A porous, hollow, microspherical composite of Li2MnO3 and LiMn1/3Co1/3Ni1/3O2 (composition: Li1.2Mn0.53Ni0.13Co0.13O2) was prepared using hollow MnO2 as the sacrificial template. The resulting composite was found to be mesoporous; its pores were about 20 nm in diameter. It also delivered a reversible discharge capacity value of 220 mAh g?1 at a specific current of 25 mA g?1 with excellent cycling stability and a high rate capability. A discharge capacity of 100 mAh g?1 was obtained for this composite at a specific current of 1000 mA g?1. The high rate capability of this hollow microspherical composite can be attributed to its porous nature.
Li[Ni1/3Co1/3Mn1/3]O2 (NCM 111) is a promising alternative to LiCoO2, as it is less expensive, more structurally stable, and has better safety characteristics. However, its capacity of 155 mAh g?1 is quite low, and cycling at potentials above 4.5 V leads to rapid capacity deterioration. Here, we report a successful synthesis of lithium-rich layered oxides (LLOs) with a core of LiMO2 (R-3m, M?=?Ni, Co) and a shell of Li2MnO3 (C2/m) (the molar ratio of Ni, Co to Mn is the same as that in NCM 111). The core–shell structure of these LLOs was confirmed by XRD, TEM, and XPS. The Rietveld refinement data showed that these LLOs possess less Li+/Ni2+ cation disorder and stronger M*–O (M*?=?Mn, Co, Ni) bonds than NCM 111. The core–shell material Li1.15Na0.5(Ni1/3Co1/3)core(Mn1/3)shellO2 can be cycled to a high upper cutoff potential of 4.7 V, delivers a high discharge capacity of 218 mAh g?1 at 20 mA g?1, and retains 90 % of its discharge capacity at 100 mA g?1 after 90 cycles; thus, the use of this material in lithium ion batteries could substantially increase their energy density.
Graphical Abstract Average voltage vs. number of cycles for the core–shell and pristine materials at 20 mA g?1 for 10 cycles followed by 90 cycles at 100 mA g?1
In this paper, the LiNi0.5Mn1.5O4 cathode materials of lithium-ion batteries are synthesized by a co-precipitation spray-drying and calcining process. The use of a spray-drying process to form particles, followed by a calcination treatment at the optimized temperature of 750 °C to produce spherical LiNi0.5Mn1.5O4 particles with a cubic crystal structure, a specific surface area of 60.1 m2 g?1, a tap density of 1.15 g mL?1, and a specific capacity of 132.9 mAh g?1 at 0.1 C. The carbon nanofragment (CNF) additives, introduced into the spheres during the co-precipitation spray-drying period, greatly enhance the rate performance and cycling stability of LiNi0.5Mn1.5O4. The sample with 1.0 wt.% CNF calcined at 750 °C exhibits a maximum capacity of 131.7 mAh g?1 at 0.5 C and a capacity retention of 98.9% after 100 cycles. In addition, compared to the LiNi0.5Mn1.5O4 material without CNF, the LiNi0.5Mn1.5O4 with CNF demonstrates a high-rate capacity retention that increases from 69.1% to 95.2% after 100 cycles at 10 C, indicating an excellent rate capability. The usage of CNF and the synthetic method provide a promising choice for the synthesis of a stabilized LiNi0.5Mn1.5O4 cathode material.
Graphical Abstract Micro/nanostructured LiNi0.5Mn0.5O4 cathode materials with enhanced electrochemical performances for high voltage lithium-ion batteries are synthesized by a co-precipitation spray-drying and calcining routine and using carbon nanofragments (CNFs) as additive.
