Ji-Ming Hu

Studies of impedance models and water transport behaviors of polypropylene coated metals in NaCl solution

Using electrochemical impedance spectroscopy (EIS) technique, the water uptake process and the evolution of impedance models of polypropylene coated mild steels and LY12 Al alloys immersed in 3.5% (weight fraction) NaCl solution were studied. The equivalent electrical circuit (EEC) fitting results suggested that there was one single semi-circle in the impedance spectra of immersed samples in the initial period of immersion, which was corresponded to one time constant. Along with the immersion time, the number of time constant in EEC for metal/coating electrode system increased. The diffusion process towards solution of corrosion products forming on the metal/coating interface might be restrained due to the influence of coating barrier, resulting in the initiation of diffusion component in EEC. This diffusion did not act as a Warburg behavior, leading to a deviation of dispersive number, n, from 0.5. The studies revealed that the water transport in polypropylene clear varnish followed the Fickian diffusion during the initial time of exposure to the solution. After a certain time of immersion, the water uptake reached a saturation value. According to the variation of coating capacitance with time, the water diffusion coefficient was deduced. The experimental results indicated that the water diffusion coefficients in polypropylene coatings were independent of substrate materials used and coating thickness. Relative dielectric constant of dry coatings (ed) and water volume fraction of the coatings at saturation (φ∞) were also calculated. The similar results were found in time dependence of coating capacitance calculated from the impedance imaginary component at a fixed high frequency and that obtained from the fitting result by EEC, which indicated that the coating capacitance from the impedance imaginary component was reliable to evaluate barrier performance of coatings against water.

Electrochemically generated sol–gel films as inhibitor containers of superhydrophobic surfaces for the active corrosion protection of metals

The present work shows a new contribution to the design of superhydrophobic surfaces with the additional function of active corrosion protection, through the encapsulation of inhibiting agents. Superhydrophobic silica films are fabricated on aluminum alloy using electro-assisted deposition from sol–gel precursors. Two kinds of inhibitors, either inorganic cerium nitrate or organic benzotriazole, are incorporated into the superhydrophobic films by a two-step or a one-step route. The corrosion protection performance is investigated using electrochemical impedance spectroscopy and a scanning vibrating electrode technique, as well as by monitoring changes in the water contact angle. The results reveal that the superhydrophobic films loaded with inhibitors show greatly improved anticorrosion properties in 3.5 wt% NaCl aqueous solution.

One step sol–gel electrochemistry for the fabrication of superhydrophobic surfaces

A novel one-step sol–gel electrochemistry route to prepare superhydrophobic surfaces is presented. High roughness and low energy surfaces were obtained simultaneously during the formation of long-chain alkyl-grouped alkoxysilane films via electrochemically assisted deposition. Furthermore, significantly improved thermal and chemical stabilities and mechanical properties of the superhydrophobic surface were achieved by the incorporation of silica.

Microstructure, electrochemical surface and electrocatalytic properties of IrO2+Ta2O5 oxide electrodes

X-ray diffraction (XRD) and scanning electron microscopy (SEM) have been used to characterize physical structure of IrO2+Ta2O5 films over the whole composition range by thermodecomposition of chloride solutions heated at 450°C. Solid solubilization between Ta component and IrO2 rutile in the mixed films was measured, and three typical surface morphologies of the oxide coatings were observed. The surface electrochemical properties of Ti/IrO2-Ta2O5 electrodes were studied by cyclic voltammetry at varying potential scan rate, and a ‘double-layer’ electrochemical structure containing the ‘inner’ and ‘outer’ layers has been distinguished. The voltammetric charge appears to decline with the decrease of grain size of oxide coatings as a result of the effect of surface tension. However, the coatings of 70% IrO2+30% Ta2O5 with the finest grains still exhibit the highest apparent activity for oxygen evolution evaluated by the anodic current at a constant potential. This result is interpreted by the measurements of open-circuit potential (Eoc) and double-layer capacitance (Cdl) using electrochemical impedance spectroscopy (EIS). Thereby, the reliability of voltammetric charge obtained in ‘double-layer’ potential region in determining the real electrocatalytic activity for O2 evolution has been discussed.

