Edge Plane Pyrolytic Graphite Electrodes for Stripping Voltammetry: a Comparison with Other Carbon Based Electrodes

The first examples of using edge plane pyrolytic graphite electrodes for anodic and cathodic stripping voltammetry (ASV and CSV) are presented, notably the ASV of silver and the CSV of manganese. In the former example, detection limits for silver (based on 3σ) of 8.1 nM and 0.185 nM for 120 s and 300 s accumulation time, respectively, were achievable using the edge plane electrode, which were superior to those observed on glassy carbon, basal plane pyrolytic graphite and boron‐doped diamond electrodes. In the second example, a detection limit for manganese of 0.3 μM was possible which was comparable with that achievable with a boron‐doped diamond electrode but with an increased sensitivity. Comparison of the edge plane pyrolytic graphite electrode with boron‐doped diamond electrodes reveals that the edge plane electrode has comparable detection limits and sensitivities whilst exhibiting a lower signal‐to‐noise ratio and large potential window for use in trace analysis suggesting boron‐doped diamond can be conveniently replaced by edge plane pyrolytic graphite as an electrode material in many applications.     

Elektrolyse substituierter Azidozimtsäure- und Azidoacrylsäureester

Several ring-substituted -azidocinnamic and -heterocyclic -azidoacrylic esters are subject to cathodic reduction under aprotic and protic conditions. Good to excellent yields of rather labile dehydroaminoacid derivatives resp. stableN,N-diacylated enaminoesters are selectively obtainable. The compounds are characterised by spectroscopic methods (¹H-NMR, IR, MS).

     

Tailoring the electrode surface structure by cathodic corrosion in alkali metal hydroxide solution: Nanostructuring and faceting of Au

Nanostructured metals are vital materials in several (electro)chemical applications. Despite the substantial progress in this field, still many limitations are associated with traditional synthetic procedures, including the availability of stable nanoparticles on appropriate supports by avoiding migration and aggregation. On that front, cathodic corrosion has emerged as a powerful technique to tailor the surface structure of metal surfaces on the nanoscale. Cathodic corrosion crucially depends on the electrode potential, the nature and the concentration of cations, as well as the electrode material. Controlling these parameters is essential for applying cathodic corrosion in materials design. In this short review, we discuss the most critical parameters controlling cathodic corrosion and highlight the importance of the nature and the concentration of alkali metal hydroxides in aqueous solution.     

Electrochemical oxidation of a carbon black loaded polymer electrode in aqueous electrolytes

The suitability of a polymeric composite material for use as part of an anode structure in a cathodic protection system has been examined. The composite material was a conductive blend (volume resistivity typically 1.5 Ω cm) of carbon black in a polyethylene binder. A long operational lifetime for the material demands that the rate of carbon loss must be low. In the work reported here, electrochemical and in situ analytical techniques were employed to characterise the performance of the material over a wide range of anodic current densities in a variety of aqueous electrolytes. The predominant anodic electrochemical reaction on the polymeric material is CO₂ formation in acid and neutral solutions, which causes loss of carbon from the surface and the development of a non-conducting layer of polyethylene. The characteristics of the reaction suggest that it occurs via the discharge of H₂O. In alkaline pH, however, the anodic reactions are more complex. A high OH⁻ concentration (pH 12 or higher) favours the formation of oxygen rather than CO₂, particularly at low anodic potentials. The presence of CO₃ ²⁻ in the electrolyte catalyses the evolution of oxygen at pH values as low as 9. The electrochemical formation of oxygen always occurs in parallel with the generation of some humic acid in the solution. Received: 23 July 1998 / Accepted: 17 November 1998     

电沉积多晶CdTe薄膜结构的电镜研究

CdTe(能隙E_g=1.45 eV)是一种制作太阳电池的理想半导体村料。用阴极电沉积法制备多晶CdTe薄膜具有方法简单、周期短、材料费用低于单晶硅而接近非晶硅等优点,颇引人注目。但该技术发展较晚,因此对其成膜机理,各种因素对薄膜质地、内部结构和光电性能的影响尚缺乏足够了解。本文通过实验发现:采用双阳极、调节电沉积电流、改变电解液组成,可使CdTe薄膜表面平整、不易产生枝晶。如进一步在氩气或空气流中进行热处理,可使薄膜中CdTe晶粒增大到0.4～0.5μm,最大可达0.7～0.8μm,并使伴生的CdTe孪晶现象也更明显,这些对CdTe薄膜光电转换性能的提高是有利的。     

