Kinetics of processes occurring at a H<Subscript>3</Subscript>PW<Subscript>12</Subscript>O<Subscript>40</Subscript>/Pt,H<Subscript>2</Subscript> interface depending on the platinum content on the electrode

Kinetics of processes occurring at H⁺/solid electrolyte/Pt, H₂ three-phase interface are studied subject to the platinum content on the electrode. The study was performed with model electrochemical cells PbO₂/H₃PW₁₂O₄₀/Pt with different platinum content at the working electrode that consisted of platinum deposited onto the E-Tek LT1200-N carbon-nanotubes paper. On the basis of the obtained results, the occurring processes were practically fully separated. It is shown by the analyzing of relaxation curves that there exist at least two processes in the system: the faster one corresponds to the hydrogen reaction; the slower, to the oxygen one. The rates of both processes depend on the platinum content at the working electrode; they have an extreme at the platinum concentration of 0.5 mg/cm². Impedance data allowed revealing the processes’ limiting stages. The experimental data allowed suggesting that at low platinum content the relaxation time is determined by the electrochemical reaction rate; at higher content, by gas diffusion through the platinum dense layer.     

Electrocatalytic properties of platinum nanocenters electrogenerated at ultra-trace levels within zeolitic phosphododecatungstate cesium salt matrices

A unique preparation method of obtaining stable composite film (with ultra-low platinum content) highly active towards oxygen reduction and hydrogen oxidation is presented here. The matrix for platinum centers consists of high-surface-area zeolite-type acidic salt of cesium phosphododecatungstate (Cs_2.5H_0.5PW₁₂O₄₀) admixed with carbon (Vulcan XC-72) carriers. Platinum nanoparticles were deposited on the working electrode modified with matrix via corrosion of platinum counter electrode during cyclic voltammetry experiment conducted in acid electrolyte containing chloride ions. The results obtained from rotating disk voltammetry revealed that the composite film containing Pt nanoparticles at very low loadings (on the level of 2–5 μg cm^?2) demonstrated remarkable electrocatalytic activity towards both oxygen reduction and hydrogen oxidation, particularly, when compared to the performance of the Cs_2.5H_0.5PW₁₂O₄₀-free system (i.e., containing only Vulcan support) prepared and examined under analogous conditions. The phenomenon should be primarily ascribed to the mesoporous nature of the matrix enabling immobilization and stabilization of small catalytic nanoparticles (1–2 nm diameters) inside the pores as well as to high surface acidity of the polyoxometalate-based salt providing proton-rich environment at the electrocatalytic interface.     

Rotating-disc electrode studies of the anodic oxidation of iodide in concentrated iodine + iodide solutions

The anodic oxidation of iodide on platinum in concentrated iodine + iodide solutions has been investigated using a rotating disc electrode. The conventional limiting diffusion current, which is produced by the diffusion of iodide ions towards the electrode, was not observed due to the formation of an iodine film on the electrode. On the other hand, the steady-state anodic current after a current/time transient is the genuine limiting diffusion current in the anodic oxidation due to diffusion of iodine species from the electrode surface towards the bulk solution. Thus, the dissolution-diffusion control mechanism of the iodine film is confirmed. This is interesting as a typical example of an anodic process in a redox system governed by diffusion of the anodic product species from the electrode surface towards the bulk solution. When an iodine film is formed on the electrode, the maximum driving force of the iodine species is Δm_I2,max, which is defined as the extent of unsaturation of the iodine, and the limiting current of the anodic oxidation of iodide is always directly proportional to Δm_I2,max, regardless of the forms of iodine species in the solution, which may be I₂, I⁻₃, i₅⁻, etc. δm_I2,max is clearly determined by the solution composition and temperature, and it is different in definition and value from the usual degree of unsaturation of iodine.     

Electrochemical Codeposition of Platinum and Molybdenum Oxides: Formation of Composite Films with Distinct Electrocatalytic Activity for Hydrogen Peroxide Detection

The electrochemical properties of gold electrode surfaces modified by molybdenum oxide films intercalated with platinum microparticles have been described. The incorporation of Pt microparticles at the oxide film was characterized by PIXE (particle induced X‐ray emission) spectroscopy. The modified electrode showed electrochemical activity at around ?0.5 V in 50 mmol L^?1 Na₂SO₄ supporting electrolyte (pH 3), corresponding to the reduction of protons at platinum sites and further transfer of hydrogen atoms to form reduced molybdenum oxides (bronzes). At 0.1 V, the MoO₃ / Pt electrode showed a better performance for hydrogen peroxide oxidation than on platinized gold electrodes. The solution pH has a marked effect on the voltammetric profile and best responses for hydrogen peroxide were obtained at the 5.0 to 6.0 pH range. The activation of the electrode by polarization at negative potentials was also studied and a mechanism by which more platinum sites are available as a consequence of this process was proposed. Calibration plots for hydrogen peroxide were highly linear (r=0.9989) in the 0.2 to 1.6 mmol L^?1 concentration range, with a relative standard deviation (RSD)<1%.     

