The introduction of oxygen vacancies (Ov) has been regarded as an effective method to enhance the catalytic performance of photoanodes in oxygen evolution reaction (OER). However, their stability ...under highly oxidizing environment is questionable but was rarely studied. Herein, NiFe‐metal–organic framework (NiFe‐MOFs) was conformally coated on oxygen‐vacancy‐rich BiVO4 (Ov‐BiVO4) as the protective layer and cocatalyst, forming a core–shell structure with caffeic acid as bridging agent. The as‐synthesized Ov‐BiVO4@NiFe‐MOFs exhibits enhanced stability and a remarkable photocurrent density of 5.3±0.15 mA cm−2 at 1.23 V (vs. RHE). The reduced coordination number of Ni(Fe)‐O and elevated valence state of Ni(Fe) in NiFe‐MOFs layer greatly bolster OER, and the shifting of oxygen evolution sites from Ov‐BiVO4 to NiFe‐MOFs promotes Ov stabilization. Ovs can be effectively preserved by the coating of a thin NiFe‐MOFs layer, leading to a photoanode of enhanced photocurrent and stability.
A core–shell Ov‐BiVO4@NiFe‐MOFs photoanode was constructed via a coordination‐assisted self‐assembly method. A NiFe‐MOFs thin layer acts as protective layer and cocatalyst to shift active sites from oxygen vacancies to NiFe‐MOFs, leading to improved stability and activity for OER. This molecular‐based approach tailors the coordination and electronic structure of active sites and provides mechanistic insights for rational design of photocatalysts.
Photoelectrochemical (PEC) water splitting into hydrogen and oxygen is a promising solution for the conversion and storage of solar energy. Because sluggish water oxidation is the bottleneck of water ...splitting, the design and preparation of an efficient photoanode is intensively investigated. Currently, all known photoanode materials suffer from at least one of the following drawbacks: ① low carriers separation efficiency; ② sluggish surface water oxidation reaction; ③ poor long‐term stability; ④ insufficient water adsorption and gas desorption. Core–shell configurations can endow a photoanode with improved activity and stability by coating an overlayer that plays energetic, catalytic, and/or protective roles. The construction strategy has an important effect on the activity of a core–shell photoanode. Nonetheless, the mechanism for the improvement of performance is still ambiguous and is worthy of a closer examination. In this review, the successes and challenges of core–shell photoanodes for water oxidation, focusing on synthesis strategies as well as functionalities (facilitating carrier separation, surface reaction promotion, corrosion prevention, and bubble detachment) are explored. Finally, the perspectives of this class of materials in terms of new opportunities and efforts are discussed.
Core–shell configurations, constructed via photo/electrodeposition, atomic layer deposition, chemical vapor deposition, ligand‐assisted strategy or ion exchange strategy, endow photoanodes with improved activity and stability by optimizing and facilitating carrier separation, surface reaction promotion, corrosion prevention, and bubble detachment process during photoelectrochemical water oxidation.
Dry reforming of methane (DRM), which involves the activation of inert CH bonds and CO bonds, at mild conditions is a tremendous challenge. The sluggish mobility of oxygen during the reaction is ...known as a key issue causing low activity and poor stability of catalysts by the coke formation. Herein, a novel Cu‐CNN/Pd‐BDCNN photocatalyst that is made up of “Cu‐nanoparticle‐loaded g‐C3N4 nanosheets” and “Pd‐nanoparticle‐loaded boron‐doped nitrogen‐deficient g‐C3N4 nanosheets” is reported. The existing dual‐reaction‐sites benefit the reactive oxygen intermediates participate in the reaction directly without distant migration. The in situ characterizations and density functional theory calculations reveal a newly dual reaction pathway through simultaneous dehydrogenation of methoxy and methyl intermediates, and demonstrate the importance of metal loading, which promote the CO2 and CH4 activation from both aspects of thermodynamics and kinetics. The optimized Cu‐CNN/Pd‐BDCNN photocatalyst displays an excellent syngas formation rate of over 800 µmol g−1 h−1 with H2/CO = 1 and splendid stability in continuous flow reaction under 300 mW cm−2 xenon lamp irradiation at room temperature. The “dual‐site” and “dual‐path” strategy shed light on the design of effective photocatalysts for methane dry reforming.
Dry reforming of methane (DRM) reaction occurs at two sites and presents two reaction pathways over the catalyst. The dual‐reaction‐site and dual‐path process not only achieves high catalytic activity, stability and syngas selectivity, but also overcomes the problems arising from poor oxygen migration on non‐oxygen‐containing catalysts. The strategy of dual reaction sites provides mechanistic insights for rational design of DRM catalysts.
Core-shell photoanodes have shown great potential for photoelectrochemical (PEC) water oxidation. However, the construction of a high-quality interface between the core and shell, as well as a highly ...catalytic surface, remains a challenge. Herein, guided by computation, we present a BiVO4 photoanode coated with ZnCoFe polyphthalocyanine using pyrazine as a coordination agent. The bidirectional axial coordination of pyrazine plays a dual role by facilitating intimate interfacial contact between BiVO4 and ZnCoFe polyphthalocyanine, as well as regulating the electron density and spin configuration of metal sites in ZnCoFe phthalocyanine, thereby promoting the potential-limiting step of *OOH desorption. The resulting photoanode displayed a high photocurrent density of 5.7±0.1 mA cm-2 at 1.23 VRHE. This study introduces a new approach for constructing core-shell photoanodes, and uncovers the key role of pyrazine axial coordination in modulating the catalytic activity of metal phthalocyanine.
