AC impedance studies of anodically treated polycrystalline and homoepitaxial boron-doped diamond electrodes

The electrochemical properties of several types of diamond electrodes, including polycrystalline and homoepitaxial films, that underwent anodic treatment were examined with the electrochemical impedance spectroscopic (EIS) technique, as well as with capacitance-potential measurements. From an analysis of the impedance behavior, it was found that an additional capacitance element, which is apparent in the relatively high-frequency range (100-1000 Hz), was generated on the polycrystalline and (1 0 0) homoepitaxial diamond electrodes after anodic treatment. This capacitive element can be characterized as being non-Faradaic, because it has negligible dependence on the applied potential. Acceptor densities and depth profiles were calculated from the Mott-Schottky plots, and the acceptor densities in the near-surface region of the anodically treated surfaces were found to be extremely low. These results indicate that passive layers were generated on the diamond surfaces by the anodic treatment. The capacitance-potential behavior was also consistent with a model consisting of a semiconductor with a passive surface film. The passive film is proposed to arise as a result of the removal of hydrogen acting as an acceptor in the subsurface region, leaving hydrogen that is paired essentially quantitatively with the boron dopant, effectively neutralizing it.     

Electrochemical behavior of the Ti–6Al–4V alloy coated with a-C:H films

In this work diamond-like carbon films were deposited on the Ti–6Al–4V alloy, which has been used in aeronautics and biomedical fields, by electrical discharges using a magnetron cathode and a 99.999% graphite target in two different atmospheres, the first one constituted by argon and hydrogen and the second one by argon and methane. Films deposited using the argon/hydrogen mixture were called a-C:H, while films deposited using the argon/methane mixture were called DLC. Raman spectroscopy was used to study the structure of the films. The Raman spectra profile of the a-C:H films is quite different from that of the DLC films. The disorder degree of the graphite crystalline phase in a-C:H films is higher than in DLC films (a-C:H films present small values for the the I_D/I_G ratio). Potentiodynamic corrosion tests in 0.5 mol l⁻¹ NaCl aqueous solution, pH 5.8, at room temperature (≈25 °C) were carried out as for the a-C:H as for the DLC coated surfaces. Comparison between the corrosion parameters of a-C:H and DLC coated surfaces under similar deposition time, showed that DLC coated surfaces present bigger corrosion potential (E_corr) and polarization resistance than those coated with a-C:H films. Electrochemical impedance spectroscopy (EIS) was also used to study the electrochemical behavior of a-C:H and DLC coated surfaces exposed to 0.5 mol l⁻¹ aqueous solution. The EIS results were simulated with equivalent electrical circuit models for porous films. The results of these simulations showed similar tendency to the one observed in the potentiodynamic corrosion tests. The DLC film resistance and the charge transfer resistance (R_ct) for the DLC coated surface/electrolyte interface were bigger than the ones determined for the a-C:H coated surfaces.     

New soluble unsaturated polyketone derived from diarylidenecycloalketone: synthesis and optical and electrochemical properties of π-conjugated poly(diarylidenecyclohexanone) with long side chains

A new type of unsaturated polyketone having cyclohexanone moiety in a π-conjugated main chain was prepared by polycondensation between 2,6-bis(4-bromobenzylidene)cyclohexanone and 2,5-dihexyloxy-p-phenylene diboric ester in the presence of Pd(PPh₃)₄. The polymer had good solubility in common organic solvents. Analysis by gel permeation chromatography (GPC; polystyrene standards) showed that the polymer had M_n and M_w values of 7800 and 18?200, respectively. The polymer exhibited a [η] value of 0.70 dl g⁻¹ in benzene at 30 °C. The chloroform solution of the polymer showed an UV-Vis peak at 392 nm, and the PL spectrum gave a peak at 533 nm. DSC exhibited that the polymer had a T_g of 85 °C. The DSC data, observation with a polarizing microscope, X-ray diffraction data and UV-Vis data of the obtained polymer showed a phase transition above 200 °C. TGA showed that the polymer had good thermal stability with 5 wt% loss temperature of 407 °C under N₂. Electrochemical oxidation (or p-doping) of the polymer started at about 0.7 V vs. Ag/AgNO₃ and gave a peak at 1.06 V vs. Ag/AgNO₃ with a color change of the film from yellow to deep red. The color change was followed by UV-Vis spectroscopy. The corresponding p-dedoping peak appeared at 0.58 V vs. Ag/AgNO₃.     

