•Fabrication of EFFC by a composite of redox-stable perovskite oxide LSCrF and SDC.•The weight ratio between LSCrF and SDC with strong effects on EFFC performance.•A Pmax of 1059 mW cm−2 achieved at 550 °C and 553 mW cm−2 at 470 °C.A novel solid oxide fuel cell (SOFC) incorporating the semiconductor with the ionic conductor to replace the traditional electrolyte layer with improved performance has been recently reported. In the present work, we found that the redox stable electrode material La0.7Sr0.3Cr0.5Fe0.5O3-δ (LSCrF) can be considered as a good candidate for such configuration, electrolyte layer-free fuel cells (EFFCs), due to its high ionic and electronic conductivities, excellent catalytic activity and good chemical stability. EFFCs based on the composite of perovskite oxide LSCrF and ionic conductor Ce0.8Sm0.2O2-δ (SDC) offered promising performances, i.e., 1059 mW cm−2 at 550 °C without any electronic short circuiting problem. It even exhibited a highly promising result of 553 mW cm−2 at 470 °C in further low-temperature operation. These high performances can be attributed to the improved conductivity, more triple-phase boundaries (TPB) and accelerated oxygen reduction reaction (ORR) of LSCrF-SDC composite. The influence of the weight ratio between LSCrF and SDC on the EFFC electrochemical performance was investigated. This new discovery indicates a great potential for exploring multifunctional perovskites for the new SOFC technologies.

Ternary nickel cobaltite (NiCo2O4) has attracted more and more attention as a promising electrode material for high performance supercapacitors (SCs) due to its high theoretical capacity, unique crystal structure and excellent electronic conductivity. In this study, a template-free chemical co-precipitation method as a general strategy has been easily developed to fabricate mesoporous NiCo2O4 nanospheres with a high specific surface area of 216 m2 g−1, which can be further self-assembled into 3D frameworks. The key to the formation of mesoporous NiCo2O4 nanospheres with a desired pore-size distribution centered at ∼2.4 nm is a unique preparation method assisted with sodium bicarbonate as a complex agent. When tested as electrode materials for SCs, the NiCo2O4 electrodes delivered excellent electrochemical performances with high specific capacitance (842 F g−1 at a current density of 2 A g−1), superior cycling stability with no capacity decrease after 5000 cycles (103% initial capacity retention), and great rate performance at a 10-time current density increase (79.9% specific capacitance retention). Furthermore, as expected in a NiCo2O4-based asymmetric supercapacitor device, a superior energy density as high as 29.8 W h kg−1 at a power density of 159.4 W kg−1 could be achieved. These results highlight a general, eco-friendly, template-free strategy for the scale-up fabrication of a promising mesoporous NiCo2O4 electrode material for high-performance SC applications.

•XPS shows valence state of Co3+/Co4+ and Cu2+/Cu+ in SBSCCo.•SBSCCo are chemical compatible with GDC and LSGM below 950 °C.•Cu partially substitute Co sites can effectively lower the TEC SBSCCo.•Lower polarization resistance of 0.0263 Ω cm2 is obtained on LSGM at 850 °C.•Higher output power density of 857 mW cm−2 is obtained on LSGM at 850 °C.Mixed ionic and electronic conductor SmBa0.5Sr0.5CoCuO5+δ (SBSCCo) is studied as a cathode material for intermediate-temperature solid oxide fuel cells (IT-SOFCs). X-ray diffraction spectra show that SBSCCo are chemical compatible with Gd0.1Ce0.9O1.95 (GDC) and La0.9Sr0.1Ga0.83Mg0.17O2.865 (LSGM) electrolyte below 950 °C. XPS analysis results indicate that the transition-metal cations on the SBSCCo sample's surface exhibit two different valence state, i.e. Co3+/Co4+ and Cu2+/Cu+. The average thermal expansion coefficient (TEC) of SBSCCo cathode is 16.14 × 10−6 K−1 between 30 °C and 850 °C in air. The electrical conductivity of SBSCCo cathode reaches 110–206 Scm−1 between 200 °C and 850 °C in air. The area specific resistances of SBSCCo cathode on LSGM and GDC electrolytes are 0.0263 and 0.0274 Ω cm2 at 850 °C, respectively. The maximum output power density of a single-cell with SBSCCo cathode on LSGM and GDC electrolyte reaches 857 and 633 mWcm−2 at 850 °C, respectively. The electrochemical performance of SBSCCo cathode based on LSGM electrolyte is better than on GDC electrolyte. These primarily results indicate that SBSCCo is a candidate cathode material for IT-SOFCs.

