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Oxygen reduction reaction is crucial for the development of intermediate/low-temperature solid oxide fuel cells (SOFCs), thus the development of cathode materials with high catalytic activity and stability is still a great challenge for the commercialization of SOFC. In this study, a series of La1–xPrxCo0.5Ni0.5O3−δ(x= 0.5, 0.75, and 1.0) perovskite oxides were prepared as oxygen reduction reaction catalysts for SOFC. First, the polycrystalline powders were synthesized by a Pechini method, and the crystal structure was confirmed as orthorhombic symmetry with Pbnm(No. 62) space group. Second, it was found that PrCo0.5Ni0.5O3−δ(PCN) presents the best electrochemical performance among the three compounds. The polarization impedance of PCN was 0.0383 Ω cm2and the peak power density reached 1.47 W cm2using wetted hydrogen as fuel and air as the oxidant measured at 850 °C. Meanwhile, the single cell with PCN as the cathode could stably work for 100 h at 750 °C without damping. Finally, combined with the first-principles calculations, it was revealed that the doping of Pr ion can effectively reduce oxygen vacancy formation energy and mainly changed the valence states of Co and Ni ions at B-site. Therefore, PCN is expected to be a promising cathode material for SOFC.

The development of multiphase composite electrocatalysts plays a key role in achieving the efficient and durable operation of intermediate-temperature solid oxide fuel cells (IT-SOFCs). Herein, a self-assembled nanocomposite is developed as the oxygen reduction reaction (ORR) catalyst for IT-SOFCs through a coprecipitation method. The nanocomposite is composed of a doped (Mn0.6Mg0.4)0.8Sc0.2Co2O4(MMSCO) spinel oxide (84 wt %), an orthorhombic perovskite phase (11.3 wt %, the spontaneous combination of PrO2additives and spinel), and a minor Sc2O3phase (4.7 wt %). The surface of the (Mn0.6Mg0.4)0.8Sc0.2Co2O4phase is activated by the self-assembled nanocoating with many heterogeneous interfaces. Thence, the ORR kinetics is obviously accelerated and an area-specific resistance (ASR) of ∼0.11 Ω cm2is obtained at 750 °C. Moreover, a single cell with the cathode shows a peak power density (PPD) of 1144.1 mW cm–2at 750 °C, much higher than that of the cell with the MnCo2O4cathode (456.2 mW cm–2). An enhanced stability of ∼120 h (0.8 A cm–2, 750 °C) is also achieved, related to the reduced thermal expansion coefficient (13.9 × 10–6K–1). The improvement in ORR kinetics and stability can be attributed to the refinement of grains, the formation of heterointerfaces, and the enhancement of mechanical compatibility.

Based on first-principles calculations with the DFT + Umethod, the couplings of lattice, charge, spin, and electronic behaviors underlying the Eu–Mn charge transfer in a strongly correlated system of EuMnO3were investigated. The potential valence transition from Eu3+/Mn3+to Eu2+/Mn4+was observed in a compressed lattice with little distortions, which is achieved under hydrostatic pressure and external strain. The intraplane antiferromagnetism (AFM) of Mn is proved to be instrumental in the emergence of Eu2+. Furthermore, we calculated the magnetic exchange interactions within two equilibrium structures of Eu3+Mn3+O3and Eu2+Mn4+O3. Mn–Mn ferromagnetic exchange in the ab-plane is enhanced strongly in the Eu2+Mn4+O3structure, contributing to the existence of mixed states. The versatile electronic structures were obtained within the Eu2+Mn4+O3phase by imposing different magnetic configurations on the Eu and Mn sublattice, attributed to the coupling of charge transfer and magnetic orderings. It is found that the intraplane ferromagnetic ordering of Mn leads to a metallic electronic structure with the coexistence of Eu2+and Eu3+, while the intraplane AFM Mn spin ordering leads to insulating states only with Eu2+. Notably, a half-metallic characteristic emerges at the magnetic ground state of CF ordering (C-type AFM for the Eu sublattice and ferromagnetic for the Mn sublattice), which makes such a supposed phase more intriguing than the conventional experimental phase. Additionally, the mixture of delocalized 4f with 5d states of Eu in the background of Mn 3d and O 2p orbitals implies a pathway of Eu 4f 5d ↔ O 2p ↔ Mn 3d for charge transfer between Eu and Mn. Our calculation shows that the Eu–Mn charge transfer could be expected in compressed EuMnO3and the introduction of Eu2+4f states near the Fermi level plays an important role in manipulating the interlinks of charge and spin together with electronic behaviors.