Chemical preparation, crystal structure, and NMR spectroscopy of a new trans-2,5-dimethylpiperazinium monophosphate are given. This new compound crystallizes in the triclinic system, with the space group P-1 and the following parameters: a = 6.5033(3), b = 7.6942(4), c = 8.1473(5) Å, α = 114.997(3), β = 92.341(3), γ = 113.136(3), V = 329.14(3) Å3, Z = 1, and Dx = 1.565 g cm?3. The crystal structure has been determined and refined to R = 0.030 and Rw(F2) = 0.032 using 1558 independent reflections. The structure can be described as infinite [H2PO4]nn? chains with (C6H16N2)2+ organic cations anchored between adjacent polyanions to form columns of anions and cations running along the b axis. This compound has also been investigated by IR, thermal, and solid-state, 13C and 31P MAS NMR spectroscopies and Ab initio calculations. 相似文献
There is a growing need for the electrode with high mass loading of active materials, where both high energy and high power densities are required, in current and near-future applications of supercapacitor. Here, an ultrathin Co3S4 nanosheet decorated electrode (denoted as Co3S4/NF) with mass loading of 6 mg cm?2 is successfully fabricated by using highly dispersive Co3O4 nanowires on Ni foam (NF) as template. The nanosheets contained lots of about 3～5 nm micropores benefiting for the electrochemical reaction and assembled into a three-dimensional, honeycomb-like network with 0.5～1 μm mesopore structure for promoting specific surface area of electrode. The improved electrochemical performance was achieved, including an excellent cycliability of 10,000 cycles at 10 A g?1 and large specific capacitances of 2415 and 1152 F g?1 at 1 and 20 A g?1, respectively. Impressively, the asymmetric supercapacitor assembled with the activated carbon (AC) and Co3S4/NF electrode exhibits a high energy density of 79 Wh kg?1 at a power density of 151 W kg?1, a high power density of 3000 W kg?1 at energy density of 30 Wh kg?1 and 73 % retention of the initial capacitance after 10,000 charge-discharge cycles at 2 A g?1. More importantly, the formation process of the ultrathin Co3S4 nanosheets upon reaction time is investigated, which is benefited from the gradual infiltration of sulfide ions and the template function of ultrafine Co3O4 nanowires in the anion-exchange reaction.
Graphical abstract The ultrathin 2D Co3S4 nanosheets fabricated on 3D Ni foam and the formation process of the ultrathin Co3S4 nanosheets upon reaction times has been investigated. At the same time, the Co3S4/NF electrode displays an outstanding specific capacitance of 2420 F g?1 at 1 A g?1 with high mass loading of 6 mg cm?2.
In this work, Bi3.64Mo0.36O6.55 nanoparticles (NPs) were successfully prepared by a facile hydrothermal method and utilized in pseudocapacitor for the first time. Within a redox potential range from ?1.0 to 0 V vs. Hg/HgO in a 1 M aqueous KOH solution by cyclic voltammetry (CV), chronopotentiometry (CP) and AC impendence, the specific capacitance could reach 998 F g?1 at 1 A g?1, which is possibly ascribed to the higher Bi content of Bi3.64Mo0.36O6.55 NPs. Furthermore, the Bi3.64Mo0.36O6.55 NP electrode exhibited good cycle stability maintaining over 85 % after 5000 cycles. These results demonstrated Bi3.64Mo0.36O6.55 NPs might be a promising electrode material for pseudocapacitor.
Graphical abstract The fabrication of uniform Bi3.64Mo0.36O6.55 nanoparticles with a diameter of 100 nm were succefully reported by a facial hydrothermal method, which exhibits a extraordinary electronic performance with 998 F g-1 at 1 A g-1 and cycling stability
Properties of CFx/Li and CFx/Na cells were examined while using galvanostatic charging/discharging, electrochemical impedance spectroscopy and scanning electron microscopy (SEM). The capacity during the first cycle was as high as ca. 1000 mAh g?1. Such an electrode is suitable for primary CFx/Li and CFx/Na batteries. SEM images of CFx cathode showed that during discharging it was transformed into amorphous carbon and LiF or NaF crystals (of diameter of ca. 5–20 μm). These systems (C?+?LiF or C?+?NaF) cannot be reversibly converted back into CFx/Li or CFx/Na, respectively. Exchange current densities are between 10?7 Acm?2 and 10?9 Acm?2 when working with LiPF6 and NaPF6 electrolytes (1.12?×?10?7 Acm?2 and 6.82?×?10?9 Acm?2, respectively). Those values are low and indicate that the charge transfer process may be the rate-determining step. Activation energies for the charge transfer process were 57 and 72 kJ mol?1 for CFx/LiPF6 and CFx/NaPF6 systems, respectively. Higher activation energy barrier for the CF/Na+?+?e??→?C?+?NaF reaction results in lower observed exchange current density in comparison to the system with lithium ions. 相似文献
We describe a chemical exfoliation method for the preparation of MoS2 nanosheets. The nanosheets were incorporated into poly(3,4-ethylenedioxythiophene) (PEDOT) by electrodeposition on a glassy carbon electrode (GCE) to form a nanocomposite. The modified GCE is shown to enable simultaneous determination of ascorbic acid (AA), dopamine (DA) and uric acid (UA). Due to the synergistic effect of MoS2 and PEDOT, this electrode displays better properties in terms of electrocatalytic oxidation of AA, DA and UA than pure PEDOT, which is illustrated by cyclic voltammetry and differential pulse voltammetry (DPV). Under optimum conditions and at pH 7.4, the respective sensitivities and best working potentials are as follows: AA: 1.20 A?mM?1?m?2, 30 mV; DA: 36.40 A?mM?1?m?2, 210 mV; UA: 105.17 A?mM?1?m?2, 350 mV. The calculated detection limits for AA, DA and UA are 5.83 μM, 0.52 μM and 0.95 μM, respectively. The modified electrode was applied to the detection of the three species in human urine samples and gave satisfactory results.
