LiNi1–xFexO2 (0 ≤ x ≤ 0.3) and LiyNi0.8Fe0.2O2 (0.8 ≤ y ≤ 1.2) catalysts for the oxygen evolution reaction (OER) were systematically investigated to discover the influence of the composition and layered structure on electrochemical activity. LiNi0.8Fe0.2O2 exhibits OER activity that is better than that of LiNiO2 and other Fe-substituted LiNiO2 catalysts, while Li1.2Ni0.8Fe0.2O2 shows OER activity that is much higher than that of LiNi0.8Fe0.2O2 and Li0.8Ni0.8Fe0.2O2. The best OER activity is achieved on Li1.2Ni0.8Fe0.2O2 with a Tafel slope of 59 mV dec–1 and a current density of 10 mA cm–2 at an overpotential of 302 mV, better than that for the benchmark IrO2 catalyst. Combined with the density functional theory calculations, the enhanced OER activity is mainly attributed to the unique electronic structure derived from the interaction of Li, Ni, and Fe in the materials and the layered structure which plays an important role in stabilizing the high valence states of Ni and Fe during the OER.

The effort on electrochemical reduction of CO2 to useful chemicals using the renewable energy to drive the process is growing fast recently. In this review, we introduce the recent progresses on the electrochemical reduction of CO2 in solid oxide electrolysis cells (SOECs). At high temperature, only CO is produced with high current densities and Faradic efficiency while the reactor is complicated and a better sealing technique is urgently needed. The typical electrolytes such as zirconia-based oxides, ceria-based oxides and lanthanum gallates-based oxides, anodes and cathodes are introduced in this review, and the cathode materials, such as conventional metal–ceramics (cermets), mixed ionic and electronic conductors (MIECs) are discussed in detail. In the future, to gain more value-added products, the electrolyte, cathode and anode materials should be developed to allow SOECs to be operated at temperature range of 573–873 K. At those temperatures, SOECs may combine the advantages of the low temperature system and the high temperature system to produce various products with high current densities.The typical electrolytes, anodes and cathodes used in solid oxide electrolysis cells for the electrochemical reduction at high temperature are discussed in this review. Download high-res image (149KB)Download full-size image

To investigate the role of Fe ions for oxygen evolution reaction, a series of BaZrxFe1-xO3-δ (0 ≤ x ≤ 0.2) perovskite oxides were synthesized and systematically evaluated as electrocatalysts. The OER activity of cubic BaZrxFe1-xO3-δ (0.05 ≤ x ≤ 0.2) is higher than that of the parent BaFeO3-δ with a monoclinic structure and close to that of Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF), indicating cubic perovskite structure is favorable to the OER, and Fe ions are active for the reaction. Moreover, for cubic BaZr0.15Fe0.85O3-δ samples, the OER performance is closely related to the ratio of Fe4+ to Fe3+, which was tuned by treating BaZr0.15Fe0.85O3-δ powders at 500 °C for 5 h at different atmospheres, such as O2, air, Ar and 5% H2/Ar mixture.Cubic BaZr0.15Fe0.85O3-δ exhibits higher OER activity than monoclinic BaFeO3-δ, indicating cubic perovskite structure is favorable and Fe element is active for the reaction.Download high-res image (161KB)Download full-size image

VMgO catalysts with different molybdenum doping amounts were prepared by an impregnation method. The structure, specific surface area, and basic and redox properties of these catalysts were determined by XRD, BET, CO2-TPD, and H2-TPR. The XRD results revealed that all catalysts contained an orthovanadate phase (Mg3(VO4)2), while no metavanadate and pyrovanadate phases were detected. BET surface area analysis showed that the Mo-doped catalysts possessed lower surface areas than the undoped one. The reducing and basicity properties of the catalysts were characterized by H2-TPR and CO2-TPD measurements, which demonstrated that Mo-doping improved the redox temperature and reduced the number of basic sites. The performances of these catalysts were investigated at different C4H10/O2 molar ratios, temperatures, and contact times. The Mo-doping not only improved the selectivity of butenes but also inhibited the deep oxidation reactions, although cracking reactions occurred with high levels of Mo doping. When the Mo/V atomic ratio was 3 : 100, n-butane conversion of 34.5% and total butene selectivity of 79.3% were achieved at 630 °C. To the best of our knowledge, the oxidative dehydrogenation performance of the synthesized Mo-doped VMgO catalysts described in this work represents a remarkable improvement compared to previous reports.