多臂碳纳米管/Nafion复合材料修饰玻碳电极测定痕量的铅离子

A composite material of nitric acid oxidized multiwalled carbon nanotube （MWNT） and Nation was prepared. Such composite was modified on a glassy carbon electrode to determine trace of lead by differential pulsed voltammetry. In pH=6.47 NaNO3 solution, Pb^2＋ ions were accumulated on the modified electrode at -0.4 V. Compared with a bare and a Nation film coated electrode, the composite coated GC electrode can reduce the accumulating potential and eliminate the toxic character of mercury. The calibration plots were linear at low concentration of 5.0× 10^-9-2.0× 10^-8 mol/L and high concentration of 2.5× 10^-8-5.0× 10^-6 mol/L. The performances characteristics indicate that the electrode can be used to determine trace Pb^2＋ ions.     

The anodic behavior of iodide at platinum in the presence of an iodine film under potentiostatic steady-state and hydrodynamic modulation conditions

The oxidation behavior of iodide on platinum covered by an iodine film was investigated using rotating ring-disk electrode under potentiostatic steady-state conditions at constant rotation speed and using hydrodynamic modulation techniques. The ring electrode response shows that there is no net accumulation of iodine species at the disk, and that the disk current is controlled by mass transport coupled to the equilibrium I⁻ +I₂(s) 6jI₃⁻. The steady-state film thickness depends on the flux of iodide at the film/solution interface. Iodide transport through the film probably occurs through a Grotthuss chain-transfer type mechanism, with a diffusion coefficient estimated to be 3×10⁻⁸ cm²/s. The modulation response for iodide oxidation is only about 15–20% of that predicted for convective-diffusion control, indicating that film relaxation processes are slower than the relaxation of the diffusion layer. The transient response to a step, change in rotation speed is the result of iodine film dissolution being limited by mass transfer of iodide ion to form triiodide at the iodine film/solution interface.     

Activation of oxygen reaction by praseodymium oxide film on platinum electrode in contact with YSZ electrolyte

The method of impedancemetry is used to study electrochemical activity of platinum electrodes in contact with the solid electrolyte of YSZ (ZrO2+10 mol % Y₂O₃). Electrodes are activated by small additives of pradeodymium oxide PrO _x (0.1–0.3 mg/cm²) by their impregnation by praseodymium nitrate solution with the further thermal treatment at 850°C and are studied in the cases when PrO _x forms a film on the electrolyte and when no activator film is formed. The effect of the number of electrode activations on the electrochemical activity of platinum electrodes is studied.     

The effect of electrochemically treated glassy carbon on the activity of supported Pt catalyst in methanol oxidation

Effect of electrochemical oxidation of glassy carbon on deposition of platinum particles and electrocatalytic activity of platinum supported on oxidized glassy carbon (Pt/GC_OX) were studied for methanol oxidation in H₂SO₄ solution. Platinum was potentiostatically deposited from H₂SO₄ + H₂PtCl₆ solution. Glassy carbon was anodically polarised in 0.5 M H₂SO₄ at 2.25 V vs. saturated calomel electrode (SCE) during 35 s. Electrochemical treatment of GC support, affecting not significantly the real Pt surface area, leads to a better distribution of platinum on the substrate and has remarkable effect on the activity. The activity of the Pt/GC_OX electrode for methanol oxidation is larger than polycrystalline Pt and for more than one order of magnitude larger than Pt/GC electrode. This increase in activity indicates the pronounced role of organic residues of GC support on the properties of Pt particles deposited on glassy carbon.     