Protonic ceramic fuel cells (PCFCs) composed of porous electrodes and dense electrolytes are considered to be a promising alternative to solid oxide fuel cells (SOFCs) at low and intermediate temperatures (≤600 °C) due to their comparative low activity barrier. It is well known that rare earth elements, such as Y, Yb, and Pr, have been applied to dope prototypical perovskite-type oxides BaCeO3and BaZrO3to improve both the conductivity and the stability. In this article, we particularly select Pr with a radius similar to that of Ce as a dopant to dope BaCeO3, aiming to exclusively extract the 4f5d electrons’ effect on the protonic conductivity as well as the influence on the stability, based on both a static density functional theory (DFT) calculation and an ab initio molecular dynamics (AIMD) simulation. The calculated results demonstrated that the oxygen vacancy formations were lowered owing to the O 2p band center shifting toward the Fermi level and the protonic conductivity was positively reduced due to the energy springboard provided by the Pr 4f orbital, and the p-type semiconductor effect originated from the different covalent states of Pr3+with Ce4+. AIMD simulations confirmed the proton transition process as previously proposed and thermodynamic stability at a temperature as high as 750 °C. In contrast, CO2and SO2adsorption calculated results indicate that Pr doping has little effect on the chemical stability. This is consistent with the experimental strategy in which multiple rare earth elements are utilized to secure the high performance of the electrolytes in these acceptor-doped perovskites.

The broad and large-scale application of solid oxide fuel cells (SOFCs) technology hinges significantly on the development of highly active and robust electrode materials. Here, Ni-free anode materials decorated with metal nanoparticles are synthesized by in situ reduction of Fe-doping Sr2CoMo1–xFexO6−δ(x= 0, 0.05, 0.1) double perovskite oxides under a reducing condition at 850 °C. The exsolved nanoparticles from the Sr2CoMo0.95Fe0.05O6−δ(SCMF0.05) lattice are Co–Fe alloys with rich multiple-twinned defects, significantly enhancing the catalytic activity of the SCMF0.05 anode toward the oxidation of H2and CH4. The electrolyte-supported single cell with the reuduced SCMF0.05 anode reaches peak power densities as high as 992.9 and 652.3 mW cm–2in H2and CH4at 850 °C, respectively, while maintaining superior stability (∼50 h at 700 °C). The reduced SCMF0.05 anode also demonstrates excellent coking resistance in CH4, which can be attributed to the increased oxygen vacancies due to Fe doping and the effective catalysis of multiple-twinned Co–Fe alloy nanoparticles for reforming of CH4to H2and CO. The findings in this work may provide a new insight for the design of highly active and durable anode catalysts in SOFCs.

Rare-earth (RE) doped ternary sulfide (KLuS2) compounds, which serve as expected X-ray phosphors and white-light-emitting diode (LED) solid-sate lighting devices, have aroused intense interest recently. However, the underlying luminescence mechanism and the rule of 4f-related electronic transition are still unknown, which are full of significance for the exploration of advanced RE-based luminescent materials. With these issues to be addressed in mind, a series of KLuS2:RE (RE = Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb) compounds are investigated using first-principles calculations. Based on the analysis of the equilibrium geometries and electronic structures, three types of electric-dipole-allowed transitions are revealed and three promising luminescence centers (RE = Dy, Ho, Er) are figured out. Furthermore, we have designed three new-style codoped KLuS2:Dy/Ho, KLuS2:Dy/Er, and KLuS2:Ho/Er materials to enrich the RE-doped KLuS2family. We hope the current contribution is conducive to understanding the role of 4f in luminescent materials and provides theoretical guidelines for further preparing desired optical materials.

The lack of highly active and robust catalysts for the oxygen reduction reaction (ORR) at the intermediate temperatures significantly hinders the commercialization of solid oxide fuel cells (SOFCs). Here, we report a novel heterostructured composite nanofiber cathode composed of La0.6Sr0.4Co0.2Fe0.8O3−δ(LSCF) and CeO2nanoparticles, synthesized by using a coaxial electrospinning technique, which exhibits remarkably enhanced ORR activity and durability as compared to single LSCF powder and nanofibers. This cathode achieves a polarization resistance of 0.031 Ω cm2at 700 °C, approximately 1/5 of that for the LSCF powder cathode (0.158 Ω cm2). Such enhancement can be attributed to the continuous paths provided by nanofibers for efficient mass/charge transport and the interdiffusion of La and Ce at the heterointerface which leads to more oxygen vacancy formation. Furthermore, the anode-supported cell with the LSCF/CeO2composite cathode shows excellent stability (0.4 V for ∼200 h at 600 °C) because of suppression of Sr segregation in LSCF by introducing CeO2and the structure of heterogeneous nanofibers. These results indicate that the microstructure design of this heterostructured composite nanofiber for LSCF/CeO2is extremely effective for enhancing ORR activity and stability. This finding may provide a new strategy for the microstructure design of highly active and robust ORR catalysts in SOFCs.

