. ► We prepare the electrolyte with the in situ reaction method.

A novel ionic conductor, BaCe0.8Sm0.2O3−δ–Ce0.8Sm0.2O2−δ (BCS–SDC, weight ratio 1:1), is reported as an electrolyte material for solid oxide fuel cells (SOFCs). Homogeneous BCS–SDC composite powders are synthesized via a one-step gel combustion method. The BCS and SDC crystalline grains play a role as matrix for each other in the composite electrolyte. The composite avoids the typical drawbacks of BCS and SDC, showing not only a better chemical stability than the single phase of BCS but much higher open circuit voltages (OCVs) than the single phase of SDC under the fuel cell conditions. Moreover, BCS–SDC exhibits mixed oxygen ionic and protonic conduction. A total conductivity of 0.0204 S cm−1 at 700 °C is achieved in wet hydrogen (3% H2O), the value of which is comparable with the state-of-the-art proton conductor BaZr0.1Ce0.7Y0.2O3−δ (BZCY). The peak power density achieves 505 mW cm−2 at 700 °C with a 30-μm-thick BCS–SDC electrolyte using wet H2 as the fuel. Resistances of the tested cell under open circuit conditions at different operating temperatures are also investigated by impedance spectroscopy.

Proton-conducting solid oxide fuel cells, incorporating BaZr0.1Ce0.7Y0.2O3−δ (BZCY) electrolyte, NiO–BZCY anode, and Sm0.5Sr0.5CoO3−δ–Ce0.8Sm0.2O2−δ (SSC–SDC) cathode, were successfully fabricated by a combined co-pressing and printing technique after a one-step co-firing process at 1100, 1150, or 1200 °C. Scanning electron microscope (SEM) results revealed that the co-firing temperature significantly affected not only the density of the electrolyte membrane but the grain size and porosity of the electrodes. Influences of the co-firing temperature on the electrochemical performances of the single cells were also studied in detail. Using wet hydrogen (2% H2O) as the fuel and static air as the oxidant, the cell co-fired at 1150 °C showed the highest maximum power density (PDmax) of 552 and 370 mW cm−2 at 700 and 650 °C, respectively, while the one co-fired at 1100 °C showed the highest PDmax of 276 and 170 mWcm−2 at 600 and 550 °C, respectively. The Arrhenius equation was proposed to analyze the dependence of the PDmax on the operating temperature, and revealed that PDmax of the cell co-fired at a lower temperature was less dependent on operating temperature. The influences of the co-firing temperature on the resistances of the single cells, which were estimated from the electrochemical impedance spectroscopy measured under open circuit conditions, were also investigated.

Ni–Ba(Zr0.1Ce0.7Y0.2)O3−δ (BZCY) metal–ceramic asymmetric membranes consisted of Ni–BZCY top membrane and porous substrate were successfully prepared and developed as hydrogen permeation membrane for the first time via a method to combine co-pressing technique and two-step sintering process. The uniform fine NiO–BZCY composite powders as the precursor of top membranes were co-synthesized through the citrate–nitrate combustion route (co-synthesis method), which was the key to fabricating Ni–BZCY thin membrane. The homogeneity and phase structure of two phases in powders were characterized using element-map technique and X-ray diffraction analysis, respectively. The fluxes through a metal–ceramic membrane of about 30-μm-thickness were measured as a function of temperature under different feed gas hydrogen partial pressures. The results indicated the asymmetric membrane displayed high hydrogen permeation flux and using 80%H2/N2 (with 3% of H2O) as feed gas and dry high purity argon as sweep gas, a maximum flux of 2.4 × 10−7 mol cm−2 s−1 was achieved at 900 °C, exhibiting the predominance of asymmetric structures.

