Mohammed A. Amin

Corrosion inhibition of aluminum by 1,1(lauryl amido)propyl ammonium chloride in HCl solution

Abstract The corrosion inhibition characteristics of 1,1(lauryl amido)propyl ammonium chloride, as a cationic surfactant (CS), on aluminum in HCl solution have been studied in the temperature range 10–60°C by means of weight loss, potentiodynamic polarization and electrochemical impedance spectroscopic (EIS) techniques. Results obtained show that the inhibition occurs through adsorption of the surfactant on the metal surface without modifying the mechanism of corrosion process. The surfactant acts predominately as anodic inhibitor. The inhibition efficiency increases with an increase in the surfactant concentration, but decreases with an increase in temperature. Maximum inhibition is observed around its critical micelle concentration (CMC). Frumkin isotherm fits well the experimental data. Thermodynamic functions for both dissolution and adsorption processes were determined. Results obtained from the three methods are in good agreement.

Reduced graphene oxide nanosheets decorated with Au, Pd and Au–Pd bimetallic nanoparticles as highly efficient catalysts for electrochemical hydrogen generation

Reduced graphene oxide (rGO) nanosheets decorated with gold nanoparticles (Au NPs/rGO), palladium nanoparticles (Pd NPs/rGO), and gold–palladium bimetallic nanoparticles (Au–Pd NPs)/rGO are synthesized by a simple solution chemistry approach using ascorbic acid as an eco-friendly reducing agent. These materials are characterized by high resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), high-angle annular diffraction field-scanning transmission electron microscopy (HAADF-STEM) and thermogravimetric analysis (TGA). The as-prepared nanocomposites are tested as electrocatalysts for efficient hydrogen evolution in deaerated 0.5 M H2SO4 aqueous solution using polarization and impedance measurements. Experimental findings show that the tested catalysts exhibit fast hydrogen evolution kinetics with onset potentials as low as −17, −7.2, and −0.8 mV vs. RHE for Au NPs/rGO, Pd NPs/rGO, and Au–Pd NPs/rGO, respectively. In addition, Tafel slopes of 39.2, 33.7 and 29.0 mV dec−1 and exchange current densities of 0.09, 0.11, and 0.47 mA cm−2 are measured for Au NPs/rGO, Pd NPs/rGO, and Au–Pd NPs/rGO, respectively. The tested materials not only maintain their high performance after 5000 sweep cycles, but their activity is simultaneously enhanced after this aging process. These findings reveal that the tested catalysts, particularly Au–Pd NPs/rGO, are promising candidates among other noble metal catalysts for hydrogen evolution, approaching the commercial Pt/C catalyst (onset potential: 0.0 mV, Tafel slope: 31 mV dec−1, and exchange current density: 0.78 mA cm−2). The high hydrogen evolution reaction (HER) activity of such materials is likely due to the abundance of active catalytic sites, the increased electrochemically accessible surface area and significantly improved electrochemical conductivity.

Electrochemical Behaviour of a Silver Electrode in NaOH Solutions

Summary. Studies of the electrochemistry of metals and alloys are very important fields of scientific and industrial work. The present investigation includes detailed studies on the corrosion and electrochemical behaviour of Ag in aqueous NaOH solutions under various conditions using cyclic voltammetry, chronoamperometry, and potentiostatic techniques. It was found that the anodic polarization curve of Ag in NaOH solutions is characterized by the occurrence of five anodic peaks (A1–A5). A1 is due to the electroformation of soluble [Ag(OH)2]− complex species, A2 to the electroformation of Ag2O, A3 to nucleation and three dimensional growth of the Ag2O layer, A4 to the formation of AgO, and A5 presumably to the formation of Ag2O3. X-ray diffraction patterns confirmed the existence of passive Ag2O and AgO layers on the electrode surface potentiodynamically polarized up to oxygen evolution.The cathodic part of the cyclic voltammograms is characterized by the occurrence of an activated anodic peak (A6) corresponding to the electrooxidation of Ag to Ag2O and three cathodic peaks (C1, C2, C2′) corresponding to the electroreduction of AgO to Ag2O and Ag2O to Ag, respectively.Zusammenfassung. Die Elektrochemie von Metallen und Legierungen stellt ein wichtiges Arbeitsgebiet in Forschung und Industrie dar. Die hier vorgestellte Untersuchung beinhaltet detaillierte Studien zur Korrosion und zum elektrochemischen Verhalten von Silber in wäßrigen Natriumhydroxidlösungen mittels cyclischer Voltammetrie, Chronoamperometrie und potentiostatischer Techniken. Die anodische Polarisationskurve von Ag in NaOH wird durch das Auftreten von fünf anodischen Peaks (A1–A5) charakterisiert. A1 resultiert aus der elektrochemischen Bildung von löslichen komplexen Species des Typs [Ag(OH)2]−, A2 aus jener von Ag2O, A3 geht auf Keimbildung und dreidimensionales Wachstum der Ag2O-Schicht zurück, A4 auf die Bildung von AgO, und A5 wird vermutlich durch die Bildung von Ag2O3 verursacht. Röntgendiffraktionsmuster bestätigen die Existenz passiver Ag2O- und AgO-Schichten an der Elektrodenoberfläche bei potentiodynamischer Polarisation bis zur Wasserstoffentwicklung.Der kathodische Teil der cyclischen Voltammogramme wird durch einen aktivierten anodischen Peak (A6, entsprechend der Elektrooxidation von Ag zu Ag2O) und drei kathodische Peaks (C1, C2, C2′, entsprechend der Elektroreduktion von AgO zu Ag2O und von Ag2O zu Ag) charakterisiert.

