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This paper involves preparation of four different crystal phases (δ, γ, α and λ) of MnO2 by redox, solid reaction, hydrothermal routes and delithiation of LiMn2O4, respectively. The obtained MnO2 samples have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and the Brunauer–Emmett–Teller (BET) method for micro-structural, morphological and porosity studies. Cyclic voltammetric and galvanostatic tests were carried out to evaluate their capacitive properties in an anti-freezing aqueous electrolyte at different operating temperatures ranging from 25 to −35 °C. The δ-MnO2 prepared by a redox method exhibits the best electrochemical performances when conducted either in the single electrode tests (from 174.7 to 148.6 F g−1) or in the capacitor measurements (from 47.4 to 42 F g−1) as the operating temperature decreased from 25 °C down to the low temperature of −35 °C. Moreover, electrochemical impedance spectroscopy has been investigated and the activation energy values of different impedance components have been analyzed. It has been discovered that the operation temperature has more effect on the charge transfer resistance than diffusion resistance. To some degrees, these results have guiding significance for the low-temperature applications of manganese oxides-based electrochemical capacitors.

A series of La-doped Li3V2(PO4)3/C cathode materials for Li-ion batteries are synthesized by a sol–gel-assisted, low-temperature sintering process. La(NO3)3 acts not only as the La source, but also, together with the intermediate product LiNO3, promotes combustion, the ultrahigh exothermic energy that is advantageous for the nucleation process. The subsequent sintering process at 600 °C for 4 h is sufficient to produce highly crystalline La-doped Li3V2(PO4)3/C composites. The as-prepared cathode materials display smaller particle size, lower electron-transfer resistance and faster Li ion migration, which is ascribed to enhanced Li-ion transfer because of the La doping. The resulting Li3V1.96La0.04(PO4)3/C cathode has a stable specific capacity of 160 mA h g−1 at low charge–discharge rates over 100 cycles, and retained a stable capacity of up to 116 mA h g−1 at a rate of 5 C, which is 40% higher than the undoped pristine cathode.

We report a novel far-infrared (FIR) thermal reduction process to effectively reduce graphene oxide films for supercapacitor electrode applications. The binder-free graphene oxide films used in this study were produced by electro-spray deposition of a graphene oxide colloidal solution onto stainless steel current collectors. The reduction of graphene oxide was performed using a commercial FIR convection oven that is ubiquitous in homes for cooking and heating food. The reduction process incorporated a simple, one-step FIR irradiation carried out in ambient air. Further, the FIR irradiation process was completed in ∼3 min, wherein neither special atmosphere nor high temperature was employed, resulting in an economic, efficient and simplified processing technique. The as-produced FIR graphene electrode gave a specific capacitance of ∼320 F/g at a current density of ∼0.2 A/g with less than 94% loss in specific capacitance over 10,000 charge/discharge cycles. This is one of the best specific capacitances reported for all-carbon electrodes without any additives. Even at ultrafast charge/discharge rates (current densities as high as ∼100 A/g), the FIR graphene electrode still delivered specific capacitances in excess of 90 F/g. The measured energy and power densities of the FIR supercapacitors were found to be ∼3–6 times higher than commercial (activated carbon) supercapacitor devices. This excellent electrochemical performance of the FIR graphene coupled with its ease of production (in air at low temperatures) using a commercial home-use FIR convection oven indicates the significant potential of this concept for large-scale commercial electrochemical supercapacitor applications.

In this paper, a series of Ce-doped Li3V2(PO4)3/C composite cathode materials for Li-ion batteries were synthesized by a facile and fast microwave assisted sol–gel route. The investigation of the influence of Ce doping on the structural and electrochemical characteristics of Li3V2(PO4)3/C shows that the resulting composite exhibits smaller particle size, lower electron-transfer resistance, and faster lithium ion migration, which are attributed to improved lithium ion transfer by the Ce doping. At low charge/discharge rates, the Ce-doped Li3V1.98Ce0.02(PO4)3/C composite delivers a stable specific capacity of ∼170 mAh g−1 for over 100 cycles. At high rates (e.g. 10C), the Ce-doped composite is still able to deliver stable capacities of up to ∼120 mAh g−1 which is ∼60% greater than its un-doped counterpart.

Mesoporous manganese oxides (MnO2) were synthesized via a facile chemical deposition strategy. Three kinds of basic precipitants including sodium carbonate (Na2CO3), sodium bicarbonate (NaHCO3), and sodium hydroxide (NaOH) were employed to adjust the microstructures and surface morphologies of MnO2 materials. The obtained MnO2 materials display different microstructures. Great differences are observed in their specific surface area and porosity properties. The microstructures and surface morphologies characteristics of MnO2 materials largely determine their pseudocapacitive behavior for supercapacitors. The MnO2 prepared with Na2CO3 precipitant exhibits the optimal microstructures and surface morphologies compared with the other two samples, contributing to their best electrochemical performances for supercapacitors when conducted either in the single electrode tests or in the capacitor measurements. The optimal MnO2 electrode exhibits a high specific capacitance (173 F g–1 at 0.25 A g−1), high-rate capability (123 F g−1 at 4 A g−1), and excellent cyclic stability (no capacitance loss after 5,000 cycles at 1 A g−1). The optimal activated carbon//MnO2 hybrid capacitor exhibits a wide working voltage (1.8 V), high-power and high-energy densities (1,734 W kg−1 and 20.9 Wh kg−1), and excellent cycling behavior (93.8 % capacitance retention after 10,000 cycles at 1 A g−1), indicating the promising applications of the easily fabricated mesoporous MnO2 for supercapacitors.

