Qinglan Zhao

Facile synthesis and performances of nanosized Li2TiO3-based shell encapsulated LiMn1/3Ni1/3Co1/3O2 microspheres

LiMn1/3Ni1/3Co1/3O2 microspheres covered by a nanosized Li2TiO3-based shell are prepared by a facile synthesis method. First, a controllable TiO2 nano-layer is grown on the surface of a spherical Mn1/3Ni1/3Co1/3CO3 precursor, and then the resultant TiO2@LiMn1/3Ni1/3Co1/3O2 hybrid is synchronously transformed in situ into a hierarchical Li2TiO3@LiMn1/3Ni1/3Co1/3O2 microsphere through a solid-phase reaction. It has been found that the hierarchical Li2TiO3@LiMn1/3Ni1/3Co1/3O2 microspheres exhibit a good rate capability with a discharge capacity of 92.3 mA h g−1 even at higher rates of 20 C between 3.0 and 4.3 V. Besides, they possess excellent cyclic stability especially at high rates, with a capacity retention of 90.3% after 500 cycles at a 20 C rate. The enhanced electrochemical performance of the hierarchical Li2TiO3@LiMn1/3Ni1/3Co1/3O2 at high rates is attributed to the stable and fast Li+-conductor characteristic of the nanosized Li2TiO3-based shell. Thus, the Li2TiO3@LiMn1/3Ni1/3Co1/3O2 microspheres will be a promising cathode material for lithium-ion batteries with high power density and excellent cycling performance.

Preparation and performance of β-MnO2 nanorod @ nanoflake (Ni, Co, Mn) oxides with hierarchical mesoporous structure

The rational design and facile synthesis of transition metal oxides are necessary to improve their application in supercapacitors. Herein three kinds of hierarchical mesoporous structured transition metal oxides, which are composed of a β-MnO2 nanorod core and one of three different nanosheet hybrid (Ni, Co, Mn) oxide shells, are facilely synthesized via a novel in situ nucleation and growth of transition metal oxides on the surface of the β-MnO2 nanorods. The crystallographic analyses demonstrated that the three kinds of hybrid oxide shells consisted of cobalt manganese oxide (CMO), nickel manganese oxide (NMO), and nickel cobalt manganese oxide (NCMO). These transition metal oxides are evaluated as electrodes for high performance supercapacitors (SCs). The results reveal that β-MnO2@CMO exhibits a good rate capability of 35% capacity retention even at 20 A g−1, while β-MnO2@NMO displays a high pseudocapacitance of 560 F g−1 at 1 A g−1. However, β-MnO2@NCMO combined the advantages of both β-MnO2@CMO and β-MnO2@NMO, and exhibits a high specific capacitance of 675 F g−1 at 1 A g−1 with excellent rate performance (about 30% capacity retention at 20 A g−1) and cycling stability (83% capacity retention after 3000 cycles). The improved electrochemical performance can be attributed to the unique hierarchical architecture and the synergistic effect of different components.

Performance improvement of activated nanoporous carbon supported gold catalyst as an anode for direct borohydride–hydrogen peroxide fuel cells

Activated nanoporous carbon (A-NPC) has been synthesized via KOH activation of a nanoporous carbon (NPC) prepared using a template metal–organic framework-5 (MOF-5), and it is firstly used as an anode electrocatalyst carrier of Au nanoparticles in borohydride–hydrogen peroxide fuel cells (DBHFCs). The samples are characterized by N2 adsorption–desorption isotherms, transmission electron microscopy (TEM), X-ray diffraction (XRD), cyclic voltammetry (CV), chronopotentiometry (CP), chronoamperometry and fuel cell tests. It has been found that the A-NPC achieves a surface area up to 2296 m2 g−1 and a pore volume of 1.59 cm3 g−1. The mean particle size of Au crystallites dispersed uniformly on the surface of the A-NPC carrier is only 2.9 nm. Besides, the peak current density for direct borohydride oxidation of the Au/A-NPC (49.1 mA cm−2) is 13.6% higher than that of the untreated NPC supported Au (43.2 mA cm−2), and 63.1% higher than that of commercial Vulcan XC-72R supported Au (30.1 mA cm−2). The DBHFC using the Au/A-NPC as anode electrocatalyst can obtain a maximum power density of 48.2 mW cm−2 at 25 °C.

Nanoflaky MnO2 grown in situ on carbon microbeads as an anode material for high-performance lithium-ion batteries

A flower-like MnO2 encapsulated carbon microbead (MnO2@CMB) nanocomposite is firstly synthesized via in situ nucleation and growth of birnessite-type MnO2 on the surface of monodisperse carbon microbeads. The structure, morphology and performance of the samples are characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), and galvanostatic charge/discharge. The results reveal that the flower textured MnO2@CMB nanocomposite is composed of a CMB core and a MnO2 nanosheet shell. As the anode material for lithium-ion batteries, the MnO2@CMB nanocomposite exhibits excellent electrochemical performance. It shows a good rate capability of 230 mA h g−1 at a current density of 1500 mA g−1 and a large reversible capacity of 620 mA h g−1 without capacity fading for the 80th cycle at 100 mA g−1, which is much better than those of pure MnO2 and graphite. The superior electrochemical performance can be attributed to the unique hierarchical architecture and the combinative effects of the MnO2 nanosheet and carbon matrices.

Effects of preparation temperature on electrochemical performance of nitrogen-enriched carbons

Abstract The activated nitrogen-enriched novel carbons (NENCs) were prepared by direct carbonization using polyaniline coating activated mesocarbon microbead composites as the precursor. Herein the influences of the carbonization temperature on the structure and morphology of the NENCs samples were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and N 2 adsorption/desorption isotherm at 77 K. The electrochemical properties of the supercapacitors were characterized by cyclic voltammetry, galvanostatic charge/discharge, electrochemical impedance spectroscopy (EIS), cycle life, leakage current and self-discharge measurements in 6 mol/L KOH solution. The results demonstrate that the NENC samples carbonized at 600 °C show the highest specific capacitance of 385 F/g at the current density of 1 A/g and the lowest ESR value (only 0.93 Ω). Furthermore, the capacity retention ratio of the NENCs-600 supercapacitor is 92.8 % over 2500 cycles.