Ruijuan Qi

Firework-shaped TiO2 microspheres embedded with few-layer MoS2 as an anode material for excellent performance lithium-ion batteries

A three-dimensional porous hierarchical architecture of uniform TiO2 microspheres embedded with MoS2 nanosheets was prepared via a facile hydrothermal self-assembly scheme. A possible growth mechanism is presented in detail based on theoretical analysis and experimental facts. Further experiments demonstrate that MoS2 nanosheets are uniformly coated on the surface of TiO2 nanorods. Besides, the obtained F-TiO2@MoS2 possesses a large surface area and stable structure. Moreover, the F-TiO2@MoS2 microspheres were successfully assembled as an electrode material for lithium-ion batteries. As expected, the electrochemical measurement demonstrates that the F-TiO2@MoS2 shows excellent electrochemical performance, which exhibits a high reversible capacity of 971 mA h g−1 at a current density of 100 mA g−1, a markedly high rate capability of over 450 mA h g−1 at a current density of 1000 mA g−1 and a superior cycling stability of 714 mA h g−1 after 200 cycles at a current density of 100 mA g−1, as an anode material for LIBs.

Hierarchical 3-dimensional CoMoO4 nanoflakes on a macroporous electrically conductive network with superior electrochemical performance

Nanoscale cobalt molybdate (CoMoO4) particles are fabricated hydrothermally on the surface and sidewall of three-dimensional nickel-coated silicon microchannel plates (also called macroporous electrically conductive network, MECN) as the active electrode in a miniature energy storage device. The relationships between the reaction time, morphology, formation mechanism of the CoMoO4 nanostructure, and electrochemical performance are studied. After an optimal hydrothermal synthesis time of 2.5 h, the CoMoO4 electrode has a capacity of 32.40 mA h g−1 (492.48 μA h cm−2) at constant current density of 1 A g−1 and retention ratio of 85.98% after 5000 cycles. The large specific capacity and excellent rate capability can be attributed to the unique 3D ordered porous architecture which facilitates electron and ion transport, enlarges the liquid–solid interfacial area, and enhances the utilization efficiency of the active materials. Furthermore, the weight and size of the device are reduced. By using the CoMoO4/MECN electrode as the positive electrode and carbon/nickel foam (carbon/NF) as the negative electrode, the faradaic electrode was packaged by a CR2025 battery cell as the miniature hybrid device exhibits stable power characteristics (5000 cycle times with 71.82% retention). After charging each hybrid device for 10 s, three devices in series can power two 5 mm diameter light-emitting diodes (LED) efficiently.

Facile synthesis of hollow hierarchical Ni/γ-Al2O3 nanocomposites for methane dry reforming catalysis

Hydrogen reduction of hierarchical spinel intermediates that were synthesized by a facile hydrothermal method results in Ni/γ-Al2O3 nanocomposites with Ni nanoparticles (∼5.5 nm) well dispersed and embedded in nanoflakes of the hollow Al2O3 microspheres. The good dispersion of small metal nanoparticles and strong metal–support interactions that resulted from decomposition of spinel intermediates during reduction are essential for the efficient and sustainable high temperature dry reforming of methane (DRM) catalysis. The high surface area (170 m2 g−1) composite catalysts show coke and sintering resistance in long term DRM catalysis at 750 °C, the highest temperature ever tested for hierarchical nanostructures. Ni loadings and the calcination temperatures of the spinel intermediate are investigated for their effect on the morphology and the catalytic performance of the final catalysts. It is interesting that some initially non-active control catalysts can be activated during long term testing.

