Self-assembled fabrication of a polycrystalline boron-doped diamond surface supporting Pt (or Pd)/Au-shell/core nanoparticles on the (111) facets and Au nanoparticles on the (100) facets

Modified boron-doped diamond (BDD) surfaces supporting different, carefully selected types of metal nanoparticles on different types of crystal facets were fabricated via a self-assembly method. A hydrogen plasma-treated BDD surface was treated with UV/ozone for 10 s followed by immersion in a Au nanoparticle (AuNP) solution to fabricate a BDD surface selectively and densely supporting AuNPs on the (111) facet (AuNP₁₁₁-BDD). The AuNP₁₁₁-BDD sample was then immersed in H₂PtCl₆/ascorbic acid or H₂PdCl₄/sodium citrate to cover the AuNP surface with Pt or Pd (Pt/AuNP₁₁₁-BDD or Pd/AuNP₁₁₁-BDD). These samples were treated with UV/ozone for 40 s followed by re-immersion in the AuNP solution to immobilize AuNPs on the (100) facets (Pt/AuNP₁₁₁-AuNP₁₀₀-BDD or Pd/AuNP₁₁₁-AuNP₁₀₀-BDD). The metal nanoparticles supported on the BDD surface were confirmed by cyclic voltammetry to be electrochemically active. The crystal-facet-selective support of the metal nanoparticles was also confirmed by two-dimensional elemental mapping via field emission Auger electron spectroscopy. The macro procedures used for the crystal-facet-selective immobilization of the AuNPs was reproducible, and this technique should be applicable to the creation of a new class of advanced materials in such fields as optics, electronics, sensing, and (electro)catalysis.     

Electrochemical degradation of diuron and dichloroaniline at BDD electrode

The degradation of diuron and 3,4-dichloroaniline (DCA) has been studied at boron-doped diamond (BDD) anode. A three electrode impinging jet cell was used to improve the mass transfer of the reactant to the electrode surface. In the whole range of experimental conditions examined, the reactants were completely mineralised and passivation of the electrode surface was not observed. HPLC and ionic chromatography analyses revealed that the reaction involves the oxidative ring-cleavage and the formation of stoichiometric amounts of chloride and ammonium ions. Depending on the specific experimental conditions, short-chained organic acids were also identified as intermediate products. Values of global current efficiencies greater than 20% were obtained even operating with low reactant concentration (0.17 mM for diuron and 2 mM for dichloroaniline) provided that a suitable ratio between applied current and mass transfer rate was guaranteed.     

CR传输线模型解析AgO-Zn电池阻抗谱

电化学阻抗谱(EIS)是研究电池的重要技术之一,但需要合适的解谱方法才能提取有效信息。本文以文献中Ag-Zn电池的阻抗谱拟合数据为例,说明根据普适性CR传输线模型可得到原作者预言存在却无法证实的结果:存在与电池荷电量(SOC)有直线关系,并在SOC=0.4发生转折的参数。结果还表明这种参数有多个,分别与Ag正极的半导体特征,以及放电过程中控制步骤的变化有关,充分显示了EIS信息丰富的特点。本方法结果客观、具有可操作性,因而有重要的理论意义和应用价值。     

Electrochemical degradation of 17β-estradiol (E2) at boron-doped diamond (Si/BDD) thin film electrode