We report the synthesis and characterization of a new ternary molybdenum pnictide superconductor, Cs2Mo3As3. The powder x-ray diffraction analysis reveals the quasi-one-dimensional (Q1D) hexagonal ...crystal structure formed by Cs+ and infinite (Mo3As3)2− chains as indicated by the wire-like grain morphology. Electrical resistivity and magnetic susceptibility characterizations exhibit superconductivity with the onset transition temperature at 11.5 K, which is the highest in all Q1D superconductors reported so far. An upper critical magnetic field of about 61.7 T at zero temperature was extrapolated from the resistivity measurement under a magnetic field, which is much higher than the Pauli paramagnetic limit, and the reason for such a high upper critical field may lie in its unconventional nature of superconducting pairing symmetry. The discovery of Cs2Mo3As3 inspires the search for new superconductors for future high field applications.
Here we report the discovery of superconductivity in the ternary LaRu2As2 compound. The polycrystalline LaRu2As2 samples were synthesized by the conventional solid state reaction method. Powder X-ray ...diffraction analysis indicates that LaRu2As2 crystallizes in the ThCr2Si2-type crystal structure with the space group 14/ mmm （No. 139）, and the refined lattice parameters are a = 4.182（6）A and c = 10.590（3）A. The temperature dependent resistivity measurement shows a clear superconducting transition with the onset Tc （critical tempera- ture） at 7.8 K, and zero resistivity happens at 6.8 K. The upper critical field at zero temperature μ0Hc2（0） was estimated to be 1.6 T from the resistivity measurement. DC magnetic susceptibility measurement shows a bulk superconducting Meissner transition at 7.0 K, and the isothermal magnetization measurement indicates that LaRu2As2 is a type-II superconductor.
Silicon-based two-dimensional (2D) materials are uniquely suited for integration in Si-based electronics. Silicene, an analogue of graphene, was recently fabricated on several substrates and was used ...to make a field-effect transistor. Here, we report that when Ru(0001) is used as a substrate, a range of distinct monolayer silicon structures forms, evolving toward silicene with increasing Si coverage. Low Si coverage produces a herringbone structure, a hitherto undiscovered 2D phase of silicon. With increasing Si coverage, herringbone elbows evolve into silicene-like honeycomb stripes under tension, resulting in a herringbone-honeycomb 2D superlattice. At even higher coverage, the honeycomb stripes widen and merge coherently to form silicene in registry with the substrate. Scanning tunneling microscopy (STM) was used to image the structures. The structural stability and electronic properties of the Si 2D structures, the interaction between the Si 2D structures and the Ru substrate, and the evolution of the distinct monolayer Si structures were elucidated by density functional theory (DFT) calculations. This work paves the way for further investigations of monolayer Si structures, the corresponding growth mechanisms, and possible functionalization by impurities.
Z-scheme Ag3PO4/Ag/MoO3-x photocatalyst was prepared by deposition of Ag and Ag3PO4 nanoparticles on the surface of MoO3-x nanosheets. With Ag mediation between Ag3PO4 and MoO3-x, there is efficient ...separation and utilization of photogenerated charge carriers. Owing to the rich presence of oxygen vacancies on the surface of MoO3-x, oxygen adsorption on the surface is enhanced. The as-prepared Ag3PO4/Ag/MoO3-x Z-scheme system shows outstanding photocatalytic activity and stability for the degradation of dyes (rhodamine B, methylene blue, as well as their mixture) and ciprofloxacin under visible light irradiation, displaying degradation rate that is 15.9, 3.4, 14.9 and 3.0 times that of MoO3-x, Ag3PO4, Ag/MoO3-x and Ag3PO4/MoO3-x, respectively. According to the results of trapping experiments, ·OH and ·O2− are the main active species, and a possible reaction mechanism has been proposed.
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•Ag3PO4/Ag/MoO3-x ternary Z-scheme system with tight interfaces was obtained.•The Z-scheme structure is beneficial for the separation of charge carriers.•The Ag3PO4/Ag/MoO3-x shows enhanced activity for dyes and ciprofloxacin degradation.•Presence of O-vacancy on the surface of MoO3-x is benefit for photocatalytic process.•Holes and ·O2− are the main active species for organic degradation.
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Here we report the discovery of the first ternary molybdenum pnictide based superconductor K2Mo3As3. Polycrystalline samples were synthesized by the conventional solid state reaction ...method. X-ray diffraction analysis reveals a quasi-one-dimensional hexagonal crystal structure with (Mo3As3)2− linear chains separated by K+ ions, similar as previously reported K2Cr3As3, with the space group of P-6m2 (No. 187) and the refined lattice parameters a = 10.145(5) Å and c = 4.453(8) Å. Electrical resistivity, magnetic susceptibility, and heat capacity measurements exhibit bulk superconductivity with the onset Tc at 10.4 K in K2Mo3As3 which is higher than the isostructural Cr-based superconductors. Being the same group VIB transition elements and with similar structural motifs, these Cr and Mo based superconductors may share some common underlying origins for the occurrence of superconductivity and need more investigations to uncover the electron pairing within a quasi-one-dimensional chain structure.
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