A high-quality sized FeFe(CN)6 was synthesized as a cathode material for a non-aqueous potassium-ion battery. The electrode delivered a reversible capacity of 124 mA h g−1 at the current rate of 0.5C and still retained a reversible capacity of 93 mA h g−1 after 500 cycles at 5C with a columbic efficiency of 100%. Structural evolution and redox couples of low and high spin FeIII/FeII were investigated by ex situ X-ray diffraction, Mössbauer spectroscopy, and X-ray photoelectric spectroscopy. The negligible volume change during the electrochemical process should be responsible for the excellent cyclic stability.

The preparation of Li4SiO4-coated LiNi0.5Mn1.5O4 materials by sintering the SiO2-coated nickel-manganese oxides with lithium salts using abundant and low-cost sodium silicate as the silicon source was reported. The samples were characterized by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. It was found that a uniform and complete SiO2 coating layer could be obtained at a suitable pH value of 10, which transformed to a good Li4SiO4 coating layer afterwards. When used as the cathode materials for lithium-ion batteries, the Li4SiO4-coated LiNi0.5Mn1.5O4 samples deliver a better electrochemical performance in terms of the discharge capacity, rate capability, and cycling stability than that of the pristine material. It can still deliver 111.1 mAh/g at 20 C after 300 cycles, with a retention ratio of 93.1% of the stable capacity, which is far beyond that of the pristine material (101.3 mAh/g, 85.6%).

LiNi0.5Mn1.5O4 nanoplates were prepared using a two-step method composed of a hydrothermal method and a solid-state reaction. At first, bimetal–organic coordination-polymers containing Ni2+ and Mn2+ were synthesized using the ligand 3,4,9,10-perylenetetracarboxylic dianhydride (ptcda) by a template-assisted self-assembly method in a hydrothermal atmosphere. This was followed by thermal treatment to remove the organic components and then calcination with lithium acetate, and nanoplate-stacked LiNi0.5Mn1.5O4 was obtained. The nanoplate structure shortens the diffusion path of the lithium ions in the bulk of LiNi0.5Mn1.5O4 and then promotes fast charge–discharge properties of the material. In addition, an amorphous Li2CO3 layer with nanometer thickness in situ generated on the surface of the LiNi0.5Mn1.5O4 particles was confirmed by TEM and XPS. This is helpful for suppressing the interfacial side reactions and thereby improving the cycling stability of the material. Owing to these advantages, the LiNi0.5Mn1.5O4/Li2CO3 material exhibits excellent rate capability and cycling stability. The as-prepared material delivers 129.8 mA h g−1 at a 1 C rate and retains 86.4% of the initial capacity even after 1000 cycles of charge–discharge at 25 °C. Even at a high discharge rate of 40 C, the specific capacity of the material is 120.9 mA h g−1, and the capacity retention is 84.7% over 500 cycles. The high-temperature stability of the material is also superior. When operating at 55 °C, the capacity loss by cycle is only 0.037% throughout 250 cycles.

Fe2O3 nanobelts/carbon nanotubes (CNTs) composites were successfully synthesized by a novel homogeneous precipitation of FeC2O4 on CNTs followed with thermal annealing. The bundle-like Fe2O3 nanobelts, with a width of 10 nm, are homogeneously dispersed on CNTs. Compared to the bare Fe2O3 nanobelts, the Fe2O3 nanobelts/CNTs composites showed significantly improved electrochemical performance which can be attributed to their uniform conducting networks structure. The Fe2O3 nanobelts/CNTs composites delivered an initial reversible capacity of 847.5 mAh g−1 at current density of 100 mA g−1, and exhibited excellent cycling performance with a reversible capacity of 865.9 mAh g−1 after 50 cycles. Meanwhile, the composites also maintained a high reversible capacity of 442.1 mAh g−1 even at a current density up to 4 A g−1.

An efficient anode with a superior high-rate capability and stability remains a challenge for development of high performance Li-ion batteries. We present a new concept by encapsulating 2 nm-sized SnO2 nanocrystals in the channels of carbon nanotubes (SnO2-in-CNTs). Characterization shows that the confined space does not only stabilize the small nanoparticles but also alleviates the stress caused by the large volume change of tin species during the charging–discharging process. In addition, well crystallized graphitic structure of CNTs with a positive curvature provides a good contact between SnO2 nanoparticles and graphene layers, and excellent electronic conductivity. As a result, SnO2-in-CNTs as an anode of lithium ion battery exhibit stable cyclability and superior high-rate capability relative to SnO2 nanoparticles dispersed on the outer walls of CNTs particularly under a high current density. The charge capacity remains about 560 mA h g−1 after 50 cycles at 50 mA g−1, and even around 400 mA h g−1 at 1000 mA g−1. Additionally, the facile preparation method we have developed makes such encapsulates appealing for further optimization and applications.