Perovskite oxides have emerged as promising electrocatalysts for the sluggish oxygen evolution reaction (OER) which limits the efficiencies of rechargeable energy storage technologies and hydrogen production from water splitting. Understanding materials characteristics that affect OER activity is of paramount importance for the optimization of perovskite oxides for the OER. Herein, a series of Sr2Fe1.3Ni0.2Mo0.5O6−δ (SFNMs) decorated with oxygen vacancies and Fe–Ni alloy nanoparticles were designed to increase both the number and the reactivity of active sites in the perovskite catalysts. Theoretical calculations reveal that oxygen vacancies have a beneficial effect on the OER by increasing the adsorption energy of H2O, in line with the experimental results that the SFNM sample enriched with oxygen vacancies possesses a high intrinsic OER activity. SFNM decorated with metallic nanoparticles, which was prepared by reducing SFNM in 5% H2/Ar, shows a Tafel slope of 59 mV dec−1 and an OER overpotential of 0.36 V at a current density of 10 mA cm−2. This performance is superior to that of Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF) and close to that of commercial IrO2. The outstanding performance is attributed to the fact that the oxygen vacancies together with the exsolved alloy nanoparticles on the perovskite backbone can increase both the number and the reactivity of active sites.

A new method for hydrogen separation to acquire high-purity hydrogen using an oxygen-permeable ceramic membrane is proposed and verified in this work. A high hydrogen separation rate of up to 16.3 mL cm−2 min−1 was achieved on an asymmetric dual-phase membrane at 900 °C. No performance degradation was observed in a long-term operation with the feed gas containing 200 ppm H2S.

The development of highly efficient and affordable electrocatalysts for the sluggish oxygen evolution reaction (OER) has been considered as a great challenge to the practical applications for water splitting and in rechargeable metal–air batteries. Herein, we report active and robust OER catalysts of Fe3+-doped β-Ni(OH)2 prepared via an atomic-scale topochemical transformation route. Based on the premise that all Fe3+ is incorporated into the β-Ni(OH)2 lattice, the OER activity increases directly with the content of Fe3+. The Fe(0.5)-doped β-Ni(OH)2 catalyst affords a current density of 10 mA cm−2 at an overpotential as low as 0.26 V and a small Tafel slope of 32 mv dec−1. Comparing the state-of-the-art IrO2 catalyst, the Fe(0.5)-doped β-Ni(OH)2 catalyst exhibits higher activity and stability from galvanostatic tests at 10 mA cm−2. Additionally, we experimentally demonstrate that Fe(0.5)-doped β-Ni(OH)2 exerts higher OER activity than Fe(0.5)-doped α-Ni(OH)2. All evidence indicates that Fe and the β-Ni(OH)2 matrix play an important role in NiFe-based catalysts.

Metal pyrophosphates have attracted considerable interests due to their high proton conductivity and potentially wide applications in the temperature range of 100–400 °C. However, great difference in conductivity was reported by different groups on the same pyrophosphates. The reason for the huge difference is still in debate up to now, and there is no coherent standpoint in literatures on the proton conduction mechanism. In this study, we chose Fe0.4Nb0.5P2O7, which was reported showing high proton conductivity recently, as an example to disclose the reason inducing the divergence in proton conductivity and conduction mechanism. We found that the as-prepared pyrophosphate grains have three layers, i.e. crystalline pyrophosphate core, amorphous phosphate shell in the middle and gel-type shell composed of amorphous phosphorus species as the outermost layer. The content of amorphous phosphorus species decreases with the increase of the calcination temperature of pyrophosphates, and the calcination temperature-dependent residual soluble phosphorus curve extremely coincides with the conductivity curve. Thus, the proton conduction of pyrophosphates is realized via a gel-type shell formed by residual amorphous phosphorus species on surfaces of pyrophosphate grains. We suggested that the phosphorus content is the key factor to explain the great difference in conductivity of pyrophosphates prepared by different groups.