Hierarchical δ-MnO2 nanosheets as electroactive materials have been directly deposited on nickel foam substrate by one-pot chelation-mediated aqueous method. The morphological evolution process has been investigated by scanning electron microscopy (SEM) at different time intervals in detail. The hierarchical δ-MnO2 electrodes which are synthesized at 30 °C, 40 °C and 50 °C are directly served as binder- and conductive-agent-free electrodes for supercapacitors and have been explored by cyclic voltammetry, galvanostatic charge-discharge test and electrochemical impedance spectroscopy. With the decrease of reaction temperature the specific capacitance of δ-MnO2 electrode increases. The vertically aligned δ-MnO2 nanosheets which have been synthesized at 30 °C exhibit a highest capacitance of 325 F g−1 at the current density of 1 A g−1. The capacitance loss is less than 15% after 1000 cycles at the scan rate of 30 mV s−1. Furthermore, it is found that the equivalent series resistance and charge transfer resistance of the electrode are 0.36 Ω and 1.7 Ω, respectively. Such superior electrochemical performance of the electrode made by directly growing porous δ-MnO2 nanosheets on nickel foam makes it has very promising applications in high-performance supercapacitors.

•A novel cubic perovskite BaBi0.05Co0.8Nb0.15O3−δ is prepared by solid-state reaction method.•BBCN cathode is chemically compatible with the electrolyte Sm0.2Ce0.8O1.9.•The power density of electrolyte-supported SOFCs with BBCN cathode is favorable.A cubic perovskite oxide, BaBi0.05Co0.8Nb0.15O3−δ (BBCN) is investigated as a cathode for intermediate-temperature solid oxide fuel cells (IT-SOFCs). XRD results show that BBCN cathode is chemically compatible with the electrolyte Sm0.2Ce0.8O1.9 (SDC) at 950 °C for 5 h. The XPS results show that the Co3+/Co4+, Nb5+, Bi3+ and Ba2+ species exist in the BBCN sample. The thermal expansion coefficient (TEC) of the BBCN sample is 19.60 × 10−6 K−1 between 30 and 850 °C in air. The Rp of BBCN cathode on SDC electrolyte is 0.047, 0.077 and 0.136 Ω cm2 at 800, 750, 700 °C, respectively. A maximum power density of 507 mW cm−2 is obtained at 800 °C for single-cell with 300 μm thick SDC electrolyte and BBCN cathode. The results of this study demonstrate that BBCN can be a promising cathode material for IT-SOFCs.

•Graphene/MnO2 is successfully fabricated by a facile co-precipitation method.•The graphene/MnO2 electrode reaches 367 Fg−1 in 1 M KOH electrolyte.•The electrode exhibits good cycling performance of 73.9% retention after 1000 cycles.Nanostructured graphene/amorphous α-MnO2 composites have been synthesized by a facile co-precipitation method under the alkaline condition, in which graphene nanosheets as a supporting substrate to grow MnO2. Characterizations of prepared samples’ morphology and microstructures indicate MnO2 is successfully formed on the surface of graphene by electrostatic interaction. Moreover, the electrochemical properties of the synthesized electrode materials for supercapacitors are studied in a three-electrode experimental setup using a 1 M KOH aqueous solution as the electrolyte. As a result, the specific capacitance of graphene/MnO2 composite (weight ratio of graphene to MnO2 is 1:1) determined by a galvanostatic charge–discharge method at a current density of 1 Ag−1 reaches 367 Fg−1, which is 1.8 and 4.6 fold higher than that of pure graphene and MnO2. The capacity retention of the graphene/MnO2 composite is 73.9% of the original capacitance after 1000 cycles, indicating graphene/MnO2 composite is a promising electrode material for supercapacitors.

