Portugaliae
Electrochimica Acta

Solar cells (Gratzel cells) have been highly regarded due to their extremely efficient and low-cost process of converting sun light into electricity. In this work screen printed electrodes were fabricated by spraying organic and organometallic dyes on glass and flexible aluminum foil. These solar cells were prepared based on three dyes, namely nickel Di thiocyanato bis(triphenyl phosphine), nickel Dimethylglyoxime and Nile blue, and the performance of these dye-sensitized solar cells (DSSC) has been experimentally evaluated. The solar cells were fabricated using thin TiO2 films; these films were characterized by FTIR. The dyes were characterized using UV–Vis and typical J-V and P-V curves of the cells. The best performance was obtained for the mixture of nickel Dithiocyanatobis (triphenyl phosphine) and Nile blue with an open circuit voltage (Voc) of 976 mV using an incident irradiation of 100 mW/cm2 at 25 ºC.

The corrosion inhibition of mild steel in hydrochloric acid by polyvinyl alcohol-g-poly(acrylamide-vinyl sulfonate) has been studied by weight loss and electrochemical methods (AC impedance and DC polarisation) techniques in the temperature range of 303 – 343 K. The inhibitor was found to provide an excellent efficiency of more than 90 %. Various adsorption isotherms have been employed for fitting the obtained results to confirm the mode of adsorption of the grafted terpolymer on mild steel. Thermodynamic parameters of adsorption such as equilibrium constant, Gibbs free energy, adsorption heat and adsorption entropy were evaluated and discussed. Various parameters that determine the kinetics of mild steel dissolution such as activation energy, enthalpy and entropy were also calculated. Results obtained from various techniques were comparable and suggest that the terpolymer follows chemical adsorption mode for inhibition.

Electroless nickel composite coatings are developed by incorporating soft/hard particles into Ni-P coatings, to improve mechanical as well as tribological properties. The objective of the present work is to investigate the effect of various coating process parameters on the corrosion behavior of Ni–P–Al2O3 composite coating deposited on mild steel substrate. The electrochemical impedance spectroscopy test is used to evaluate the corrosion behavior of the heat treated composite coatings at various annealing temperatures (300 °C, 400 °C, and 500 °C). Corrosion properties, charge transfer resistance (Rct) and double layer capacitance (Cdl), are optimized using Taguchi based grey relational analysis to improve the corrosion resistance of the coating. Concentration of nickel source, concentration of reducing agent, concentration of alumina particles and annealing temperature, are considered as a main design factor for optimization of electrochemical properties. Analysis of variance (ANOVA) is used to find out the optimum combination of coating process parameters. From ANOVA result, it is found that the concentration of Al2O3 particles and annealing temperature have significant influence on the corrosion resistance of the composite coatings. Concentration of reducing agent has moderate influence on the corrosion resistance. Surface morphology of the coated surface is studied using SEM (scanning electron microscopy) and chemical composition of the coating is studied using EDX (energy dispersive X-ray analysis). The XRD (X–ray diffraction analysis) is used to understand the phase transformation behavior of the composite coatings.

In this paper, a glassy carbon electrode is modified by Bismuth-Chitosan (Bi-Chit) nanosheets. Bismuth, that is “environmentally friendlier” than mercury, is deposited on a glassy carbon electrode by electrolysis at - 0.75 V vs. SCE in a stirring solution containing 0.18 mg mL-1 Bi(NO3)3, 0.05 mg mL-1 KBr and acetate buffer 0.1 M (pH=4.5) for 200 s. Furthermore, the electrode is modified by chitosan by the means of sonication of bismuth-modified glassy carbon electrode in chitosan solution for 15 minutes. Study of the field emission by scanning electron microscopy (SEM) shows the formation of Bi-Chit nanosheets on the glassy carbon electrode. The modified electrode surface is also characterized by energy dispersive X-ray analysis (EDX). In this research the Bi-Chit modified glassy carbon electrode exhibits excellent catalytic activity toward the electro-reduction of Tartrazine. The modified electrode is successfully used for determination and measurement of Tartrazine in Bisacodyle tablets and chocolates with colorful coatings.

