Qiliang Wei

Porous hollow α-Fe2O3@TiO2 core–shell nanospheres for superior lithium/sodium storage capability

Porous hollow α-Fe2O3@TiO2 core–shell nanospheres for use as anode materials in lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs) have been successfully fabricated by a simple template-assisted method, which has been rarely reported before. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and N2 adsorption–desorption isotherms reveal that the as-prepared α-Fe2O3@TiO2 is composed of a hollow inner cavity and an outer shell with massive mesopores. This porous hollow structure is capable of buffering the large volume variation of α-Fe2O3 during cycling and preventing the electrode from pulverization and aggregation, as well as providing sufficiently large interstitial space within the crystallographic structure to host alkalis (Li and Na). As a consequence, this hybrid composite exhibits outstanding electrochemical properties, e.g., high specific capacity, excellent cyclability, satisfactory rate performance, and splendid initial coulombic efficiency for both LIBs and SIBs.

A facile synthesis of Fe3O4 nanoparticles/graphene for high-performance lithium/sodium-ion batteries

In this study, a facile, simple, and inexpensive co-precipitation method is used to fabricate diamond-like Fe3O4 nanoparticle/graphene composites for use as lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs) electrode materials. In our synthesis, high-temperature treatment and complicated procedures and apparatus are avoided. Physical characterizations reveal that the as-prepared product is composed of a large fraction of diamond-like Fe3O4 nanoparticles uniformly distributed on thin graphene nanosheets. Compared to bare Fe3O4 and most of the previously reported studies, the as-obtained Fe3O4/graphene composite exhibits greatly enhanced electrochemical properties for both LIBs and SIBs, including excellent reversible capacity, superior cyclability and good rate performance. Specifically, when tested as an anode for LIBs, the Fe3O4/graphene composite shows specific capacity of 1430 mA h g−1 after 100 cycles at 200 mA g−1. The initial discharge capacity tested in SIBs is 855 mA h g−1, and after 40 cycles, the discharge capacity stabilizes at ∼210 mA h g−1 for 250 cycles. The excellent performance can be attributed to the greatly improved electrical conductivity, large surface area and excellent stability of the electrode material.

3D Porous Fe/N/C Spherical Nanostructures As High-Performance Electrocatalysts for Oxygen Reduction in Both Alkaline and Acidic Media

Exploring inexpensive and high-performance nonprecious metal catalysts (NPMCs) to replace the rare and expensive Pt-based catalyst for the oxygen reduction reaction (ORR) is crucial for future low-temperature fuel cell devices. Herein, we developed a new type of highly efficient 3D porous Fe/N/C electrocatalyst through a simple pyrolysis approach. Our systematic study revealed that the pyrolysis temperature, the surface area, and the Fe content in the catalysts largely affect the ORR performance of the Fe/N/C catalysts, and the optimized parameters have been identified. The optimized Fe/N/C catalyst, with an interconnected hollow and open structure, exhibits one of the highest ORR activity, stability and selectivity in both alkaline and acidic conditions. In 0.1 M KOH, compared to the commercial Pt/C catalyst, the 3D porous Fe/N/C catalyst exhibits ∼6 times better activity (e.g., 1.91 mA cm-2 for Fe/N/C vs 0.32 mA cm-2 for Pt/C, at 0.9 V) and excellent stability (e.g., no any decay for Fe/N/C vs 35 mV negative half-wave potential shift for Pt/C, after 10000 cycles test). In 0.5 M H2SO4, this catalyst also exhibits comparable activity and better stability comparing to Pt/C catalyst. More importantly, in both alkaline and acidic media (RRDE environment), the as-synthesized Fe/N/C catalyst shows much better stability and methanol tolerance than those of the state-of-the-art commercial Pt/C catalyst. All these make the 3D porous Fe/N/C nanostructure an excellent candidate for non-precious-metal ORR catalyst in metal-air batteries and fuel cells.

Litchi-like porous Fe/N/C spheres with atomically dispersed FeNx promoted by sulfur as highly efficient oxygen electrocatalysts for Zn–air batteries

The fabrication of carbon-based electrocatalysts that are highly active and stable as well as with plenty of pores for mass transport is essential for high-performance metal–air batteries. Herein, a new simple route involving sulfur (S) as a “promoter” was developed to achieve a litchi-like porous Fe/N/C catalyst with abundant FeNx species. The obtained electrocatalyst exhibits a large surface area with a high pore volume and shows high activity for oxygen reduction. Moreover, a Zn–air battery device adopting this S-promoted litchi-like Fe/N/C catalyst shows superior power density (double that of the untreated counterpart).

Highly-ordered microporous carbon nanospheres: a promising anode for high-performance sodium-ion batteries

Highly-ordered microporous carbon (MPC) nanospheres were prepared by a simple hydrothermal route based on a soft template. The interlayer spacing of the MPC was well tuned by simply adjusting the heat-treatment temperatures. The as-obtained carbon spheres treated at 700 °C (MPC-700) combine the features required for high-performance sodium-ion battery (SIB) electrode materials, such as a large interlayer spacing (∼0.457 nm), high surface area, structural stability and plenty of micropores for Na insertion, which synergistically contribute to their impressive electrochemical properties. When applied as an anode for SIBs, the MPC-700 electrode exhibits a high reversible capacity, good cycling stability, and an excellent high-rate performance (∼160 mA h g−1 after 500 cycles at 1000 mA g−1), making it a promising candidate for SIB anodes.

Aligned copper nanorod arrays for highly efficient generation of intense ultra-broadband THz pulses

We demonstrate an intense broadband terahertz (THz) source based on the interaction of relativistic-intensity femtosecond lasers with aligned copper nanorod array targets. For copper nanorod targets with a length of 5 μm, a maximum 13.8 times enhancement in the THz pulse energy (in ≤20 THz spectral range) is measured as compared to that with a thick plane copper target under the same laser conditions. A further increase in the nanorod length leads to a decrease in the THz pulse energy at medium frequencies (≤20 THz) and increase of the electromagnetic pulse energy in the high-frequency range (from 20–200 THz). For the latter, we measure a maximum energy enhancement of 28 times for the nanorod targets with a length of 60 μm. Particle-in-cell simulations reveal that THz pulses are mostly generated by coherent transition radiation of laser produced hot electrons, which are efficiently enhanced with the use of nanorod targets. Good agreement is found between the simulation and experimental results.

Pt/TiSix-NCNT Novel Janus Nanostructure: A New Type of High-Performance Electrocatalyst

Novel Janus nanostructured electrocatalyst (Pt/TiSi x-NCNT) was prepared by first sputtering TiSi x on one side of N-doped carbon nanotubes (NCNTs), followed by wet chemical deposition of Pt nanoparticles (NPs) on the other side. Transmission electron microscopy (TEM) studies showed that the Pt NPs are mainly deposited on the NCNT surface where no TiSi x (i.e., between the gaps of TiSi x film). This feature could benefit the increase in the stability of the Pt NP catalyst. Indeed, compared to the state-of-the-art commercial Pt/C catalyst, this novel Pt/TiSi x-NCNT Janus structure showed ∼3 times increase in stability as well as significantly improved CO tolerance. The obvious performance enhancement could be attributed to the better corrosion resistance of TiSi x and NCNTs than the carbon black that is used in the commercial Pt/C catalyst. Pt/TiSi x-NCNT Janus nanostructures open the door for designing new type of high-performance electrocatalyst for fuel cells and other oxygen reduction reaction-related energy devices.