BaZr0.1Ce0.7Y0.2O3−δ (BZCY)-based proton-conducting solid oxide fuel cells (H-SOFC) with a cobalt-free proton-blocking La0.7Sr0.3FeO3−δ–Ce0.8Sm0.2O2-δ (LSF–SDC) composite cathode were fabricated and evaluated. The effect of firing temperature of the cathode layer on the chemical compatibility, microstructure of the cathode and cathode–electrolyte interface, as well as electrochemical performance of single cells was investigated in detail. The results indicated that the cell exhibited the most desirable performance when the cathode was fired at 1000 °C; moreover, at the same firing temperature, the power performance had the least temperature dependence. With humidified hydrogen (∼2% H2O) as the fuel and ambient air as the oxidant, the polarization resistance of the cell with LSF–SDC cathode fired at 1000 °C for 3 h was as low as 0.074 Ω cm2 at 650 °C after optimizing microstructures of the anode and anode-electrolyte interface, and correspondingly the maximum power density achieved as high as 542 mW cm−2, which was the highest power output ever reported for BZCY-based H-SOFC with a cobalt-free cathode at 650 °C.Highlights► Proton-blocking La0.7Sr0.3FeO3−δ–Ce0.8Sm0.2O2−δ (LSF–SDC) was employed as cathode for proton-conducting SOFC. ► The effect of firing temperature of LSF–SDC on cell performances was investigated. ► The cell exhibited the best performance when LSF–SDC was fired at 1000 °C for 3 h ► The cell performance was significantly improved after optimizing the anode microstructure.

The low-frequency mechanical properties of La0.6Sr0.4Co1−xFexO3−δ (0 ≤ x ≤ 0.8) materials have been measured using a computer-controlled pendulum. For undoped sample, five internal friction peaks (P0, P1, P2, P3 and P4) were observed. However, with the Fe doping, only two peaks (P3 and P4) were found at high temperature. The peaks of P0 and P1 have the feature of phase transition-induced internal friction, while the peaks of P2, P3 and P4 are the relaxation-type. From the analysis, it is suggested that the peak of P0 is due to the phase separation and the peak of P1 is related to the ferromagnetic (FM)–paramagnetic (PM) phase transition. For the peaks of P2, P3 and P4, they were associated with the motion of domain walls. The formation of this kind of domain structure is a consequence of a transformation from the paraelastic cubic phase to ferroelastic rhombohedral phase.Research highlights► In this paper, in order to clarify the nature of some phase transitions and origin of inelastic information, we carried out an investigation on the mechanical properties of La0.6Sr0.4Co1−xFexO3−δ (0 ≤ x ≤ 0.8) materials by using low frequency internal friction technique. The results show that the inelastic deformation of La0.6Sr0.4Co1−xFexO3−δ materials can be understood in virtue of the motion of domain walls, and domains were formed during the cubic–rhombohedral phase transition. Below the ferromagnetic ordering temperature TC, La0.6Sr0.4CoO3−δ system presents a phase transition, which is related to magnetization intrinsic phase separation.

Dense Bi1.5Y0.3Sm0.2O3–La0.8Sr0.2MnO3 − δ hollow fiber membrane was fabricated by the combined phase inversion/sintering technique. The hollow fiber possessed an asymmetric structure. The oxygen permeability of the hollow fiber was measured by exposing its shell side to ambient air and sweeping the core side with helium to carry away the permeated oxygen. An oxygen permeation flux 3.9 × 10− 7 mol cm− 2 s− 1 was obtained at 850 °C under a gradient of air/helium. The oxygen permeation flux was related to the helium sweeping rate, the length of the hollow fiber and the oxygen partial pressure on the feed side, and can be further increased by modifying the membrane surfaces.Highlights►Dense Bi1.5Y0.3Sm0.2O3–La0.8Sr0.2MnO3 − δ hollow fiber membrane was fabricated. ►It shows appreciable oxygen permeability at moderate temperatures. ►Oxygen permeation is related to helium sweeping rate and oxygen partial pressure. ►Oxygen permeation flux can be further increased by modifying the surfaces.

Electrical conductivity, internal friction techniques and dilatometer have been used to investigate the oxygen relaxation, phase transition and thermal expansion behavior of GdBaCo2O5 + δ. The main electronic charge carriers in GdBaCo2O5 + δ are electronic holes, which could be assigned to the formation of Co4+. The oxygen exchange kinetics intensely depends on oxygen partial pressure and is also closely related to temperature. Both electrical conductivity and internal friction give rise to an abnormal at about 75 °C, which are related to the insulator-metal transition occurring in GdBaCo2O5 + δ. One large relaxation internal friction peak, due to the motion of oxygen within Gd–O plane, is also found in the oxide. The average thermal expansion coefficient (TEC) of GdBaCo2O5 + δ is about 21.4 × 10−6 K−1 between 500 °C and 900 °C.