Electrochemical degradation of aqueous solutions containing 17β-estradiol (E2), concentrations range of 250-750 μg dm⁻³, has been extensively studied using boron-doped diamond (BDD) anode with a working solution volume of 250 ml under galvanostatic control. Cyclic voltammetric experiments were performed to examine the redox response of E2 as a function of cycle number. The effect of operating variables such as initial concentration of E2, applied current density, supporting medium (Na₂SO₄, NaNO₃, and NaCl) and initial pH of the electrolyte (pH 2-10) were systematically examined and discussed. Electrolysis at high anodic potential causes complex oxidation of E2 that leads to form the final sole product as CO₂. A pseudo first-order kinetics for E2 decay was found against varying applied current density. Also, kinetic analysis suggests that electrooxidation reaction of E2 undergo the control of applied current density. It was observed that electrolyte pH and supporting medium have a vital role on E2 degradation. From a comparison study with other anode materials such as platinum (Pt) and glassy carbon (GC), the superiority of the BDD anode was proved. Total organic carbon results have shown that almost complete mineralization could be accomplished at higher applied current density with specific electrical charge 22.5 × 10⁻² A h dm⁻³. Mineralization current efficiency was comparatively lower with increasing applied current density.     

Electrochemical behavior of carbon electrodes in organic liquid electrolytes containing tetrafluoroborate and hexafluorophosphate anionic species in different non-aqueous solvent systems

Electrochemical behavior of tetrabutylammonium salts containing tetrafluoroborate (BF₄⁻) and hexafluorophosphate (PF₆⁻) anionic species in different non-aqueous solvents had been investigated on glassy carbon (GC), boron-doped diamond (BDD) and Pt electrodes. Though both BF₄⁻ and PF₆⁻ ionic species are considered to be inert, they are found to undergo electrochemical oxidation only on GC electrode rather than BDD and Pt as found out from their anodic peaks in linear sweep and cyclic voltammograms (LSV and CV). The voltammetric peak is influenced by the sweep rate as well as by the concentration of the ionic species and the electron transfer process appears to be diffusion controlled one. The formation of an inhibitory C-F film on the electrode surface during anodic polarization either by potentiostatic or potentiodynamic techniques was clearly established by X-ray photoelectron spectroscopy (XPS) analysis and the charge transfer resistance (θ) is higher under latter conditions than the former. The inhibitory effect of this surface film towards the electron transfer reaction of Fe(CN)₆]⁴⁻/[Fe(CN)₆]³⁻ redox couple using impedance technique reveals that among the high permittivity non-aqueous solvents investigated in this work, CH₃CN shows maximum θ value and produces C-F film of optimum thickness than the others. A direct correlation was also found out from the plot of θ versus peak potential E_p and peak current density (i_p) obtained from LSV. The mechanism of film formation on GC electrode and the absence of such phenomenon on BDD were explained from the product analysis using ¹⁹F nuclear magnetic resonance (NMR) spectra resulting from the constant current electrolysis of BF₄⁻ and PF₆⁻ ionic species on both electrodes in CH₃CN medium.     

Optimization of deposition voltage of cataphoretic automotive primers assessed by EIS and AC/DC/AC

The dependence of the anticorrosive properties of a cataphoretic paint with the applied deposition voltage was studied by the so-called EIS tests; an accelerated cyclic test used in the automotive industry; and a rapid electrochemical test (AC/DC/AC) which combines EIS measurements with cathodic polarizations. DSC and TGA were employed for the coating characterisation. The traditional accelerated cyclic test was unable to distinguish the influence of the deposition voltage on the anticorrosive properties while electrochemical tests found an optimal range of deposition voltage between 270 and 320 V. The AC/DC/AC test obtained the same results as EIS tests but in only 24 h instead of months of evaluation. The technique AC/DC/AC is suggested as an accelerated technique able to determine the optimum range of deposition voltages to obtain the higher anticorrosive properties of an epoxy cataphoretic primer.     

