Corrosion resistance of 316L stainless steel in acetic acid by EIS and Mott-Schottky

The properties of the passivation film formed on 316L stainless steel were studied by Electrochemical Impedance Spectroscopy （EIS）, Mott-Schottky and Voltammetry measurements in high- temperature acetic acid. The results show that the passivation film formed on 316L stainless steel is stable in 60% acetic acid solution from 25 ℃ to 85 ℃. As temperature increased, the polarization resistance decreased but the interface capacitance increased. There was hardly any relation between temperature and the intrinsic property semiconductor. The passivation film represents the p-semiconductor property in the potential interval of -0.5-0.1 V; represents the n-semiconductor property in the potential interval of 0.1-0.9 V; and represents the p-semiconductor property in the potential interval of 0.9-1.1 V. The voltammetry measurements show that the structure of the passivation film is stable when the temperature is lower than 55 ℃ and that its stability decreased when this temperature is exceeded.     

n-Type nitrogenated nanocrystalline diamond thin-film electrodes: The effect of the nitrogenation on electrochemical properties

Nitrogenated nanocrystalline diamond thin-film electrodes with controlled conductivity are grown from microwave- or arc-plasma in CH₄-Ar-H₂-N₂ gas mixtures. Their electrochemical behavior is studied using cyclic voltammetry and electrochemical impedance spectroscopy techniques. It is concluded from Mott-Schottky plots that the studied material has n-type conductance; the donor concentration is estimated. The character of electrode behavior is controlled by the degree of nitrogenation of the material. In particular, with the increasing of nitrogen concentration in the feeding gas (0-25%) supplied to plasma-chemical reactor, the potential window in the supporting electrolyte (2.5 M H₂SO₄) becomes somewhat narrower, the reversibility of electrochemical reactions in the [Fe(CN)₆]^3−/4− redox couple becomes more pronounced. Kinetic parameters of redox reactions in this couple are determined. By and large, with the increasing of the nitrogenation the electrochemical behavior of “poor conductor” gives way to that of metal-like conductor.     

Modified titanium electrodes: Application to Ti/TiO2/PbO2 dimensionally stable anodes

Titanium is a valve metal able to withstand corrosion, due to the presence of a passivating layer of titanium oxide on its surface. But, due to that more or less insulating layer, titanium cannot be used directly as an anodic material. However, modification of the surface of a Ti/TiO₂ substrate may lead to the formation of new structures: Ti/TiO₂/M or Ti/TiO₂/OX, in which M is a metal such as platinum and OX a conducting oxide exhibiting electrocatalytic properties. These structures have interesting electrochemical properties and may be used as efficient electrode materials.In this paper, after a review of the electrochemical behaviour of these structures, we give new results concerning the selective electrodeposition of lead dioxide on Ti/TiO₂ substrates and we propose an interpretation of the results taking into account the dielectric properties of the underlying TiO₂. It is shown that there is a dramatic decrease of the resistance of the electrode when a PbO₂ layer is electrodeposited onto a Ti/TiO₂ structure. That effect allows the preparation of electrodes (low-cost DSAs) that may be used as anodes in spite of the presence of the underlying TiO₂ layer, that layer being useful to avoid corrosion of the titanium substrate. At last, the effect of stabilization of the underlying TiO₂ layer is discussed.     

Influences of temperature, H2SO4 concentration and Sn content on corrosion behaviors of PbSn alloy in sulfuric acid solution

The influences of temperature, H₂SO₄ concentration and Sn content on corrosion behaviors of PbSn alloys in sulfuric acid solution were investigated by potentiodynamic curve, cyclic voltammetry (CV), linear sweeping voltage (LSV), electrochemical impedance spectra (EIS), a.c. voltammetry (ACV) and Mott-Schottky analysis. The microstructure of the corrosion layer on PbSn alloy was analyzed by scanning electron microscopy (SEM). The results showed that the corrosion resistance of PbSn alloy increased with ascending Sn content and H₂SO₄ concentration, the increment of temperature can decrease the corrosion resistance of PbSn alloy in H₂SO₄ solution. The conductivity of the anodic film on PbSn alloy was enhanced with increasing temperature, ascending Sn content and descending H₂SO₄ concentration. SEM result revealed that the corrosion film after cyclic voltammetry was consisted of tetragonal crystal, the porosity enlarged with decreasing temperature, Sn content and H₂SO₄ concentration.     

A comparative electrochemical study of iron deposition onto n- and p-type porous silicon prepared from lightly doped substrates

Electrodeposition of iron from acidic sulfate solutions onto porous silicon (PS) prepared from n- and p-type (1 0 0) substrates is studied by electrochemical measurements. Results from current-potential curves show that deposition of iron on p-type PS can only be achieved under illumination and cathodic polarization, whereas the deposition is found to proceed on n-type even in the dark. The measurements of the cathodic current efficiency indicate that the fraction of current used for iron deposition decreases with the applied potential due to hydrogen evolution reaction which is a competing reaction to metal deposition. Scanning electron microscopy shows that very fine iron crystallites with an average size of 40-70 nm are formed under double potential step conditions. The energy band diagrams of silicon-solution interfaces determined by electrochemical impedance measurements reveal that the iron deposition mechanism on both substrates is electron transfer from the conduction band.     