The objective of this study is the valorization of the essential oil (EO) of Lippia citriodora irrigated by urban wastewater from the city of Settat-Morocco. We have tested it as a corrosion inhibitor of aluminum in 0.1 M Na2CO3 using polarization method, weight loss, and EIS measurements. The inhibition efficiency of lippia citriodora oil was calculated and compared. We found good agreement between the referred methods. The results obtained revealed that the tested inhibitor reduces differently the kinetic of the corrosion process of aluminum. Its efficiency increases with the concentration and attained 90.33% at 1800 ppm. The effect of temperature on the corrosion behaviour of aluminum in 0.1 M Na2CO3 was also studied in the range 283 K and 313 K. The thermodynamic data of activation were determined. The analysis of Lippia citriodora oil, obtained by hydro-distillation, using gas chromatography (GC), showed that the major components are neral 13.85%, geranial 14.06% and limonene 28.32%.

The corrosion inhibition and adsorption of ethanol extracts of leaves (LV), stems (ST) and roots (RT) of Rotula aquatica plant for mild steel in H2SO4 solutions were investigated using conventional weight loss, gasometric techniques, electrochemical polarizations and electrochemical impedance spectroscopy. The results showed that all the three extracts of Rotula aquatica plant performed well as inhibitor for the corrosion of steel in sulphuric acid media and the inhibition efficiencies of the extract follow the trend RT > LV > ST. Inhibition efficiencies increased with increasing concentration of the plant extracts but decreased with the temperature rise for all cases. Both the cathodic hydrogen evolution and the anodic dissolution of mild steel were inhibited, hence the active molecules of all the extracts studied acted as mixed type corrosion inhibitors.

Electrochemical reduction of boron from boron containing fluoroborate species present in KCl (81.54 mol%)-KF (18.45 mol%)-NaBF4 (1.67x10-4 mol cm-4) melt on a platinum electrode was studied by cyclic voltammetry and chronoamperometry. These studies were carried out over the temperature range 1073 – 1123 K. Boron-containing electroactive species is shown to reduce quasi-reversibly at low scan rates (ν < 0.1 Vs-1) and irreversibly at higher scan rates (> 0.1 V s-1) through a single-step three-electron process (B(III) + 3e → B). The transfer and diffusion coefficients of the electroactive species were measured for sodium fluoroborate in KCl-KF melt over the temperature range 1073 – 1123 K.

Inhibition effect of poly 3-dodecyloxy aniline polymeric surfactant (PC12H) on the corrosion of aluminum in 0.5 M HCl solution was investigated using potentiodynamic polarization technique under different experimental conditions. Inhibition efficiency and thermodynamic functions for dissolution and adsorption of PC12H are compared with Poly 3-(dodecyloxy sulfonic acid) aniline (PC12SO3H) to explain the effect of terminal side chain on the corrosion protection. Data show that the presence of –SO3H as a terminal group in PC12SO3H decreases the inhibition efficiency from 88.7%, in case of PC12H, to 55.1% in case of PC12SO3H. Quantum chemical calculations were performed on PC12H and PC12SO3H to investigate the relationship between the molecular structures and their inhibition efficiencies.

The present article considers an experimental study of tribo-corrosion behavior of electroless Ni–P coatings in alkaline environment sliding against alumina. The study of wear and friction behaviour is carried out using different load and sliding speed with the help of a pin-on-disk tribometer. The wear rate increases with decrease in sliding speed and increase in the applied load. The friction coefficient initially decreases with increase in the applied load and then remains at nearly steady level at higher applied load. Also, it is found that the friction coefficient is lower at higher sliding speed. The friction coefficient does not change with the sliding duration after the initial transient running-in time. The coating is characterized using scanning electron microscopy (SEM), energy dispersive X-ray (EDX) analysis and X-ray diffraction (XRD) analysis. The wear mechanism is also studied and has been found to be mostly abrasive in nature.

The inhibitive effect of aqueous extract of leaves of Polyalthia longifolia on the corrosion of mild steel was studied using the gravimetric (weight loss) method at the temperatures 303 and 318 K. The results show that the aqueous extract of Polyalthia longifolia leaves inhibited the corrosion of mild steel in dilute H2SO4 solution. It was found that the inhibition efficiency increased with inhibitor concentration and decreased with rise in temperature. Values of the activation energy of the inhibited corrosion reaction range between 45.40 kJ/mol and 62.22 kJ/mol. This is much higher than the 25.74 kJ/mol obtained for the blank. The adsorption of the extract was spontaneous and occurs according to Flory-Huggins adsorption isotherm. The corrosion inhibition of Polyalthia longifolia leaves extract was attributed to the adsorption of phytochemical molecules present in the extract onto the surface of the mild steel. Physical adsorption mechanism has been proposed for the adsorption of the inhibitor.