Graphical abstract MoS2 nanosheets were prepared by a facile chemical exfoliation method. MoS2 and poly(3,4-ethylenedioxythiophene) nanocomposite modified glassy carbon electrodes were fabricated, which are shown to enable simultaneous determination of ascorbic acid, dopamine and uric acid with high sensitivity and selectivity.
A H3PW12O40/ZrO2 catalyst for effective dimethyl carbonate (DMC) formation via methanol carbonation was prepared using the sol–gel method. X-ray photoelectron spectra showed that reactive and dominant (63%) W(VI) species, in WO3 or H2WO4, enhanced the catalytic performances of the supported ZrO2. The mesoporous structure of H3PW12O40/ZrO2 was identified by nitrogen adsorption–desorption isotherms. In particular, partial sintering of catalyst particles in the duration of methanol carbonation caused a decrease in the Brunauer–Emmett–Teller surface area of the catalyst from 39 to 19 m2/g. The strong acidity of H3PW12O40/ZrO2 was confirmed by the desorption peak observed at 415 °C in NH3 temperature-programmed desorption curve. At various reaction temperatures (T?=?110, 170, and 220 °C) and CO2/N2 volumetric flow rate ratios (CO2/N2?=?1/4, 1/7, and 1/9), the calculated catalytic performances showed that the optimal methanol conversion, DMC selectivity, and DMC yield were 4.45, 89.93, and 4.00%, respectively, when T?=?170 °C and CO2/N2?=?1/7. Furthermore, linear regression of the pseudo-first-order model and Arrhenius equation deduced the optimal rate constant (4.24?×?10?3 min?1) and activation energy (Ea?=?15.54 kJ/mol) at 170 °C with CO2/N2?=?1/7 which were favorable for DMC formation. 相似文献
The three-dimensional porous Li3V2(PO4)3/nitrogen-doped reduced graphene oxide (LVP/N-RGO) composite was prepared by a facile one-pot hydrothermal method and evaluated as cathode material for lithium-ion batteries. It is clearly seen that the novel porous structure of the as-prepared LVP/N-RGO significantly facilitates electron transfer and lithium-ion diffusion, as well as markedly restrains the agglomeration of Li3V2(PO4)3 (LVP) nanoparticles. The introduction of N atom also has positive influence on the conductivity of RGO, which improves the kinetics of electrochemical reaction during the charge and discharge cycles. It can be found that the resultant LVP/N-RGO composite exhibits superior rate properties (92 mA h g?1 at 30 C) and outstanding cycle performance (122 mA h g?1 after 300 cycles at 5 C), indicating that nitrogen-doped RGO could be used to improve the electrochemical properties of LVP cathodes for high-power lithium-ion battery application.
Graphical abstract The three-dimensional porous Li3V2(PO4)3/nitrogen-doped reduced graphene oxide composite with significantly accelerating electron transfer and lithium-ion diffusion exhibits superior rate property and outstanding cycle performance.
