The efficient use of natural gas will require catalysts that can activate the first C-H bond of methane while suppressing complete dehydrogenation and avoiding overoxidation. We report that single iron sites embedded in a silica matrix enable direct, nonoxidative conversion of methane, exclusively to ethylene and aromatics. The reaction is initiated by catalytic generation of methyl radicals, followed by a series of gas-phase reactions. The absence of adjacent iron sites prevents catalytic C-C coupling, further oligomerization, and hence, coke deposition. At 1363 kelvin, methane conversion reached a maximum at 48.1% and ethylene selectivity peaked at 48.4%, whereas the total hydrocarbon selectivity exceeded 99%, representing an atom-economical transformation process of methane. The lattice-confined single iron sites delivered stable performance, with no deactivation observed during a 60-hour test.

Doping single-atom metals into MoS2 matrix can efficiently trigger the electrocatalytic hydrogen evolution activity of inert S atoms on 2D MoS2 surface and meanwhile enhance catalytic stability and anti-poison ability.

Energy storage and conversion remain signifi cantly challenging to the research community. Among the candidates, lithium-ion batteries show great attraction and have been used in a wide range of applications, from small electronic devices, such as mobile phones and notebook computers, to increasing numbers of electric vehicles and large-scale energy storage equipments. [1][2][3][4][5][6] However, the relatively high cost of lithium resources shows the potential problems in terms of the long-term and large-scale applications of lithium-ion batteries. Lithium resources are limited; lithium makes up about 0.0065% of the earth ′ s crust and is unevenly distributed in South America. Thus, development of alternative storage devices is not only desirable but also necessary. Given this background, intense interest in the use of sodium-ion batteries particularly for largescale energy storage has recently been rekindled. Sodium, an element of electrochemical equivalence and proper potential, could be used as a substitute for lithium to meet the demands of rechargeable batteries. Furthermore, the sodium resources are considered to be unlimited and sodium salts widely exist in the sea. Therefore, sodium-ion batteries demonstrate the potential to substitute for lithium-ion batteries in the particular application in large-scale energy storage for renewable solar and wind power as well as smart grid. [ 7 , 8 ] Tremendous attention has been paid to sodium-ion batteries in recent years. Many electrode materials, such as Na x CoO 2 , [ 9 ] NaCrO 2 , [ 10 ] Na 1.0 Li 0.2 Ni 0.25 Mn 0.75 O δ , [ 11 , [ 17 ] hard carbon [ 13 , 18 , 19 ] and TiO 2 [ 20 ] have been investigated for application in sodium-ion batteries. Very recently, we reinvestigated the sodium ion insertion/extraction into/from Na 3 V 2 (PO 4 ) 3 with a NASICON structure. [ 21 ] The NASICON structure features a highly covalent three-dimensional framework that generates large interstitial spaces through which sodium ions may diffuse. [22][23][24] Our previous study was the fi rst to demonstrate that carbon coating can signifi cantly improve its sodium storage performance. [ 21 ] Carbon-coated Na 3 V 2 (PO 4 ) 3 electrodes show two fl at plateaus at 3.4 V and 1.6 V vs. Na + / Na, respectively. The voltage plateau located at 3.4 V is relatively higher than that of other cathode materials for sodium-ion batteries in recent reports. [9][10][11][12][13][14][15] However, the coulombic efficiency of the Na 3 V 2 (PO 4 ) 3 electrode in a half-cell is not as high as 99.5%, and does not even increase after the fi rst cycle, [ 21 ] likely because of the NaClO 4 /PC electrolyte used. Moreover, the storage capacity could also be enhanced by decreasing the carbon content of the composite and using optimized electrolyte system. In this contribution, Na 3 V 2 (PO 4 ) 3 /C nanocomposites with different carbon contents were prepared by a one-step solid state reaction and evaluated in different electrolyte systems. It was found that the sodium storage performance in terms of capacity...

A coordinatively unsaturated single iron site confined in a graphene matrix shows an ultrahigh activity for catalytic oxidation.

Magnetic skyrmions are topologically protected vortex-like nanometric spin textures that have recently received growingly attention for their potential applications in future highperformance spintronic devices. Such unique mangetic naondomains have been recently discovered in bulk chiral magnetic materials, such as MnSi [1][2][3][4] , FeGe [5,6] , FeCoSi [7] , Cu 2 OSeO 3 [8][9][10] , -Mn-type Co-Zn-Mn [11] , and also GaV 4 S 8[12] a polar magnet. The crystal structure of these materials is cubic and lack of centrosymmetry, leading to the existence of Dzyaloshinskii-Moriya (DM) interactions. Unlike the conventional spin configurations, such as helical or conical, that are usually found in chiral magnets, a magnetic skyrmion has a particle-like swirling-spin configuration characterized by a topological index called the skyrmion number [13,14] . The nontrivial topology of magnetic skyrmions results in a number of