Electrochemical degradation of clofibric acid in water by anodic oxidation: Comparative study with platinum and boron-doped diamond electrodes

Aqueous solutions containing the metabolite clofibric acid (2-(4-chlorophenoxy)-2-methylpropionic acid) up to close to saturation in the pH range 2.0-12.0 have been degraded by anodic oxidation with Pt and boron-doped diamond (BDD) as anodes. The use of BDD leads to total mineralization in all media due to the efficient production of oxidant hydroxyl radical (OH). This procedure is then viable for the treatment of wastewaters containing this compound. The effect of pH, apparent current density, temperature and metabolite concentration on the degradation rate, consumed specific charge and mineralization current efficiency has been investigated. Comparative treatment with Pt yields poor decontamination with complete release of stable chloride ion. When BDD is used, this ion is oxidized to Cl₂. Clofibric acid is more rapidly destroyed on Pt than on BDD, indicating that it is more strongly adsorbed on the Pt surface enhancing its reaction with OH. Its decay kinetics always follows a pseudo-first-order reaction and the rate constant for each anode increases with increasing apparent current density, being practically independent of pH and metabolite concentration. Aromatic products such as 4-chlorophenol, 4-chlorocatechol, 4-chlororesorcinol, hydroquinone, p-benzoquinone and 1,2,4-benzenetriol are detected by gas chromatography-mass spectrometry (GC-MS) and reversed-phase chromatography. Tartronic, maleic, fumaric, formic, 2-hydroxyisobutyric, pyruvic and oxalic acids are identified as generated carboxylic acids by ion-exclusion chromatography. These acids remain stable in solution using Pt, but they are completely converted into CO₂ with BDD. A reaction pathway for clofibric acid degradation involving all these intermediates is proposed.     

Electrochemical destruction of chlorophenoxy herbicides by anodic oxidation and electro-Fenton using a boron-doped diamond electrode

The degradation of herbicides 4-chlorophenoxyacetic acid (4-CPA), 4-chloro-2-methylphenoxyacetic acid (MCPA), 2,4-dichlorophenoxyacetic acid (2,4-D) and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) in aqueous medium of pH 3.0 has been comparatively studied by anodic oxidation and electro-Fenton using a boron-doped diamond (BDD) anode. All solutions are totally mineralized by electro-Fenton, even at low current, being the process more efficient with 1 mM Fe²⁺ as catalyst. This is due to the production of large amounts of oxidant hydroxyl radical (OH) on the BDD surface by water oxidation and from Fenton’s reaction between added Fe²⁺ and H₂O₂ electrogenerated at the O₂-diffusion cathode. The herbicide solutions are also completely depolluted by anodic oxidation. Although a quicker degradation is found at the first stages of electro-Fenton, similar times are required for achieving overall mineralization in both methods. The decay kinetics of all herbicides always follows a pseudo first-order reaction. Reversed-phase chromatography allows detecting 4-chlorophenol, 4-chloro-o-cresol, 2,4-dichlorophenol and 2,4,5-trichlorophenol as primary aromatic intermediates of 4-CPA, MCPA, 2,4-D and 2,4,5-T, respectively. Dechlorination of these products gives Cl⁻, which is slowly oxidized on BDD. Ion-exclusion chromatography reveals the presence of persistent oxalic acid in electro-Fenton by formation of Fe³⁺-oxalato complexes, which are slowly destroyed by OH adsorbed on BDD. In anodic oxidation, oxalic acid is mineralized practically at the same rate as generated.     

Electrochemical impedance spectroscopy investigation of the electrochemical behaviour of copper coated with artificial patina layers and submitted to wet and dry cycles

Due to rain events historical monuments exposed to the atmosphere are frequently submitted to wet and dry cycles. During drying periods wetness is maintained in some confined regions and the corrosion product layer, generally denominated patinas, builds up and gets thicker. The aim of this study is to use electrochemical impedance spectroscopy (EIS) to investigate the electrochemical behaviour of pure copper coated with two artificial patina layers and submitted either to continuous or to intermittent immersion tests, this latter aiming to simulate wet and dry cycles. The experiments were performed in 0.1 mol dm⁻³ NaCl solution and in artificial rainwater containing the most significant pollutants of the city of São Paulo. The results of the continuous immersion tests in the NaCl solution have shown that the coated samples behave like a porous electrode with finite pore length. On the other hand, in the intermittent tests a porous electrode response with semi-infinite pore length can be developed. The results were interpreted based on the model of de Levie and a critical comparison with previous interpretations reported in the literature for similar systems is presented.     