A Sm0.5Sr0.5CoO3−δ–Ce0.8Sm0.2O2−δ (SSC–SDC) composite is employed as a cathode for proton-conducting solid oxide fuel cells (H-SOFCs). BaZr0.1Ce0.7Y0.2O3−δ (BZCY) is used as the electrolyte, and the system exhibits a relatively high performance. An extremely low electrode polarization resistance of 0.066 Ω cm2 is achieved at 700 °C. The maximum power densities are: 665, 504, 344, 214, and 118 mW cm−2 at 700, 650, 600, 550, and 500 °C, respectively. Moreover, the SSC–SDC cathode shows an essentially stable performance for 25 h at 600 °C with a constant output voltage of 0.5 V. This excellent performance implies that SSC–SDC, which is a typical cathode material for SOFCs based on oxide ionic conductor, is also a promising alternative cathode for H-SOFCs.

A dense BaZr0.8Y0.2O3−δ (BZY) proton-conducting electrolyte membrane is successfully fabricated on a NiO–BaZr0.1Ce0.7Y0.2O3−δ (NiO–BZCY) anode substrate by a co-pressing process after co-firing at 1400 °C. BZY powders are synthesized via a citric acid–nitrate gel combustion process after calcination at 1100 °C. The SEM results reveal that the BZY membrane is crack-free, very dense, and 20 μm thick. A single cell with Sm0.5Sr0.5CoO3−δ–Ce0.8Sm0.2O2−δ (SSC–SDC) as the cathode is assembled and tested with wet hydrogen (2% H2O) as the fuel and static air as the oxidant. The open circuit voltages (OCVs) are 0.953, 0.987, 1.014, and 1.039 V at 700, 650, 600, and 550 °C, respectively. A maximum power density of 170 mW cm−2 is obtained at 700 °C. Resistances of the testing cell are investigated under open circuit conditions at different operating temperatures by impedance spectroscopy.

BaCe1−xGaxO3−δ (x = 0.1, 0.2) and BaCe0.8Y0.2O3 (BCY) powders are successfully synthesized by a solid-state reaction method. According to thermal gravity analysis in the atmosphere of CO2, BaCe0.9Ga0.1O3−δ (BCG10) and BaCe0.8Ga0.2O3−δ (BCG20) are quite stable while BaCeO3 shows obvious reaction and decomposes into CeO2 and BaCO3. A fuel cell with electrolyte of BaCe0.8Ga0.2O3−δ is prepared by a suspension spray combining with in situ sintering method and tested from 600 to 700 °C with humidified hydrogen (∼3% H2O) as the fuel and the static air as the oxidant. An open-circuit potential of 0.99 V and a maximum power density of 236 mW cm−2 are obtained for the single cell with an interface resistance 0.32 Ω cm2 at 700 °C.

The cermet consisting of electronic conductor Ni and proton conductor La2Ce2O7 (LDC) shows good chemical stability but poor hydrogen permeability. In order to improve the hydrogen permeability, novel Ni–La2−xSmxCe2O7 (x = 0, 0.025, 0.05, 0.075, 0.1 and 0.2) cermets were developed for hydrogen separation. The results show that Sm element doping of LDC can affect the rate of hydrogen permeation, with Ni–La1.95Sm0.05Ce2O7 possessing the highest hydrogen permeation fluxes.

Composite membranes consisting of a proton-conducting ceramic and an electronic conductor are promising in reducing the cost in the separation of hydrogen from CO2. However, the lack of a stable ceramic in CO2 with sufficient proton conductivity remains a great hurdle. In this study, we investigated the hydrogen permeation performance and chemical stability of composite membranes based on doped ceria and Ni. Doped ceria used to be considered as a very poor proton conductor for a long time. However, our results show that ceria heavily doped with rare earth element possesses significant proton conductivity. Compared with membranes based on perovskite-type oxides, hydrogen separation membranes based on fluorite-type ceria show much higher stability in H2O and CO2.

Proton-conducting BaCeO3 membranes with different In-doping levels (from 10 to 30%) were fabricated on NiO-based anode substrates. Indium, which was only used as a trivalent element to create oxygen vacancies in BaCeO3 previously, was found to have the function of stabilizing BaCeO3 in this study. The In-doped BaCeO3 showed improved chemical stability against CO2, while even the traditional BaCeO3 substituting with a small amount of Zr decomposed in the same environment. Furthermore, unlike other strategies for stabilizing BaCeO3, the supported In-doped BaCeO3 membrane became dense after firing at relatively low temperatures. We also investigated the influences of the sintering temperatures and the In-doping levels on the densification and the electrical properties of the supported BaCeO3 membranes, which revealed that the In-doping strategy increased both the chemical stability and sinterability for BaCeO3 with little loss of electrical performance.