Electrochemical insertion of lithium ions into disordered carbons derived from reduced graphite fluoride

Both covalent (obtained by direct fluorination at high temperature) and semi-ionic carbon fluorides (synthesized at room temperature) were reduced in order to obtain disordered carbons containing very small content of fluorine and different physical properties according to the reduction treatment (chemical, thermal or electrochemical). After a physical characterization (X-ray diffraction, electron spin resonance and FT-IR spectroscopies), the electrochemical behaviours of the pristine carbon fluorides and of the treated samples were investigated during the insertion of lithium using liquid carbonate-based electrolytes (LiClO₄-EC/PC, 50:50%, v/v). Both galvanostatic and voltammetric modes were performed and revealed that the voltage profiles and the capacities differed according to the starting material and the reduction treatment. Semi-ionic carbon fluoride treated in F₂ atmosphere for 2 h at 150 °C and then chemically reduced in KOH exhibits high reversible capacities (the reversible capacity is 530 mAh g⁻¹ in the second cycle); in this case, the voltage profiles show a large flat portion at potentials lower than 0.3 V which is attributed to the insertion/deinsertion of lithium ions between the small graphene sheets and/or the absorption of pseudo metallic lithium into the microporosity of the sample. Nevertheless, a part of the lithium ions are removed at potentials higher than 0.5 V versus Li⁺/Li limiting the useful capacity.     

Preparation of a Gas Diffusion Electrode by Ozone Gas Pretreatment and an Ion-exchange Method

Surface oxidation using ozone gas, produced by an electrolytic ozone generator, was applied for preparation of a gas-diffusion electrode (GDE) for an electrochemical energy conversion system. An uncatalyzed carbon sheet containing poly(tetrafluoroethylene) binder was first placed into contact with ozone gas to form active functional groups on the surface of the carbon; then ion-exchange between a weakly bound hydrogen of the functional groups and a platinum cation complex was performed. A GDE having highly dispersed particles of a platinum metal deposited on a porous carbon sheet ws developed by this method. The fuel cell using this GDE showed high performance.     

A sustainable printed circuit board derived hierarchically porous carbon/polyaniline composites for supercapacitors

The hierarchically porous carbon/polyaniline electrodes derived from the nonmetallic part of waste printed circuit board have been synthesized by a convenient carbonization and activation method. A detailed analysis of the morphology, structure, and electrochemical performances of as-prepared composites is presented. As expected, the balanced specific surface area and porous structure manifest their remarkable electrochemical performances. Apparently, the multiple synergistic effects are crucial to simultaneously achieving high capacity and significantly increased stability. As a result, the electrodes display exceptional rate capability, superior cyclic stability, and high specific capacitance (520.0 F/g at 1 A/g). Furthermore, the asymmetrical device possesses an improved energy density of 9.3 Wh/kg with a power density of 62.4 W/kg in H₂SO₄ electrolyte. Moreover, a potential mechanism contributing to the superior performance of hierarchically porous carbon/polyaniline composites has been studied in detail. Noteworthy, this study provides a feasible strategy for recycling waste printed circuit boards. Importantly, this approach will provide a path toward the rational synthesis and design of electrode materials for supercapacitors that take both high-performance and cost-effective into account.     