An ion selective membrane sensor from dioctyl phthalate as a plasticizer in a polymeric matrix of polyvinyl chloride (PVC) and β-cyclodextrin as an ionophore was constructed and evaluated according to IUPAC recommendations. Linear Nernstian response of DPPH• within the concentration ranges of 10−6 to 10−2 mol L−1 was obtained with average recovery 99.87±0.617. Nernstian slope of 58.5 mV/decade with excellent selectivity over the pH range of 3-8 was observed. The suggested method was standardized using butylated hydroxyl anisole (BHA). The 50% radical scavenging activity (IC50) determined by the proposed sensor correlated well with that of the common spectrophotometric method based on scavenging of 2,2-diphenyl-1-picrylhydrazyl (DPPH•). An algorithm implemented in Microsoft Visual Basic® 6.0 was used for calculating (IC50) values which are 7.38 μg/mL ± 0.35, 89.98 μg/ mL ± 0.45 and 1.45 mg/ mL ± 1.50 for BHA, Paracetamol and Dipyridamole, respectively. The proposed sensor represents a simple and reproducible tool for measuring DPPH• scavenging activity of Paracetamol and Dipyridamole in bulk powder, pharmaceutical formulations and simulated intestinal fluid (SIF) without sophisticated separation techniques.

The inhibition effect of 2- amino, 5- ethyl- 1, 3, 4 thiadiazole (TTD) compound on the corrosion of type 304 stainless steel in 3 M H2SO4 test solution was investigated using potentiodynamic polarization, weight loss techniques and open circuit potential measurements. Results showed TTD to be very effective with an average inhibition efficiency of 98% from weight loss analysis and 87% from polarization test. Data from open circuit potential measurement are well within passivation potentials at specific concentrations of TTD. Scanning electron microscopy showed the effect of the inhibiting compound on the surface topography of the steel, while X - ray diffractometry determined the phase compounds formed on the surface due to inhibitor adhesion. Adsorption of the compound was determined to obey the Langmuir isotherm model. Thermodynamic calculations showed the inhibition process occurred through chemisorption mechanism and results from statistical analysis revealed the overwhelming influence of inhibitor concentration over exposure time on the inhibition performance of the compound.

Poly para aminophenol (PpAP)/Al2O3 composite was prepared by in situ chemical polymerization of para aminophenol using ammonium persulphate as an oxidizing agent in an aqueous medium containing anionic surfactants like DBSA (dodecyl benzene sulphonic acid) and SDS (sodium dodecyl sulphate) at 0 ˚C. The synthesized composites were characterized by UV–VIS-NIR spectroscopy, FTIR, XRD and TGA. The inhibiting effect of synthesized composites on the corrosion of mild steel in 1 M HCl solution has been investigated by different techniques like potentiodynamic polarization and electrochemical impedance spectroscopy methods for four different concentrations ranging from 50 to 300 mg/L. The results indicated that the corrosion inhibition efficiency increased on increasing composites concentration till 200 mg/L and decreased on further increasing concentration. It has been found that PpAP/Al2O3-DBSA has got higher corrosion protection efficiency than that of PpAP/ Al2O3-SDS. Polarization studies reveal that composites act as a mixed type corrosion inhibitor and adsorption follows Langmuir adsorption isotherm.

The electrochemical properties of rhodium(III) 1-3 and iridium(III) 4-6 complexes containing bis(pyrazolyl)alkane ligands [MCp*Cl(R2C(3,5-R’2pz)2)]X (M = Rh (1) or Ir (4), R = R’ = H, X = Cl; M = Rh (2) or Ir (5), R = H, R’ = Me, X = Cl; M = Rh (3) or Ir (6), R = Me, R’ = H, X = OTf; pz = pyrazolyl; Cp* =h5-C5Me5) were investigated by cyclic voltammetry and controlled potential electrolysis. They exhibit two sequential irreversible reductions assigned to the M(III) -> M(II) and M(II) ->M(I) reductions, which are dependent on the methylation of the bis(pyrazolyl)alkane ligands.

The inhibition performance of a non-oxidising surfactant, namely cetyl trimethyl ammonium bromide (CTAB), and its co-adsorption behaviour with zinc ion on carbon steel in well water was studied by potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), weight loss, as well as atomic force microscopy (AFM) and scanning electron microscopy. Results indicated that the formulation acted as an anodic inhibitor. Adsorption of the used inhibitor led to a reduction in the double layer capacitance and an increase in the charge transfer resistance. A synergistic effect was also observed for the studied inhibitor with Zn(II) in weight loss measurements and electrochemical studies.

