The kinetics of methanol oxidation on supported 47.5 wt.% Pt and 54 wt.% PtRu (with nominal Pt:Ru ratios of 2:3) catalysts are measured in 0.5 M H
2SO
4 and 0.1 NaOH at 295 and 333 K using thin-film ...rotating disk electrode (RDE) method. It was found that the activity of Pt and PtRu for methanol oxidation is a strong function of pH of solution and temperature. The kinetics are much higher in alkaline than in acid solution; at 333 K, a factor of 30 for Pt and a factor of 20 for Pt
2Ru
3 at 0.5 V. The pH effect is attributed to the pH competitive adsorption of oxygenated species with anions from supporting electrolytes. The activity of Pt and Pt
2Ru
3 catalysts at 333 K is higher (a factor of 5) than at 295 K. Irrespective of pH, only negligible differences in the kinetics are observed between Pt and on high Ru content Pt alloys, presumably owing to a slow rate of methanol dehydrogenation on the Ru-rich surface and insufficient number of Pt sites required for dissociative chemisorption of methanol.
•Polyaniline in the form of base and salt was prepared chemically and electrochemically.•Corrosion of mild steel with different composite coatings were investigated.•Chemically prepared emeraldine ...salt posses good anticorrosion properties.•Anticorrosion properties were connected with the content of oligomers in the samples.•It was proposed that polyaniline acts as active barriers.
The protective abilities of composite coatings based on electrochemically and chemically formed polyaniline powder against the corrosion of mild steel were investigated. A polyaniline powder has been prepared in the form of an emeraldine base and benzoate salt through chemical dedoping and doping. The composite coatings using polyaniline powders, which were obtained through different routes, and base coatings, which were not corrosion-resistant, with different formulations were prepared and applied on mild steel samples. The corrosion was investigated using an electrochemical impedance technique in 3% NaCl, and the atmospheric corrosion was assessed in a humidity chamber. Emeraldine–benzoate salts, which are a chemically synthesized polyaniline, offer the best protection with an optimal polyaniline concentration of approximately 5wt%. The different corrosion behaviors were assessed relative to the presence of aniline oligomers in the samples after characterization using UV–vis spectrophotometry. Upon comparison between the corrosion behavior in 3% NaCl with commercial primer paint for iron and that with a paint containing 5wt% PANI, the composite coating has superior anticorrosion characteristics. The mechanism for the protection of mild steel from corrosion through composite polyaniline coatings was also considered.
The variation of the adsorption pseudocapacitance with temperature is used to obtain the enthalpy, entropy, and free energies of adsorption of Hupd and OHad on Pt(111) as a function of pH and nature ...of the anion of the supporting electrolyte. It is shown that the heat (enthalpy) of adsorption of hydrogen on Pt(111) at the electrochemical interface is essentially independent of either the pH of the electrolyte or the nature of the supporting anion. The heat of adsorption has a linear decrease with ϑHupd, from ∼42 kJ/mol at ϑHupd = 0 ML to ∼24 kJ/mol at ϑHupd = 0.66 ML. The heat of adsorption of OHad is more sensitive to the nature of the anion in the supporting electrolyte. This is presumably due to coadsorption of the anion and OHad in electrolytes other than the simple alkali bases. From the isosteric heat of adsorption of OHad in alkaline solution (ca. ∼200 kJ/mol) and the enthalpy of formation of OH• we estimated the Pt(111)−OHad bond energy of 136 kJ/mol. This value is much smaller than the Pt−Oad bond energy at a gas−solid interface (∼350 kJ/mol). In basic solution the electrooxidation of CO proceeds at low overpotentials (<0.2 V) between the adsorbed states of COad and OHad, the latter forming at low overpotentials selectively at defect sites. In acid solution, however, these sites are not active because they are blocked by specific adsorption of anions of the supporting electrolyte.
The corrosion behavior of mild steel and mild steel covered by electrochemically deposited (a) polyaniline (PANI) film, (b) epoxy coating and (c) PANI/epoxy coating system in 0.1
M sulfuric acid ...solution were investigated by electrochemical impedance spectroscopy (EIS). Electrochemical deposition of PANI film was performed from aqueous solution of 0.5
M sodium benzoate and 0.1
M aniline at constant current density of 1.5
mA
cm
−2. Epoxy coatings on mild steel and mild steel modified by PANI film were deposited at constant voltage. It was shown that thin PANI film had provided good corrosion protection of mild steel in 0.1
M sulfuric acid solution, and could be used for modification of mild steel prior to epoxy coating deposition. The increased corrosion protection of mild steel by PANI/epoxy coating system in the same solution was obtained.
