Spectroelectrochemical study of the oxidation of diaminophenols on platinum electrodes in acidic medium

The electrochemical oxidation of 2,3- 2,4- and 2,5-diaminophenol, on platinum electrode, in acid medium was studied using cyclic voltammetry, in situ UV-vis and in situ FTIR spectroscopies. The spectroscopic data indicates that 2,4-diaminophenol suffers hydrolysis giving the formation of 2-amino-hydroquinone/2-amino-p-benzoquinone in solution. The oxidation mechanism of 2,5-diaminophenol is similar to the p-phenylenediamine giving 2-hydroxy-p-benzoquinoneimine and its hydrolysis product, 2-hydroxy-p-benzoquinone. The electrochemical results suggest that 2,3-diaminophenol generates a non-electroactive polymeric material on the electrode surface.     

Cyclic voltammetry study of arsenic in acidic solutions

An electrochemical investigation of arsenic species in acidic solutions, using cyclic voltammetry at a platinum rotating disk electrode, has been carried out. A well defined peak at about 1 V_SCE, with a large overpotential (>0.5 V) is attributed to the oxidation of As(III) to As(V). The reaction is under the mixed control of ionic transport and charge transfer. The corresponding reduction of As(V) is not observed in the potential range of the study (−0.6 to +1.2 V_SCE). As(V) is not electrochemically active in this range and it has no effect on hydrogen evolution. With As(III) in solution, hydrogen evolution on Pt is shifted towards more negative potentials and it takes place simultaneously with arsine production. A small cathodic peak at −0.2 V_SCE and a corresponding anodic peak at +0.3 V_SCE are attributed to the deposition of a thin layer of As by reduction of As(III) and its dissolution.     

The role of platinum oxide in the electrode system Pt(O2)/yttria-stabilized zirconia

The existence and role of platinum oxide in the solid state electrode system Pt(O₂)/yttria-stabilized zirconia is discussed. Covering and porous model-type Pt film electrodes on YSZ single crystals are investigated by cyclic voltammetry, electrochemical impedance spectroscopy, and in situ scanning photoelectron microscopy. The formation of Pt oxide and its amount strongly depend on the experimental conditions, such as temperature, oxygen partial pressure, and oxygen flux towards the electrode during anodic polarization. Electrode activation and deactivation processes can be explained by formation and decomposition of Pt oxide, which is reducing or inhibiting the oxygen exchange rate.     

氯苯在铂电极上电解特征的研究

为探索电化学处理工业废水的技术要点和测控方法 ,以氯苯作为研究对象 ,自行设计组装了循环伏安系统。考察了氯苯在铂电极上的循环伏安特性。结果表明 ,在铂电极上 ,氯苯发生的是电还原反应 ;氯苯在电解过程中可能受中间产物对电极界面的极化效应 ,污染了电极 ,导致了电流密度的降低。建议在有机物的电化学处理过程中应采用精密在线测量控制手段 ,提供及时合适的电压电流条件 ,使得各环节在速率方面达到平衡 ,防止和减缓聚合物的极化影响 ,以促进有机物的有效矿化或分离。     

Electrochemical reduction of nitrate in weakly alkaline solutions

The electrocatalytic activity of several materials for the nitrate reduction reaction was studied by cyclic voltammetry on a rotating ring disc electrode in solutions with different concentrations of sodium bicarbonate. Copper exhibited highest catalytic activity among the materials studied. Nitrate reduction on copper was characterized by two cathodic shoulders on the polarization curve in the potential region of the commencement of hydrogen evolution. In this potential range an anodic current response was observed on the Pt ring electrode identified as nitrite to nitrate oxidation. This indicates that nitrite is an intermediate product during nitrate reduction. These conclusions were verified by batch electrolysis using a plate electrode electrochemical cell. Copper and nickel, materials representing the opposite ends of the electrocatalytic activity spectra, were used in batch electrolysis testing.     

Electrochemical study of azo-azulene compounds

An electrochemical study of several azo-azulene compounds (Az-NN-Y, where Y = substituted phenyl, pyridine, thiazole) was performed with cyclic and differential pulse voltammetry, as well as rotating-disk electrode methods. The objective of this work was to characterize their electrochemical properties and establish the influence of donor and acceptor substituents on azulene and azo group behaviour. Calculations were performed, using quantum mechanics-based methods, to correlate electrochemical reactivity with structure. Satisfactory correlations were found between experimental oxidation and reduction potentials as well as calculated ionization potentials and LUMOs.     