电沉积工艺对p-CuSCN薄膜结构及半导体性质的影响

以乙二胺四乙酸二钠(ethylenediamjn tetraacetic acid disodium,EDTA)为鳌合剂,在水溶液络合体系中采用电沉积法制备了CuSCN半导体薄膜,应用电子隧穿成核和表面态热激发机理以及Mott-Schottky曲线分析了沉积电位和温度对薄膜结构和半导体性质的影响.结果表明:室温下,价带电子隧穿产生的电流与表面态空穴热激发电流在同一数量级,表面态空穴热激发电流不随电位改变,价带电子隧穿电流的变化趋势反映了整体电流的变化.随着阴极电位的升高,由于价带电子的隧穿几率变化,晶粒尺寸先减小后增大;半导体空穴浓度减小,p型性质减弱.由于沉积反应受活化能控制,在高温条件下主要表现为晶粒生长,导致晶粒尺寸增大,薄膜致密度降低;同时也使半导体空穴浓度减小,p型性质减弱.     

Effect of the final annealing of cold rolled stainless steels sheets on the electronic properties and pit nucleation resistance of passive films

Semiconducting properties of passive films formed on AISI 304 stainless steel grade were investigated by capacitances measurements in chloride containing aqueous solutions for different surface finishes: BA (bright annealing in hydrogen containing atmospheres) and 2B (standard annealing in oxidising atmospheres followed by pickling in acid, then water rinsing). Mott-Schottky analysis shows that for high enough electrode potential, and whatever the surface finish, the films behave like n-type semiconductors. 2B passive film appears to be more donor-doped than BA one and the density of donor states increases with chloride concentration. The electron donor levels are assumed to be generated by negatively charged cations vacancies produced by the chloride ions reaction with the outer passive film. This reaction looks easier for 2B than BA condition, which explains why BA resists better than 2B to pit nucleation.     

Efficient and stable inverted polymer solar cells using TiO2 nanoparticles and analysized by Mott-Schottky capacitance

The performance of both inverted and conventional polymer solar cells (PSCs) were examined with a low-temperature, solution-processed synthesized TiO₂ nanoparticles (TiO₂ NPs) as the electron extraction layer. The performance of inverted PSCs based on P3HT:PCBM bulk-heterojunction with a TiO₂ NPs layer was dramatically improved and the highest power conversion efficiency (PCE) of 4.56% was achieved via 24 h exposure in air, which is one of the highest PCEs for P3HT:PCBM bulk-heterojunction PSCs using TiO₂ as electron extraction layer. Meanwhile, the performance of inverted PSCs was superior to regular PSCs. Mott-Schottky capacitance analysis was carried out for both inverted and regular PSCs to obtain the built-in potential, the depletion width, as well as the doping level of the active layer, which all support the performance improvement of PSCs devices with inverted structure. In addition, inverted PSCs show excellent stability in air without encapsulation. The PCE can retain 87% of its original values after 400 h exposure in air, which is much better than that of regular PSCs. The results indicate that solution-processed TiO₂ NPs shows great potential applications in the fabrication of highly efficient and stable inverted PSCs as well as large-area, flexible printed PSCs.     

阳极钝化电位对黄铜表面钝化膜半导体性能的影响

目的研究黄铜在不同阳极钝化电位下形成的钝化膜的半导体性能。方法通过动电位极化曲线获取黄铜在硼酸盐缓冲溶液中的维钝电位区间,并选取3个钝化电位值对黄铜进行钝化处理,采用电化学阻抗谱和Mott-Schottky半导体理论研究阳极钝化电位对钝化膜半导体性能的影响,并进一步利用PDM模型进行点缺陷扩散系数的计算。结果黄铜在硼酸盐缓冲溶液中有明显的钝化区间,不同钝化电位对应的Mott-Schottky直线斜率均为负值,且点缺陷扩散系数均为10-14数量级。随着阳极钝化电位的正移,钝化膜的阻抗值不断增加,受主密度降低,平带电位变小,空间电荷层厚度增加。结论黄铜在不同钝化电位下形成的钝化膜均表现出p型半导体的特性,膜中载流子以空穴为主,随着阳极钝化电位的正移,钝化膜的导电性能变差,耐蚀性能增强,对基体的保护作用更好。     

Controlled growth of Cu2O thin films by electrodeposition approach

Thin films of Cu₂O comprised of wavelike surface characteristic of compact nanoparticles were synthesized using a facile and cost-effective electrodeposition approach. The distinct surface morphologies with well-aligned crystal orientation were obtained through the controlled electrodeposition parameters. The high resolution AFM combined with the peak force AFM images mapped the nanomechanical and chemical properties of the Cu₂O nanostructured films. The structural, optical, and compositional analyses of the as-deposited thin films show bulk Cu₂O material. The electrodeposition approach could proceed non-intermittently under ambient conditions, and provides a facile and economic way of depositing thin films of Cu₂O with wavelike characteristics. The photoluminescence lifetime was found be very short in the range of 0.8–1.3 ns for Cu₂O films. The Mott-Schottky measurement exhibited p-type conductivity and carrier density was found to be ~2×10¹⁸. The observed photoluminescence lifetimes, and carrier densities could help implementing the Cu₂O films as an efficient hole-conducting, and photoelectrode materials in solar cells and water splitting devices.