Evidence by EIS of the interaction between proteins and tin oxide electrode surface

Macromolecules like proteins are able to adhere to tin oxide electrodes at open circuit potential as proved by electrogravimetry experiments. In this work, electrochemical impedance studies were performed at aqueous electrolyte/F- or Sb-doped semiconducting tin oxide interfaces, including natural seawater. By this way, it was possible to characterize the potential dependence of the interfacial capacitance in various physicochemical conditions, without or in the presence of bovine serum albumin (BSA). In the potential range where tin oxide is in the depletion regime (blocking interface), a capacitance excess is evidenced which can be attributed to the formation of surface states which are the signature of chemical bonding. By simulating the so-called surface state capacitance, three states have been pointed out. They are centred at 0.7, 0.9 and 1.1 eV in the tin oxide bandgap. On the basis of experimental arguments, the state at 1.1 eV was ascribed to the OH-terminated tin oxide surface, the two other states were found to be specific of the interaction of organic matter with the oxide surface. In the presence of BSA, the density of surface atoms (about 10¹³ cm⁻²) involved in bonding is of the order of magnitude of the surface concentration of one BSA monolayer. The lasting character of these bonds was also shown. This finding shows the definitive protein immobilisation at the SnO₂ surface.     

Electrochemical behaviour of uranium (IV) in DMF at vitreous carbon

The electrochemical behaviour of UCl₄ (0.01 mol L⁻¹ up to 0.05 mol L⁻¹) in 0.1 mol L⁻¹ TBAPF₆/DMF solution at vitreous carbon was studied, at room temperature, by cyclic voltammetry and potentiostatic techniques. The electrolytic solutions were analyzed by UV spectroscopy (UV), and the electrodeposited films were characterized by Rutherford Backscattering Spectroscopy (RBS) and X-ray diffraction (XRD). The cyclic voltammetric results, at low UCl₄ concentrations (0.01 mol L⁻¹), point that the reduction of U(IV) to U(0) occurs in two steps involving mainly U(IV) and U(III) species. The first electron transfer reaction is quasi-reversible and the second irreversible. The diffusion coefficient of U(IV) in DMF and the charge rate constant were determined to be 4.78 × 10⁻⁷ cm² s⁻¹ and 1.93 × 10⁻³ cm s⁻¹ (at 0.02 V s⁻¹), respectively.RBS data obtained from samples prepared at constant potential (−3.10 V) during 3 h at room temperature, indicated the presence of uranium particles deposited all over the vitreous carbon surface with aggregates in some places, confirming that the second reduction step corresponds to uranium electrodeposition. No crystallographic ordering could be seen by XRD, pointing to an amorphous character of the uranium films.     

Corrosion protection of galvanized steel by polyimide coatings: EIS and SEM investigations

Coatings of two types of polyimides (PI), as poly(4,4′-oxydiphtalic anhydride-co-2,5-bis(4,4′-methylenedianiline)-1,4-benzoquinone) (AQ) and poly(pyromellitic dianhydride-co-4,4′-oxydianiline) (PM), were synthesized on galvanized steel panels and studied and compared in terms of chemical structure, microstructure and corrosion performance in 0.5 M NaCl solution. Infra-red spectroscopy, scanning electron microscopy and in situ electrochemical impedance spectroscopy were employed in the investigations. The results showed that, although both studied PI coatings provided the galvanized steel substrate with corrosion protection during the test period, there were evident differences in electrochemical behaviour of the coatings, which could be primarily explained by the different nanostructures. FE-SEM examinations revealed AQ PI coating to be heterogeneous and discontinuous but PM PI coating homogeneous and continuous in nanostructure. Electrochemical behaviour of AQ PI coated galvanized steel obeyed that of a defect-containing coating and indicated gradual decrease in protectivity. In contrast, PM PI coating behaved like a defect-free coating and it provided the galvanized steel substrate with effective corrosion protection all through the 960 h test. The explanations for these observations and the mechanisms of coating damage are discussed in this paper.     