Hybrid MnO2/C nano-composites on a macroporous electrically conductive network for supercapacitor electrodes

A two-step hydrothermal process is designed to synthesize hybrid MnO2/C nano-composites on a macroporous electrically conductive network (MECN) via a redox reaction in a 30 mM KMnO4 solution with carbon microspheres. The microstructure, surface morphology, and electrochemical properties of the MnO2/C coated on MECN are determined systematically. The MnO2 nanoflakes, which are about 40–200 nm, are deposited regularly on the carbon microspheres coated on the MECN electrode. The MnO2 nano-lamellas offer fast ion transport and adsorption–desorption to/from the MnO2 surface, and the microporous carbon microspheres enhance the electrical storage and ion transfer. The in situ growth of MnO2 on the carbon microspheres on the MECN substrate leads to a small contact resistance and short current transfer length. The materials are demonstrated to be excellent electrodes in supercapacitors boasting a high capacitance of 497 F g−1 at 1 A g−1 with a 1 cm2 electrode and excellent long-term cycling stability over 5000 cycles in 1 M Na2SO4. The MnO2/C/MECN||active carbon/Ni-foam asymmetrical supercapacitors (ASCs) deliver an energy density of 0.50 mW h cm−3 (55.5 W h kg−1 at a power density of 4000 W kg−1) with 87.6% retention of the specific capacitance after 5000 cycles.

Dielectric behaviors of Aurivillius Bi5Ti3Fe0.5Cr0.5O15 multiferroic polycrystals: Determining the intrinsic magnetoelectric responses by impedance spectroscopy.

Bismuth layer ferroelectrics (BLFs) pioneered by Aurivillius about sixty years ago have been revived recently because of the fatigue- and lead-free behaviors and high Curie temperature, and especially the robust magnetoelectric (ME) effect. However, discerning the intrinsic ME nature, and the inherence between charged defect dipole induced relaxation and spin-related behaviors are still an arduous task. Here, we report a quantitative analysis to reveal the intrinsic spin-lattice coupling in Aurivillius Cr-doped Bi5Ti3FeO15 (BTFCO) multiferroic polycrystals. Dielectric responses are systemically investigated by the temperature-dependent dielectric, module, impedance spectroscopy and equivalent circuit model, and two different dielectric relaxation processes occurred in grain interior of Aurivillius BTFCO polycrystals are clarified. One relaxation is proposed to associate with localized transfer of electrons between Fe3+ and Fe2+ while another one arises from the competition interaction of localized hopping of electrons between Fe3+ and Fe2+ and short-range migration of holes between Cr3+ and Cr6+. The variation of the intrinsic permittivity unambiguously confirms the coupling between spin and dipolar orderings in BTFCO polycrystals. These results offer a vital avenue for identifying the intrinsic and extrinsic signals of the electric and ME responses, and will give significant impetus to exploring the ME electronic devices of Aurivillius materials.

Coral-Shaped MoS2 Decorated with Graphene Quantum Dots Performing as a Highly Active Electrocatalyst for Hydrogen Evolution Reaction

We report a new CVD method to prepare coral-shaped monolayer MoS2 with a large amount of exposed edge sites for catalyzing hydrogen evolution reaction. The electrocatalytic activities of the coral-shaped MoS2 can be further enhanced by electronic band engineering via decorated with graphene quantum dot (GQD) decoration. Generally, GQDs improve the electrical conductivity of the MoS2 electrocatalyst. First-principles calculations suggest that the coral MoS2@GQD is a zero-gap material. The high electric conductivity and pronounced catalytically active sites give the hybrid catalyst outstanding electrocatalytic performance with a small onset overpotential of 95 mV and a low Tafel slope of 40 mV/dec as well as excellent long-term electrocatalytic stability. The present work provides a potential way to design two-dimensional hydrogen evolution reaction (HER) electrocatalysts through controlling the shape and modulating the electric conductivity.

Three-dimensional homo-nanostructured MnO2/nanographene membranes on a macroporous electrically conductive network for high performance supercapacitors

A three-step hydrothermal route was designed to fabricate three-dimensional (3D) homo-nanostructured MnO2 (MnO2–MnO2)/nanographene membranes on a macroporous and electrically conductive network (MECN). The preparation technology, structure and morphology, and electrochemical properties of samples are determined systematically. The nanographene/MECN electrode with more defects as the active surface had been synthesized by hydrothermal carbonization. The in situ growth of δ-MnO2 with a carbon-assisted reaction on the nanographene/MECN was strongly adhered to the substrate. The additional α-MnO2 with a redox reaction enhanced the mass loading of MnO2, developing the specific capacitance of the MnO2–MnO2/nanographene/MECN electrode. The materials are demonstrated as an electrode with a maximum capacitance of 4.5 F cm−2 or 179 F cm−3 (894 F g−1) at 1 mA cm−2 for 1 cm2 samples and retaining over 83% after 20 000 cycles in 1 M Na2SO4. The MnO2–MnO2/nanographene/MECN||AC/Ni-foam supercapacitors with high volumetric energy densities exhibit the ideal performance of a supercapacitor (1 mW h cm−3, 40.3 W h kg−1, at 1000 W kg−1), indicating a promising future for supercapacitors.

