Jiajia Zhu

3D porous layered double hydroxides grown on graphene as advanced electrochemical pseudocapacitor materials

A 3D hybrid nickel-aluminum layered double hydroxide (NiAl-LDH)–graphene nanosheets (GNS) composite as a supercapacitor material has been fabricated by in situ deposition of LDH nanosheets on graphene oxide (GO) through a liquid phase deposition method. The results reveal that NiAl-LDH homogeneously grew on the surface of GNS as spacers to keep the neighboring sheets separate. Optimum effects could be achieved when feeding ratio, reaction time and temperature are tuned. The obtained porous GNS/NiAl-LDH composite exhibited high-capacitance performance with a specific capacitance of 1255.8 F g−1 at a current density of 1 A g−1 and 755.6 F g−1 at 6 A g−1, respectively. Moreover, the composite exhibited excellent cycling performance with an increase of 6% capacitance compared with the initial capacitance after 1500 cycle tests. Such high specific capacitance, rate capability and exceptional cycling ability of the composite offered great promise in energy storage device applications.

Preparation and properties of polystyrene nanocomposites with graphite oxide and graphene as flame retardants

In this study, graphite oxides (GOs) with different oxidation degrees and graphene nanosheets were prepared by a modified Hummers method and thermal exfoliation of the prepared GO, respectively. Polystyrene (PS)/GO and PS/graphene nanocomposites were prepared via melt blending. X-ray diffraction results showed that GOs and graphene were exfoliated in the PS composites. It could be observed from the scanning electron microscope images that GOs and graphene were well dispersed throughout the matrix without obvious aggregates. Dynamic mechanical thermal analysis suggested that the storage modulus for the PS/GO1 and PS/graphene nanocomposites was efficiently improved due to the low oxygen content of GO1 and the elimination of the oxygen groups from GO. The flammability of nanocomposites was evaluated by thermal gravimetric analysis and cone calorimetry. The results suggested that both the thermal stability and the reduction in peak heat release rate (PHRR) decreased with the increasing of the oxygen groups in GOs or graphene. The optimal flammability was obtained with the graphene (5xa0wt%), in which case the reduction in the PHRR is almost 50xa0% as compared to PS.

Zinc cobalt sulfide nanosheets grown on nitrogen-doped graphene/carbon nanotube film as a high-performance electrode for supercapacitors

To improve the energy density of supercapacitors, a new type of electrode material with high electrochemical activity and favorable morphology is extremely desired. Ternary metal sulfides with higher electrochemical capacity and activity than mono-metal sulfides hold great promise in the field of energy storage devices. Herein, an advanced electrode composed of zinc cobalt sulfide nanosheets supported on sandwich-like nitrogen-doped graphene/carbon nanotubes (NGN/CNTs) film has been successfully fabricated through a two-step synthesis. Benefiting from the characteristic features and 3D electrode architectures, the Zn0.76Co0.24S electrode exhibits a high specific capacitance of 2484 F g−1 at 2 A g−1 and excellent cycling stability (almost no capacitance fading after 10000 cycles at 30 A g−1). This creative nanostructure design of ternary transition metal sulfides could provide a promising prospect for application in energy storage devices. Moreover, an asymmetric supercapacitor was also fabricated by using Zn0.76Co0.24S/NGN/CNTs film as the positive electrode and NGN/CNTs film as the negative electrode, exhibiting a high energy density of 50.2 W h kg−1 at 387.5 W kg−1 and superior cycling stability of 100% initial capacity retention over 2000 cycles. This creative nanostructure design could provide a promising new way to develop high-performance supercapacitors and shed new light on configuring carbon-based ternary transition metal sulfide electrode materials in energy storage and conversion devices.

Electrochemical reduction of graphene oxide and its electrochemical capacitive performance

A convenient method for the production of graphene is developed using the electrochemical reduction of graphite oxide (GO) in solution without assembling it onto the electrode. The samples were examined by X-ray diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and Raman spectroscopy. The results show that the number of oxygen functional groups can be significantly decreased. The electrochemical capacitance of the prepared graphene after 8xa0h of reduction is 158.5xa0Fxa0g−1 at 0.5xa0Axa0g−1, much higher than that of GO and carbon nanotubes. The mechanism for this reaction is also proposed in this paper.

