Shujun Qiu

Fabrication and characterization of a novel nanoporous Co–Ni–W–B catalyst for rapid hydrogen generation

A highly active nanoporous Co–Ni–W–B alloy has been prepared using chemical reduction in an ethanol solution and tested as a novel catalyst for hydrolysis of ammonia borane. Compared with the alloy prepared in an aqueous solution, the as-prepared alloy shows a much higher surface area and hydrogen generation rate.

Simple synthesis of graphene-doped flower-like cobalt–nickel–tungsten–boron oxides with self-oxidation for high-performance supercapacitors

In this study, we devised an easy and simple approach to synthesize a composite of flower-like cobalt–nickel–tungsten–boron oxides (Co–Ni–W–B–O) that were doped with reduced graphene oxide (rGO); the composite was designed for supercapacitor applications. A Co–Ni–W–B alloy was first deposited on rGO through one-pot chemical reduction in an ethanol solution at room temperature. The resulting Co–Ni–W–B alloy self-oxidized in air on the rGO surface. The Co–Ni–W–B–O/rGO composites resembled three-dimensional flowers with a high surface area; they also exhibited superior electrochemical performance when compared to most previously reported electrodes based on nickel–cobalt oxides. Furthermore, the Co–Ni–W–B–O/rGO composite prepared in an ethanol solution showed much higher electrochemical performance than the composite prepared in water. The Co–Ni–W–B–O/rGO electrode showed an ultrahigh specific capacitance of 1189.1 F g−1 at 1 A g−1 and exhibited a high energy density of 49.9 W h kg−1 along with remarkable cycle stability (10 000 cycles with 80.7% capacitance retention at 15 A g−1), which is promising for its application in energy storage devices.

Self-assembly synthesis of nitrogen-doped mesoporous carbons used as high-performance electrode materials in lithium-ion batteries and supercapacitors

Nitrogen-doped mesoporous carbons (NMCs) have been employed as electrode materials for energy storage devices such as lithium-ion batteries (LIBs) and supercapacitors due to their high accessible porosity and nitrogen content. However, how to maintain the structural stability of NMCs with abundant nitrogen atoms in their 2D honeycomb lattice is still a significant challenge. Herein, NMCs with a high nitrogen content of 18.86 wt% have been successfully synthesized via a self-assembly route in the presence of guanine as a nitrogen source. Furthermore, the nitrogen content and porosity of NMCs can be tuned by controlling the experimental conditions. Benefiting from the high N content, appropriate specific surface area (455 m2 g−1), and high accessible porosity, NMC exhibits superior electrochemical performance. This NMC anode for LIBs can retain a discharge capacity as high as 610 mA h g−1 with a coulombic efficiency of 98.5% after 50 cycles. In addition, it also displays good potential towards supercapacitor application with a specific capacitance of 227 F g−1 (in 6 M KOH) at a current density of 0.5 A g−1. The enhanced electrochemical performance could be attributed to both the low charge transfer resistance and the incremental electrochemical activity resulting from the existence of optimized nitrogen atoms.

Organic carbon gel assisted-synthesis of Li1.2Mn0.6Ni0.2O2 for a high-performance cathode material for Li-ion batteries

Lithium-rich layered oxide Li1.2Ni0.2Mn0.6O2 with a stable network flake structure has been synthesized through a facile resorcinol–formaldehyde (RF) organic carbon gel-assisted method. The as-prepared sample used as a cathode material in lithium ion batteries (LIBs) was characterized by X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and electrochemical measurements. The stable network flake structure is assembled through a dense stack of nanoparticles with an average size of 50–200 nm. As an active material for LIB cathodes, the Li1.2Ni0.2Mn0.6O2 sample shows excellent rate capacities and cycling stability, and delivers a high initial discharge capacity of 273.3 mA h g−1 at 0.1C (1C = 200 mA g−1) between 2.0 V and 4.8 V. When the discharge rate is increased to 2C, an initial capacity of 196.7 mA h g−1 is obtained. After 150 cycles, a discharge capacity of 183.7 mA h g−1 and a high capacity retention of 93.4% are yielded at a rate of 2C.