Galvanostatic anodization of pure Al in some aqueous acid solutions Part I: Growth kinetics, composition and morphological structure of porous and barrier-type anodic alumina films

The growth kinetics of anodic films formed on the surface of high purity Al by anodization under galvanostatic conditions at current densities in the range 5–75 mA cm−2 in thermostatically controlled and vigorously stirred solutions of chromic, sulfuric, phosphoric, citric, tartaric and oxalic acids at different temperatures, were studied. It has been shown that chromic acid solution produces a typical barrier type oxide growth at any given temperature, while the specific kinetic curve representing the combined barrier/porous type film growth is observed when the anodization process is carried out in a nonstirred chromic acid solution. The oxide growth in the rest of the anodizing solutions occurs in different ways depending on the bath temperature. Barrier oxide growth is observed at temperatures lower than 30 °C. Above this temperature, combined barrier/porous oxide growth is observed. In all cases, the slope of the linear part of the potential against time curves, and therefore the rate of barrier oxide growth, increases with increasing anodizing current density and acid concentration, while it decreases with increase in temperature. The composition and surface morphology of the anodic films have been studied by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and atomic force microscopy (AFM).

Perchlorate Pitting Corrosion of a Passivated Silver Electrode

Summary. The passivation and pitting breakdown of a silver electrode in sodium hydroxide solutions containing sodium perchlorate was studied using potentiodynamic and potentiostatic techniques. In perchlorate-free alkali solution, the voltammogram exhibits three anodic peaks prior to oxygen evolution. The first two peaks correspond to the oxidation of Ag and formation of a passive film of Ag2O on the electrode surface, the third to the conversion of Ag2O to AgO. In the presence of ClO4−, the voltammogram depends considerably on perchlorate concentration. ClO4− increases the height of the three anodic peaks, and at potentials above a limiting value breakdown of the anodic passivity and initiation of pitting corrosion occurs. The pitting potential decreases linearly with ClO4− concentration but increases with scan rate. The potentiostatic current/time transients show that pitting corrosion can be described in terms of an instantaneous three dimensional growth under diffusion control.Zusammenfassung. Passivierung und Lochfraßkorrosion einer Silberelektrode in Natriumperchlorat enthaltenden Natriumhydroxidlösungen wurden mit potentiodynamischen und potentiostatischen Methoden untersucht. In perchloratfreier alkalischer Lösung zeigt das Voltammogramm vor Beginn der Sauerstoffentwicklung drei anodische Peaks. Die ersten beiden entsprechen der Oxidation von Ag und der Bildung einer passivierenden Ag2O-Schicht auf der Elektrodenoberfläche, der dritte einer Umwandlung von Ag2O in AgO. In Gegenwart von ClO4− wurde eine ausgeprägte Abhängigkeit der Voltammogramme von der Perchloratkonzentration festgestellt. Durch die Anwesenheit von ClO4− wird die Intensität der drei anodischen Peaks erhöht, und ab einem gewissen Potential bricht die Passivierung unter Eintreten von Lochfraßkorrosion zusammen. Das Lochfraßpotential nimmt linear mit der Konzentration von ClO4− ab und steigt mit der Scangeschwindigkeit. Die potentiostatischen Strom/Zeit-Diagramme zeigen, daß die Lochfraßkorrosion als diffusionskontrolliertes dreidimensionales Wachstum charakterisiert werden kann.