Electropolymerization of chlorinated phenols on a Pt electrode in alkaline solution Part III: A Fourier transformed infrared spectroscopy study

FTIR spectroscopy was employed to investigate high molecular weight substances formed on a platinum electrode surface during the electrochemical oxidation of phenol and its chlorinated derivatives. Potentiodynamic (potential range from –0.80 V to 0.85 V vs SHE; scan rate 200 mV s^–1) and potentiostatic (at 0.78 V vs SHE) electropolymerization was used in alkaline solutions (1 M NaOH) containing 0.1 M of phenol, monochlorophenols, dichlorophenols, trichlorophenols and pentachlorophenol. The IR spectra of the corresponding monomers were recorded for the comparison. The FTIR spectroscopy studies revealed that the polymers formed under potentiodynamic and potentiostatic conditions are of aromatic nature (–C=C– stretching vibrations at 1450–1600 cm^–1), they have ether-linkages (=C—O—C= stretching vibrations at 1100–1300 cm^–1) and quinone groups (–C=O stretching vibrations at 1630–1800 cm^–1 and –C—H out-of-plane bending at 760 cm^–1). The intensities of the hydroxyl group bands in most of the polymers are rather weak compared to those in the corresponding monomers. Vibrations at 2850–2960 cm^–1, which are present in most of the IR spectra of polymers formed under cyclic voltammetry conditions, correspond to the stretching vibrations of the sp³ hybridized C—H bond and suggest that the cleavage of the benzene ring occurs to some extent during electrooxidation–electropolymerization of phenol and its chlorinated derivatives when reaching the potential of oxygen evolution (0.85 V vs SHE).     

Electrochemical and AFM study of cobalt nucleation mechanisms on glassy carbon from ammonium sulfate solutions

Nucleation mechanisms of cobalt on a glassy carbon electrode (gce) from aqueous ammonium sulfate solutions were investigated through the electrochemical techniques of cyclic voltammetry (cv) and chronoamperometry (ca), coupled with atomic force microscopy (AFM) studies. The studied parameters were pH, cobalt concentration, temperature, scanning rate, and deposition potential. It was found that scanning in the cathodic direction produced two peaks, corresponding to cobalt and hydrogen reduction, respectively. Scanning in the anodic direction was characterized by cobalt dissolution, which was interrupted by formation of cobalt hydroxide, causing a second anodic peak. The amperometric study found progressive nucleation mechanisms, in contrast to the instantaneous nucleation mechanisms determined by the AFM study. An explanation for the contradictory nucleation mechanisms shown in the two studies is provided.     

Electrochemical and DFT-studies of substituted thiophenes

UV-vis absorption spectra and cyclic voltammograms of a selection of substituted thiophenes and their oligomers carrying trifluoracetyl acetone functional groups have been obtained. A comparison with calculated values of HOMO-LUMO energies (the former corresponding to the ionization potentials E_i) shows strong correlations between calculated and experimentally obtained data; they are in close agreement with estimates in terms of electron-donating and -withdrawing effects from an empirical point of view.     

Electrocatalytic oxygen reduction on single-walled carbon nanotubes supported Pt alloys nanoparticles in acidic and alkaline conditions

The objective of this study is to improve the catalytic activity of platinum by alloying with transition metal (Pd) in gas diffusion electrodes (GDEs) by oxygen reduction reaction (ORR) at cathode site and comparison of the acidic and alkaline electrolytes. The high porosity of single-walled carbon nanotubes (SWCNTs) facilitates diffusion of the reactant and facilitates interaction with the Pt surface. It is also evident that SWCNTs enhance the stability of the electrocatalyst. Functionalized SWCNTs are used as a means to facilitate the uniform deposition of Pt on the SWCNT surface. The structure of SWCNTs is nearly perfect, even after functionalization, while other types of CNTs contain a significant concentration of structural defects in their walls. So catalysts supported on SWCNTs are studied in this research. The electrocatalytic properties of ORR were evaluated by cyclic voltammetry, polarization experiments, and chronoamperometry. The morphology and elemental composition of Pt alloys were characterized by X-ray diffraction (XRD) analysis and inductively coupled plasma atomic emission spectroscopy (ICP-AES) system. The catalytic activities of the bimetallic catalysts in GDEs have been shown to be not only dependent on the composition, but also on the nature of the electrolytes. The GDEs have shown a transition from the slow ORR kinetics in alkaline electrolyte to the fast ORR kinetics in the acidic electrolyte. The results also show that introduction of Pd as transition metal in the Pt alloys provides fast ORR kinetics in both acidic and alkaline electrolytes. The performance of GDEs with Pt–Pd alloy surfaces towards the ORR as a function of the alloy’s overall composition and their behavior in acidic electrolyte was also studied. These results show that the alloy’s overall composition and also the nature of the electrolytes have a large effect on the performance of GDEs for ORR.     