Using the rotating ring-disk technique (RRDE) the oxygen reduction reaction (orr) was studied on the Pt(111) surface in the presence of Br
− anions. We found that the orr at the Pt(111)
∣
Br
ad ...interface is always accompanied quantitatively by H
2O
2 oxidation currents on the ring electrode, implying that in the presence of Br
− anions the orr does not proceed entirely through the 4e
− reduction pathway, as in the Br
−-free solution. We propose that strongly adsorbed Br
− can simultaneously suppress both the adsorption of the O
2 molecule and the formation of pairs of platinum sites needed for the breaking of the O–O bond. Besides elucidating the effects of Br
ad, these studies also shed some light on the role of OH
ad on the kinetics of the orr on the Pt(111) surface in solution free of Br anions. We have developed a theoretical model and from simulations of
I–
E curves we propose two modes of action of the OH
ad state on the kinetics of the orr on the Pt(111) surface: (i) OH
ad can block the adsorption of O
2 on active platinum sites, i.e. they compete for the same sites, and (ii) OH
ad can alter the adsorption energy of intermediates which are formed during the orr on the bare Pt sites adjacent to the OH
ad.
The hydrogen evolution (HER) and the hydrogen oxidation reaction (HOR) were studied on platinum single crystals in a sulfuric acid solution over the temperature range 274−333 K. We found, for the ...first time, that at a fixed temperature (274 K) the exchange current densities (i o) increase in the order (111) ≪ (100) < (110), with the i o on the (110) surface being 3 times that on the (111) surface. We also found that each crystal face has an unique, temperature-dependent Tafel slope for the HOR, and that the activation energies for the HER and the HOR decrease in the sequence > > , the same sequence as the order of activity. These differences in activation energy with crystal face are attributed to structure-sensitive heats of adsorption of the active intermediate, Had, whose physical state is unclear. We analyzed the kinetic data with a model for the coupling of this unknown state, Had, with the well-known adsorbed state of hydrogen, Hupd, whose adsorption energy is strongly structure-sensitive. We concluded that on Pt(110), the reaction follows the Tafel−Volmer mechanism with the Tafel (recombination) step rate determining. On Pt(100), the reaction follows the Heyrovsky−Volmer sequence, with the Heyrovsky (ion−atom) reaction step being the rate-determining step. The reaction mechanism on Pt(111) could not, however, be resolved by analyzing the kinetic parameters. The relatively low activity and high activation energy for the (111) surface is attributed to strong repulsive interaction between Had adatoms on this surface.
Polypyrrole (PPy) thin film electrode was galvanostatically synthesized and characterized in 0.1
M HCl on graphite electrode as cathode materials for the aqueous-based rechargeable zinc batteries. ...The charge/discharge characteristics of PPy and zinc electrode in 0.1
M ammonium chloride and in the 0.1
M ammonium chloride with addition of 0.1
M sodium citrate were investigated. Electrochemical characteristic of possible Zn|PPy cell in chloride/citrate containing electrolyte was discussed and simulated.
Polyaniline (PANI) enzyme electrode was formed by immobilisation of Glucose oxidase (GOx) via glutaraldehyde into electrochemically polymerised PANI on graphite electrode. Electrochemical ...polymerisation of PANI on graphite was performed from aqueous solution of 1.0
mol
dm
−3 HCl and 0.25
mol
dm
−3 aniline at constant current density of 2.0
mA
cm
−2. Hronopotentiometric curves of the PANI enzyme electrode obtained at current density of 10
μA
cm
−2 were recorded in different glucose concentrations. The linearity response range was between 1.0 and 5.0
mmol
dm
−3 of glucose concentration. The estimated apparent Michaelis–Menten constant, was
K
m
′
=
0.30
mmol
dm
−3, which is significantly lower than that of free enzyme.
Electrocatalysis of CO oxidation and the interfacial structure of the CO adlayer (COad) on the Pt(111) surface in 0.5 M H2SO4 were examined by using the rotating disk electrode method in combination ...with in situ surface X-ray diffraction measurements. The results presented here elucidate the roles played by two different forms of COad: one which is oxidized at lower overpotentials, in the so-called preoxidation region, we characterize as a weakly adsorbed state (COad.w), and a strongly adsorbed state (COad,s) which is oxidized at higher overpotentials. The COad,w state forms at saturation coverage by adsorption at E < 0.15 V and assumes a compressed p(2 × 2) structure containing 3 CO molecules in the unit cell (0.75 CO/Pt). We propose that oxidative removal of COad,w is accompanied by simultaneous relaxation of the CO adlayer, and that the remaining COad (≈0.6 CO/Pt) assumes a new bonding state which we identify as COad,s. The COad,s state is present in a structure lacking long-range order. Despite the reduced coverage by COad, H2 electrooxidation is still completely poisoned at potentials below 0.6 V. The electrooxidation of CO in solution is proposed to occur via the COad,w state at 0.6−0.8 V, and via the COad,s at higher potentials.
The electrochemical synthesis and corrosion behavior of polyaniline (PANI) on mild steel from sodium-benzoate solutions were investigated. Thin, adherent, polyaniline films were obtained by anodic ...oxidation with current densities between 0.3 and 1.5
mA
cm
−2. During electropolymerization induction period was not observed. The corrosion behavior of mild steel with polyaniline coating in 0.1
M sulfuric acid and 0.5
M NaCl (pH=3) solutions, was investigated by spectrophotometric method and electrochemical impedance technique. The atmospheric corrosion behavior was also investigated. It was concluded that this coatings had provided corrosion protection of mild steel in all mentioned corrosion environments.