Structural,chemical and nanomechanical investigations of SiC/polymeric a-C:H films deposited by reactive RF unbalanced magnetron sputtering

Amorphous carbon (or diamond-like carbon, DLC) films have shown a number of important properties usable for a wide range of applications for very thin coatings with low friction and good wear resistance. DLC films alloyed with (semi-)metals show some improved properties and can be deposited by various methods. Among those, the widely used magnetron sputtering of carbon targets is known to increase the number of defects in the films. Therefore, in this paper an alternative approach of depositing silicon-carbide-containing polymeric hydrogenated DLC films using unbalanced magnetron sputtering was investigated. The influence of the C₂H₂ precursor concentration in the deposition chamber on the chemical and structural properties of the deposited films was investigated by Raman spectroscopy, X-ray photoelectron spectroscopy and elastic recoil detection analysis. Roughness, mechanical properties and scratch response of the films were evaluated with the help of atomic force microscopy and nanoindentation. The Raman spectra revealed a strong correlation of the film structure with the C₂H₂ concentration during deposition. A higher C₂H₂ flow rate results in an increase in SiC content and decrease in hydrogen content in the film. This in turn increases hardness and elastic modulus and decreases the ratio H/E and H³/E². The highest scratch resistance is exhibited by the film with the highest hardness, and the film having the highest overall sp³ bond content shows the highest elastic recovery during scratching.     

Study on the Impedance Characteristic and Electrocatalytic Activity of Platinum‐Modified Polyaniline Film

The composite electrode of platinum‐modified polyaniline film is formed in 0.5 M H₂SO₄ + 3 mM H₂PtCl₆ solution by cyclic potential or constant potential deposition of platinum particles in polyaniline film. To make a comparison, the polyaniline film with the same initial thickness and structure is also treated with the cyclic potential or constant potential polarization in 0.5 M H₂SO₄ solution. The electrochemical impedance spectroscopy (EIS) of the composite electrode of platinum‐modified polyaniline film is studied in sulfuric acid solution and compared with the EIS of the polyaniline film without platinum dispersion. The results show that the different modes of potential polarization affect greatly the nature and distribution of the platinum particles, instead of the structure of the polyaniline film (matrix). The electrode reaction kinetics and mass transport process parameters involving charge transfer resistance (R_ct), double layer capacitance (C_dl), constant phase elements (CPE) and Warburg impedance in platinum substrate/platinum‐modified polyaniline film/solution interface are discussed on the basis of the interpretation of the characteristic impedance spectra and connected to the electrocatalytic activity on the oxidation of methanol molecules.     

Nickel oxide hydroxide/platinum double layers modified n-silicon electrode for hydrogen peroxide determination

A novel photo-electrochemical and non-enzymatic hydrogen peroxide (H₂O₂) sensor was fabricated by electrochemically cathodic plating nickel hydroxide (Ni(OH)₂) on platinum films coated n-silicon (Pt/n-n⁺-Si electrode). Nickel oxide hydroxide (Ni(OH)₂-NiOOH) films on the Pt/n-n⁺-Si electrode were formed by cyclic voltammetry in 0.2 M KOH solution. The morphology and composition of Ni(OH)₂-NiOOH film were characterized via scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS), respectively. A two-electrode cell based on Ni(OH)₂-NiOOH/Pt/n-n⁺-Si electrode and a platinum counter has been used for determination of H₂O₂ in the absence of reference electrode by photocurrent measurement at a zero bias. In these conditions a sensitivity of 96.9 μA mM^?1 cm^?2 and a linear response range from 0.02 up to 0.16 mM with a determination limit (S/N?=?3) of 5.4 μM were achieved in KOH solution at pH 13.3. In addition, the electrode also exhibited superior stability, anti-interference and selectivity.     

A novel photoelectrochemical hydrogen peroxide sensor based on nickel(II)-potassium hexacyanoferrate-graphene hybrid materials modified n-silicon electrode

A platinum (Pt) film coated n-silicon (Pt/n-n⁺-Si) was modified with nickel(II)-potassium hexacyanoferrate (NiHCF)-graphene sheets (GS) hybrid and used as a photo-electrochemical (PEC) sensor for non-enzyme hydrogen peroxide (H₂O₂) detection. A NiHCF film was deposited on the surface of GS/Pt/n-n⁺-Si electrode by chemical method. The structure and composition of the NiHCF film was characterized by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). PEC behavior of the NiHCF-GS/Pt/n-n⁺-Si electrode was investigated using cyclic voltammetry (CV) under illumination. The modified electrode has been used as PEC sensor for H₂O₂ detection with a linear range of 2.0 × 10^?6–2.9 × 10^?3 M and a detection limit of 1.0 × 10^?6 M at a signal-to-noise ratio of 3 in a two-electrode cell with a Pt plate as counter electrode. The characteristics of GS layer have been discussed in both the improvement of sensibility and selectivity.     