[Mn(NH3)6](NO3)2 crystallizes in the cubic, fluorite (C1) type crystal lattice structure (Fm\( \overline{3} \)m) with a = 11.0056 Å and Z = 4. Two phase transitions of the first-order type were detected. The first registered on DSC curves as a large anomaly at TC1h = 207.8 K and TC1c = 207.2 K, and the second registered as a smaller anomaly at TC2h = 184.4 K and TC2c = 160.8 K (where the upper indexes h and c denote heating and cooling of the sample, respectively). The temperature dependence of the full width at half maximum of the band associated with the δs(HNH)F1u mode suggests that the NH3 ligands in the high temperature and intermediate phase reorientate quickly with correlation times in the order of several picoseconds and with activation energy of 9.9 kJ mol?1. In the phase transition at TC2c probably only a some of the NH3 ligands stop their reorientation, while the remainders continue to reorientate quickly with activation energy of 7.7 kJ mol?1. Thermal decomposition of the investigated compound starts at 305 K and continues up to 525 K in four main stages (I–IV). In stage I, 2/6 of all NH3 ligands were seceded. Stages II and III are connected with an abruption of the next 2/6 and 1/6 of total NH3, respectively, and [Mn(NH3)](NO3)2 is formed. The last molecule of NH3 per formula unit is freed at stage IV together with the simultaneous thermal decomposition of the resulting Mn(NO3)2 leading to the formation of gaseous products (O2, H2O, N2 and nitrogen oxides) and solid MnO2. 相似文献
Hydrothermally synthesized Co3O4 microspheres were anchored to graphite oxide (GO) and thermally reduced graphene oxide (rGO) composites at different cobalt weight percentages (1, 10, and 100 wt%). The composite materials served as the active materials in bulk electrodes for two-electrode cell electrochemical capacitors (ECCs). GO/Co3O4–1 exhibited a high energy density of 35 W kg?1 with a specific capacitance (Csp) of 196 F g?1 at a maximum charge density of 1 A g?1. rGO/Co3O4-100 presented high specific power output values of up to 23.41 kW h kg?1 with linear energy density behavior for the charge densities applied between 0.03 and 1 A g?1. The composite materials showed Coulombic efficiencies of 96 and 93 % for GO/Co3O4–1 and rGO/Co3O4–100 respectively. The enhancement of capacitive performance is attributed to the oxygenated groups in the GO ECC and the specific area in the rGO ECC. These results offer an interesting insight into the type of carbonaceous support used for graphene derivative electrode materials in ECCs together with Co3O4 loading to improve capacitance performance in terms of specific energy density and specific power.
LiMn2O4 is one of the most promising cathode materials due to its high abundance and low cost. However, the practical application of LiMn2O4 is greatly limited owing to its low volumetric energy density. Therefore, increasing its energy density is an urgent problem to be resolved. Herein, using the simple and mass production preferred solid-state reaction, surficial Nb-doped LiMn2O4 composed of the truncated octahedral or spherical-like primary particles are successfully synthesized. Auger electron spectroscopy (AES) and X-ray diffraction (XRD) characterizations confirm that most of Nb5+ enrich in the surficial layer of the particles to form a LiMn2-xNbxO4 phase. This kind of doping can increase the specific discharge capacity of LiMn2O4 materials. Contrast with the pristine LiMn2O4, the discharge capacity of LiMn1.99Nb0.01O4-based 18650R-type battery increases from 1497 to 1705 mAh with the volumetric energy density increasing by ~?13.9%, benefiting from the joint increments of the specific discharge capacity from 119.5 to 123.7 mAh g?1 and the compacted density from 2.81 to 3.10 g cm?3. Furthermore, the capacity retention after 500 cycles at 1 C (1500 mA) is also improved by 17.1%.
A magnetic sorbent was fabricated by coating the magnetized graphene oxide with polystyrene (PS) to obtain a sorbent of the type GO-Fe3O4@PS. The chemical composition and morphology of the sorbent were characterized. The sorbent was employed for the enrichment of polycyclic aromatic hydrocarbons (PAHs) from water samples. Various parameters affecting the enrichment were investigated. The PAHs were then quantified by gas chromatography with flame ionization detection. Linear responses were found in the range of 0.03–100 ng mL?1 for naphthalene and 2-methylnaphthalene, and of 0.01–100 ng mL?1 for fluorene and anthracene. The detection limits (at an S/N ratio of 3) range between 3 and 10 pg mL?1. The relative standard deviations (RSDs) for five replicates at three concentration levels (0.05, 5 and 50 ng mL?1) of analytes ranged from 4.9 to 7.4%. The method was applied to the analysis of spiked real water samples. Relative recoveries are between 95.8 and 99.5%, and RSD% are <8.4%.