A series of cobalt-free and low cost BaCexFe1−xO3−δ (x = 0.15, 0.50, 0.85) materials are successful synthesized and used as the cathode materials for proton-conducting solid oxide fuel cells (SOFCs). The single cell, consisting of a BaZr0.1Ce0.7Y0.2O3−δ (BZCY7)-NiO anode substrate, a BZCY7 anode functional layer, a BZCY7 electrolyte membrane and a BaCexFe1−xO3−δ cathode layer, is assembled and tested from 600 to 700 °C with humidified hydrogen (∼3% H2O) as the fuel and the static air as the oxidant. Within all the cathode materials above, the cathode BaCe0.5Fe0.5O3−δ shows the highest cell performance which could obtain an open-circuit potential of 0.99 V and a maximum power density of 395 mW cm−2 at 700 °C. The results indicate that the Fe-doped barium cerates can be promising cathodes for proton-conducting SOFCs.

In this study, an anode-supported hollow-fiber solid oxide fuel cell (SOFC) of diameter 1.7 mm has been successfully fabricated using the phase inversion and vacuum assisted coating techniques. The cell has a special structure consisting of a 12-μm-thick yttria-stabilized zirconia (YSZ) electrolyte film and a Ni-YSZ anode layer which has large finger-like pores on both sides of the hollow-fiber membrane. The hollow-fiber SOFC has an active electrode area of 0.63 cm2 and generates maximum power densities of 124, 287 and 377 mW cm−2 at 600, 700 and 800 °C, respectively, indicating that its use in applications requiring high power density is promising.

Proton-conducting solid oxide fuel cells (SOFCs), consisting of BaCe0.7In0.3O3−δ (BCI30)-NiO anode substrates, BCI30 anode functional layers, BCI30 electrolyte membranes and BCI30-LaSr3Co1.5Fe1.5O10−δ (LSCF) composite cathode layers, were successfully fabricated at 1150 °C, 1250 °C and 1350 °C respectively by a single step co-firing process. The fuel cells were tested with humidified hydrogen (∼3%H2O) as the fuel and static air as the oxidant. The single cell co-fired at 1250 °C showed the highest cell performance. The impedance studies revealed that the co-firing temperature affected the interfacial polarization resistance of a single cell as well as its overall electrolyte resistance.

Stable BaCe0.5Zr0.3Y0.16Zn0.04O3−δ (BCZYZ) thin membrane was successfully prepared by in situ tape casting/co-firing method for proton-conducting solid oxide fuel cells. The starting powders were BaCO3, CeO2, ZrO2, Y2O3, ZnO for electrolyte and BaCO3, CeO2, ZrO2, Y2O3, ZnO, NiO, graphite for anode. The anode/electrolyte bi-layers were prepared by a simple multi-layer tape casting/co-firing method. The phase characterizations and microstructures were studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The anode–electrolyte bi-layers were sintered at 1450 °C. The electrolytes were extremely dense with pure perovskite phase and the thickness was about 25 μm. The anodes were porous and no obvious reaction was found between NiO and BCZYZ. With LaSr3Co1.5Fe1.5O10−δ (LSCF)/BCZYZ as cathode, the open current voltage and maximum power density respectively, reached 1.00 V and 247 mW cm−2 at 650 °C.

A novel single phase BaCe0.5Bi0.5O3 − δ (BCB) was employed as a cathode material for a proton-conducting solid oxide fuel cell (SOFC). The single cell, consisting of a BaZr0.1Ce0.7Y0.2O3 − δ (BZCY7)-NiO anode substrate, a BZCY7 anode functional layer, a BZCY7 electrolyte membrane and a BCB cathode layer, was assembled and tested from 600 to 700 °C with humidified hydrogen (∼3% H2O) as the fuel and the static air as the oxidant. An open-circuit potential of 0.96 V and a maximum power density of 321 mW cm−2 were obtained for the single cell. A relatively low interfacial polarization resistance of 0.28Ω cm2 at 700 °C indicated that the BCB was a promising cathode material for proton-conducting SOFCs.

