Mesoporous Cr2O3 as negative electrode in lithium batteries: TEM study of the texture effect on the polymeric layer formation

Mesoporous single crystal (PSC) oxides have been reported as presenting higher electrochemical performances than bulk materials in lithium ion batteries operating via intercalation processes. Here, we extend this study to the electrochemical behaviour of mesoporous Cr₂O₃ versus Li⁺/Li⁰. We confirm that the Cr₂O₃ reacts towards Li through a conversion reaction mechanism leading, upon discharge, to the formation of large metallic chromium nanoparticles (10 nm); the latter are embedded into a Li₂O matrix together with, in this specific case, a copious amount of polymeric materials coming from electrolyte degradation, surrounding the particles, and filling the pores. During the following charge, re-oxidation of the nanoparticles occurs with the formation of CrO_1−x, with the main difference, as opposed to bulk Cr₂O₃ electrodes, being the preservation of the polymeric layer at the end of the charge. We believe the material mesoporosity, via capillary effects, to be at the origin of such a difference. These electrolyte degradation products are shown to help in maintaining the material mesoporosity for a great number of cycles; and interestingly they are not detrimental to the cell performance in terms of capacity retention while presenting great advantages in terms of charge transfer by reducing diffusion lengths, namely for Li⁺ ions. The positive attributes of mesoporous material-based electrodes noticed for insertion reactions can then be extended to conversion reaction electrodes as long as we can master their synthesis while controlling their mesoporosity through either soft or hard templating techniques.     

Tribocorrosion of 316L stainless steel and TA6V4 alloy in H2SO4 media

Tribocorrosion of stainless steel 316L and titanium alloy TA6V4 has been conducted in a sulphuric acid solution using an apparatus designed and built for evaluating the joint action of corrosion and wear. The material electrochemical and wear behaviours have been investigated during friction tests under electrochemical potential control. The specimens have been submitted to friction against an alumina ball under cathodic, free and anodic potentials. The friction coefficient, the wear rate and the current density were measured and the obtained results were discussed in terms of passivating film stability and repassivation kinetics.     

Second Harmonic Generation studies of the oxidation of metal electrodes: Compact and hydrous oxide growth at gold electrodes in acid solutions

The oxidation of gold electrodes in aqueous media has been examined using Second Harmonic Generation (SHG). Initial growth of the compact or α oxide causes a substantial drop in SH generation even when only partial coverage of oxide is attained and this is suggested to be due to the effect of the development of the oxide on a surface plasmon derived from d-electrons in gold, the involvement of these electrons in oxide formation meaning that the surface plasmon can no longer propagate. When thicker hydrous (or β) oxides are grown on top of the α oxide by holding at constant potential, the subsequent reduction of the oxide leads to unusual narrow peaks (dips) in the SHG response which occur before any significant reduction charge is passed. As the amount of hydrous oxide increases, the initial single narrow SHG peak changes to a pair of peaks and these then merge into one broad peak. The SHG peaks are suggested to be related to an order-disorder transition at the interface between α and β oxides, or perhaps due to the presence of surface traps. Second Harmonic Generation is shown again to be a sensitive and informative technique Having sub-monolayer sensitivity for α oxide growth and offering insight into the reduction process of multilayer oxides.     

Cathodic disbonding of a thick polyurethane coating from steel in sodium chloride solution

The cathodic disbonding of a thick, pigmented polyurethane coating from steel in 3.5 wt.% NaCl solution was studied by using an electrochemical AC impedance technique. Double-cylinder electrolyte cells were designed to separate the measurements of cathodic disbonding process from the influence of the impedance of an artificial defect. It was found that for a thick, pigmented polyurethane coating, the more important transport pathway of the reactive species is along the coating/steel interface rather than through the coating. There existed a delay time for the cathodic disbonding process, and cathodic polarization was not a predominant factor in determining the cathodic disbonding behavior in the early stages. The thick polyurethane coating, which was applied on a well sand-blasted steel surface, had excellent resistance to cathodic disbonding.     

Electrochemical investigations on composite iron electrodes

In spite of the many studies performed since the beginning of the last century, the Fe electrode, used as negative of both Ni/Fe and Fe/Air batteries, still poses several problems. For instance, according to the current literature, the following points are still not clear: (i) whether and how the depth of discharge affects electrode performance; (ii) what pathway the discharge follows, generally assumed as it is to involve consecutive Fe → Fe^II and Fe^II → Fe^III oxidation; (iii) why, at room temperature, only a minor fraction of the large theoretical capacity can be exploited. The present paper shows that deep discharges do increase Fe electrode performance, since they induce a transitory inhibition of hydrogen evolution. Likewise, Fe/Metal oxide composite electrodes have shown that the formation of Fe^III in discharge can take place directly from Fe, when the discharging rate applied is no longer compatible with the increase in electrode resistance due to oxidation products. Fe/Intermetallic compound composite electrodes have been studied as possible routes for increasing the efficiency of Fe capacity: useful indications have been gained as regards the compatibility of Fe with an IMC for charge storage.     