The high-energy nature of grain boundaries makes them a common source of undesirable phase transformations in polycrystalline materials. In both metals and ceramics, such grain-boundary-induced phase transformation can be a frequent cause of performance degradation. Here, we identify a new stabilization mechanism that involves inhibiting phase transformations of perovskite materials by deliberately introducing nanoparticles at the grain boundaries. The nanoparticles act as “roadblocks” that limit the diffusion of metal ions along the grain boundaries and inhibit heterogeneous nucleation and new phase formation. Ba0.5Sr0.5Co0.8Fe0.2O3−δ, a high-performance oxygen permeation and fuel cell cathode material whose commercial application has so far been impeded by phase instability, is used as an example to illustrate the inhibition action of nanoparticles toward the phase transformation. We obtain stable oxygen permeation flux at 600 °C with an unprecedented 10–1000 times increase in performance compared to previous investigations. This grain boundary stabilization method could potentially be extended to other systems that suffer from performance degradation due to a grain-boundary-initiated heterogeneous nucleation phase transformations.

•Principle of hydrogen production from water splitting in MIEC membrane reactors.•Factors affecting hydrogen production rate and membrane stability.•Coupling water splitting reaction and catalytic oxidation reactions in membrane reactors.Hydrogen as a clean energy carrier for power generation through fuel cells has attracted much attention. Water is a suitable source for hydrogen production by the splitting reaction. Significant amount of hydrogen can be produced at moderate temperature if a mixed ionic-electronic conducting (MIEC) membrane is used to remove the produced oxygen from water splitting reaction, although the equilibrium constant for water splitting is small. In this review, the principle of hydrogen production via water splitting in MIEC membrane reactor is illustrated, and the factors affecting the hydrogen production rate (such as membrane materials, thickness, modification of membrane surface) and the stabilities of membranes under high oxygen chemical potential gradient are discussed. Furthermore, following the concept of process intensification, the researches on water splitting coupling with other catalytic reactions in membrane reactors are summarized.

A transition layer between Ce0.8Sm0.2O2−δ (SDC) electrolyte and Sr0.8Co0.8Fe0.2O3−δ (SCF0.8) nano cathode was introduced to improve electrochemical performances of solid oxide fuel cells (SOFCs). A calcining – stripping method was used to introduce the transition layer on the SDC electrolyte. Then a nano porous cathode was coated on the transition layer. The microstructure of the nano cathode was optimized by adjusting its calcining temperature. It was found that the transition layer played a vital role in improving the electrochemical performances of the nanostructured cathode by enhancing the interface connection between cathode and electrolyte. Good electrochemical performance was obtained as the nano cathode calcined at 700 °C after introducing the transition layer. The polarization resistance of the anode-supported SOFC at 700 °C was significantly reduced from 0.20 Ω cm2 to 0.05 Ω cm2, while the power density of the single cell was increased from 116 to 444 mW cm−2.

•Asymmetric dual-phase membranes were prepared via tape-casting and co-lamination.•The thickness of the dense layer is ~40 μm.•Oxygen permeation flux reaches to 3.9 mL cm−2 min−1.•Catalyst layers for oxygen activation are important for the membranes.Asymmetric dual-phase membranes with a composition of 75 wt% Ce0.85Sm0.15O2−δ–25 wt% Sm0.6Sr0.4Al0.3Fe0.7O3−δ (SDC–SSAF) were prepared by tape-casting and co-lamination technique. The membrane has a thin dense layer of ~40 μm and a porous support of ~460 μm. It demonstrated an oxygen permeation flux as high as 3.9 mL cm−2 min−1 at 950 °C. This high value is commercially attractive for pure oxygen production via asymmetric dual-phase membranes.