Non-graphitic carbon nanotubes (NGCNTs) are successfully prepared by carbonization of polypyrrole (PPy) nanotubes precursor synthesized via a self-assembly process. It is observed from transmission electron microscopy (TEM) that the diameter and length of the NGCNTs are 100–200 nm and 2–10 μm, respectively. The electrochemical performances of the NGCNTs are evaluated by cyclic voltammograms and galvanostatic discharge–charge cycling. The results show that NGCNTs deliver an initial reversible capacity of 635.7 mAh g−1 at current density of 100 mA g−1 with a high capacity retention ratio of 85.7% after 150 cycles. Even up to 4 A g−1, the reversible capacity of NGCNTs remains in 280.1 mAh g−1. The improved performance of NGCNTs is attributed to the non-graphitic form, tubular morphology and cross-linked conducting networks. Therefore, it is a potential anode material for lithium-ion battery.

A fast sol–gel process that differs in important details from previously reported methods for preparing Li2MnSiO4/C nanocomposite was reported. In the process, hydrochloric acid was used to enhance the hydrolysis of tetraethyl orthosilicate (TEOS) to obtain silanols firstly. And then propylene oxide was added to promote the condensation of the silanols to form a jelly-like SiO2 gel precursor containing lithium and manganese sources in about 3 min at room temperature. The final product of Li2MnSiO4/C was obtained by calcining the gel precursor with sucrose. The structure, micro-morphology and electrochemical property of the as-prepared Li2MnSiO4/C nanocomposite were characterized by XRD, TEM, N2 adsorption–desorption, cyclic voltammetry (CV), galvanostatic charge–discharge, and electrochemical impedance spectroscopy (EIS). The results indicate that the Li2MnSiO4/C nanocomposite with mesoporous structure is composed of 10–20 nm nanoparticles homogenously coated by the carbon. The electrochemical measurements reveal that the initial charge and discharge specific capacities of the prepared Li2MnSiO4/C nanocomposite are 275.2 mAh g−1 and 164.2 mAh g−1, respectively. After 60 cycles, the discharge capacity retention is 80%. The excellent electrochemical performance can be attributed to the nano-sized composites with a mesoporous structure and the in situ surface carbon coating.Graphical abstractHighlights► Mesoporous and 10–20 nm nano Li2MnSiO4/C was prepared by a fast sol–gel method. ► SiO2 gel containing Li and Mn sources was formed in 3 min at room temperature. ► Hydrochloric acid and propylene oxide play key roles in the fast sol–gel synthesis. ► The prepared nano Li2MnSiO4/C presents improved electrochemical performance. ► Discharge capacity retention of prepared material reaches to 80% after 60 cycles.

Anode material for lithium-ion battery based on Sn/carbon nanotube (CNT) composite is synthesized via a chemical reduction method. The Sn/CNT composite is characterized by thermogravimetry, X-ray diffraction, and transition electron microscopy. The Sn/CNT composite delivers high initial reversible capacity of 630.5 mAh g−1 and exhibits stable cycling performance with a reversible capacity of 413 mAh g−1 at the 100th cycle. The enhanced electrochemical performance of the Sn/CNT composite could be mainly attributed to the well dispersion of Sn nanoparticles on CNT and partially filling Sn nanoparticles inside the CNT. It is proposed that the chemical treatment of CNT with concentrated nitric acid, which cuts carbon nanotube into short pieces and increases the amount of oxygen-functional groups on the surface, plays an important role in the anchoring of Sn nanoparticles on carbon nanotube and inhibiting the agglomeration of Sn nanoparticles during the charge–discharge process.