Enhancing the electrochemical performance of Li1.2Ni0.2Mn0.6O2 by surface modification with nickel–manganese composite oxide

Li-rich layered Li1.2Ni0.2Mn0.6O2 has been surface modified by nickel–manganese composite oxide (Ni0.5Mn1.5Ox) to serve as a novel cathode material with novel layered spinel structure for lithium-ion battery. The as-prepared Li1.2Ni0.2Mn0.6O2 before and after surface modification by Ni0.5Mn1.5Ox as well as simply blended Li1.2Ni0.2Mn0.6O2 with spinel LiNi0.5Mn1.5O4, have been characterized by X-ray diffraction, field emission scanning electron microscopy, transmission electronic microscopy, and differential scanning calorimetry. Electrochemical studies indicate that the Ni0.5Mn1.5Ox surface modified Li1.2Ni0.2Mn0.6O2 with peculiar layered spinel character dramatically represented increased discharge capacity, improved cycling stability as well as excellent rate capability at high-voltage even up to 5.0xa0V.

Synthesis and electrochemical performances of mixed-valence vanadium oxide/ordered mesoporous carbon composites for supercapacitors

Mixed-valence vanadium oxide (VOx)/ordered mesoporous carbon (CMK-3) composite (VOC) were synthesized through a facile liquid-phase method followed by calcination. The microstructures of the composite were characterized by X-ray diffraction (XRD), nitrogen adsorption and desorption, X-ray photoelectron spectra (XPS), scanning election microscopy (SEM) and transmission election microscopy (TEM). The relevant results showed that vanadium oxide nanoparticles with mixed valence were successfully embedded in mesoporous channels in the conductive matrix and dispersed on the CMK-3 surface to form the interwoven composite. The introduction of the CMK-3 framework not only improves electron transfer but also prevents the structure collapsing during cycling. As expected, the composite exhibits excellent electrochemical properties. It delivered a specific capacitance of 257 F g−1 at 0.5 A g−1 and maintained 77.3% at 8 A g−1 in 5 M LiNO3. After 5000 cycles, the capacitance only decreased 20%.

Preparation of Polyaniline Covalently Grafted Carbon Nanotubes Supported Pt Catalysts and Its Electrocatalytic Performance for Methanol

Recently, covalently functionalization carbon nanotubes have been received special attention because of the ex- pansive application prospect in the areas of nanoscience and nanotechnology. Moreover, covalent functionalization of carbon nanotubes can readily deal with fundamental issues of purification, solubilization, and processing. In particular, polyaniline, due to its high electronic conductivity, good environmental stability, easy preparation and reversible acid-base dop- ing-dedoping chemistry, has been one of the most studied conducting polymers. Recently, CNTs-PANI composites were in- vestigated widely, such as supercapacitor, optoelectronic devices, sensing and catalysis as well. In this work, uniform struc- tures PANI covalently grafted onto CNTs functionalization with -NH2 groups composites have been obtained by using liq- uid/liquid(L/L) interfacial polymerization method. The interfacial system was established by using CNTs, FeCl3, HCl as top aqueous phase and aniline, CH2Cl2 as bottom organic phase, which effective suppress second growth of PANI and obtain uniform CNTs-NH-PANI composites. Concerning CNTs-NH-PANI composites, PANI can covalently be grafted on CNTs with -NH2 groups. The resulted CNTs-NH-PANI composites have abundant -NH2 groups on their surface, serving as anchor centers for achieving high Pt dispersion. More important, PANI uniformly grafted on CNTs is prone to disperse the bundle of CNTs into separated lines and improve water dispersibility of obtained CNTs-NH-PANI composites. Subsequently, PtNPs were successfully deposited on the CNTs-PANI to form ternary hybrids. Potential application of the ternary hybrids as high performance catalysts for direct methanol fuel cells has been explored. The catalyst samples were characterized by transmis- sion electron microscopy (TEM), X-ray diffraction (XRD) and electrochemical methods. TEM results showed that the hier- archical CNTs-PANI composites with uniform morphology have been successfully prepared due to hydrophilic -OH and -NH2 groups covalently functionalized onto the surface of CNTs. Moreover, the electrochemical measurement show that the Pt/CNTs-NH-PANI hybrid have better stabilities compared with commercial JM (Pt/C) catalyst. The long-term durability test of the Pt/CNTs-CO-PANI, Pt/CNTs-NH-PANI and Pt/C catalysts shows that PANI grafted on CNTs as catalyst supports have better stabilities and more tolerant toward poisoning. Moreover, PANI covalently grafted on CNTs as catalyst supports has more excellent performance. The If/Ib of Pt/CNTs-NH-PANI catalyst for electrocatalytic methanol oxidation is 1.65 which is nearly 1.6 and 1.2 times than that of the commercial JM(Pt/C) and Pt/CNTs-CO-PANI catalysts, respectively. The results show that carbon nanotubes covalently grafting polyaniline as support can effectively improve the catalyst stability, increas- ing the service life of the catalyst. Keywords carbon nanotube; polyaniline; covalently; catalyst; methanol oxidation; CO-tolerance