•A novel precipitation-aging method to produce single-crystal Mn3−xCoxO4 octahedra.•The products respectively show {111} and {011} facets of cubic and tetragonal phases.•Well-defined octahedra controlled by rates of spinel nucleation and octahedra growth.•Single crystal x = 1.0&0.5 octahedra respectively show high 4e− and 2e− ORR selectivity.•High ORR activity and selectivity depend on octahedral shape, facet and Mn4+/B ratio.Single-crystal (Mn,Co)3O4 octahedra were synthesized through a novel precipitation-aging method. Well-defined single-crystal octahedra can be formed by carefully controlling the precipitation-dissolution equilibrium, oxygen concentration, and solution temperature during synthesis to match the rates of spinel nucleation and octahedra growth. The single-crystal (Mn,Co)3O4 octahedra expose {111} and {011} facets of cubic and tetragonal phases, respectively, depending on the Mn/Co ratio. However, only single-crystal octahedra of Mn2CoO4 and Mn2.5Co0.5O4 with exposed {011} facets show the highest selectivity towards 4e− and 2e− oxygen reduction reactions (ORR) in alkaline solution, respectively. Furthermore, the single-crystal Mn2CoO4 octahedra with exposed {011} facets shows ∼30 times higher area specific activity for ORR than that of nanoparticles with random/mixed facets. The high electrocatalytic activity and selectivity towards ORR are correlated with the octahedral shape, the exposed facet, and the ratio of cations on the exposed facets (especially the octahedrally coordinated Mn4+ cations). This facet dependent catalytic performance provides a new route for obtaining highly selective and active ORR electrocatalysts.Single crystal (Mn,Co)3O4 octahedra synthesized by a novel precipitation-aging method show high electrocatalytic activity and facet-tuned selectivity towards either the 4e− or 2e− process of oxygen reduction reaction.

•Three dual-phase membranes were synthesized by the one-pot methods.•Oxygen permeation fluxes of the dual-phase membranes increase with the content of calcium in the perovskite phase.•The Ca-contained dual-phase membranes are CO2 tolerant in the investigated temperature range.The integration of mixed ionic and electronic conducting (MIEC) membranes into the oxyfuel process can significantly reduce the energy penalty introduced by the CO2 capture. For this integration, a CO2 tolerant oxygen permeable membrane is required. Here, dual-phase membranes were prepared via a one-pot method containing a samarium doped CeO2 as the oxygen ionic conducting phase for ionic transport and a calcium doped perovskite SmCoO3 as the mixed conducting phase for both ionic and electronic transport. Both phases of the prepared membranes are spontaneously formed from the mixed precursors via a one-pot method, which indicates that both phases are chemical compatible with each other. The effects of Ca doping amount in the perovskite oxide on total conductivity, oxygen permeation flux, permeation stability as well as structural stability under CO2 atmosphere were investigated. All the experimental results indicate that the Ca-contained dual-phase membranes have high stability and permeation flux under the sweep of CO2.

The spinel-type oxides of (Mn, Co, Cu)3O4 prepared via a citric–EDTA acid process were investigated as candidate cathodes of intermediate temperature solid oxide fuel cells (IT-SOFCs). (Mn, Co)3O4 spinel oxide shows a phase transition from tetragonal to cubic when the doping amount of cobalt element increases. Their electric conductivities increase with the cobalt content and are enough high for them used as cathodes of IT-SOFCs. A fuel cell with (Mn, Co)3O4 spinel cathode was successfully evaluated based on YSZ electrolyte. (Mn, Co)3O4 spinel cathodes show good electrochemical activities, demonstrating the feasibility of the spinel oxide being a cathode of IT-SOFC. As copper doped into (Mn, Co)3O4 spinel, the Ppeak for Cu0.5MnCo1.5O4 cathode rise to 343, 474 and 506 mW cm−2 at 700, 750 and 800 °C, respectively. The results reveal that the spinel-type oxides are promising cathodes for IT-SOFCs, especially for Cu0.5MnCo1.5O4.Highlights► Spinel-type oxides are feasible to be candidate cathodes for IT-SOFC. ► The fuel cell with (Mn, Co)3O4 spinel cathode shows good electrochemical performance. ► As Cu doped into (Mn, Co)3O4, an enhanced performance is obtained for Cu0.5MnCo1.5O4.