Electroless preparation and electrochemical behavior of a platinum-doped nickel hexacyanoferrate film–zinc modified electrode: catalytic ability of the electrode for electrooxidation of methanol

The use of a zinc substrate as an electrode and the modification of its surface by means of a thin film of platinum-doped nickel hexacyanoferrate (Pt-NiHCF) were developed. The modification conditions of the zinc surface including the electroless deposition of metallic nickel on the electrode surface from NiCl₂ solution, chemical derivatization of the deposited nickel to the NiHCF film in 0.5 M K₃[Fe(CN)₆] solution, and electrochemical penetration of metallic platinum into the modified film are described. The modified zinc electrodes prepared under optimum conditions show a well-defined redox couple due to the [Ni^IIFe^III/II(CN)₆]^1–/2– system. The effects of pH, the alkali metal cation, and the anion of the supporting electrolyte on the electrochemical characteristics of the modified electrode were studied in detail. The diffusion coefficients of hydrated alkali metal cations in the film (D), the transfer coefficient (), and the transfer rate constant for the electron (k_s) were calculated in the presence of some alkali metal cations. The electrocatalytic activity of the modified electrode for methanol oxidation was demonstrated. The stability of the modified electrode under various experimental conditions was investigated.     

Enhancement of the efficiency of dye-sensitized solar cell with multi-wall carbon nanotubes/polythiophene composite counter electrodes prepared by electrodeposition

For the purpose of increasing the energy conversion efficiency of dye-sensitized solar cells (DSSCs), multi-wall carbon nanotube (MWCNT)/polythiophene (PTh) composite film counter electrode has been fabricated by electrophoresis and cyclic voltammetry (CV) in sequence. The morphology and chemical structure have been characterized by transmission electron microscopy (TEM), scanning electron microscope (SEM), and Raman spectroscopy respectively. The overall energy conversion efficiency of the DSSC employing the MWCNT/PTh composite film has reached 4.72%, which is close to that of the DSSC with a platinum (Pt) counter electrode (5.68%). Compared with a standard DSSC with MWCNT counter electrode whose efficiency is 2.68%, the energy conversion efficiency has been increased by 76.12% for the DSSC with MWCNT/PTh counter electrode. These results indicate that the composite film with high conductivity, high active surface area, and good catalytic properties for I₃⁻ reduction can potentially be used as the counter electrode in a high-performance DSSC.     

Voltammetric Determination of Neonicotinoid Pesticides at Disposable Screen‐Printed Sensors Featuring a Sputtered Bismuth Electrode

This work reports the determination of 5 neonicotinoid pesticides (Clothianidin, Imidacloprid, Thiamethoxam, Nitenpyram and Dinotefuran) in water samples by cathodic differential pulse (DP) voltammetry at screen‐printed disposable sensors featuring a sputtered bismuth thick‐film working electrode, a Ag reference electrode and a carbon counter electrode. The performance of the bismuth thick‐film electrodes was compared to that of a home‐made bismuth thin‐film electrode and a bismuth‐bulk electrode. The electrodes were further characterized by electrochemical and optical techniques. The effect of the pH of the supporting electrolyte on the DP reduction currents of the 5 pesticides was studied. The limits of quantification (LOQs) in 4 water matrices (distilled water, tap water, mineral water and surface water) were in the range 0.76 to 2.10 mg L^?1 but severe matrix effects were observed in the analysis of mineral and, especially, surface water samples. Using a solid‐phase extraction (SPE) procedure using Lichrolut EN cartridges and elution with methanol, the matrix effects were substantially reduced and the LOQs were in the range 9 to 17 µg L^?1_. The recoveries of surface water samples spiked with the 5 target neonicotinoids at two concentration levels (20 and 50 µg L^?1) were in the range 89 to 109 % and the % relative standard deviations ranged from 4.3 to 7.2 %.     

One-step electrochemical synthesis of Pt–CeO2 composite thin films on a glassy carbon electrode

A Pt–CeO₂ composite thin film was prepared on a glassy carbon electrode by one-step electrochemical deposition technique. The film was constructed of Pt particles well dispersed and embedded in a porous CeO₂ substrate. The prepared Pt–CeO₂/GC electrode showed a better catalytic performance toward methanol electrooxidation compared with the bulk Pt electrode.     