Ln1−xSrxCoO3(Ln = Sm, Dy) for the electrode of solid oxide fuel cells

The perovskite-type oxides were synthesized in the series of Ln_1−xSr_xCoO₃(Ln = Sm, Dy). The formation of solid solutions in Dy_{1 − x}Sr_xCoO₃ was limited, compared with that in Sm_{1 − x}Sr_xCoO₃. The electrical conductivities of the sintered samples were measured as a function of x in the temperature range 30 to 1000 °C. The highest conductivity of around 500 S/cm at 1000 °C was found in Sm_0.7Sr_0.3CoO₃. The reactivity of all the samples with YSZ was examined at 800–1000 °C for 96 h. The Sr-doped perovskite oxides were more reactive with YSZ and produced SrZrO₃ at 900 °C after 96 h. However, no reaction product between SmCoO₃ and YSZ was observed at 1000 °C for 96 h. The cathodic polarization of the oxide electrodes, sputtered on yttria stabilized zirconia (YSZ), was studied at 800–1000 °C in air. SmCoO₃ shows no degradation of the electrode performance at higher temperatures. The thermal expansion measurements on the sintered samples were carried out from room temperature to 1000 °C. Large thermal expansion coefficients were found in these samples.     

Influence of treating frequency on microstructure and properties of Al2O3 coating on 304 stainless steel by cathodic plasma electrolytic deposition

Alumina ceramic coatings were fabricated on 304 stainless steel by cathodic plasma electrolytic deposition (CPED). Influence of treating frequency of the power supply on the microstructure and properties of the coatings were studied. The results indicated that coatings obtained at various frequencies on 304 stainless steels were all composed of α-Al₂O₃ and γ-Al₂O₃, and α-Al₂O₃ was the dominant phase. The contents of α-Al₂O₃ decreased gradually in a very small rate with increasing the frequency and γ-Al₂O₃ gradually increased. The surface of alumina ceramic coating was porous. With increasing the frequency, the coating surface gradually became less rough and more compact, resulting in low surface roughness. The bonding strength of Al₂O₃ coating was higher than 22 MPa and was not strongly affected by treating frequency. With increasing the frequency, the alumina coated steels showed better and gradually increasing corrosion resistance than the uncoated one in 3.5% NaCl solution. The coating steel with desirable corrosion resistance was obtained at 800 Hz whose corrosion current potential and corrosion density were −0.237 V and 7.367 × 10⁻⁸ A/cm², respectively.     

能源催化材料的电化学合成

电催化是发展可持续洁净能源技术的基础科学,是电化学能源转换和物质转化的关键环节.精准合成催化活性纳米结构是制约很多电催化反应走向实际应用的重要挑战.与湿化学合成、固相合成和气相沉积等传统方法相比,电化学合成是一种简单、快速、廉价及可控的高效催化材料制备方法,也是一种最为直接的一体化电极制备方法.本文综述了近年来利用电化...     

Interfacial Water Tuning by Intermolecular Spacing for Stable CO2 Electroreduction to C2+ Products

Electroreduction of CO₂ to multi-carbon (C₂₊) products is a promising approach for utilization of renewable energy, in which the interfacial water quantity is critical for both the C₂₊ product selectivity and the stability of Cu-based electrocatalytic sites. Functionalization of long-chain alkyl molecules on a catalyst surface can help to increase its stability, while it also tends to block the transport of water, thus inhibiting the C₂₊ product formation. Herein, we demonstrate the fine tuning of interfacial water by surface assembly of toluene on Cu nanosheets, allowing for sustained and enriched CO₂ supply but retarded water transfer to catalytic surface. Compared to bare Cu with fast cathodic corrosion and long-chain alkyl-modified Cu with main CO product, the toluene assembly on Cu nanosheet surface enabled a high Faradaic efficiency of 78 % for C₂₊ and a partial current density of 1.81 A cm⁻². The toluene-modified Cu catalyst further exhibited highly stable CO₂-to-C₂H₄ conversion of 400 h in a membrane-electrode-assembly electrolyzer, suggesting the attractive feature for both efficient C₂₊ selectivity and excellent stability.