•Targets of this research are hydrophobic series ionic liquids.•Density, dynamic viscosity and electrical conductivity were determined.•Influences of methylene to properties were discussed.•Influences of methyl group on pyridinium ring position to properties were discussed.•Relationship of ρ, η and σ were described systematically.Air and water stable hydrophobic ionic liquids (ILs) were synthesized: N-propyl-3-methylpyridinium bis(trifluoromethylsulfonyl)imide [C33mpy][NTf2], N-hexyl-3-methylpyridinium bis(trifluoromethylsulfonyl)imide [C63mpy][NTf2], and N-hexyl-4-methylpyridinium bis(trifluoromethylsulfonyl)imide [C64mpy][NTf2]. Density, dynamic viscosity, and electrical conductivity of ILs were determined at atmospheric pressure in the temperature range of (278 to 353) K. The effects of methylene and methyl groups to density, dynamic viscosity, and electrical conductivity, respectively, were discussed. The thermal expansion coefficient, molecular volume, standard molar entropy, and lattice energy of the samples were estimated in terms of empirical and semi-empirical equations based on the density values. The temperature dependence on dynamic viscosity and electrical conductivity values of the ILs were discussed by Vogel–Fulcher–Tamman (VFT) and Arrhenius equations. The molar conductivities were calculated by density and electrical conductivity values.

LiFePO4/C nanocomposites are synthesized by a propylene oxide-assisted fast sol–gel method using FeCl3, LiNO3, NH4H2PO4, and sucrose as the starting materials. It was found that after adding propylene oxide into the solution containing the starting materials, a monolithic jelly-like FePO4 gel containing lithium and carbon source is generated in a few minutes without controlling the pH value of the solution and a time-consuming heating process. Propylene oxide plays a key role in the fast generation of the precursor gel. The final products of LiFePO4/C are obtained by sintering the dry precursor gel. The structures, micro-morphologies, and electrochemical properties of the LiFePO4/C composites are investigated using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, nitrogen adsorption–desorption analysis, electrochemical impedance spectrum, and charge–discharge cycling tests. The results indicate that the LiFePO4/C composite prepared by sintering the precursor gel at 680 °C for 5 h is about 30 nm in size with a meso-porous structure (the main pore size distribution is around 3.4 nm). It delivers 166.7 and 105.8 mAh g−1 at 0.2 and 30 C, respectively. The discharge specific capacity is 97.8 mAh g−1 even at 40 C. The cycling performance of the prepared LiFePO4/C composite is stable. The excellent electrochemical performance of the LiFePO4/C composite is attributed to the nano-sized and mesoporous structure of LiFePO4/C and the in-situ surface coating of the carbon. It was also found that propylene oxide is crucial for the generation of mesoporous and nano-structured LiFePO4/C.

Two air and water stable hydrophobic ionic liquids N-alkyl-4-methylpyridinium bis(trifluoromethylsulfonyl)imide ([Cn4mpy][NTf2], n = 2, 4) were synthesized and characterized. The density, electrical conductivity, and dynamic viscosity were measured and estimated in the range of T = (278.15 to 363.15) K. The melting temperature, glass transition temperature, and decomposition temperature of the two ILs were determined according to the differential scanning calorimetry (DSC) and thermogravimetric analyzer (TG). The molecular volume, standard molar entropy, and lattice energy were estimated in terms of empirical equations on the basis of the density values. The electrical conductivity and dynamic viscosity values dependence on temperature were fitted by the Vogel–Fulcher–Tamman equation. The molar conductivity was calculated by the density and electrical conductivity.

A PTMA (poly(4-methacryloyloxy-2,2,6,6-tetramethyl-piperidine-N-oxyl)) electrode with high energy density is prepared with Black Pearl 2000 (BP-2000). For comparisons, vapor grown carbon fiber (VGCF) and acetylene black (AB) are also employed to fabricate the PTMA-electrodes. The electrochemical properties of the electrode are improved obviously by employing BP-2000. The specific capacity of the PTMA-BP electrode based on the mass of PTMA is 26.7% larger than that of the PTMA-VGCF and PTMA-AB electrodes at a 1 C rate. At higher discharge rates, the polarization degree of the Li/PTMA-BP cell is the minimum one. At a discharge rate of 50 C, the specific capacity of the PTMA-BP electrode is 104.9 mA h g−1, and is 27.6 and 16.7% larger than that of the PTMA-VGCF and PTMA-AB electrodes, respectively. Besides, the discharge plateau of the Li/PTMA-BP cell is 3.35 V, and is 0.03 and 0.13 V higher than that of the Li/PTMA-AB and Li/PTMA-VGCF cells, respectively. The larger specific capacity of BP-2000 and the improved electrochemical kinetics of PTMA at the surface of BP carbon, resulted from the larger surface area of BP-2000, are the main factors for improving the capacity and rate capability of the PTMA-electrode. The high specific surface area of BP-2000 is also beneficial to the thorough contact of PTMA with BP carbon, resulting in the improved conductivity of the PTMA-BP composites. The cycling performance of the PTMA-BP electrode is also satisfied.