Structure and electrical properties of epitaxial SrRuO3 thin films controlled by oxygen partial pressure

SrRuO3 (SRO) thin films have been grown on (001)-oriented SrTiO3 substrate under various oxygen partial pressures (PO2). A typical step-and-terrace surface morphology and coherent epitaxy characteristics are found in the SRO films for high oxygen pressure growth (PO2 ≥ 10 Pa). Under such high PO2, SRO films exhibit metallic behavior over a temperature range of 10 K ≤ T ≤ 300 K. A detailed study on the transport properties of the metallic SRO films reveals that the resistivity (ρ) follows the law ρ(T)-ρ0 ∝ Tx (x = 0.5, 1.5, or 2). Below ferromagnetic transition temperature (Tc), ρ(T) follows T2 dependence below 30 K and T1.5 dependence at T > 30 K, respectively. This result demonstrates that a transition between the Fermi-liquid (FL) and non-Fermi-liquid (NFL) behavior occurs at ∼30 K. Furthermore, ρ(T) follows T0.5 dependence at T > Tc in the paramagnetic metal state. We have found that the FL to NFL transitions as well as the ferromagnetic transition are corresponding to the abnormal peaks in the magneto...

Fermi level alignment by copper doping for efficient ITO/perovskite junction solar cells

Different from band edge alignment, the Fermi level mismatch induced by band bending can manipulate charge collection at the ITO/(CH3NH3)1−xCuxPbI3 heterojunctions. In this work, we employed a feasible spin-coating process to prepare copper defect compensation in CH3NH3PbI3. The related work function was shown to shift with the copper doping density by Kelvin probe force microscopy (KPFM). Next, we applied transient surface photovoltage (TSPV) spectroscopy and first-order series reactions simulations to confirm that interface charge recombination at the ITO/perovskite junction can be eliminated through Cu+ doping. Nanoelectric photoconductive AFM analysis showed enhanced charge transfer and a higher photovoltage at the ITO/Cu-perovskite junction. Owing to efficient Fermi level alignment, the ITO/(CH3NH3)1−xCuxPbI3/PCBM/Ag devices displayed high power conversion efficiencies of 15.14 ± 0.67% at ambient conditions for inverted perovskite solar cells without any hole transport layer.

Three-dimensional tetsubo-like Co(OH)2 nanorods on a macroporous electrically conductive network as an efficient electroactive framework for the hydrogen evolution reaction

Conducting the hydrogen evolution reaction (HER) in an alkaline environment using a non-precious transition metal catalyst with high efficiency is challenging. Here, we report excellent HER activity achieved using three-dimensional (3D) tetsubo-like Co(OH)2 nanorods on a macroporous electrically conductive network (MECN) synthesized by a hydrothermal method. This unique framework comprises three levels of porous structures, including a bottom-ordered MECN substrate, an intermediate layer of vertically porous Co(OH)2 nanowires with a mean diameter of 100 nm and length of about 2 μm, and outmost Co(OH)2 nanosheets (≈20 nm). The 3D array structure with a large aspect ratio provides a large specific surface area and exposes more active sites to catalyze electrochemical reactions at the electrode–electrolyte interface. Compared with Co(OH)2 nanosheets on an MECN and foamy Co(OH)2 on an MECN structure, the synthesized architecture has excellent HER catalytic reactivity, including a low potential of −69.2 mV vs. RHE, a cathodic current density of 10 mA cm−2, a small Tafel slope of 61.9 mV dec−1, a high current density, and robust catalytic stability in 1 M KOH, and is promising in HER applications.