燃料电池中铁基氧还原催化剂的研究进展

阴极氧还原反应是燃料电池的核心反应之一。目前催化氧还原反应的催化剂通常是贵金属铂,但其普遍存在成本高、对甲醇耐受性差、易CO中毒等缺点,因此开展非贵金属催化剂的研究显得尤为重要。铁基催化剂因催化活性好、稳定性高、甲醇耐受性好、价格低廉等备受青睐,最有希望成为铂基催化剂的替代品。本文主要综述了几类铁基氧还原催化剂的研究现状、催化机理及活性影响因素,并在此基础上阐述了各类催化剂目前尚待解决的问题和发展方向。     

焙烧条件对Na3V2(PO4)3/C的制备及储锌性能影响

采用喷雾干燥法合成了Na₃V₂(PO₄)₃(NVP)前驱体,然后经过高温煅烧得到水系锌离子电池正极复合材料Na₃V₂(PO₄)₃/C(NVP/C),考察了煅烧温度和煅烧时间对NVP/C性能的影响。通过XRD、SEM和BET对样品结构和形貌进行了表征,通过循环伏安和充放电测试了样品的电化学性能。结果表明,不同煅烧温度和煅烧时间制备样品均为纯相的NVP/C,且并没有改变NVP/C的晶体结构;煅烧温度过高或煅烧时间过长会导致晶粒尺寸增大,性能迅速衰减。NVP/C制备最佳条件为煅烧温度700℃、煅烧时间8 h,在该条件下所制备的NVP/C(记为NVP/C-700-8)形貌更为规整,结晶性良好,具有较小的阻抗以及更好的离子扩散能力,进而表现出最佳的电化学性能。在0.1 A/g电流密度下表现出最佳的放电比容量(122.4 mA·h/g)。在1.0 A/g电流密度下经过200圈循环后放电比容量仍高达103.9 mA·h/g。     

Structural and electrochemical properties of mixed calcium-zinc spinel ferrites nanoparticles

In the current work, we provide the electrochemical (EC) characteristics and considerable size of Ca-doped ZnFe₂O₄ nanoparticles. Mixed transition metal oxides are widely used as excellent electrode materials in superior supercapacitors because of their superior capacitance, low cost, and environmental friendliness. The prepared nanoparticles were characterized by X-ray diffraction (XRD), Field-emission scanning electron microscope (FE-SEM), energy-dispersive X-ray (EDX) spectroscopy, X-ray photoelectron spectroscopy (XPS), and EC methods. The results exhibited that the as-synthesized nanoparticles had a cubic spinel crystal structure and efficient EC properties. The EC properties of the prepared electrodes were explored by cyclic voltammetry (CV), galvanostatic charge/discharge (GCD), and electrochemical impedance spectroscopy (EIS) studies. The Ca_0.1Zn_0.9Fe₂O₄ electrode demonstrated a specific capacitance (SC) ～208 Fg^-1 at a 2 mV/s scan rate due to significant morphological behavior. Therefore may be the prepared materials are the finest electrodes for supercapacitor applications.     

Novel electrochemical sensing platform based on palygorskite nanorods/Super P Li carbon nanoparticles-graphitized carbon nanotubes nanocomposite for sensitive detection of niclosamide

We reported an one-pot ultrasonic-assisted method for the preparation of palygorskite nanorods/Super P Li carbon nanoparticles-graphitized carbon nanotubes (PNRs/SPCNPs-g-CNTs) nanocomposite, which was used to modify the glassy carbon electrode (GCE) for the fabrication of PNRs/SPCNPs-g-CNTs/GCE sensor. For the PNRs/SPCNPs-g-CNTs nanocomposite, PNRs with good stability presented large specific surface area and high adsorption, which promoted the enrichment of NA molecules on the electrode surface. SPCNPs with pearl chain-like nanostructure exhibited good electrical conductivity, and the combination of SPCNPs and g-CNTs with high graphitization degree formed an interconnected carbon conductive network with excellent electrical conductivity, which enhanced the charge transport efficiency. Moreover, the interconnected carbon conductive network of SPCNPs-g-CNTs not only promoted the dispersion degree of PNRs but also made up for the poor conductivity property of PNRs. When used for the detection of niclosamide (NA), an acceptable limit of detection (3.6 nM) was achieved at the PNRs/SPCNPs-g-CNTs/GCE sensor in linear NA concentration range of 0.01–10 μM. The PNRs/SPCNPs-g-CNTs/GCE sensor exhibited good reproducibility, repeatability, and anti-interference performance. For the practicability measurement, the fabricated sensor showed good practicability with satisfactory recoveries (97.0–102.7%) and low RSD values of 0.99–4.78% for the detection of NA in tap water and lake water samples.