Electrochemical behaviour of thorium(IV) in molten LiF-CaF2 medium on inert and reactive electrodes

The electrochemical behaviour of the Th(IV)/Th system was examined in molten LiF-CaF₂ medium on inert (molybdenum), reactive (nickel) and liquid (bismuth) electrodes in the 810-920 °C temperature range by several electrochemical techniques. Experimental results showed that (i) thorium fluoride was reduced in a single step exchanging 4 electrons and limited by thorium ions diffusion in the solution, (ii) the oxide ions induce the precipitation of Th(IV) in the form of thorium oxide (ThO₂), in a process involving as intermediate compound a soluble oxifluoride (ThOF₂), (iii) the reduction of thorium ions on reactive (Ni and liquid Bi) electrodes yields compounds Ni-Th and Bi-Th with a potential shift of around 0.7 V (for Ni and Bi) more anodic than the reduction of Th(IV) on inert substrate.     

Electrochemical impedance spectroscopy (EIS) studies of the corrosion of pure Fe and Cr at 600 °C under solid NaCl deposit in water vapor

The corrosion behavior of pure Fe and pure Cr at 600 °C under a deposit of solid NaCl, with and without the presence of water vapor, was studied by using electrochemical impedance spectroscopy (EIS) and mass gain measurements. The mass gain of both metals sharply increased when water vapor was introduced into the system. In EIS measurement, only one capacitive loop obtained on the pure Fe and Cr coated with solid NaCl and gave the information of oxide layer on them. For the oxide in air, there is a good relationship between the R_ox and the reaction rate for both pure Fe and Cr with different oxide time. The lower the R_ox is, the higher the reaction rate is. Although no good relationship can be set up between the R_ox and the reaction rate when water vapor presented, its trend with oxide time for both metals is generally in accordance with that of the corrosion rate measured by the mass gain curves. The electrochemical technique is an effective method for studying corrosion performance at high temperature.     

EIS and GITT studies on oxide cathodes, O2-Li(2/3)+x(Co0.15Mn0.85)O2 (x=0 and 1/3)

Li ion kinetics in the O2-phase layered manganese oxides, Li_2/3(Co_0.15Mn_0.85)O₂ (O2(Li)) and Li_(2/3)+x(Co_0.15Mn_0.85)O₂ (x=1/3 (O2(Li+x))), has been studied by the electrochemical impedance spectroscopy (EIS) and galvanostatic intermittent titration technique (GITT) at room temperature and the results were correlated with the observed cathodic behaviour. Both compounds show a reversible capacity of ∼180 mA h/g at low current density (∼5 mA/g). EIS studies as a function of cycle number show an increased contribution of resistance associated with surface film formation and bulk contribution which is in agreement with the increased capacity fading observed in O2(Li+x) after 10-15 cycles. The Li ion diffusion coefficient (D_Li) vs voltage plots show minima during the first charge cycle coinciding with the irreversible plateau of the voltage vs capacity profiles reflecting the irreversible phase change in both the compounds. The values of D_Li (GITT method) observed for the second and subsequent cycles (≤6) in the full voltage range (3.0-4.4 V) are 2×10⁻¹¹-10×10⁻¹¹ cm²/s for O2(Li+x) and 0.5×10⁻¹⁰-3.0×10⁻¹⁰ cm²/s for O2(Li). Variation of D_Li as a function of cycle number (up to 35) indicates that, in addition to the interface kinetics, changes in the D_Li values with cycling also contribute to the capacity fading of the compounds, especially in O2(Li+x).     

