Mohamed I. Awad

Tailor-Designed Platinum Nanoparticles Electrodeposited onto Gold Electrode Catalytic Activity for Oxygen Reduction

This work examines the electrocatalytic reduction of molecular oxygen at Pt nanoparticles (nano-Pt) electrodeposited onto polycrystalline gold (poly-Au) electrode in O 2 -saturated 0.5 M KOH. Cyclic and hydrodynamic voltammetry techniques were used for the evaluation of the electrocatalytic activity of the nano-Pt modified poly-Au electrodes. The nano-Pt was electrodeposited onto unmodified poly-Au electrode (nano-Pt/Au) and poly-Au electrode modified with a submonolayer (Au sm ) of a thiol compound (typically cysteine) (nano-Pt/Au sm ). In the latter case, Pt nanoparticles were electrodeposited, preferentially, at the bare fraction of the poly-Au electrode free from cysteine [i.e., the Au(111) domains of the poly-Au] while the other facets (i.e., Au(100) and Au(110)) were under the protection of cysteine. The nano-Pt electrodeposited onto the Au sm is characterized by small average particle size (ca. 10 nm) compared to that electrodeposited onto the unmodified Au electrode (ca. 50-100 nm). The nano-Pt/Au sm electrode offers a high electrocatalytic activity toward the oxygen reduction reaction (ORR) as compared with the nano-Pt/Au and bare polycrystalline Pt electrodes. A 60 mV positive shift of the onset potential of the ORR was obtained at the nano-Pt/Au sm electrode as compared to the bare Pt electrode. A proper design of the nano-Pt/Au binary catalyst is the key point which controls the catalytic activity of the proposed electrocatalyst.

Potentiometric analysis of peroxyacetic acid in the presence of a large excess of hydrogen peroxide

The potentiometric analysis of peroxyacetic acid (PAA) in the presence of a large excess of hydrogen peroxide (H2O2), up to 500 times the concentrations of PAA, has been presented for the first time. This method is based on the detection of the potential change of the glassy carbon indicator electrode in the I−/I2 potential buffer which is caused by the change in the concentrations of I− and I2 as a result of the redox reaction of the PAA and/or H2O2 with I−. Based on the fact that the reaction rate of PAA and I− is much faster than that of H2O2 and I−, a high selective response for PAA was obtained. The different factors, such as the concentrations of I− and I2 in the potential buffer, affecting the selectivity and sensitivity have been studied. A good calibration curve for PAA, the slope of which is in close agreement with that expected from the Nernst equation, i.e., 29.6 mV per decade, was obtained with a correlation coefficient higher than 0.993. The detection limit for PAA was found to be in the micromolar range depending on the concentration of the coexistent H2O2.

Electroreduction of Peroxyacetic Acid at Gold Electrode in Aqueous Media

The kinetics of electroreduction of peroxyacetic acid (PAA) has been studied at a gold electrode in acetate buffer solutions of pH in the range 3-6. The electroreduction of PAA was irreversible. The relevant kinetic parameters including the Tafel slope, the standard rate constant (k°), the electrochemical reaction order (m), the product (αn a ) of the transfer coefficient and the number of electrons involved in the rate-determining step, and the number (n) of electrons involved in the overall electrode reaction were determined using cyclic voltammetry, hydrodynamic voltammetry, and hydrodynamic chronocoulometry. The Tafel slope = 0.215 V/decade, m = 1, k° = 9.4 X 10 -11 cm s -1 , αn a = 0.32, and n = 2. The formal potential of the PAA/acetic acid redox couple was also theoretically calculated to be 1.762 V vs. Ag/AgCl based on the equilibrium constant for the reaction of PAA and hydrogen peroxide (H 2 O 2 ) in the presence of acid catalyst and the standard redox potential of H 2 O 2 . The diffusion coefficient of PAA was also estimated. Based on the obtained results, the overall electroreduction of PAA is considered to be composed of two one-electron reduction steps with the formation of acetate or hydroxyl radical as probable reaction intermediates.

Ozone Electrogeneration on Pt-Loaded Reticulated Vitreous Carbon Using Flooded and Flow-Through Assembly

Electrogeneration of ozone (O 3 ) was investigated at platinum-loaded reticulated vitreous carbon (RVC). Stationary and flowing H 2 SO 4 solutions, i.e., flooded and flow-through porous electrodes, respectively, were used at room temperature (25°C). The study evaluates the flow-through porous electrode for a continuous production of O 3 -aqueous solutions. O 3 was generated potentiostatically by applying a constant potential for 5 min. The flooded electrode showed a negligible O 3 current efficiency at the bare RVC compared to a value of 2.2% at the Pt-loaded RVC electrode (RVC/Pt). At the flow-through porous electrode, the effects of acid concentration and electrolyte flow rate on the concentration of O 3 generated and on the current efficiency of O 3 electrogeneration at RVC/Pt were explored. The O 3 concentration increased in the outlet stream with H 2 SO 4 concentration. The current efficiency did not change significantly with the electrolyte flow rate, but the higher concentration of O 3 in the outlet stream was obtained at lower flow rates. The current efficiency remained nearly unchanged but the specific electrical energy consumption (kWh kg -1 of O 3 ) decreased significantly with the acid concentration. The stability of the RVC/Pt electrodes was examined by measuring the time-course of the electrolysis current at a given applied potential and the scanning electron microscopy images of the electrode surfaces before and after the electrolysis.