Electrochemical and spectroelectrochemical study on bilayer films composed of C60 and poly(3,4-ethylenedioxythiophene) PEDOT

Bilayers of drop casted C₆₀ fullerene films and electrochemically synthesized poly(3,4-ethylenedioxythiophene) (PEDOT) films have been studied. The PEDOT film was polymerised by cyclic voltammetry on top of the drop casted C₆₀ fullerene film. The bilayer films were produced and characterized in three different electrolytes; tetrabutylammoniumhexafluorophosphate (TBAPF₆) and lithium hexafluorophosphate (LiPF₆) in acetonitrile (ACN) and in the ionic liquid 1-butyl-3-methyl-imidazolium tetrafluoroborate (BMIMBF₄). The bilayers were studied by cyclic voltammetry and in situ Fourier transform infrared attenuated total reflection (FTIR-ATR) spectroscopy. Both p- and n-doping of the bilayer films were studied and compared with PEDOT films prepared in organic media.     

SFG study on potential-dependent structure of water at Pt electrode/electrolyte solution interface

Structure of water at Pt/electrolyte solution interface was investigated by sum frequency generation (SFG) spectroscopy. Two broad peaks were observed in OH stretching region at ca. 3200 cm⁻¹ and ca. 3400 cm⁻¹, which are known to be due to the symmetric OH stretching (υ₁) of tetrahedrally coordinated, i.e., strongly hydrogen bonded “ice-like” water, and the asymmetric OH stretching (υ₃) of water molecules in a more random arrangement, i.e., weakly hydrogen bonded “liquid-like” water, respectively. The SFG intensity strongly depended on electrode potential. Several possibilities are suggested for the potential dependence of the SFG intensity.     

Kinetic parameters for anodic oxidation of hypochlorite ion on Pt and Pt oxide electrodes in alkaline solution

Kinetic parameters for the anodic oxidation of hypochlorite ion have been determined by means of normal pulse voltammetry by using a platinum disk as the working electrode. By using the working electrode that formed an oxide film by electrochemical pretreatment, the effect of the lattice oxygen of the surface oxide on the reaction was also examined. The measurement results were analyzed by the classical method, and then the analytical results were evaluated by digital simulation. The normal pulse voltammogram of the hypochlorite ion showed quasi-reversible oxidation waves. The apparent rate constant was calculated to be 5.0-8.1 × 10⁻⁴ cm s⁻¹, depending on the electrode surface state. At the low-concentration range of <4.0 mg Cl dm⁻³, the oxidation current was concentration dependent at the cathodically polarized electrode, while it became independent after the anodic polarization.     

Effect of hydrogen charging on the stability of SAE 10B22 steel surface in alkaline solutions

The influence of hydrogen charging into a quenched and tempered boron steel membrane electrode (SAE 10B22) was studied using borate buffer (pH 8.4) and NaOH solutions (pH 12.7), with or without the addition of 0.01 M EDTA. At the hydrogen input side, hydrogen charging influenced cyclic voltammograms increasing the anodic charge of iron(II) hydroxide formation, and decreasing the donor density of passive films. These results suggest that the hydrogen ingress caused instability of metallic surface, increasing the surface area activity.     

Electrochemical quartz crystal nanobalance (EQCN) studies of the adsorption behaviour of an enzyme, mandelate racemase, and its substrate, mandelic acid, on Pt

The adsorption behaviour of the enzyme, mandelate racemase (MR), and its substrate, (S)-mandelic acid (MA), was studied at a polycrystalline Pt surface in pH 7.4 phosphate buffer at 294 K using the electrochemical quartz crystal nanobalance (EQCN) technique of simultaneous cyclic voltammetry (CV) and frequency measurements. It was shown that the EQCN frequency measurements did not directly monitor the molar mass of the adsorbed protein at anodic potentials, but instead measured changes in the surface oxide in the absence and presence of adsorbed protein. However, at a potential characteristic of the double layer for platinum, EQCN frequency measurements gave a measure of the extent of solvent displacement by the adsorbed protein. The adsorption process was modelled using the Langmuir adsorption isotherm. The values for the Gibbs energy of adsorption, ΔG_ADS, obtained with these EQCN frequency measurements gave excellent agreement within experimental uncertainty with those obtained from the simultaneous CV measurements for both the enzyme and substrate, and showed the enzyme to have a greater affinity for the surface than the substrate molecule. The maximum surface concentrations from CV and EQCN frequency measurements gave excellent agreement for the two techniques and showed MA to be adsorbed in a tilted orientation with monolayer coverage. On the other hand, the surface concentrations showed the presence of ∼2.5 monolayers of enzyme from charge transfer CV measurements, while the frequency results showed the presence of a densely packed monolayer from the “footprint” of solvent displacement by the adsorbed enzyme molecules on the electrode surface. The two techniques provide valuable complementary information on the interfacial behaviour of molecules.     

