AbstractOwing to unique lamellar nanostructures, 2D inorganic materials are considered as promising candidates in energy storage and conversion. In this paper, a facile two-step synthesis is developed to fabricate 3D hierarchical dual Fe3O4/MoS2 nanosheets (HD-FMNs), in which few-layered MoS2 nanosheets are anchored in 3D Fe3O4 nanosheet network to form the heterojunction structure. Furthermore, it is proved that the synergistic effects on both electron/lithium-ion transport kinetics and mechanical cycling stability benefit from Fe3O4/MoS2 nanosheet incorporation in 3D HD-FMN anode for lithium-ion batteries (LIBs), resulting in the dramatically enhanced performance. The Fe3O4 nanosheet incorporation effectively improves the electronic conductivity due to its half-metal characteristic, while the defect-rich structure in the MoS2 nanosheets can facilitate the lithium ion transport. When tested as potential anode materials, 3D HD-FMNs exhibit a high reversible capacity (650 mAh g−1) at current rate of 5 C (1 C = 1 A g−1) after superior long-term cycles (1000 times), as well as an excellent rate capability even at high current rates. The outstanding electrochemical property of 3D HD-FMNs allows their application in high-performance anode materials for next-generation LIBs. This strategy also opens a new way to design the novel 2D composite materials for electrochemical devices.

•EB0.98CO has an average TEC value of 16.7 × 10−6 K−1 at 50–800 °C.•EB0.98CO cathode gives the low ASR of 0.107 Ω cm2 at 700 °C.•EB0.98CO-based fuel cell delivers a peak power density of 505 mW cm−2 at 700 °C.•Rate-limiting steps for ORR at cathode/electrolyte interface are determined.A-site Ba-deficiency layered perovskite oxides, EuBa1−xCo2O6−δ (EB1−xCO, x = 0.02 and 0.04), have been synthesized by a citric acid-ethylene diamine tetraacetic acid complexation sol-gel method, and evaluated as potential cathode materials for intermediate-temperature solid oxide fuel cells (IT-SOFCs). Room temperature powder X-ray diffraction patterns indicate that the EB1−xCO oxides crystallize in an orthorhombic symmetry with space group Pmmm. Among all of components, EB0.98CO exhibits a good chemical compatibility with Ce0.9Gd0.1O1.95 (CGO) electrolyte, as evidenced by phase analysis of mixed EB0.98CO-CGO after calcining at 950 °C for 12 h in air. Thermal expansion analysis gives an average thermal expansion coefficient of 16.7 × 10−6 K−1 for EB0.98CO. Thermogravimetric measurement confirms the high oxygen nonstoichiometric characteristic of EB0.98CO at elevated temperatures. The electrical conductivity values of EB0.98CO exceed 300 S cm−1 in the temperature range of 100–750 °C. When tested as cathode in IT-SOFCs, the polarization resistance of 0.107 Ω cm2 and the overpotential of 10 mV at current density of 77 mA cm−2 are achieved in the EB0.98CO cathode at 700 °C in air. The EB0.98CO cathode-based anode-supported single cell delivers the maximum power density of 505 mW cm−2 at 700 °C. Finally the rate-limiting steps for oxygen reduction reaction at the EB0.98CO cathode interface are determined to be the charge transfer reaction and gas-phase diffusion process.Download high-res image (388KB)Download full-size image

•Pr0.94BaCo2O6-δ cathode shows the low ASR of 0.11 Ω cm2 at 600 °C.•CGO-Ni|CGO|P0.94BCO fuel cell delivers a power density of 1.05 W cm−2 at 600 °C•Rate-limiting step for ORR in Pr0.94BaCo2O6-δ cathode is determined.Praseodymium-deficiency Pr0.94BaCo2O6-δ (P0.94BCO) double perovskite has been evaluated as a cathode material for intermediate-temperature solid oxide fuel cells. X-ray diffraction pattern shows the orthorhombic structure with double lattice parameters from the primitive perovskite cell in Pmmm space group. P0.94BCO has a good chemical compatibility with Ce0.9Gd0.1O1.95 (CGO) electrolyte even at 1000 °C for 24 h. It is observed that the Pr-deficiency can introduce the extra oxygen vacancies in P0.94BCO, further enhancing its electrocatalytic activity for oxygen reduction reaction. P0.94BCO demonstrates the promising cathode performance as evidenced by low polarization are-specific resistance (ASR), e. g. 0.11 Ω cm2 and low cathodic overpotential e. g. −56 mV at a current density of −78 mA cm−2 at 600 °C in air. These features are comparable to those of the benchmark cathode Ba0.5Sr0.5Co0.8Fe0.2O3-δ. The fuel cell CGO-Ni|CGO|P0.94BCO presents the attractive peak power density of 1.05 W cm−2 at 600 °C. Furthermore, the oxygen reduction kinetics of P0.94BCO material is also investigated, and the rate-limiting steps for oxygen reduction reaction are determined.