Electrocatalytic Oxidation of Perfluoroalkylvinyl Ethers in Fluorosulfonic Acid

Direct anodic oxidation of perfluoroalkylvinyl ethers R_FOCF=CF₂ (PVE) and terminal fluoroolefins R_FCF=CF₂ (TFO) in fluorosulfonic acid is studied using cyclic voltammetry; electrolysis at a monitored potential; and analyses of synthesized products by ¹⁹F NMR, gas-liquid chromatography, and chromato-mass spectrometry, with simultaneous preparative isolation of the products. Proposals on some regularities of the direct oxidation of PVE and TFO are made. The corrosion behavior of platinum, iridium, and their alloys is studied. The formation of oxide films on various electrode materials and a fluorosulfate film on glassy carbon is found to correlate with catalytic activity in reactions of direct oxidation of perfluoroolefins.     

Electrochemical characterization of a new system for detection of superoxide ion in alkaline solution

A new medium system containing dimethyldistearylammonium bromide (DSAB) was developed for the electrochemical detection of superoxide ion in alkaline solution. The reductions of molecular oxygen in alkaline media as a function of the electrode material were evaluated for Pt, Ag, Au and glassy carbon (GC) electrode. And a quasi-reversible redox process for the O₂/O₂⁻ couple was only obtained at the Pt electrode. The electrochemical responses of the O₂/O₂⁻ couple at a platinum electrode and a platinized platinum electrode were compared, which suggesting that the electrochemical behavior of the O₂/O₂⁻ couple was improved greatly at a platinized Pt electrode. The frequency change (mass change) on the surface of Pt electrode was characterized by the electrochemical quartz crystal microbalance. The reduction of the dissolved oxygen at a platinized Pt electrode in the presence of DSAB was also studied by using chronocoulometry and the result indicated that a one-electron reduction was involved. In addition, the scavenging activity of cysteine towards superoxide ion was evaluated by cyclic voltammetry.     

Potassium ion-selective electrode based on a cobalt(II)-hexacyanoferrate film-modified electrode

A potassium ion-selective electrode based on a cobalt(II)-hexacyanoferrate(III) (CHCF) film-modified glassy carbon electrode is proposed. The electroactive film is introduced onto the glassy carbon electrode surface by electrodeposition of cobalt, which forms a thin CHCF film on subsequent anodic scanning in KClHCl solution (pH 5.0–5.5) containing K₃Fe(CN)₆. The thickness of the film on the electrode surface can be controlled by changing the electrodeposition time and the concentrations of cobalt(II) and Fe(CN)^3?₆ ions. The modified electrode exhibits a linear response in the concentration range 1 × 10^?1 ?3 × 10^?5 M potassium ion activity, with a near-Nernstian slope (48–54 mV per decade) at 25 ± 1°C. The detection limit is 1 × 10^?5 M. The stability, response time and selectivity were investigated. The electrode exhibits good selectivity for potassium ion with the twelve cations investigated. The relative standard deviation is 1.5% (n=10). The effects of the thickness of the electroactive film and the pH of the solution on the electrode response were also investigated.     

Electrochemistry and scanning electron microscopy of polyaniline/peroxidase-based biosensor

An amperometric biosensor was prepared by in situ deposition of horseradish peroxidase (HRP) enzyme on a polyaniline (PANI)-doped platinum disk electrode. The PANI film was electrochemically deposited on the electrode at 100 mV s⁻¹/Ag-AgCl. Cyclic voltammetric characterization of the PANI film in 1 M HCl showed two distinct redox peaks, which prove that the PANI film was electroactive and exhibited fast reversible electrochemistry. The surface concentration and film thickness of the adsorbed electroactive species was estimated to be 1.85×10⁻⁷ mol cm⁻² and approximately 16 nm, respectively. HRP was electrostatically immobilized onto the surface of the PANI film, and voltammetry was used to monitor the electrocatalytic reduction of hydrogen peroxide under diffusion-controlled conditions. Linear responses over the concentration range 2.5×10⁻⁴ to 5×10⁻³ M were observed. Spectroelectrochemistry was used to monitor the changes in UV-vis properties of HRP, before and after the catalysis of H₂O₂. The biosensor surface morphology was characterized by scanning electron microscopy (SEM) using PANI-doped screen-printed carbon electrodes (SPCEs) in the presence and absence of (i) peroxidase and (ii) peroxide. The SEM images showed clear modifications of the conducting film surface structure when doped with HRP, as well as the effect of hydrogen peroxide on the morphology of biosensor.