Noncentrosymmetric MoS2 semiconductors (1H, 3R) possess not only novel electronic structures of spin–orbit coupling (SOC) and valley polarization but also remarkable nonlinear optical effects. A more ...interesting noncentrosymmetric structure, the so-called 1T‴-MoS2 layers, was predicted to be built up from MoS6 octahedral motifs by theoreticians, but the bulk 1T‴ MoS2 or its single crystal structure has not been reported yet. Here, we have successfully harvested 1T‴ MoS2 single crystals by a topochemical method. The new layered structure is determined from single-crystal X-ray diffraction. The crystal crystallizes in space group P31m with a cell of a = b = 5.580(2) Å and c = 5.957(2) Å, which is a √3a × √3a superstructure of 1T MoS2 with corner-sharing Mo3 triangular trimers observed by the STEM. 1T‴ MoS2 is verified to be semiconducting and possesses a band gap of 0.65 eV, different from metallic nature of 1T or 1T′ MoS2. More surprisingly, the 1T‴ MoS2 does show strong optical second-harmonic generation signals. This work provides the first layered noncentrosymmetric semiconductor of edge-sharing MoS6 octahedra for the research of nonlinear optics.
Cu‐nanowire‐doped graphene (Cu NWs/graphene) is successfully incorporated as the back contact in thin‐film CdTe solar cells. 1D, single‐crystal Cu nanowires (NWs) are prepared by a hydrothermal ...method at 160 °C and 3D, highly crystalline graphene is obtained by ambient‐pressure CVD at 1000 °C. The Cu NWs/graphene back contact is obtained from fully mixing the Cu nanowires and graphene with poly(vinylidene fluoride) (PVDF) and N‐methyl pyrrolidinone (NMP), and then annealing at 185 °C for solidification. The back contact possesses a high electrical conductivity of 16.7 S cm−1 and a carrier mobility of 16.2 cm2 V−1 s−1. The efficiency of solar cells with Cu NWs/graphene achieved is up to 12.1%, higher than that of cells with traditional back contacts using Cu‐particle‐doped graphite (10.5%) or Cu thin films (9.1%). This indicates that the Cu NWs/graphene back contact improves the hole collection ability of CdTe cells due to the percolating network, with the super‐high aspect ratio of the Cu nanowires offering enormous electrical transport routes to connect the individual graphene sheets. The cells with Cu NWs/graphene also exhibit an excellent thermal stability, because they can supply an active Cu diffusion source to form an stable intermediate layer of CuTe between the CdTe layer and the back contact.
1D Cu‐nanowire‐doped graphene (Cu NWs/graphene) is used as the back contact for CdTe solar cells. The efficiency of cells with the Cu NWs/graphene reaches up to 12.1%, which is higher than for those with traditional back contacts using Cu‐particle‐doped graphite (10.5%) or Cu thin films (9.1%). The Cu‐NW cells also exhibit an excellent thermal stability.
In this paper, three-dimensional (3D) graphene network was prepared by chemical vapor deposition (CVD) on 3D porous Ni template. The as-prepared 3D graphene showed high conductivity of similar to 600 ...S cm-1 and low square resistance of 1.6 Omega sq-1. With the aid of 3D graphene network, the poorly conductive LiFePO4 exhibited high conductivity and good rate performance of 109 mA h g-1 at 10 C, indicating potential application in high rate lithium ion batteries.
Few layer graphene was grown on hexagonal boron nitride single crystal flakes by chemical vapor deposition without using metal catalysts. High quality and thickness controllability of the graphene ...layers are confirmed by Raman spectroscopy and transmission electron microscopy. Chemical vapor deposition of graphene on this perfect-lattice-matching dielectric substrate offers many advantages including cost effectiveness, easy scalability and compatibility with standard intergraded circuit processes and promises an advance to graphene’s applications in microelectronics and optoelectronics.
An efficient titania supported Au nanocluster (NC) has been prepared for the direct synthesis of useful EtOH from CO2 and H2. The unique creation of an excellent synergistic effect between Au NCs and ...the underlying TiO2 support, especially the anatase crystal phase with abundant oxygen vacancies, can achieve the high performance for EtOH synthesis under moderate and practical conditions.
The development of an efficient electrocatalyst toward the hydrogen evolution reaction (HER) is of significant importance in transforming renewable electricity to pure and clean hydrogen by water ...splitting. However, the construction of an active electrocatalyst with multiple sites that can promote the dissociation of water molecules still remains a great challenge. Herein, a partial‐single‐atom, partial‐nanoparticle composite consisting of nanosized ruthenium (Ru) nanoparticles (NPs) and individual Ru atoms as an energy‐efficient HER catalyst in alkaline medium is reported. The formation of this unique composite mainly results from the dispersion of Ru NPs to small‐size NPs and single atoms (SAs) on the Fe/N codoped carbon (Fe–N–C) substrate due to the thermodynamic stability. The optimal catalyst exhibits an outstanding HER activity with an ultralow overpotential (9 mV) at 10 mA cm−2 (η10), a high turnover frequency (8.9 H2 s−1 at 50 mV overpotential), and nearly 100% Faraday efficiency, outperforming the state‐of‐the‐art commercial Pt/C and other reported HER electrocatalysts in alkaline condition. Both experimental and theoretical calculations reveal that the coexistence of Ru NPs and SAs can improve the hydride coupling and water dissociation kinetics, thus synergistically enhancing alkaline hydrogen evolution performance.
A nanocomposite of partial‐single‐atom and partial‐nanoparticle formed within the Fe–N–C matrix serves as a multiple‐site electrocatalyst toward hydrogen evolution reaction with an ultralow overpotential of 9 mV to achieve 10 mA cm−2, a high turnover frequency, and ≈100% Faradaic efficiency. Theoretical calculations reveal that ruthenium single‐atoms effectively facilitate water dissociation, and ruthenium nanoparticles promote hydrogen desorption.
A new class of oxyhalide photocatalysts,
xBiOI–(1
−
x)BiOCl, were prepared by a soft chemical method. The samples with
x
=
0.2–1.0 have intense absorptions in the visible light region and the optical ...band gaps are in the range 1.92–2.31
eV. They possess high photocatalytic activities under visible light irradiation for the degradation of methyl orange. This high photocatalytic activity is in close relation with the deep valance band edge position and the internal electric fields between Bi
2O
2 slabs and halogen anionic slabs.
Anatase TiO2 is one of the most important energy materials but suffers from poor electrical conductivity. Nb doping has been considered as an effective way to improve its performance in the ...applications of photocatalysis, solar cells, Li batteries, and transparent conducting oxide films. Here, we report the further enhancement of electron transport in Nb-doped TiO2 nanoparticles via pressure-induced phase transitions. The phase transition behavior and influence of Nb doping in anatase Nb-TiO2 have been systematically investigated by in situ synchrotron X-ray diffraction and Raman spectroscopy. The bulk moduli are determined to be 179.5, 163.3, 148.3, and 139.0 GPa for 0, 2.5, 5.0, and 10.0 mol % Nb-doped TiO2, respectively. The Nb-concentration-dependent stiffness variation has been demonstrated: samples with higher Nb concentrations have lower stiffness. In situ resistance measurements reveal an increase of 40% in conductivity of quenched Nb-TiO2 in comparison to the pristine anatase phase. The pressure-induced conductivity evolution is discussed in detail in terms of the packing factor model, which provides direct evidence for the rationality of the correlation of packing factors with electron transport in semiconductors. Pressure-treated Nb-doped TiO2 with unique properties surpassing those in the anatase phase holds great promise for energy-related applications.
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