Diffusion coefficients of the vanadium ions across Nafion 115 (Dupont) in a vanadium redox flow battery (VRFB) are measured and found to be in the order of V2+ > VO2+ > VO2+ > V3+. It is found that both in self-discharge process and charge–discharge cycles, the concentration difference of vanadium ions between the positive electrolyte (+ve) and negative electrolyte (−ve) is the main reason causing the transfer of vanadium ions across the membrane. In self-discharge process, the transfer of water includes the transfer of vanadium ions with the bound water and the corresponding transfer of protons with the dragged water to balance the charges, and the transfer of water driven by osmosis. In this case, about 75% of the net transfer of water is caused by osmosis. In charge–discharge cycles, except those as mentioned in the case of self-discharge, the transfer of protons with the dragged water across the membrane during the electrode reaction for the formation of internal electric circuit plays the key role in the water transfer. But in the long-term cycles of charge–discharge, the net transfer of water towards +ve is caused by the transfer of vanadium ions with the bound water and the transfer of water driven by osmosis.

Pt/TiO2/C catalysts are employed as the cathode catalysts for proton exchange membrane fuel cell (PEMFC). The comparative studies on the Pt/C and Pt/TiO2/C catalysts are conducted with the physical and electrochemical techniques.After the accelerating aging test (AAT), the remaining electrochemical active surface area (EAS) of the Pt/TiO2/C catalysts is 75.6%, which is larger than that of the Pt/C catalysts (42.6%). The apparent exchange current density (iapp0) of the oxygen reduction reaction (ORR) at the Pt/C catalysts decreases from 3.02 × 10−9 to 1.32 × 10−11 A cm−2 after the AAT. And the value of iapp0 of the ORR at the Pt/TiO2/C catalysts is 2.88 × 10−9 A cm−2 before the AAT and 2.51 × 10−9 A cm−2 after the AAT. Furthermore, the output performance degradation of the PEMFC using the Pt/TiO2/C cathode catalysts is also less than that using the Pt/C catalysts. The particle size of the Pt/C catalysts increases significantly from 5.3 to 26.5 nm after the AAT. The mean particle size of the Pt/TiO2/C catalysts is 7.3 nm before the AAT and 9.2 nm after the AAT. It can be concluded that the long-term durability of the Pt/TiO2/C catalysts in a PEMFC is much better than that of the Pt/C catalysts.

For a proton exchange membrane fuel cell (PEMFC), dry layer preparation was optimized and applied to fabricate a micro-porous layer (MPL) for a gas diffusion layer (GDL). The MPLs fabricated by dry layer preparation and the conventional wet layer preparation were compared by physical and electrochemical methods. The PEMFC using dry layer MPLs showed better performance than that using wet layer MPLs, especially when the cells were operated under conditions of high oxygen utilization rate and high humidification temperature of air. The mass transport properties of the GDLs with the dry layer MPLs were also better than with the wet layer MPLs, and were found to be related to the pore size distribution in GDLs. The differences in surface morphology and pore size distribution for the GDLs with the dry layer and wet layer MPLs were investigated and analyzed. The dry layer preparation for MPLs was found to be more beneficial for forming meso-pores (pore size in the range of 0.5–15 μm), which are important and advantageous for facilitating gas transport in the GDLs. Moreover, the GDLs with the dry layer MPLs exhibited better electronic conductivity and more stable hydrophobicity than those with the wet layer MPLs. The reproducibility of the dry layer preparation for MPLs was also satisfying.

Hemoglobin (Hb) and myoglobin (Mb) were immobilized at the didodecyldimethylammonium bromide (DDAB)-modified powder microelectrode (PME) to fabricate Hb–DDAB–PME and Mb–DDAB–PME. Direct electrochemistry of Hb and Mb were achieved on the DDAB-modified PME. The formal potential was −0.224 V for Hb and −0.212 V for Mb (vs. SCE). The apparent surface concentration of Hb and Mb at the electrode surface was 2.83 × 10−8 and 9.94 × 10−8 mol cm−2. The Hb–DDAB–PME and Mb–DDAB–PME were successfully applied for measurement of NO in vitro. The anodic current peaks for NO oxidation at +0.7 V and the cathodic current peaks for NO reduction at −0.85 V on the CV curves were obtained on the modified electrodes. For detection of NO at +0.7 V, the sensitivity is 3.31 mA μM−1 cm−2 for Hb–DDAB–PME and 0.6 mA μM−1 cm−2 for Mb–DDAB–PME. The detection limit is 5 nM for Hb–DDAB–PME and 9 nM for Mb–DDAB–PME. The linear response range is 9–100 and 28–330 nM for Hb- and Mb-modified PME, respectively. For the electrochemical detection of NO at −0.85 V by using Hb–DDAB–PME, the detection sensitivity is 39.56 μA μM−1 cm−2; the detection limit is as low as 0.2 μM; and the linear response range is 1.90–28.08 μM.