Aluminum Titania Nanoparticle Composites as Nonprecious Catalysts for Efficient Electrochemical Generation of H2

In this paper, we demonstrated, for the first time, aluminum titania nanoparticle (Al-TiO2 NP) composites with variable amounts of TiO2 NPs as nonprecious active catalysts for the electrochemical generation of H2. These materials were synthesized by mixing desired amounts of hydrogen titanate nanotubes (TNTs), fabricated here by a cost-effective approach at moderate hydrothermal conditions, with aluminum powder (purity 99.7%; size 35 μm). The mixture was compacted under an applied uniaxial stress of 300 MPa followed by sintering at 500 °C for 1 h. After sintering had been completed, all TNTs were found to convert to TiO2 NPs (average particle size 15 nm). Finally, Al-xTiO2 NP nanocomposites (x = 1, 3, 5, and 10) were obtained and characterized by scanning electron microscopy/energy-dispersive X-ray, X-ray diffraction, and X-ray photoelectron spectroscopy. The hydrogen evolution reaction (HER) activity of these materials was studied in 0.5 M H2SO4 at 298 K using polarization and impedance measurements. The nanocomposite of chemical composition Al-5% TiO2 NPs showed the best catalytic performance for the HER, with an onset potential (EHER), a Tafel slope (βc), and an exchange current density (j0) of -100 mV (RHE), 59.8 mV decade(-1), and 0.14 mA cm(-2), respectively. This HER activity is not far from that of the commercial platinum/carbon catalyst (EHER = 0.0 mV, βc = 31 mV dec(-1), and j0 = 0.78 mA cm(-2)). The best catalyst also exhibited good stability after 10000 repetitive cycles with negligible loss in current.

Catalytic impact of alloyed Al on the corrosion behavior of Co50Ni23Ga26Al1.0 magnetic shape memory alloy and catalysis applications for efficient electrochemical H2 generation

The electrochemical and corrosion behaviour of Co50Ni23Ga27−xAlx (x = 0 and 1.0 wt%) magnetic shape memory alloys (MSMAs) was studied in 0.5 M NaCl solutions using various electrochemical techniques. Results showed remarkable activation of the tested MSMA toward pitting corrosion upon alloying it with Al. XPS examination confirmed the activation influence of alloyed Al. It proved that the presence of Al in the alloys matrix weakens its passivity, as manifested by a lower amount of gallium oxides and Cl− adsorption in the aluminium containing MSMA sample. Alloyed Al also activated significantly the tested MSMA for the hydrogen evolution reaction (HER), as indicated by cathodic polarization, electrochemical impedance spectroscopy (EIS), and faradaic efficiency (FE) measurements. Such measurements were performed in 0.1 M KOH solutions and showed that the Co50Ni23Ga26Al1.0 alloy is much more active for the HER than Co, Ni, Co50Ni50, and Co50Ni23Ga27 electrodes. The catalytic impact of pitting corrosion, proved to be catalyzed by Al, on the HER activity of the CoNiGaAl alloy was also studied. The pitted Co50Ni23Ga26Al1.0 MSMA, the best catalyst here, exhibited high HER catalytic performance with an exchange current density (jo) of 0.2 mA cm−2 and FE 96%, and thus approached Pt/C (jo = 0.6 mA cm−2 and FE ∼ 100%). Our best catalyst also showed good stability and durability after 3000 cycles of cathodic polarization between the corrosion potential (Ecorr) and −1.0 V vs. RHE, and 24 h of electrolysis at a high cathodic current density of 100 mA cm−2. Microstructure changes made by Al, together with findings obtained from SEM/EDX mapping and XPS studies, were used to interpret its activation influence towards the HER.

Inhibition Performance and Adsorptive Behavior of Three Amino Acids on Cold-Rolled Steel in 1.0 M HCl—Chemical, Electrochemical, and Morphological Studies

Three selected amino acids, namely, serine (Ser), threonine (Thr), and glutamine (Glu), were tested as corrosion inhibitors for cold-rolled steel (CRS) in 1.0 M hydrochloric acid (HCl) solutions at different temperatures (283 K to 333 K). Chemical (weight loss) and electrochemical (Tafel polarization) methods were used in this study. Electrochemical frequency modulation (EFM), a non-destructive corrosion measurement technique that can directly give values of corrosion current without prior knowledge of Tafel constants, was also used. Experimental corrosion rates determined by the Tafel extrapolation method were compared with those obtained using the EFM technique and the weight-loss method. Morphologies of the corroded and the inhibited surfaces were studied by means of atomic force microscopy (AFM) and scanning electron microscopy (SEM). Tafel plots showed that the three tested amino acids act as mixed-type inhibitors. The three tested amino acids appeared to function through adsorption following the Tem...