•Three one-pot methods were comparatively investigated for the powders synthesis.•Membranes derived from solid state reaction method show the highest permeation flux.•Microstructure influences the formation of continuous electronic conduction network.•The membrane shows CO2-stable and high flux swept by CO2.As alternatives of single-phase mixed conducting materials, dual-phase materials have been suggested as candidates for application as oxygen separation membranes, since it is difficult to meet all the requirements in a single-phase membrane material. The influence of synthetic methods on the performance of the 75 wt.%Ce0.85Sm0.15O1.925–25 wt.%Sm0.6Sr0.4Al0.3Fe0.7O3 (SDC–SSAF) dual-phase membranes has been investigated. Three one-pot methods, i.e. the solid state reaction (SSR), EDTA-citrate complex (EC) and co-precipitation (CP) methods, were used to prepare the SDC–SSAF powder. The structure, surface morphologies, electrical conductivity, oxygen permeation, and stability in a CO2 atmosphere were investigated. It was found that the membrane derived from the SSR method shows the highest oxygen permeation flux and total conductivity. The significant differences between the performances of the dual-phase membrane derived from the different methods relates to the different microstructures developed during membrane preparation, which further influences the formation of a continuous electronic conduction network across the membranes. The stability of the dual-phase membrane was studied by treating the membrane materials under a CO2 atmosphere and by sweeping the membrane with pure CO2. The results show that the membrane is CO2-stable and is potentially integrated with the oxyfuel process for CO2 capture.

Ceria-based dual-phase membranes showing high oxygen permeation fluxes and stability under a CO2 environment are promising materials for CO2 capture via an oxyfuel route. The high oxygen permeation fluxes compared with other dual-phase membranes are derived from the mixed conducting properties of the perovskite oxides used in the dual-phase membranes.

The design of oxide ceramic dual-phase membranes is discussed in detail from the point of view of solid state chemistry. Dual-phase membranes with high performance have been designed by considering the permeability, stability and compatibility of the dual-phase system. It is deduced that dual-phase membranes made of Fe-based perovskite oxides (such as Sm0.6Sr0.4FeO3, mixed conductors) and Ce-based fluorite oxides (such as Ce0.85Sm0.15O1.925, ionic conductors) have both good permeability and stability. A dual-phase membrane made of an ionic conductor and pure electronic conductor was studied for comparison purposes, with a nominal composition of 75 wt.%Ce0.85Sm0.15O1.925–25 wt.%Sm0.6Sr0.4CrO3. Experimental investigation of selected membranes is reported with attention to processing, microstructures, conductivity and oxygen permeation properties. Microstructure effects of dual-phase membranes on oxygen exchange reactions and bulk oxide ionic transport were investigated by AC impedance spectroscopy, high resolution transmission electron microscopy and oxygen permeation. Oxygen permeation experiments revealed when the Fe-based mixed conducting perovskite is used in dual-phase membranes, higher oxygen permeation fluxes were achieved than that of the Cr-based pure electronic conducting perovskite was used in the dual-phase membrane. The phenomenon can be well explained by the mutual blocking of electronic and ionic transport by pure electronic conductors and ionic conductors, and the enrichments of Cr-based impurities between the ionic conducting grains. Membranes with various weight ratios of the two phases were synthesized to find the optimal composition. 75 wt.%Ce0.85Sm0.15O1.925–25 wt.%Sm0.6Sr0.4FeO3 was found to be the best membrane from the point of view of both oxygen permeability and stability. The idea of designing dual-phase membranes was verified by the comparison.Graphical abstractHighlights► Composition and microstructure of membrane were optimized. ► Impurities and pure electronic conductor block ionic transport. ► Clear grain boundaries and the mixed conductor help the ionic transport.