Thermal, optical, electrochemical properties and conductivity of trans- and cis-poly(1-ethynylpyrene): a comparative investigation

The thermal, optical and electrochemical properties of trans-poly(1-ethynylpyrene) (trans-PEP) and cis-poly(1-ethynylpyrene) (cis-PEP) have been studied as a function of polymer backbone configuration and internal stacking. Absorption spectra of the polymers showed that trans-PEP possesses a higher degree of conjugation than its homologue, cis-PEP. Intramolecular interactions occur between adjacent pendant pyrene units (associated pyrenes) present in each polymer, giving rise to static excimer emissions, strongest in cis-PEP because of the shorter distances between aromatic rings. Data resulting from excitation spectra and fluorescence decay profiles proved that such interactions take place in the ground state. Cyclic voltammetry of trans- and cis-PEP exhibited irreversible behaviors with different oxidation potentials as a result of their dissimilar geometry.     

利用Wiener过程探究镁水泥混凝土中涂层钢筋在盐类环境下的腐蚀寿命

采用氯盐溶液和硫酸盐溶液浸泡镁水泥钢筋混凝土构件,使构件中的涂层钢筋加速锈蚀,并利用电化学工作站进行电化学试验;以腐蚀电流密度作为钢筋耐久性退化指标,建立一元Wiener过程预测模型进行钢筋腐蚀寿命预测.结果 表明:在氯盐溶液环境下,镁水泥混凝土构件中的钢筋受腐蚀问题较之硫酸盐溶液环境更为突出,且涂层在2种盐溶液环境中均对钢筋起到了较好的防护效果;在氯盐溶液环境中,涂层钢筋在1500 d附近进入中等腐蚀阶段,在硫酸盐溶液环境中,涂层钢筋在22000 d进入中等腐蚀阶段.     

Platinum Nanoparticles Anchored on TiO2/C Nanowires as a High Performance Catalyst for Hydrogen Peroxide Eletroreduction

In this paper, we employed the as‐prepared TiO₂/C core/shell nanoarrays (TiO₂/C) obtained by a facile thermal evaporation method as a three‐dimensional (3D) architecture to support Pt nanoparticles through an optimized electrodeposition process. The morphology and structure of the as‐prepared electrode are characterized by X‐ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Its catalytic performance towards H₂O₂ electroreduction in basic medium is evaluated by linear sweep voltammetry (LSV) and chronoamperometry (CV). Results revealed that the electrode exhibits significantly high catalytic activity. The current density reached –0.172 A cm⁻² in 1 mol dm⁻³ NaOH and 0.5 mol dm⁻³ H₂O₂ at –1.1 V (vs. Ag/AgCl). This high performance might be due to the 3D electrode architecture inheriting the high electronic conductivity from carbon shell and providing a short pathway for the ion diffusion, and the using of Pt owning an excellent catalytic activity.     

Construction and study on corrosion protective property of polydopamine-based 3-layer organic coatings on aluminum substrate

Metal aluminum (Al) is being widely used in industry and can be easily corroded in severe conditions. Recently, dopamine has been demonstrated to be an effective adhesive molecular that can be attached to virtually all material surfaces to form stable polydopamine coating (PDAc), exhibiting promising prospects in many fields. In this work, to improve the anti-corrosion performance of Al sheet, a novel polydopamine-based 3-layer organic coating has been constructed by a multi-step self-assembly technique for the first time. In brief, a self-assembled monolayer of (3-mercaptopropyl)trimethoxysilane (coded as MPTS-SAM) was firstly prepared for enhancing the adhesion between the PDAc and the Al substrate. Subsequently, a PDAc was assembled onto the Al substrate by a simple immersion into the dopamine hydrochloride solution at a pH of 8.5. At last, a layer of tetradecanoyl chloride was grafted onto the PDAc surface through amidation, which could apparently slow down the water diffusion to the interface of PDAc and Al for its prominent hydrophobicity. Corrosion resistance of the synthesized coating in NaCl solution was evaluated by potentiodynamic polarization test and electrochemical impedance spectroscopy (EIS) measurement, respectively. As results show, PDAc on bare Al can protect the substrate from corrosion to a certain extent. Significantly, after being mediated by MPTS-SAM underlayer and covered by tetradecanoyl chloride outer layer, the anti-corrosion capability of the coating has been improved markedly.