Graphical abstract A magnetic sorbent was fabricated by polystyrene coated on the magnetic graphene oxide for the extraction and preconcentration of PAHs in water samples prior to their determination by gas chromatography with flame ionization detection.
The authors have prepared organized assemblies of a hemoglobin-chitosan(CS)@Fe3O4 composite on glassy carbon electrodes (GCEs) via three strategies with the aim of preparing tunable Hb-coated GCEs with good stability and long-term oxygen storage capability. The formation and morphology of the Hb-CS@Fe3O4 composite was characterized by scanning electrochemical microscopy, XRD and UV–vis spectroscopy. It is shown that Hb is fully integrated into the CS@Fe3O4 and can be manipulated by a magnetic field whilst maintaining its biological activity. In the absence of oxygen, a surface-controlled electrode process occurs with an interfacial electron transfer rate (ks) of 2.14 s?1. The modified GCE also has a favorable oxygen storage lifetime (almost 6 h). One Hb-CS@Fe3O4 film on the electrode displays particularly good electrocatalytic reduction activity towards oxygen. The linear range for detection of O2 is 1.2?×?10?7?~?2.0?×?10?4 mol L?1 with a detection limit of 4.0?×?10?8 mol L?1. In our opinion, this method has great potential in terms of enhanced oxygen storage capability of Hb, which can be applied in special situations such as space operations, down hole mining, mountaineering and diving.
Graphical Abstract Hb-CS@Fe3O4 composites were prepared by three strategies, and oxygen carrying capability was studied. The corresponding modified electrode constructed on the basis of the magnetic field environment was superior in terms of stability, sensitivity and O2 storage time, showing wider linear range and lower detection limit.
This study describes an amperometric sensor for hydrogen peroxide (H2O2) that uses an ITO glass electrode which was modified with a nanocomposite consisting of electrochemically reduced graphene oxide and gold nanoclusters (AuNCs). The sensor was used to quantify extracellular H2O2 released from human neuroblastoma cells of type SH-SY5Y. The calibration plot, established best at a working voltage of ?0.4 V (vs. Ag/AgCl) is linear in the 40 nmol?L?1 to 2 μmol?L?1 concentration range, and the detection limit is 20 nmol?L?1 (at a signal-to-noise ratio of 3). The method was further applied to study bupivacaine-induced cell damage and the protective effects of α-lipoic acid. The study indicated that pretreatment of the cells with lipoic acid retards cell damage induced by bupivacaine. The sensor can be easily fabricated, is disposable and highly sensitive. The sensor is perceived to represent an alternative for studying the interactions of drugs with cells, and as an effective tool to quantify cell-secreted H2O2.
Graphical abstract One-step electrochemical synthesis of graphene oxide and gold nanoclusters on an ITO electrode for studying the release of H2O2 from SH-SY5Y cells and for evaluation of drug-induced cell damage
The authors describe magnetic nanoparticles consisting of an Fe3O4 core and a poly(methacrylic acid) coating for dispersive solid phase extraction (DSPE) of arsenic prior to its determination by hydride-generation microwave plasma AES (HG-MP-AES). The particles have an average size of 25 nm, can be prepared at low costs, and provide improved operational safety in combination with plasma generation. The methods allows arsenic to be determined with detection limits (at 3σ/m) of 3.0 ng?L?1 for As(III) and of 10.0 ng?L?1 of As(V). Recoveries of (spiked) samples range from 99.0 to 102%. This is the first report on the use of HG-MP-AES for speciation and preconcentration of arsenic using DSPE. The method displays detection limits that come close to those of ICP-OES and ICP-MS.
Graphical abstract A core/shell Fe3O4@poly(methacrylic acid) coated sorbent was synthesised and employed to the speciation of arsenic prior to its determination by hydride-generation microwave plasma atomic emission spectrometry.