•EBCO-10CGO composite cathode shows a ASR of 0.055 Ω cm2 at 700 °C.•Power density of single cell with EBCO-10CGO cathode is 0.81 W cm−2 at 700 °C.•Rate-limiting steps for ORR at EBCO-10CGO cathode interface are determined.The characteristics and electrochemical performance of double perovskite EuBaCo2O5+δ (EBCO) have been investigated as a composite cathode for intermediate-temperature solid oxide fuel cells (IT-SOFCs). The thermal expansion coefficients can be effectively reduced in the case of EBCO-Ce0.9Gd0.1O2−δ (CGO) composite cathodes. No chemical reactions between EBCO cathode and CGO electrolyte are observed after sintering at 1000 °C for 24 h. The maximum electrical conductivities of EBCO-CGO materials reach 28-77 S cm−1 with the change of CGO weight ratio from 40 wt. % to 5 wt. %. Among all these components, the EBCO-10 wt. % CGO (EBCO-10CGO) composite cathode gives the lowest area-specific resistance of 0.055 and 0.26 Ω cm2 in air at 700 and 600 °C, respectively. The maximum power density of Ni-CGO anode-supported single cell consisted of the EBCO-10CGO composite cathode and CGO electrolyte achieves 0.81 W cm−2 at 700 °C. These results indicate that the EBCO-10CGO composite materials can be used as a promising cathode candidate for IT-SOFCs. Furthermore, the rate-limiting steps for the oxygen reduction reaction at the EBCO-10CGO composite cathode interface are determined to be the charge transfer and dissociation of adsorbed molecule oxygen processes.

•PBxCO (0.90 ≤ x ≤ 1.0) cathodes show the low ASRs of 0.042–0.1 Ω cm2 at 600 °C.•PB0.94CO shows the promising polarization performance compared to LSCF cathode.•Rate-limiting step for ORR in PB0.94CO cathode changes with decreasing temperature.The layered perovskite PrBaxCo2O5+δ (PBxCO, x = 0.90–1.0) oxides have been synthesized by a solid-state reaction technique, and evaluated as the potential cathode materials for intermediate-temperature solid oxide fuel cells (IT-SOFCs). Room temperature X-ray diffraction patterns show the orthorhombic structures which double the lattice parameters from the perovskite cell parameter as a ≈ ap, b ≈ ap and c ≈ 2ap (ap is the cell parameter of the primitive perovskite) in the Pmmm space group. There is a good chemical compatibility between the PBxCO cathode and the Ce0.9Gd0.1O1.95 (CGO) electrolyte at 1000 °C. The electrical conductivity and thermal expansion coefficient of PBxCO are improved due to the increased amount of electronic holes originated from the Ba-deficiency. The results demonstrate the high electrochemical performance of PBxCO cathodes, as evidenced by the super low polarization resistances (Rp) over the intermediate temperature range. The lowest Rp value, 0.042 Ω cm2, and the cathodic overpotential, −15 mV at a current density of −25 mA cm−2, are obtained in the PrBa0.94Co2O5+δ cathode at 600 °C in air, which thus allow to be used as a highly promising cathode for IT-SOFCs. A CGO electrolyte fuel cell with the PrBa0.94Co2O5+δ cathode presents the attractive peak power density of ∼1.0 W cm−2 at 700 °C. Furthermore, the oxygen reduction kinetics of the PrBa0.94Co2O5+δ cathode is also studied, and the rate-limiting steps for oxygen reduction reaction are determined at different temperatures.