Inhibitory action of quaternary ammonium bromide on mild steel and synergistic effect with other halide ions in 0.5 M H2SO4

The corrosion inhibition of mild steel in 0.5 M H2SO4 solution has been investigated using electrochemical methods, X-ray diffraction (XRD) and scanning electron microscope (SEM). The adsorption and inhibition action of acid corrosion of mild steel using cetyltrimethylammonium bromide (CTABr) and different halides (NaCl, NaBr and NaI) has shown synergetic effect. The results showed that the protection efficiency (P%) has high values at considerable high concentration of CTABr. However, in the presence of the different halides, the P increases dramatically at low concentration of CTABr. Physisorption was proposed from the the values of ΔGads0. The synergism parameter (Sθ) is found to be greater than unity indicating that the enhanced P% caused by the addition of the halides to the CTABr is due to a co-operative adsorption of both species. Corrosion products phases and surface morphology were studied using X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively.

ELECTROANALYSIS OF PERACETIC ACID IN THE PRESENCE OF A LARGE EXCESS OF HYDROGEN PEROXIDE

The simultaneous electroanalysis of peracetic acid (PAA) and H2O2 in the presence of a large excess of H2O2, up to hundred times the concentrations of PAA, has been presented for the first time. Square wave voltammetry using a gold electrode was successfully applied for this purpose. It was found that a careful electrochemical pretreatment of the gold electrode is the key for obtaining reproducible data. Good calibration curves for the reduction of both species were obtained with correlation coefficients higher than 0.996. The detection limit for PAA was found to be 45 μM.

Ozone electrogeneration on Pt-TaOy sol-gel film modified titanium electrode: Effect of electrode composition on the electrocatalytic activity

Abstract This work examines the ozone electrogeneration (OE) at a binary coating of different nominal compositions (Pt) x -(TaO y ) (100– x ) , where x (percentage in the precursor solution) varied between 1% and 100%, coated on titanium substrate prepared by a sol-gel technique. The OE is performed in an artificial tap water at room temperature (25°C). The percentages of Pt and TaO y in the coating significantly affect the electrocatalytic activity towards oxygen evolution. The oxygen evolution was retarded to a different extent based on the electrode composition. The largest retardation was obtained at the (Pt) 10 -(TaO y ) 90 electrode (ca. 480 mV positive shift) as compared with the (Pt) 100 -(TaO y ) 0 electrode. This was reflected in a high current efficiency (CE) of OE (ca. 19.3%) at the former electrode. This value is considered to be among the highest values reported for OE at 25°C in neutral media. The composite electrodes were characterized by voltammetric and surface techniques. A plausible explanation for the change of the efficiency of OE with the electrode composition is given based on the electrochemical results.

SPECTROPHOTOMETRIC QUANTIFICATION OF PEROXONE

A simple spectrophotometric method is proposed for the simultaneous quantification of the ozone (O3) and hydrogen peroxide (H2O2) mixture, the so-called peroxone. This method is based on the measurements of the absorbance of the produced by the oxidation of I– by peroxone. The oxidation rates of I– by O3 and H2O2 are largely different and pH-dependent and, moreover, the oxidation of I– by H2O2 can be accelerated by a molybdate catalyst. In addition, the present method was successfully applied at concentrations as low as 10 µM for the analysis of a real peroxone sample prepared by electrolysis of water.

Co-adsorption of a triazole derivative and copper ions on mild steel

The adsorption of 4-(3-methoxypropyl)-4H-1,2,4-triazole-3-thiol (MT) compound on mild steel in sulfuric acid solution both in the absence and presence of copper ions has been studied using potentiodynamic polarization technique. It has been found that the adsorption of MT on mild steel is not efficient; the surface coverage reached around 0.68 in the presence of ca. 1.0 mM MT. Interestingly it reached 0.75 in the presence of around one tenth of this concentration when 50 μM Cu2+ is added, with synergistic parameters 2.23 reflecting the enhanced adsorption of MT in the presence of copper ions. The reason behind the synergistic adsorption is investigated using cyclic voltammetric technique.

Electroanalysis of a Ternary Disinfectant Mixture

The analysis of a ternary mixture containing ozone (O3), sodium hypochlorite (NaClO), and hydrogen peroxide (H2O2), in their coexistence was simultaneously performed using a potentiometric method. In this method, the change in the open circuit potential of a Pt indicator electrode dipped in a potential buffer containing I−/ upon the addition of the ternary mixture is measured. The analysis was based on the different reaction kinetics of the three oxidants with I−. The kinetics of the reaction of O3 and I− is about three orders of magnitude faster than that of sodium hypochlorite, and the reaction of hydrogen peroxide and I− is negligible compared with those of O3 or hypochlorite ion and I− unless a molybdate catalyst is added. Several factors, including the iodide concentration, pH, and the molybdate concentration were investigated to optimize the analysis and achieve a reasonable separation among the reactions of the three oxidants and I−. A theoretical model was developed to compare with the experimental results and a reasonable correlation was obtained.