An amine-Fe3O4 modified glassy carbon (GC) electrode was constructed for detecting Pb(II) ions in wastewater. The electrode was characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Square wave anodic stripping voltammetry (SWASV) was used to detect the Pb(II), and the detection limit of Pb(II) was 0.15 µM. The sensitivity of the electrode to detect Pb(II) was about 10.07 µA/µM, with a correlation coefficient of 0.991, which was approximately 10 times bigger than that of a pure Fe3O4 modified electrode. The electrode also showed good selectivity and stability. This results indicated that the amine-magnetite material could have some potential applications in heavy metal ions detection in wastewater.

We present a new method for specific detection of oxytetracycline (OTC) at nanomolar concentrations based on a microfabricated cantilever array. The sensing cantilevers in the array are functionalized with self-assembled monolayers (SAMs) of OTC-specific aptamer, which acts as a recognition molecule for OTC. While the reference cantilevers in the array are functionalized with 6-mercapto-1-hexanol SAMs to eliminate the influence of environmental disturbances. The cantilever sensor shows a good linear relationship between the deflection amplitude and the OTC concentration in the range of 1.0-100 nM. The detection limit of the cantilever array sensor is as low as 0.2 nM, which is comparable to some traditional methods. Other antibiotics such as doxycycline and tetracycline do not cause significant deflection of the cantilevers. It is demonstrated that the cantilever array sensors can be used as a powerful tool to detect drugs with high sensitivity and selectivity.

Carbon coated LiFePO 4 cathode materials were successfully synthesized by heating the precursors of FePO 4 @PAn (polyaniline) and equimolar LiOH·H 2 O under Ar flow. We demonstrated a method that could precisely control the carbon shell in a single reaction step. The precursors of FePO 4 @PAn were prepared by in situ polymerization of aniline and precipitation of FePO 4 in one pot in the presence of hydrogen peroxide as oxidizer. In the obtained core–shell cathode composite, the LiFePO 4 core phase was crystalline while the carbon shell had the thickness of several nanometers. The optimized cathode material exhibited satisfactory rate and cycle performance, which virtues are quite suitable for power lithium ion batteries.

For enhancement of lithium-ion transference number, lithium-ion-conductive polymer electrolytes have been prepared from polyethylene oxide (PEO), lithium salt of LiCF3SO3 or LiF, plasticizer of polyethylene glycol dimethylether (PEGDME), and anion receptor of tris(pentafluorophenyl)borane (TPFB). Transport properties of the resultant polymer electrolytes have been studied by AC impedance spectroscopy. As a result, lithium-ion transference number increased with increasing TPFB due to the restriction of anion conduction by the interaction between anion and anion receptor. Effects of anion receptor on transport properties are discussed.

The effects of plasticizer ethylene carbonate (EC) on the AC impedance spectra and the ionic conductivity are reported. With increasing of EC concentration the semicircle in high frequency disappears, and the slope of the straight line in low frequency decreases. The data obtained from impedance experiments can be explained using an equivalent circuit proposed. On the other hand, the room temperature conductivity increases with EC concentration because of the increase of the segmental flexibility of PEO. For lower EC concentration samples, the temperature dependence of conductivity in low temperature range follows Arrhenius type, but when EC concentration is larger than 20%, the temperature dependence of conductivity obeys the Vogel-Tamman-Fulcher (VTF) equation in all temperature ranges.

Composite polymeric electrolytes of PEO-LiClO4-Al2O3 and PEO-LiClO4-EC were prepared and the ionic conductivity by a.c. impedance was calculated using four different methods, and three kinds of representations of a.c. impedance spectra were adopted. The first is based on the Nyquist impedance plot of the imaginary part (Z″) versus the real part (Z′) of the complex impedance. The second and the third correspond to the plots of imaginary impedance Z″ as a function of frequency (f), and the absolute value (|Z|) and phase angle (θ) as a function of f, respectively. It was found that the values of the ionic conductivity calculated using the three representations of a.c. impedance spectra are basically identical.

The heterogeneous electron transfer rate constant (ks) of dimethylferrocene (DMFc) was estimated using cyclic voltammetric peak potential separations taken typically in a mixed diffusion geometry regime in a polyelectrolyte, and the diffusion coefficient (D) of DMFc was obtained using a steady-state voltammogram. The heterogeneous electron transfer rate constant and diffusion coefficient are both smaller by about 100-fold in the polymeric solvent than in the monomeric solvent. The results are in agreement with the difference of longitudinal dielectric relaxation time (τL) in the two kinds of solvents, poly(ethylene glycol) (PEG) and CH3CN, indicating that ks varies inversely with τL; ks is proportional to D of DMFc. Both D and ks of DMFc in PEG containing different supporting electrolytes and at different temperatures have been estimated. These results show that D and ks of DMFc increase with increasing temperature in the polyelectrolyte, whereas they vary only slightly with changing the supporting electrolyte.