The inhibition effect of Mentha pulegium extract (MPE) on the acid corrosion of carbon steel in 1 M HCl solution was investigated using weight loss, potentiodynamic polarisation, and electrochemical impedance spectroscopy. The results show that the Mentha pulegium extract is a good inhibitor, and that the inhibition efficiency depends on the concentration of the plant extract. Efficiency is higher than 88 % for 33% Mentha pulegium extract. Polarization measurements also show that Mentha pulegium extract is a good mixed inhibitor. The remarkable inhibition efficiency of MPE was discussed in terms of blocking of the electrode surface by adsorption of inhibitor molecules through active centres. Mentha pulegium extract is adsorbed on the carbon steel surface according to the Temkin adsorption model. The effect of temperature on the corrosion behaviour of carbon steel in 1 M HCl with addition of 33% MPE was studied in the temperature range 308-338 K. SEM also confirmed the adsorption of MPE on carbon steel surface.

In this study polypyrrole (PPy) bilayers films were electrodeposited onto SAE 4140 steel. The inner layer was electropolymerized in the presence of molibdate and nitrate and the outer layer in a solution containing sodium bis (2-ethylhexyl) sulfosuccinate (AOT). The electrosynthesis was done under potentiostatic conditions. The corrosion protection properties of the films were examined in sodium chloride solution by open circuit measurements, linear polarization and electrochemical impedance spectroscopy (EIS). The bilayer coatings present an improved anticorrosive performance with respect to single PPy films.

Electroreduction properties of salicylic (SA) and acetylsalicylic (ASA) acids were investigated at platinum electrode using the voltammetry method. Cyclic voltammograms (CV) of the tested compounds were used in determining half-wave potential (E1/2) - the parameter describing the anti-reductive properties. The content of active substances (SA and ASA) in the selected pharmaceuticals (salicylic alcohol, Bayer aspirin, etopirin and polopirin) was examined with the application of electrochemical and spectrophotometric methods.

Examination of the physical (colour, odour, pH, solubility in various solvents) and chemical (GCMS and FTIR) characteristics of Ficus benjamina gum revealed that the gum is yellowish in colour, mildly acidic and ionic in nature. Major constituents of the gums were found to be sucrose and d-glucose, which constituted 60.92 % of their chemical constituents, while various carboxylic acids [(albietic acid (1.00%), hexadecanoic acid (4.41 %), 9-octadecanoic acid (1.00 %), octadecanoic acid (3.01 %), oleic acid (0.10 %), octadecanoic acid (9.12 %) and 6,13-pentacenequinone (20.43 %)] accounted for the remaining constituents. Functional groups identified in the gum were found to be those typical for other carbohydrates. From the knowledge of the chemical structures of compounds that constitute the gum, the corrosion inhibition potentials of the gum were ascertained and from weight loss analysis, the gum was found to be an active inhibitor against the corrosion of aluminum in solutions of tetraoxosulphate (VI) acid. The gum acted as an adsorption inhibitor that favours the mechanism of chemical adsorption and supported the Frumkin and Dubinin-Radushkevich adsorption models.

Electrochemical monitoring techniques were employed in this study to assess anticorrosion performance of Phyllanthus muellerianus leaf-extract on concrete steel-reinforcement in 0.5 M H2SO4, used for simulating industrial/microbial environment. For this, steel-reinforced concretes admixed with different concentrations of the natural plant leaf-extract were partially immersed in the acidic test-solution and subjected to electrochemical monitoring of corrosion potential, corrosion current and corrosion rate. Test responses analysed as per ASTM G16¬-95 R04, showed that the corrosion rate correlated, r = 84.93%, ANOVA p-value = 0.0403, with the leaf-extract concentration admixed in concrete and the ratio of the standard deviation of potential to the standard deviation of current. These identified the 0.3333% Phyllanthus muellerianus (per weight of cement) with optimum effectiveness at inhibiting steel-reinforcement corrosion both by the experimental model, η = 91.662.51%, and by the prediction from the correlation fitting model, η = 85.5414.44%. Fittings of both the experimental and the predicted data followed the Flory–Huggins and the Frumkin adsorption isotherms which suggest prevalent mechanism of physical adsorption (physisorption) of the extract on steel-rebar surface. These support the use of Phyllanthus muellerianus as environmentally-friendly admixture for inhibiting concrete steel-reinforcement corrosion in the industrial/microbial service-environment.