Electrochemical study of catechol-boric acid complexes

The electrochemical behavior of catechol-boric acid complexes in aqueous solutions has been studied using cyclic voltammetry and steady-state voltammetry with a rotating disk electrode. Different patterns of reactivity and various kinetic pathways have been examined. Based on a CE mechanism, the dissociation constant and homogeneous rate constants of complex formation and dissociation were estimated for each pathway by comparing the experimental cyclic voltammograms with the digitally simulated results. Also, the effects of pH and substituted groups on dissociation constants and reaction kinetics were studied.     

Electrochemical degradation of polyfuran in wet acetonitrile and aqueous solutions

The degradation of polyfuran in a wet acetonitrile solution and in an aqueous solution has been investigated with a cyclic voltammetry technique, along with Fourier transform infrared and Fourier transform Raman spectroscopy techniques. Infrared spectroscopy shows that the main defects that exist in polyfuran after cycling in dried acetonitrile are mainly saturated C? H structures, whereas those after cycling in an aqueous solution are mainly carbonyl groups in the polymer chain. This may be because polyfuran can undergo degradation through a crosslinking mechanism in a dried acetonitrile solution, whereas in an aqueous solution, it undergoes degradation through a nucleophilic attack mechanism. Raman spectroscopy shows that not all the furan rings are involved in the degradation process, although the electrochemical activity of polyfuran is totally lost in an aqueous solution after only one cycle. The sites that are sensitive to the degradation process may be the electrochemically active sites, that is, the positively charged sites in polyfuran chains. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 3160–3165, 2002     

Fast methanol oxidation on polycrystalline Pt

Fast cyclic voltammetry and a combined chronoamperometry/cyclic voltammetry pulse-sweep technique are used to study methanol oxidation on platinum in sulphuric acid. Measurement of suppression of hydrogen desorption charges simultaneously with charges for stripping of the CO poison allows for accurate baseline correction of the CO stripping peaks. Saturation coverages of CO formed from methanol, formic acid and dissolved CO are not all the same and differ in their potential dependence. Only dissociative adsorption of methanol to give adsorbed CO and subsequent oxidation of CO to CO₂ occurs during continuous cycling, but in the pulse-sweep method evidence was found for the existence of a parallel pathway occurring independently of adsorbed CO production, provided there is some surface not covered by CO or oxide.     

Electrochemical investigation of platinum electrode in solid electrolyte cell

Electro-oxidation of platinum film electrode deposited on yttria-stabilized zirconia (YSZ) is examined in situ using potential programmed voltammetry at 450 °C in oxygen containing atmosphere. Under prolonged anodic oxidation different sorts of oxidized species are formed which are consumed subsequently during a linear cathodic potential scan resulting in three distinct reduction peaks, one of them being fairly reversible while the two others strongly irreversible. Higher oxidation potential and longer time of polarization favor the irreversible processes. The coexistence of three electrochemical processes is explained with the extension of the triple phase boundary. The rapid first process is identified as formation of PtO_x at the electrode/metal interface, the second process - a much slower, parallel one - is related to the phenomenon of oxygen backspillover at the metal/gas interface, and the slowest third process - consecutive to the first one - is attributed to growth of the PtO_x layer at the electrode/metal interface toward the bulk of the metal by analogy to electro-oxidation of platinum in aqueous liquid electrochemistry.     

One step fabrication and characterization of platinum nanopore electrode ensembles formed via amphiphilic block copolymer self-assembly

A novel one-step approach to Pt nanopore electrode ensembles (NEEs) has been developed using an amphiphilic block copolymer [polystyrene-block-poly (acrylic acid)] self-assembly. This procedure is simple and fast, and requires only conventional, inexpensive electrochemical instrumentation. Electrochemical methods are used to characterize the Pt nanopore electrode ensembles prepared using this new procedure. And the capacitance and voltammetric characteristics for the NEEs have been examined. At lower scan rates, it remains the features of a single nanoelectrode, while at high scan rates the nanoelectrodes act independently. This is an important feature for vivo sensing and other electroanalytical applications.