•A single-phase layered-perovskite PrBa0.5Sr0.5CoCuO5+δ (PBSCCu) is prepared by the EDTA–citrate complexing method.•PBSCCu cathode has a good chemical compatible with GDC electrolyte.•Partial substitution of Cu for Co can efficiently lower the thermal expansion coefficient.•Performances of PrBa0.5Sr0.5CoCuO5+δ cathode based on Gd0.1Ce0.9O1.95 electrolyte is reported firstly.Layered perovskite PrBa0.5Sr0.5CoCuO5+δ (PBSCCo) oxide is synthesized by EDTA–citrate complexing method and investigated as a novel cathode material for intermediate-temperature solid oxide fuel cells (IT-SOFCs). X-ray diffraction results show that PBSCCo is chemical compatible with Gd0.1Ce0.9O1.95 (GDC) electrolyte below 950 °C. The thermal expansion coefficient of PBSCCo is 17.58 × 10−6 K−1 between 30 °C and 900 °C. The maximum electrical conductivity of PBSCCo is 483 S сm−1 at 325 °C. The polarization resistance of PBSCCo cathode on GDC electrolyte is as low as 0.06 Ω cm2 at 800 °C. The maximum power density of the electrolyte-supported single cell with PBSCCo cathode achieves 521 mW cm−2 at 800 °C. Preliminary results indicate that PBSCCo is a potential cathode material for application in IT-SOFCs.

PrBa0.5Sr0.5Co2O5+x (PBSC) oxides have been evaluated as cathode materials for intermediate-temperature solid oxide fuel cells (IT-SOFCs) with Ce0.9Gd0.1O1.95 (GDC) and La0.9Sr0.1Ga0.8Mg0.2O3−δ (LSGM) as electrolytes. XRD results show that PBSC cathode is chemically compatible with the intermediate-temperature electrolyte materials GDC and LSGM. The maximum electrical conductivity is 1522 S cm−1 at 100 °C and its value is higher than 581 S cm−1 over the whole temperature range investigated. Microstructures show that the contact between PBSC and LSGM is better than that between PBSC and GDC. The area-specific resistances (ASRs) of PBSC cathode on GDC and LSGM electrolytes are 0.048 and 0.027 Ωcm2 at 800 °C, respectively. The electrolyte-supported (thickness of electrolyte is 300 μm) fuel cells generate good performance with the maximum power densities of 617 mW cm−2 on GDC electrolyte and 1021 mW cm−2 on LSGM electrolyte at 800 °C. All results demonstrate that PBSC oxide is a very promising cathode material for application in IT-SOFCs and this cathode based on LSGM electrolyte obtained better performance than on GDC electrolyte.Highlights► Synthesize a double-layered perovskite PrBa0.5Sr0.5Co2O5+x as a cathode material. ► Chemical compatibility between cathodes and electrolytes is investigated. ► Performance of PBSC cathode based on La0.9Sr0.1Ga0.8Mg0.2O3−δ is reported firstly. ► Compare the cell performance of PBSC based on LSGM and GDC electrolytes.