•YBa1−xSrxCo2O5+δ (0 ≤ x ≤ 0.5) cathodes show the low ASRs of 0.21–0.59 Ω cm2 at 700 °C.•YBaCo2O5+δ has an overpotential of −40 mV at the current density of −136 mA cm−2.•Charge transfer reaction is rate-limiting step for ORR in YBaCo2O5+δ cathode.•Large oxygen vacancy concentrations in YBSC are beneficial for the high performance.This study is focused on the structural characteristics, oxygen nonstoichiometry, electrical conductivity, electrochemical performance and oxygen reduction mechanism of YBa1−xSrxCo2O5+δ (x = 0, 0.1, 0.2, 0.3, 0.4 and 0.5). The high oxygen nonstoichiometry, δ = 0.18–0.43 at 700 °C, indicates the large oxygen vacancy concentrations in oxides. The electrical conductivity is improved due to the greater amount of electronic holes originated from the increased interstitial oxygen, and the conductivities of all samples are above 100 S cm−1 at 400–700 °C in air. The results demonstrate the promising performance of YBa1−xSrxCo2O5+δ cathodes at intermediate temperatures, as evidenced by low area-specific resistances (ASRs) e.g. 0.21–0.59 Ω cm2 at 700 °C. The lowest ASR, 0.44 Ω cm2, and the cathodic overpotential, −40 mV at a current density of −136 mA cm−2, are obtained in YBaCo2O5+δ cathode at 650 °C. The dependence of polarization resistance on oxygen partial pressure suggests that the charge transfer process is the rate-limiting step for oxygen reduction reaction in YBaCo2O5+δ cathode.

•La0.57Sr0.15TiO3 is evaluated as the anode component material for IT-SOFCs.•Ni/CGO-impregnated LSTO composite anodes are fabricated and characterized.•6.3%Ni-8.3%CGO-LSTO composite anode shows Rp of 0.73 Ω cm2 at 800 °C in 3%H2O/H2.A-site deficient perovskite La0.57Sr0.15TiO3 (LSTO) materials are synthesized by a modified polyacrylamide gel route. X-ray diffraction pattern of LSTO indicates an orthorhombic structure. The thermal expansion coefficient of LSTO is 10.0 × 10−6 K−1 at 600 °C in 5%H2/Ar. LSTO shows an electrical conductivity of 2 S cm−1 at 600 °C in 3%H2O/H2. A new composite material, containing the porous LSTO backbone impregnated with small amounts of Ce0.9Gd0.1O2−δ (CGO) (3.4–8.3 wt.%) and Ni/Cu (2.0–6.3 wt.%), is investigated as an alternative anode for solid oxide fuel cells (SOFCs). Because of the substantial electro-catalytic activity of the fine and well-dispersed Ni particles on the surface of the ceramic framework, the polarization resistance of 6.3%Ni-8.3%CGO-LSTO anode reaches 0.73 Ω cm2 at 800 °C in 3%H2O/H2. In order to further improve the anodic performance, corn starch and carbon black are used as pore-formers to optimize the microstructure of anodes.

•UMCN-HCs show high capacity, excellent stability, and good rate capability.•UMCN-HCs retain a capacity of 1067 mAh g−1 after 100 cycles at 100 mA g−1.•UMCN-HCs deliver a capacity of 507 mAh g−1 after 500 cycles at 2 A g−1.Herein, Ultrathin mesoporous Co3O4 nanosheets-constructed hierarchical clusters (UMCN-HCs) have been successfully synthesized via a facile hydrothermal method followed by a subsequent thermolysis treatment at 600 °C in air. The products consist of cluster-like Co3O4 microarchitectures, which are assembled by numerous ultrathin mesoporous Co3O4 nanosheets. When tested as anode materials for lithium-ion batteries, UMCN-HCs deliver a high reversible capacity of 1067 mAh g−1 at a current density of 100 mA g−1 after 100 cycles. Even at 2 A g−1, a stable capacity as high as 507 mAh g−1 can be achieved after 500 cycles. The high reversible capacity, excellent cycling stability, and good rate capability of UMCN-HCs may be attributed to their mesoporous sheet-like nanostructure. The sheet-layered structure of UMCN-HCs may buffer the volume change during the lithiation-delithiation process, and the mesoporous characteristic make lithium-ion transfer more easily at the interface between the active electrode and the electrolyte.Ultrathin mesoporous Co3O4 nanosheets-constructed hierarchical clusters (UMCN-HCs) have been successfully synthesized via a facile hydrothermal method followed by a subsequent thermolysis treatment. When tested as anode materials for LIBs, UMCN-HCs achieve high reversible capacity, good long cycling life, and rate capability.