Quantitative susceptibility mapping (QSM) has enabled MRI of tissue magnetic susceptibility to advance from simple qualitative detection of hypointense blooming artifacts to precise quantitative measurement of spatial biodistributions. QSM technology may be regarded to be sufficiently developed and validated to warrant wide dissemination for clinical applications of imaging isotropic susceptibility, which is dominated by metals in tissue, including iron and calcium. These biometals are highly regulated as vital participants in normal cellular biochemistry, and their dysregulations are manifested in a variety of pathologic processes. Therefore, QSM can be used to assess important tissue functions and disease. To facilitate QSM clinical translation, this review aims to organize pertinent information for implementing a robust automated QSM technique in routine MRI practice and to summarize available knowledge on diseases for which QSM can be used to improve patient care. In brief, QSM can be generated with postprocessing whenever gradient echo MRI is performed. QSM can be useful for diseases that involve neurodegeneration, inflammation, hemorrhage, abnormal oxygen consumption, substantial alterations in highly paramagnetic cellular iron, bone mineralization, or pathologic calcification; and for all disorders in which MRI diagnosis or surveillance requires contrast agent injection. Clinicians may consider integrating QSM into their routine imaging practices by including gradient echo sequences in all relevant MRI protocols.

We have investigated the magnetoresistive behavior of Dirac semi-metal Cd3As2 down to low temperatures and in high magnetic fields. A positive and linear magnetoresistance (LMR) as large as 3100% is observed in a magnetic field of 14 T, on high-quality single crystals of Cd3As2 with ultralow electron density and large Lande g factor. Such a large LMR occurs when the magnetic field is applied perpendicular to both the current and the (100) surface, and when the temperature is low such that the thermal energy is smaller than the Zeeman splitting energy. Tilting the magnetic field or raising the temperature all degrade the LMR, leading to a less pronounced quadratic behavior. We propose that the phenomenon of LMR is related to the peculiar field-induced shifting/distortion of the helical electrons' Fermi surfaces in momentum space.Compared with those negative magnetoresistive behaviors such as giant magnetoresistance [1] and colossal magnetoresistance [2] whose mechanisms have been well understood, positive large LMR was also reported in past decades but its mechanism is not fully clarified. Such behavior was found in highly disordered nonmagnetic narrow-band semiconductors such as Ag 2±δ Te and Ag 2±δ Se [3], in bismuth thin films [4], and in Dirac electron systems such as epitaxial graphene [5] and topological insulators-related materials [6][7][8][9][10]. Large LMR was also observed in InSb [11], a material with very small electron effective mass and very large electron Lande g factor. Several theories have been proposed to explain the phenomenon. Abrikosov proposed that the LMR is a quantum magnetoresistance of linearly dispersed electron systems, arising when all the electrons are filled in the first Landau level (LL), i.e., in the extreme quantum limit [12,13]. Wang and Lei proposed that the LMR can still arise when the LLs are smeared, if with a positive g factor [14]. There are also pictures involving no LLs. Parish and Littlewood explained the LMR in Ag 2±δ Te and Ag 2±δ Se by modeling the materials as a network due to disorder-induced mobility fluctuation [15]. So far the mechanism of LMR is still waiting to be clarified.In this work, we revisit the LMR issue by investigating the magnetoresistive behavior of Cd 3 As 2 single crystals. Cd 3 As 2 is predicted to be a three-dimensional (3D) Dirac semimetal [16], with linearly dispersed electron states in the bulk, and Fermi arcs at the surface which connect the bulk Dirac cones. The existence of 3D Dirac cones has been confirmed by angular resolved photoemission spectroscopy study [17]. And a LMR behavior has recently been observed on samples with Fermi level well above the Dirac point [9, 10], i.e., with carrier density of the order 10 18 cm −3 . Here, we report our investigations on single crystals of Cd 3 As 2 with a much lower carrier density, such that the Fermi surfaces are small spheres very close to the Dirac points in the momentum space, rather than near the Lifshitz transition (i.e., touching with each other). We observed a positive, very large an...

The design of catalysts that are both highly active and stable is always challenging. Herein, we report that the incorporation of single metal active sites attached to the nitrogen atoms in the basal plane of graphene leads to composite materials with superior activity and stability when used as counter electrodes in dye-sensitized solar cells (DSSCs). A series of composite materials based on different metals (Mn, Fe, Co, Ni, and Cu) were synthesized and characterized. Electrochemical measurements revealed that CoN4 /GN is a highly active and stable counter electrode for the interconversion of the redox couple I(-) /I3 (-) . DFT calculations revealed that the superior properties of CoN4 /GN are due to the appropriate adsorption energy of iodine on the confined Co sites, leading to a good balance between adsorption and desorption processes. Its superior electrochemical performance was further confirmed by fabricating DSSCs with CoN4  /GN electrodes, which displayed a better power conversion efficiency than the Pt counterpart.