The performance of SmBaCoCuO5+x (SBCCO) cathode has been investigated for their potential utilization in intermediate-temperature solid oxide fuel cells (IT-SOFCs). The powder X-ray diffraction (XRD), thermal expansion and electrochemical performance on Ce0.9Gd0.1O1.95 (GDC) electrolyte are evaluated. XRD results show that there is no chemical reaction between SBCCO cathode and GDC electrolyte when the temperature is below 950 °C. The thermal expansion coefficient (TEC) value of SBCCO is 15.53 × 10−6 K−1, which is ∼23% lower than the TEC of the SmBaCo2O5+x (SBCO) sample. The electrochemical impedance spectra reveals that SBCCO symmetrical half-cells by sintering at 950 °C has the best electrochemical performance and the area specific resistance (ASR) of SBCCO cathode is as low as 0.086 Ω cm2 at 800 °C. An electrolyte-supported fuel cell generates good performance with the maximum power density of 517 mW cm−2 at 800 °C in H2. Preliminary results indicate that SBCCO is promising as a cathode for IT-SOFCs.Research highlights▶ We synthesize a new kind of layered perovskite SmBaCoCuO5+x (SBCCO) as a cathode material of a solid oxide fuel cell. ▶ There are some reports on the performance of cathodes in proton-conducting SOFCs based on BaCe0.8Sm0.2O3−δ electrolyte. ▶ However, to the best of our knowledge, the performance of SBCCO cathodes in oxygen-ion conducting SOFCs has not been reported to date. ▶ In this work, the ceramic powder SBCCO is examined as a cathode for IT-SOFCs based on Ce0.9Gd0.1O1.95 (GDC) electrolyte.

Layered perovskite oxide NdBa0.5Sr0.5Co2O5+x is investigated as a cathode material for intermediate-temperature solid oxide fuel cells. The NBSC cathode is chemically compatible with the electrolyte La0.9Sr0.1Ga0.8Mg0.2O3−δ (LSGM) at temperatures below 1000 °C. It is metallic in nature and the maximum and minimum conductivities are 1368 S cm−1 at 100 °C and 389 S cm−1 at 850 °C. The area specific resistance (ASR) value for the NBSC cathode is as low as 0.023 Ω cm2 at 850 °C. The electrolyte-supported fuel cell generates good performance with the maximum power density of 904, 774 and 556 mW cm−2 at 850, 800 and 750 °C, respectively. Preliminary results indicate that NBSC is promising as a cathode for IT-SOFCs.

The performance of SmBaCoFeO5+δ (SBCF)–xCe0.9Gd0.1O1.95 (GDC) (x = 0, 10, 30, 50, 60, wt%) composite cathodes has been investigated for their potential utilization in intermediate-temperature solid oxide fuel cells (IT-SOFCs). The powder X-ray diffraction (XRD), thermal expansion coefficient (TEC) and electrochemical property measurements are employed to study the materials. The XRD results prove that there is no serious reaction between SBCF and GDC oxides even at 1000 °C. The thermal expansion behavior shows that the TEC value of SBCF cathode decreases greatly with GDC addition. The addition of GDC to SBCF cathode further reduces the polarization resistance. The lowest polarization resistance of 0.036 Ω cm2 is achieved at 800 °C for SBCF–50GDC composite cathode. An electrolyte-supported fuel cell is prepared using SBCF–50GDC as cathode and NiO–GDC (65:35 by weight) as anode. The cell generates good performance with the maximum power density of 691 mW cm−2, 503 mW cm−2 and 337 mW cm−2 at 800 °C, 750 °C and 700 °C, respectively. Preliminary results indicate that SBCF–50GDC is especially promising as a cathode for IT-SOFCs.

Cathode materials consisting of Pr1−xSrxCo0.8Fe0.2O3−δ (x = 0.2–0.6) were prepared by the sol–gel process for intermediate-temperature solid oxide fuel cells (IT-SOFCs). The samples had an orthorhombic perovskite structure. The electrical conductivities were all higher than 279 S cm−1. The highest conductivity, 1040 S cm−1, was found at 300 °C for the composition x = 0.4. Symmetrical cathodes made of Pr0.6Sr0.4Co0.8Fe0.2O3−δ (PSCF)–Ce0.85Gd0.15O1.925 (50:50 by weight) composite powders were screen-printed on GDC electrolyte pellets. The area specific resistance value for the PSCF–GDC cathode was as low as 0.046 Ω cm2 at 800 °C. The maximum power densities of a cell using the PSCF–GDC cathode were 520 mW cm−2, 435 mW cm−2 and 303 mW cm−2 at 800 °C, 750 °C and 700 °C, respectively.