A silica co-electrodeposition route to highly active Ni-based film electrodes

We report a novel silica co-electrodeposition route to prepare highly active nickel films. Firstly, Ni–SiO2 composite film was fabricated on a stainless steel substrate by electrodeposition, and then the SiO2 template was removed in alkaline electrolyte by consecutive cyclic voltammetry scans, leading to the formation of a porous Ni (po-Ni) matrix. The structure and morphology of the obtained films were characterized using Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The highly porous property of the po-Ni matrix is believed to be quite favourable for electrochemical applications. The electrochemical properties of the po-Ni film were evaluated by cyclic voltammetry (CV), galvanostatic charge–discharge (GCD) and steady-state polarization curves. The results showed that the porous Ni derived from the Ni–SiO2 composite film exhibits good electrochemical performance for potential use as a supercapacitor material and catalyst for water splitting.

Enhancement of Corrosion Performance of Epoxy Coatings by Chemical Modification With GPTMS Silane Monomer

In this paper, commercial epoxy resin was chemically modified by different amounts of 3-glycidoxypropyltrimethoxysilane (GPTMS) monomer using an organotin compound as catalyst, aiming to improve the anti-corrosion performance of epoxy coatings on 2024-T3 aluminum alloy substrate. Electrochemical impedance spectroscopy (EIS) was used to evaluate the barrier properties against water permeation and protectiveness of silane-modified epoxy coatings. The results showed that all the modified coatings presented higher barrier performance and better corrosion performance than pure epoxy coating, which were characterized by higher charge transfer resistance (R ct) and lower double-layer capacitance (C dl) at the electrolyte/metal interface. The improvements in corrosion performance and wet adhesion of modified epoxy coatings were also observed by the Machu test and boiling water test, respectively. Interestingly, it was found that the glass-transition temperature (T g) of silane-modified epoxy coatings decreased only slightly during immersion in 3.5 wt% NaCl solution, in contrast with pure epoxy coating, which was observed to decrease significantly after water permeation. The corrosion performance of epoxy coatings was, thus, improved when the amount of chemically grafted silane monomer increased in the content range investigated in the present work.

Electrodeposited SiO2 film: a promising interlayer of a highly active Ti electrode for the oxygen evolution reaction

Ti-supported IrO2 or RuO2 oxide coated electrodes are widely used for the oxygen evolution reaction (OER) in acidic media. Electrocatalytic activity and long-term stability need to be further improved for these types of electrodes. A highly porous and well-adhered electrodeposited SiO2 (e-SiO2) film is proposed as the interlayer in this work to meet the above-mentioned requirements. The results show that the active oxide fully fills in the porous network throughout the whole thickness of the e-SiO2 film, to form “total-depth” highly porous oxide electrocatalytic coatings. For this reason, more than 1 order of magnitude higher apparent activity towards the OER at the Ti/e-SiO2/IrO2 (or RuO2) electrode is achieved compared to that of the conventional Ti/IrO2 or Ti/RuO2 electrode. Literature survey indicates that these novel electrodes are one of the most active Ti electrodes ever reported. The service life of this type of electrode is also obviously enhanced due to the “inter-locking” structure formed between the active oxide layer and e-SiO2 film.

Enhanced Electrocatalytic Activity for Morphine Oxidation at 2-Aminoethanethiol Self-Assembled Monolayer (SAM)-Modified Gold Electrode

Abstract2-aminoethanethiol self-assembled monolayer (SAM)-modified gold electrode (SAM/Au) was fabricated for electrochemical oxidation of morphine (MO). The SAM/Au shows an enhanced electrocatalytic activity for MO oxidation, as described by more negative oxidation peak potential and much higher current response as compared to the bare gold electrode. The enhanced performance of SAM/Au electrode might be attributed to the possible chemical interaction between the amino group in SAM and phenolic group in MO.