Electrochemical decomplexing and oxidation of organic (chelating) additives in effluents from surface treatment and metal finishing

The electrochemical decomplexing and oxidation of two frequently used complexing agents in surface treatment and metal finishing—EDTA (ethylenediaminetetraacetic acid) and NTA (nitrilotriacetic acid)—and of organic non‐complexing additives used in nickel‐plating baths were the subject of this study. Using a Ti–RuO₂ electrode, a partial indirect oxidation by in‐situ electrochemical generation of chlorine compounds could be achieved for EDTA and NTA. At a boron‐doped diamond (BDD) electrode however, complete decomplexing and high COD (Chemical Oxygen Demand) and TOC (Total Organic Carbon) (up to 95%) removal occurred at an average current density of 2 A dm^?2. It is shown that direct electrochemical oxidation at a BDD electrode resulted in lower energy consumption and higher treatment rates than indirect oxidation at a Ti–RuO₂ electrode. Decomplexing at the BDD electrode occurred at high current efficiencies ranging from 71% to 95% with decomplexing rates in the order of 3.13 mmol (Ah)^?1 and 5.02 mmol (Ah)^?1 for EDTA and NTA respectively. COD removal rates obtained were 0.090 g (Ah)^?1 for EDTA, 0.100 g (Ah)^?1 for NTA and 0.205 g (Ah)^?1 for the nickel‐plating additives. Electrochemical decomplexing and oxidation of common chelating agents can render the subsequent metal precipitation and biological wastewater treatment of surface treatment and metal finishing effluents more efficient. Copyright © 2003 Society of Chemical Industry     

The importance of electrode material in environmental electrochemistry: Formation and reactivity of free hydroxyl radicals on boron-doped diamond electrodes

A model describing the hydroxyl radical (HO) concentration profile at the boron-doped diamond (BDD) electrode, in the presence and absence of organic compounds, is presented. It is shown that this profile depends strongly on the reaction rate constant between the HO and the organic compound. Furthermore, it is shown that the presence of organics affects the current-potential (I-V) curves. In fact, the higher the reaction rate between organics and HO, the higher is the shift of the I-V curves toward lower potential with respect to oxygen evolution. Supposing that water discharge to free hydroxyl radicals on BDD is governed by Nernst equation, this shift of the I-V curves toward lower potentials has been calculated and compared with the experimental data obtained on BDD using two model compounds: methanol and formic acid.     

Poly(m-phenylendiamine-co-o-aminophenol) coatings on mild steel: Effect of comonomers feed ratio on surface and corrosion protection aspects

Copolymer of m-phenylendiamine (mPD) and o-aminophenol (oAP) has been electrochemically deposited on mild steel from an aqueous solution of oxalic acid using cyclic voltammetric technique. The copolymer structure was confirmed by Proton Nuclear Magnetic Resonance (¹H NMR) and Attenuated Total Reflection Infrared (ATR-IR) spectroscopic techniques. Surface characterisation results indicated that the formed copolymer coatings posses uniform, smooth surface and strong adherence towards the metal surface. Corrosion performance of copolymer coatings was investigated in 0.5 M HCl solution using potentiodynamic polarisation and electrochemical impedance spectroscopy (EIS) methods. Results showed that corrosion performance of copolymer coatings depends on the feed ratio of both the monomer units in copolymer chain. It was found that the copolymer feed ratio of mPD:oAP = 70/30 in coatings exhibited the highest performance due to its superior surface nature than other copolymer coatings.     

The point of zero charge of adsorbed monolayers: Pt(111) covered by Ag

The pzc of an Ag monolayer on Pt(111) has been determined according to the Gouy Chapman theory by recording the capacitance-potential curves. A value of −0.48 V versus SCE was found which is 0.24 V higher than that of Ag(111). This difference is close to that expected from the difference in work functions of Ag(111) and a monolayer of Ag on Pt(111) (0.26 eV). The pzc of bulk Ag deposits is identical to that of Ag(111), confirming that Ag deposition is epitaxial.