SrCo0.8Fe0.2O3-δ is a controversial material whether it is used as an oxygen permeable membrane or as a cathode of solid oxide fuel cells. In this paper, carefully synthesized powders of perovskite-type SrxCo0.8Fe0.2O3-δ (x = 0.80–1.20) oxides are utilized to investigate the effect of A-site nonstoichiometry on their electrochemical performance. The electrical conductivity, sintering property and stability in ambient air of SrxCo0.8Fe0.2O3-δ are critically dependent on the A-site nonstoichiometry. Sr1.00Co0.8Fe0.2O3-δ has a single-phase cubic perovskite structure, but a cobalt-iron oxide impurity appears in A-site cation deficient samples and Sr3(Co, Fe)2O7-δ appears when there is an A-site cation excess. It was found that the presence of the cobalt-iron oxide improves the electrochemical performance. However, Sr3(Co, Fe)2O7-δ has a significant negative influence on the electrochemical activity for intermediate-temperature solid oxide fuel cells (IT-SOFCs). The peak power densities with a single-layer Sr1.00Co0.8Fe0.2O3-δ cathode are 275, 475, 749 and 962 mW cm−2 at 550, 600, 650 and 700 °C, respectively, values which are slightly lower than those for Sr0.95Co0.8Fe0.2O3-δ (e.g. 1025 mW cm−2 at 700 °C) but much higher than those for Sr1.05Co0.8Fe0.2O3-δ (e.g. only 371 mW cm−2 at 700 °C). This remarkable dependence of electrochemical performance of the SrxCo0.8Fe0.2O3-δ cathode on the A-site nonstoichiometry reveals that lower values of electrochemical activity reported in the literature may be induced by an A-site cation excess. Therefore, to obtain a high performance of SrxCo0.8Fe0.2O3-δ cathode for IT-SOFCs, an A-site cation excess must be avoided.

Mn1.5Co1.5O4 spinel oxide as a cathode or one component of a composite cathode presents no visible reaction with an Y2O3-stabilized ZrO2 electrolyte. The low electrode polarization resistances and good performance compared with traditional Sr-doped LaMnO3–YSZ composite cathodes imply promising application for the next generation of intermediate-temperature solid oxide fuel cells.

The effects of sintering temperature on the properties of Ce0.85Sm0.15O3−δ–Sm0.6Sr0.4FeO3−δ (SDC–SSF) dual-phase membranes were investigated. X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive X-ray analysis (EDX), alternating current impedance and oxygen permeation techniques were employed to study the phase structure, element transport, microstructure, grain size and oxygen permeation through dual-phase membranes sintered at different temperatures. Sintering temperature has complex effects on dual-phase membranes compared with single-phase perovskite membranes. XRD and EDX analysis results reveal that the surfaces of dual-phase membranes were mainly coated by fluorite oxide with a thickness of about 45 μm when the membrane was sintered at 1500 °C. Fluorite grains were gradually transferred from the inner layer to the outer layer with the increase of sintering temperature, which leads to a decrease in electronic conductivity of the membrane surface. The grain size increased with the rising of sintering temperature, which has negatively effect on oxygen permeation when the sintering temperature is higher than 1425 °C.Graphical abstractResearch highlights▶ Over high sintering temperature leads to enrichment of fluorite phase on surface. ▶ Enrichment of fluorite phase increases the surface resistances. ▶ Growth of grains decreases the homogeneous of the two phases and permeation fluxes. ▶ The optimal sintering temperature for Ce0.85Sm0.15O3−δ–Sm0.6Sr0.4FeO3−δ is 1425 °C.

Unsteady-state permeation in the initial stage was investigated on ceria-based dual-phase membranes by coating La0.6Sr0.4CoO3–δ (LSC) active porous layers onto the surface of membranes. It is found that the unsteady period is greatly influenced by the active porous layer. The membrane with LSC porous layers coated on both sides reaches a steady state immediately while starting the permeation testing. However, the membranes without LSC porous layers coated on one side or both sides need several to tens of hours to achieve the steady state. The active porous layer can improve the oxygen flux and decrease the permeation activation energy, and the membrane with coating on both sides had the highest flux and lowest Ea. In addition, the active porous layer can eliminate oxygen exchange limitations on the membrane surface. The changes of surface microstructures are suggested as the cause of unsteady-state permeation.Research highlights► Unsteady-state permeation in the initial stage of dual-phase membranes were investigated. ► The unsteady period can be shortened or eliminated by coating the active porous layers on membrane surfaces. ► The active porous layer can improve the oxygen flux and decrease the permeation activation energy. ► The changes of surface microstructures are related to the unsteady-state permeation.