Light metal borohydrides/amides combined hydrogen storage systems: composition, structure and properties

The implementation of a future economy based on hydrogen-related energy needs an urgent development of efficient, safe, and economic solid-state hydrogen-storage materials. During the search process for novel materials for storing hydrogen, research interests in the past few decades have been intensively focused on light metal borohydrides and amides as two representative chemical complex hydrides with high hydrogen capacities. Recently, a large number of studies have reported new borohydride/amide combined systems that expand the scope of hydrogen-storage materials. Here, we review the interaction between light metal borohydrides and amides for storing hydrogen, with a special emphasis on the synthetic strategies and structural, physical, and chemical properties, which reveal a correlation between the composition, structure, and dehydrogenation properties and also provide general principles to the design of new combined systems with tailored functionality. This review also demonstrates the current progress on the dehydrogenation kinetic improvement of borohydride/amide combined systems.

Nitrogen-rich sandwich-like carbon nanosheets as anodes with superior lithium storage properties

Carbon materials such as graphite have been used as anode material for Li-ion batteries (LIBs). However, the energy stored in carbon materials is greatly dependent on their structural characteristics. Herein, nitrogen-rich sandwich-like carbon nanosheets (NSCN) have been prepared through a facile hydrothermal carbonization (HTC) method followed by pyrolysis. The nitrogen-rich sandwich-like carbon nanosheets synthesized at 600 °C (NSCN-600) have a higher specific surface area of 1112 m2 g−1 and a total nitrogen content of 11.4 wt% (therein 9.30 wt% for both pyridinic-N and pyrrolic-N), giving rise to high discharge capacity (910 mA h g−1 at 100 mA g−1 after 50 cycles) and remarkable rate capability (719 mA h g−1 at 500 mA g−1 after 200 cycles and 390 mA h g−1 at 2000 mA g−1). Such desirable electrochemical properties could be attributed to the unique sandwich-like nanostructures consisting of a number of amorphous carbon nanoparticles closely covered with carbon sheet layers. Such a simple preparation method could provide a strategy for rational engineering of nanostructured nitrogen-rich carbonaceous materials for high-performance LIBs.

Microencapsulation of phase change materials with carbon nanotubes reinforced shell for enhancement of thermal conductivity

Novel microencapsulated phase change materials (micro-PCMs) were synthesized via in-situ polymerization with modified carbon nanotubes(CNTs) reinforced melamine-formaldehyde resin as shell material and CNTs reinforced n-octadecane as PCMs core. DSC results confirm that the micro-PCMs possess good phase change behavior and excellent thermal cycling stability. Melting enthalpy of the micro-PCMs can achieve 133.1 J/g and has slight changes after 20 times of thermal cyclings. And the incorporation of CNTs supplies the micro-PCMs with fast thermal response rate which increases the crystallization temperature of the micro-PCMs. Moreover, the thermal conductivity of the micro-PCMs has been significantly enhanced by introducing CNTs into their shell and core materials. And the thermal conductivity of micro-PCMs with 1.67 wt.% CNTs can increase by 25%. These results exhibit that the obtained micro-PCMs have a good prospect in thermal energy storage applications.

Effect of Ball Milling on the Electrochemical Properties of La0.7(Mg0.25Ti0.05)(Ni0.85Co0.15)3.5 Hydrogen Storage Alloy

The influence of ball milling on the structure and the electrochemical properties of La0.7(Mg0.25Ti0.05)(Ni0.85Co0.15)3.5 hydrogen storage alloy was investigated systematically. The XRD results show that the main phases of the alloy are a (LaMg)Ni3 phase with the PuNi3- type rhombohedral structure and a LaNi5 phase with the CaCu5-type hexagonal structure. The electrochemical studies show that the maximum discharge capacity and the high rate dischargeability decrease with the increase of milling time. Furthermore, the exchange current density first increases and then decreases with the increase of milling time from 0 (as-cast) to 120 min, consistent with the variation of the charge-transfer resistance from the electrochemical impedance spectra. However, the limiting current density first decreases from 2472.8 mA/g (as-cast) to 1719.6 mA/g (BM 30 min) and then increases to 2360.4 mA/g (BM 120 min).