A high In-dopant level BaCeO3 material was used as an electrolyte for a proton-conducting solid oxide fuel cell (SOFC). Indium behaved as an ideal dopant for BaCeO3, which improved both the chemical stability and sinterability for BaCeO3 greatly. The anode supported BaCe0.7In0.3O3−δ (BCI30) membrane reached dense after sintering at 1100 °C, much lower than the sintering temperature for other BaCeO3-based materials. Additionally, the BCI30 membrane showed adequate chemical stability against CO2 compared with the traditional rare earth doped BaCeO3. The BCI30-based fuel cell also showed a reasonable cell performance and a good long-term stability under the operating condition. Besides, the LaSr3Co1.5Fe1.5O10−δ (LSCF) was also evaluated as a potential cathode candidate for a proton-conducting SOFC.

La0.3Sr0.7FeO3-δ (LSF)/CeO2 cathode supported Ce0.8Sm0.2O2-δ (SDC) electrolyte was prepared by a simple multilayer tape casting and co-firing method. SDC electrolyte slurry and LSF/CeO2 cathode slurry were optimized and the green bi-layer tapes were co-fired at different temperature. Phase characterizations and microstructures of electrolyte and cathode were studied by X-ray diffraction (XRD) and Scan Electronic Microscopy (SEM). No additional phase peak line was observed in electrolyte and cathode support when the sintering temperature lower was than 1400 °C. The electrolytes were extremely dense with the thickness of about 20 μm. The cathode support was porous with electrical conductivity of about 4.21 S/cm at 750 °C. With Ni/SDC as anode, Open Current Voltage and maximum power density reached 0.61 V and 233 mW cm−2 at 750 °C, respectively.

Composite membranes based on Ni and Zr-doped BaCeO3 are promising for hydrogen separation. Such composites show high proton conductivity and adequate chemical stability in H2O and CO2, but may be unstable in H2S. In this work, the hydrogen permeation performance of Ni–BaZr0.1Ce0.7Y0.2O3−δ was measured in an H2S-containing atmosphere at 900 °C. The hydrogen permeation flux began to degrade in 60 ppm H2S and decreased by about 45% in 300 ppm H2S. After hydrogen permeation tests, X-ray diffraction analysis revealed the formation of BaS, doped CeO2, Ni3S2 and Ce2O2S. Analysis of the microstructure and phase composition, and results of thermodynamic calculations suggest that reaction between H2S and doped BaCeO3 caused the performance loss of the Ni–BaZr0.1Ce0.7Y0.2O3−δ.

A mixed conducting YBa2Cu3O7−δ (YBC)-based composite was developed via addition of excess BaO and iso-molar ZrO2 to form BaZrO3 (BZ) dispersed particles in situ. XRD shows that as-synthesized composites are composed of binary phases of YBC and BZ. It is found that the dispersed BZ particles can effectively suppress the grain growth of basic phase YBC especially in the longitudinal c-axis direction, leading to change in grains from bar-like to cubic-like. Compared with the pure phase YBC, the composite with 10 mol% of BZ exhibits higher relative density and oxygen permeability and much improved mechanical strength. The electrical conductivity measurement shows that the electrical transporting properties of the composites are also affected due to the change in microstructure and densification.

A perovskite-type BaCe0.5Fe0.3Bi0.2O3-δ (BCFB) was employed as a novel cathode material for proton-conducting solid oxide fuel cells (SOFCs). The single cells with the structure of NiO-BaZr0.1Ce0.7Y0.2O3-δ (BZCY7) anode substrate|NiO-BZCY7 anode functional layer|BZCY7 electrolyte membrane|BCFB cathode layer were fabricated by a dry-pressing method and investigated from 550 to 700 °C with humidified hydrogen (~3% H2O) as the fuel and the static air as the oxidant. The low interfacial polarization resistance of 0.098 Ω cm2 and the maximum power density of 736 mW cm−2 are achieved at 700 °C. The excellent electrochemical performance indicates that BCFB may be a promising cathode material for proton-conducting SOFCs.

This report describes the facile solvothermal synthesis of highly monodispersed nickel microspheres with surfaces uniformly covered by nickel dots. Synthesis parameters including reaction times and reagent concentrations significantly influence the microspheric particle characteristics. The novelty of the synthetic method in this work is twofold: first, the controlled synthesis of Ni metallic microspheres using ethylene glycol as the precursor of a reductant and urea as the origin of OH− has never been reported. Second, there are few studies on the construction of Ni microspheres covered by uniform Ni dots using a one-step solvothermal method. Importantly, the as-prepared Ni microspheres show an improved ability to remove Cd2+ ions even at high concentrations in water and a unique adsorption isotherm having an increasing adsorption capacity for Cd2+ ions. The presence of Ni dots was considered to play an important role in the onset of the adsorption process. We believe that this work opens up new and possibly exciting opportunities in the field of adsorption of heavy metal ions.