Pitting Corrosion of Zinc in Na2S2O3Solutions. Part I. Polarization Studies and Morphology of Pitting

Abstract As a first step towards studying pitting corrosion of Zn in aerated neutral 1.0 M sodium thiosulphate solution (pH 6.6), we have reported the results of cyclic polarization measurements on the passivity and passivity breakdown of Zn in this solution. The recorded voltammograms involved two oxidation processes labeled as AI and AII, and two reduction processes labeled as CII and CI on the forward (anodic) and reverse (cathodic) scans, respectively. The cathodic peak CII was attributed to the reduction of the pitting corrosion products (process AII). On the other hand, the cathodic process CI was related to the reduction of Zn2+ species formed during the course of the forward scan (process AI and the subsequent formation of the passive region), and the reduction of the adsorbed S2O32− anions to S2− and SO32−. The reduction products of S2O32−, namely S2− and SO32− anions, were detected in solution as a function of starting potential and time of holding the electrode at a cathodic potential of −2.0 V (Ag/AgCl). These anions were found to cooperate with the aggressive S2O32− anion itself in passivity breakdown and initiation of pitting corrosion. The effect of solution temperature (15–70 ºC) on the cyclic polarization behaviour of Zn was also studied, and metastable and stable pitting events observed at high temperatures were discussed. The morphology of pitting was also studied by ex situ scanning electron microscopy (SEM) as a function of applied anodic potential, bulk concentration of S2O32− and solution temperature. Cross-sectional view of pits revealed the formation of irregular deep and shallow pits. The aspect ratios (the ratio of pit width to pit depth) of the growing pits were estimated as a function of potential, electrolyte concentration and solution temperature. The aspect ratio of the growing pits was found to be potential and concentration independent, while it increased with temperature.

Room-Temperature Wet Chemical Synthesis of Au NPs/TiH2/Nanocarved Ti Self-Supported Electrocatalysts for Highly Efficient H2 Generation

Self-supported electrocatalysts are a new class of materials exhibiting high catalytic performance for various electrochemical processes and can be directly equipped in energy conversion devices. We present here, for the first time, sparse Au NPs self-supported on etched Ti (nanocarved Ti substrate self-supported with TiH2) as promising catalysts for the electrochemical generation of hydrogen (H2) in KOH solutions. Cleaned, as-polished Ti substrates were etched in highly concentrated sulfuric acid solutions without and with 0.1 M NH4F at room temperature for 15 min. These two etching processes yielded a thin layer of TiH2 (the corrosion product of the etching process) self-supported on nanocarved Ti substrates with different morphologies. While F--free etching process led to formation of parallel channels (average width: 200 nm), where each channel consists of an array of rounded cavities (average width: 150 nm), etching in the presence of F- yielded Ti surface carved with nanogrooves (average width: 100 nm) in parallel orientation. Au NPs were then grown in situ (self-supported) on such etched surfaces via immersion in a standard gold solution at room temperature without using stabilizers or reducing agents, producing Au NPs/TiH2/nanostructured Ti catalysts. These materials were characterized by scanning electron microscopy/energy-dispersive spectroscopy (SEM/EDS), grazing incidence X-ray diffraction (GIXRD), and X-ray photoelectron spectroscopy (XPS). GIXRD confirmed the formation of Au2Ti phase, thus referring to strong chemical interaction between the supported Au NPs and the substrate surface (also evidenced from XPS) as well as a titanium hydride phase of chemical composition TiH2. Electrochemical measurements in 0.1 M KOH solution revealed outstanding hydrogen evolution reaction (HER) electrocatalytic activity for our synthesized catalysts, with Au NPs/TiH2/nanogrooved Ti catalyst being the best one among them. It exhibited fast kinetics for the HER with onset potentials as low as -22 mV vs. RHE, high exchange current density of 0.7 mA cm-2, and a Tafel slope of 113 mV dec-1. These HER electrochemical kinetic parameters are very close to those measured here for a commercial Pt/C catalyst (onset potential: -20 mV, Tafel slope: 110 mV dec-1, and exchange current density: 0.75 mA cm-2). The high catalytic activity of these materials was attributed to the catalytic impacts of both TiH2 phase and self-supported Au NPs (active sites for the catalytic reduction of water to H2), in addition to their nanostructured features which provide a large-surface area for the HER.