Hollow titanium dioxide (TiO2) microspheres were synthesized in one step by employing tetrabutyl orthotitanate (TBOT) as a precursor through a facile solvothermal method in the presence of NH4HCO3. XRD analysis indicated that anatase TiO2 can be obtained directly without further annealing. TiO2 hollow microspheres with diameters in the range of 1.0–4.0 μm were confirmed through SEM and TEM measurements. The specific surface area was measured to be 180 m2 g?1 according to the nitrogen adsorption–desorption isotherms. Superior photocatalytic performance and good lithium storage properties were achieved for resultant TiO2 samples. The H2 evolution rate of the optimal sample is about 0.66 mmol h?1 after loaded with 1 wt.% Pt (20 mg samples). The reversible capacity remained 143 mAh g?1 at a specific current of 300 mA g?1 after 100 charge–discharge cycles. This work provides a facile strategy for the preparation of hollow titanium dioxide microspheres and demonstrates their promising photocatalytic H2 evolution and the lithium storage properties.
Graphical abstract Hollow titanium dioxide spheres are directly synthesized via a facile template-free solvothermal method with the presence of NH4HCO3 based on inside-out Ostwald ripening (see picture), and demonstrated both as a photocatalyst for water splitting and a promising anode material for lithium-ion batteries. Superior photocatalytic performance and excellent lithium storage properties are achieved for resultant TiO2 hollow microspheres.
The authors describe the synthesis of a multifunctional nanocomposite with an architecture of type Fe3O4@SiO2@graphene quantum dots with an average diameter of about 22 nm. The graphene quantum dots (GQDs) were covalently immobilized on the surface of silica-coated magnetite nanospheres via covalent linkage to surface amino groups. The nanocomposite displays a strong fluorescence (with excitation/emission peaks at 330/420 nm) that is fairly selectively quenched by Hg2+ ions, presumably due to nonradiative electron/hole recombination annihilation. Under the optimized experimental conditions, the linear response to Hg2+ covers the 0.1 to 70 μM concentration range, with a 30 nM lower detection limit. The high specific surface area and abundant binding sites of the GQDs result in a good adsorption capacity for Hg2+ (68 mg?g?1). The material, due to its superparamagnetism, can be separated by using a magnet and also is recyclable with EDTA so that it can be repeatedly used for simultaneous detection and removal of Hg2+ from contaminated water.
Graphical abstract A schematic view of preparation process for the Fe3O4@SiO2@graphene quantum dots nanocomposite (denoted as Fe3O4@SiO2@GQDs). The graphene quantum dots were covalently immobilized on the surface of silica-coated magnetite nanospheres (Fe3O4@SiO2) via covalent linkage to surface amino groups.
A series of Ni0.37Co0.63S2-reduced graphene oxide nanocomposites with different graphene contents (NCS@rGO-x) has been successfully prepared via a facile one-step hydrothermal method and applied as the catalysts for the oxygen evolution reaction (OER) and degradation of organic pollutants. The XRD and FESEM analyses revealed that the phase structure and morphology of NCS nanoparticles were substantially influenced by the graphene contents. The phase structure of NCS nanoparticles gradually transformed from primary NiCo2S4 to Ni0.37Co0.63S2 and the morphology and size of NCS nanoparticles were found to become more regular and homogeneous with the increase of graphene concentration. On the NCS@rGO-x nanocomposites, the NCS@rGO-2 sample demonstrated the best catalytic activity toward the OER, which delivers a stable current density of 10 mA cm?2 at a small overpotential of ～276 mV (vs. RHE) with a Tafel slope as low as 48 mV dec?1. Furthermore, the NCS@rGO-2 sample showed the remarkable photocatalytic activity for degradation of methylene blue (MB), which may be attributed to the increased reaction sites and high separation efficiency of photogenerated charge carries due to the electronic interaction between NCS nanoparticles and rGO. All these impressive performances indicate that the NCS@rGO-2 nanocomposite is a promising catalyst in energy and environmental fields.
Graphical abstract A series of Ni0.37Co0.63S2-reduced graphene oxide nanocomposites with different graphene contents has been successfully prepared and applied as the catalysts for the oxygen evolution reaction (OER) and degradation of organic pollutants. The NCS@rGO-2 catalyst-modified stainless steel wire mesh (SSWM) electrode delivers a stable current density of 10 mA cm?2 at a small overpotential of ～276 mV (vs. RHE) with a Tafel slope as low as 48 mV dec?1. At the same time, the NCS@rGO-2 catalyst is also first investigated as an efficient photocatalyst for degradation of MB.
