A flatband representing a highly degenerate and dispersionless manifold state of electrons may offer unique opportunities for the emergence of exotic quantum phases. To date, definitive experimental demonstrations of flatbands remain to be accomplished in realistic materials. Here, we present the first experimental observation of a striking flatband near the Fermi level in the layered Fe_{3}Sn_{2} crystal consisting of two Fe kagome lattices separated by a Sn spacing layer. The band flatness is attributed to the local destructive interferences of Bloch wave functions within the kagome lattices, as confirmed through theoretical calculations and modelings. We also establish high-temperature ferromagnetic ordering in the system and interpret the observed collective phenomenon as a consequence of the synergetic effect of electron correlation and the peculiar lattice geometry. Specifically, local spin moments formed by intramolecular exchange interaction are ferromagnetically coupled through a unique network of the hexagonal units in the kagome lattice. Our findings have important implications to exploit emergent flat-band physics in special lattice geometries.

The correlation and competition between antiferromagnetism and superconductivity are one of the most fundamental issues in high temperature superconductors. Superconductivity in high temperature cuprate superconductors arises from suppressing an antiferromagnetic (AFM) Mott insulator1 while in iron-pnictide superconductors arises from AFM semimetals and can coexist with AFM orders23456789. This difference raises many intriguing debates on the relation between the two classes of high temperature superconductors. Recently, superconductivity at 32 K has been reported in iron-chalcogenide superconductors AxFe2−ySe2 (A = K, Rb, and Cs)101112. They have the same structure as that of iron-pnictide 122-system131415. Here, we report electronic and magnetic phase diagram of KxFe2−ySe2 system as a function of Fe valence. We find a superconducting phase sandwiched between two AFM insulating phases. The two insulating phases are characterized by two distinct superstructures caused by Fe vacancy orders with modulation wave vectors of q1 = (1/5, 3/5, 0) and q2 = (1/4, 3/4, 0), respectively.

The development of highly efficient and stable electrocatalysts is one of the keys to the blossom and popularization of a series of new green energy sources. [2] However, the complex preparation process, low catalytic activity, and poor stability are still the main obstacles restricting the large-scale application of electrocatalysts. [3] 3D nanostructures usually have sufficient nanopores and larger specific surface areas, which greatly promote the transmission of ions within the nanostructures, thereby exhibiting extraordinary electrocatalytic activity. [4] Therefore, the rational design and preparation of electrocatalysts with stereo-structure and rich surface area is an effective strategy to achieve highly efficient and stable catalytic activity. [3a,5] Generally, anisotropic 3D electrocatalysts exhibit more excellent electrocatalytic activity and stability due to their heterogeneous elemental distribution or unsymmetrical nanostructure. [6] Most reported 3D anisotropic electrocatalysts are mainly achieved by adjusting the heterogeneous distribution of elements. [7] The heterogeneous distribution of elements can directly affect the local coordinative environment, which could greatly change the adsorption performance of nanostructures. [8] However, the construction of 3D nanostructures with heterogeneous element composition requires a multistep synthesis or complex replacement process, which causes poor repeatability. In addition, 3D electrocatalysts with anisotropic morphology can realize the comprehensive adjustment of the migration and the reaction path of reactants, greatly enhancing the electrocatalytic activity and stability. [4b,9] Up to now, there is still a tremendous challenge to design 3D electrocatalyst combining both of anisotropically distributed elements and anisotropic morphologies to achieve a great electrocatalytic activity.Herein, we successfully prepared 3D anisotropic Au@Pt-Pd hemispherical nanostructures (Au@Pt-Pd H-Ss) accompanied with both the heterogeneity of elements and the anisotropy of morphology as efficient electrocatalysts for oxidation reaction for the first time. The addition of BO 2 − with ultra-low concentration in the growing solution leads to its non-uniform adsorption on Au seed surface. Meanwhile, density functional theory (DFT) simulation shows that the formation energy Anisotropic 3D nanostructures exhibit excellent electrocatalytic activity and stability due to their heterogeneous elemental distribution and unsymmetrical configuration. However, it is still a huge challenge to combine anisotropically distributed elements and anisotropic morphologies within one 3D nanostructure. Herein, 3D Au@Pt-Pd hemispherical nanostructures (Au@Pt-Pd H-Ss) are fabricated as highly efficient electrocatalysts for oxidation reaction, which present heterogenous element distribution and anisotropic morphology. It is demonstrated that the non-uniform adsorption of BO 2 − on Au-CTA + surface, as well as the simulated lower formation energy of Pt-Pd atoms for Au-CTA + -BO 2 −

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The large amount of 4-nitrophenol (4-NP) wastewater produced by the chemical industry has received increased concern over the growing risk of environmental pollution. The ability to catalyze the reduction of highly concentrated 4-NP wastewater is highly desirable for the practical treatment of industrial wastewater, yet it remains a significant challenge. Herein, we report Pd nanoparticle-decorated 3D-printed hierarchically porous TiO 2 scaffolds (Pd/TiO 2 scaffolds) for the efficient reduction of highly concentrated 4-NP wastewater (2 g•L −1 , ∼14.38 mM). The millimeter-sized interconnected channels in the scaffolds are conducive to rapid mass and ion transportation; meanwhile, the abundant micrometer-and nanometer-sized pores on the surface of the scaffolds offer adequate anchoring sites for Pd nanoparticles. The turnover frequency of the hierarchically porous Pd/TiO 2 scaffold (16 layers) is up to 2.69 min −1 , which is 1063 times higher than that of the Pd/TiO 2 -bulk material with the same size (0.00253 min −1 ). Importantly, no obvious deactivation of the catalytic activity is observed even after 20 cycles of catalytic reduction of 4-NP, showing excellent catalytic stability and reusability. Our strategy of loading the nanostructured catalyst on 3D-printable hierarchically porous structures put forward a flexible and versatile approach for boosting the catalytic performance of the catalysts, including catalytic activity, stability, and reusability, which can help promote their practical application in industry.

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