One-, two- and three-dimensional nanostructures of copper molybdenum oxide hydroxide were successfully constructed by a simple approach through a pH-dependent dimensional transformation of ammonium copper molybdate. Thin nanoplates of copper molybdate, which were obtained by sintering the two-dimensional nanobelts of copper molybdenum oxide hydroxide, exhibited remarkably high reversible lithium storage capacity, good rate capability and excellent cycling stability.

Two types of proton-blocking composites, La2NiO4+δ–LaNi0.6Fe0.4O3−δ (LNO–LNF) and Sm0.2Ce0.8O2−δ–LaNi0.6Fe0.4O3−δ (SDC–LNF), were evaluated as cathode materials for proton-conducting solid oxide fuel cells (H-SOFCs) based on the BaZr0.1Ce0.7Y0.2O3−δ (BZCY) electrolyte, in order to compare and investigate the influence of two different oxygen transfer mechanism on the performance of the cathode for H-SOFCs. The X-ray diffraction (XRD) results showed that the chemical compatibility of the components in both compounds was excellent up to 1000 °C. Electrochemical studies revealed that LNO–LNF showed lower area specific polarization resistances in symmetrical cells and better electrochemical performance in single cell tests. The single cell with LNO–LNF cathode generated remarkable higher maximum power densities (MPDs) and lower interfacial polarization resistances (Rp) than that with SDC–LNF cathode. Correspondingly, the MPDs of the single cell with the LNO–LNF cathode were 490, 364, 266, 180 mW cm−2 and the Rp were 0.103, 0.279, 0.587, 1.367 Ω cm2 at 700, 650, 600 and 550 °C, respectively. Moreover, after the single cell with LNO–LNF cathode optimized with an anode functional layer (AFL) between the anode and electrolyte, the power outputs reached 708 mW cm−2 at 700 °C. These results demonstrate that the LNO–LNF composite cathode with the interstitial oxygen transfer mechanism is a more preferable alternative for H-SOFCs than SDC–LNF composite cathode with the oxygen vacancy transfer mechanism.

A Sm0.075Nd0.075Ce0.85O2−δ–Er0.4Bi1.6O3 bilayer structured film, which showed an encouraging performance in LT-SOFCs, was successfully fabricated by a simple low cost technique combining one-step co-pressing with drop-coating.

Partial internal short circuit resulting from the Ce4+/Ce3+ redox reaction is currently one of the most critical issues that hinder the practical application of solid oxide fuel cells (SOFCs) with doped ceria electrolytes. In this work, a new strategy utilizing a Sr diffusion induced in situ solid-state reaction to generate a blocking layer to prevent Ce0.8Sm0.2O1.9 (SDC) from reduction is proposed for the first time. As a proof of concept, Ni-SrCe0.95Yb0.05O3−δ is deployed as a Sr source for the electron-blocking interlayer and was evaluated as an anode for SDC-based SOFCs. A thin interlayer composed of SrCe1−x(Sm,Yb)xO3−δ and SDC is formed in situ during the sintering process of the half cell due to the interdiffusion of metal cations, and the interlayer thickness is highly dependent on the sintering temperature. The high-resolution TEM results indicate that the SrCe1−x(Sm,Yb)xO3−δ perovskite phase is generated and coated on the SDC grains, forming an SDC@SrCe1−x(Sm,Yb)xO3−δ core–shell structure. The SrCe1−x(Sm,Yb)xO3−δ phase effectively suppresses the Ce4+/Ce3+ redox reaction and hence eliminates electronic conduction through the electrolyte membrane. Consequently, the OCVs of the fuel cell are significantly improved after incorporating the electron-blocking interlayer and increase with increasing the interlayer thickness. The OCVs of the cell sintered at 1250 °C reach 0.962, 0.989, 1.017, and 1.039 V at 650, 600, 550, and 500 °C, respectively. The present results demonstrate that Ni-SrCeO3-based composites are promising alternative anodes for CeO2-based SOFCs towards enhanced working efficiency at high operating voltages.