The phase transitions that take place in Sr1 + xCo0.8Fe0.2O3 − δ (− 0.2 ≤ x ≤ 0.1) oxides are reported here. Thermogravimetric analysis (TGA) showed that the oxides with − 0.2 ≤ x ≤ 0 were prone to undergo oxygen-vacancy disorder–order phase transitions, while others with x = 0.05, 0.1 had more stable crystal structures during oxygen-desorption processes in nitrogen. These results were further confirmed by high-temperature in-situ X-ray techniques. The changes in activation energies of three typical oxides, Sr1 + xCo0.8Fe0.2O3 − δ (x = − 0.2, 0, 0.1), used as oxygen-permeable membranes were investigated. The phase transitions in Sr1 + xCo0.8Fe0.2O3 − δ (x = − 0.2, 0) have also been detected in differential scanning calorimetry (DSC) profiles.

The development of highly efficient and affordable electrocatalysts for the sluggish oxygen evolution reaction (OER) has been considered as a great challenge to the practical applications for water splitting and in rechargeable metal–air batteries. Herein, we report active and robust OER catalysts of Fe3+-doped β-Ni(OH)2 prepared via an atomic-scale topochemical transformation route. Based on the premise that all Fe3+ is incorporated into the β-Ni(OH)2 lattice, the OER activity increases directly with the content of Fe3+. The Fe(0.5)-doped β-Ni(OH)2 catalyst affords a current density of 10 mA cm−2 at an overpotential as low as 0.26 V and a small Tafel slope of 32 mv dec−1. Comparing the state-of-the-art IrO2 catalyst, the Fe(0.5)-doped β-Ni(OH)2 catalyst exhibits higher activity and stability from galvanostatic tests at 10 mA cm−2. Additionally, we experimentally demonstrate that Fe(0.5)-doped β-Ni(OH)2 exerts higher OER activity than Fe(0.5)-doped α-Ni(OH)2. All evidence indicates that Fe and the β-Ni(OH)2 matrix play an important role in NiFe-based catalysts.

Ceria-based dual-phase membranes showing high oxygen permeation fluxes and stability under a CO2 environment are promising materials for CO2 capture via an oxyfuel route. The high oxygen permeation fluxes compared with other dual-phase membranes are derived from the mixed conducting properties of the perovskite oxides used in the dual-phase membranes.

Mn1.5Co1.5O4 spinel oxide as a cathode or one component of a composite cathode presents no visible reaction with an Y2O3-stabilized ZrO2 electrolyte. The low electrode polarization resistances and good performance compared with traditional Sr-doped LaMnO3–YSZ composite cathodes imply promising application for the next generation of intermediate-temperature solid oxide fuel cells.

SrCo0.8Fe0.2O3-δ is a controversial material whether it is used as an oxygen permeable membrane or as a cathode of solid oxide fuel cells. In this paper, carefully synthesized powders of perovskite-type SrxCo0.8Fe0.2O3-δ (x = 0.80–1.20) oxides are utilized to investigate the effect of A-site nonstoichiometry on their electrochemical performance. The electrical conductivity, sintering property and stability in ambient air of SrxCo0.8Fe0.2O3-δ are critically dependent on the A-site nonstoichiometry. Sr1.00Co0.8Fe0.2O3-δ has a single-phase cubic perovskite structure, but a cobalt-iron oxide impurity appears in A-site cation deficient samples and Sr3(Co, Fe)2O7-δ appears when there is an A-site cation excess. It was found that the presence of the cobalt-iron oxide improves the electrochemical performance. However, Sr3(Co, Fe)2O7-δ has a significant negative influence on the electrochemical activity for intermediate-temperature solid oxide fuel cells (IT-SOFCs). The peak power densities with a single-layer Sr1.00Co0.8Fe0.2O3-δ cathode are 275, 475, 749 and 962 mW cm−2 at 550, 600, 650 and 700 °C, respectively, values which are slightly lower than those for Sr0.95Co0.8Fe0.2O3-δ (e.g. 1025 mW cm−2 at 700 °C) but much higher than those for Sr1.05Co0.8Fe0.2O3-δ (e.g. only 371 mW cm−2 at 700 °C). This remarkable dependence of electrochemical performance of the SrxCo0.8Fe0.2O3-δ cathode on the A-site nonstoichiometry reveals that lower values of electrochemical activity reported in the literature may be induced by an A-site cation excess. Therefore, to obtain a high performance of SrxCo0.8Fe0.2O3-δ cathode for IT-SOFCs, an A-site cation excess must be avoided.