Oxygen vacancy (VO) formation energy and its migration barrier are two determining factors for the effectiveness of solid electrolytes (SEs) in solid oxide fuel cells (SOFCs). In this work, a series of aliovalent rare-earth-doped ceria (LnxCe1–xO2−δ, Ln = lanthanides) compounds serving as SEs are comprehensively and comparatively calculated, through which the determinant factors for oxygen vacancy formations and their migration activity are figured out at an atomistic level via the first-principles calculations with the consideration of electronic correlations. Initially, it is found that the oxygen vacancy formation energies of the Ln-doped ceria are largely reduced in contrast to the undoped ceria (CeO2−δ), which obviously agree with the literature. Then, the migration activity of an oxygen vacancy in LnxCe1–xO2−δis closely correlated to the association energies of Ln–VO, in which the different 4f5d bonding properties for different Ln ions should be taken into account. Additionally, the analysis of charge difference gradient (CDG) is revealed to be the intrinsic driving force for oxygen vacancy migration. We hope that our investigation provides a microscopic insight into the oxygen vacancy defect physics, and it is also a benefit for the design of more advanced relevant functional materials.

The A-site ordered negative thermal expansion material LaCu3Fe4O12(LaCFO) was comprehensively investigated by using first-principles calculations. A pressure-triggered crystal structural phase transition from space group Im3̅ (No. 204) to Pn3̅ (No. 201) and magnetic transformation from a G-type antiferromagnetic (G_AFM) ground state to ferrimagnetic (FerriM) coupling were observed in LaCFO via gradual compression of the equilibrium volume. Correspondingly, the Fe–Cu intersite charge transfer from Fe to Cu 3dxyorbital, expressed as 4Fe3++ 3Cu3+→ 4Fe3.75++ 3Cu2+, was simulated along with the magnetic phase transformation from the G_AFM configuration to the FerriM state. Intriguingly, the Fe charge disproportionation, formulated as 8Fe3.75+→ 5Fe3++ 3Fe5+, appeared and was attributed to the strong hybridization between Fe 3d and O 2p orbitals in the FerriM state when the volumes were substantially compressed up to less than or equal to 80%V. Meanwhile, the external hydrostatic pressure also leads to a spin flip from a high-spin Fe3+antiferromagnetically arranged LaCu3+3Fe3+4O12Mott insulator at low pressure and goes through a FerriM LaCu2+3Fe3.75+4O12half-metal to a low-spin FerriM coupled LaCu2+3Fe3+5/2Fe5+3/2O12metal at high pressure. Therefore, the crossover from high spin to low spin is responsible for the charge disproportionation in LaCFO. Essentially, the charge transfer and spin flip originate from the discontinuous changes of metal–oxygen bond lengths and angles in the compressed atomic structure. Finally, the negative thermal expansion behavior and mechanism of LaCFO were theoretically examined and clearly revealed.

Gastric carcinoma (GC) is one of the most common malignancies and the third leading cause of cancer-related deaths worldwide. Long noncoding RNAs (lncRNAs) may be an important class of functional regulators involved in human gastric cancers development. In this study, we investigated the clinical significance and function of lncRNA SNHG1 in GC. SNHG1 was significantly downregulated in GC tumor tissues compared with adjacent noncancerous tissues. Overexpression of SNHG1 in BGC-823 cells remarkably inhibited not only cell proliferation, migration, invasion in vitro, but also tumorigenesis and lung metastasis in the chick embryo chorioallantoic membrane (CAM) assay in vivo. Conversely, inhibition of SNHG1 by transfection of siRNA in AGS cells resulted in opposite phenotype changes. Mechanically, SNHG1 was found interacted with ILF3, NONO and SFPQ. RNA-seq combined with bioinformatic analysis identified a serial of downstream genes of SNHG1, including SOCS2, LOXL2, LTBP3, LTBP4. Overexpression of SNHG1 induced SOCS2 expression whereas knockdown of SNHG1 decreased SOCS2 expression. In addition, knockdown of SNHG1 promoted the activation of JAK2/STAT signaling pathway. Taken together, our data suggested that SNHG1 suppressed aggressive phenotype of GC cells and regulated SOCS2/JAK2/STAT pathway.