Ordered porous cabon with a 2-D hexagonal structure, high specific surface area and large pore volume was synthesized through a two-step heating method using tri-block copolymer as template and phenolic resin as carbon precursor. The results indicated the electrochemical performance of the sulfur/carbon composites prepared with the ordered porous carbon was significantly affected by the pore structure of the carbon. Both the specific capacity and cycling stability of the sulfur/carbon composites were improved using the bimodal micro/meso-porous carbon frameworks with high surface area. Its initial discharge capacity can be as high as 1200 mAh·g−1 at a current density of 167.5 mA·g−1. The improved capacity retention was obtained during the cell cycling as well.The unique bimodal mesoporous structure in the carbon framework MC-2 has been shown to contribute to the excellent electrochemical performances of S/MC-2 composite for the Li-S battery cathode.Download full-size image

An efficient anode with a superior high-rate capability and stability remains a challenge for development of high performance Li-ion batteries. We present a new concept by encapsulating 2 nm-sized SnO2 nanocrystals in the channels of carbon nanotubes (SnO2-in-CNTs). Characterization shows that the confined space does not only stabilize the small nanoparticles but also alleviates the stress caused by the large volume change of tin species during the charging–discharging process. In addition, well crystallized graphitic structure of CNTs with a positive curvature provides a good contact between SnO2 nanoparticles and graphene layers, and excellent electronic conductivity. As a result, SnO2-in-CNTs as an anode of lithium ion battery exhibit stable cyclability and superior high-rate capability relative to SnO2 nanoparticles dispersed on the outer walls of CNTs particularly under a high current density. The charge capacity remains about 560 mA h g−1 after 50 cycles at 50 mA g−1, and even around 400 mA h g−1 at 1000 mA g−1. Additionally, the facile preparation method we have developed makes such encapsulates appealing for further optimization and applications.

LiNi0.5Mn1.5O4 nanoplates were prepared using a two-step method composed of a hydrothermal method and a solid-state reaction. At first, bimetal–organic coordination-polymers containing Ni2+ and Mn2+ were synthesized using the ligand 3,4,9,10-perylenetetracarboxylic dianhydride (ptcda) by a template-assisted self-assembly method in a hydrothermal atmosphere. This was followed by thermal treatment to remove the organic components and then calcination with lithium acetate, and nanoplate-stacked LiNi0.5Mn1.5O4 was obtained. The nanoplate structure shortens the diffusion path of the lithium ions in the bulk of LiNi0.5Mn1.5O4 and then promotes fast charge–discharge properties of the material. In addition, an amorphous Li2CO3 layer with nanometer thickness in situ generated on the surface of the LiNi0.5Mn1.5O4 particles was confirmed by TEM and XPS. This is helpful for suppressing the interfacial side reactions and thereby improving the cycling stability of the material. Owing to these advantages, the LiNi0.5Mn1.5O4/Li2CO3 material exhibits excellent rate capability and cycling stability. The as-prepared material delivers 129.8 mA h g−1 at a 1 C rate and retains 86.4% of the initial capacity even after 1000 cycles of charge–discharge at 25 °C. Even at a high discharge rate of 40 C, the specific capacity of the material is 120.9 mA h g−1, and the capacity retention is 84.7% over 500 cycles. The high-temperature stability of the material is also superior. When operating at 55 °C, the capacity loss by cycle is only 0.037% throughout 250 cycles.

A high-quality sized FeFe(CN)6 was synthesized as a cathode material for a non-aqueous potassium-ion battery. The electrode delivered a reversible capacity of 124 mA h g−1 at the current rate of 0.5C and still retained a reversible capacity of 93 mA h g−1 after 500 cycles at 5C with a columbic efficiency of 100%. Structural evolution and redox couples of low and high spin FeIII/FeII were investigated by ex situ X-ray diffraction, Mössbauer spectroscopy, and X-ray photoelectric spectroscopy. The negligible volume change during the electrochemical process should be responsible for the excellent cyclic stability.