Papers by Keyword: Hydrogen Evolution

Abstract: Presented paper studies corrosion kinetics of zinc dust in cement paste using acoustic emission and impedance spectroscopy (measurement of electric resistance of compact samples) method. The focus is on determination of hydrogen evolution period and its effect on porous structure of cement paste. Results more or less confirm results of other authors that the corrosion products of zinc are unable to efficiently fill the pores forming due to hydrogen. Time period of hydrogen evolution - cathodic corrosion reaction of zinc in alkaline environment of cement paste can be up to several days long. Keywords: hot-dip galvanized reinforcement, corrosion of zinc dust, acoustic emission method, hydrogen evolution, porosity of cement paste, electrochemical impedance spectroscopy

Abstract: Magnesium has been developed as a biodegradable bone implant material due to its similarity in elasticity modulus of bone. However, magnesium has a higher corrosion rate and a lower strength. Gadolinium is alloyed to magnesium in order to improve the corrosion resistance and then rolled to improve the strength due to grain refinement in rolling. Cold roll produced the finest grain, but magnesium has a poor formability. Due to this fact, warm rolling with temperature 247 – 375 oC is applied. Optical Microscope, Scanning Electron Microscope (SEM), and Energy Dispersive Spectrometry (EDS) are used for characterization. Electrochemical Impedance Spectroscopy (EIS) and Polarization test were carried out to observe the corrosion mechanism of Mg-Gd in SBF Kokubo to replicate a human body condition. The result of polarization test shows that the cross-rolled sample experienced an increase in E corr, with 0,15 and –0,048 V due to a better distribution of Gadolinium. EIS states that the single pass rolled sample has a stronger passive layer with 116 and 126 kΩ value of Rf due to a smaller grain size which resulted a fewer compression stress. The hydrogen evolution was also observed with immersion test. Keywords: uni-directional rolling, cross-directional rolling, corrosion, simulated body fluid, hydrogen evolution.

Abstract: In this study, the influence of varying sulphuric acid – sodium chloride electrolyte composition to the electrochemical noise behaviour of a high-alloy cast steel was analysed. The noise analysis was carried out in a bare 0.1 M sulphuric acid solution, in a pure 5 wt.% sodium chloride solution and three solutions with defined ratios of both. The electrochemical current noise signal was recorded with a sampling rate of 100 Hz for 1 hour in each test solution. For the identification of the frequency content of notified characteristic transients, the current-time records were analysed by the continuous wavelet transform (CWT). The characteristic transients were extracted from the noise signal for a further analysis of their frequency and amplitude characteristics. The results show high-frequency transients in the bare sulphuric acid and low-frequency transients in the pure sodium chloride solution. In the combined electrolyte solutions the portion of low-frequency components increases when the NaCl content increases and indicates the enhancing influence of localised damage evolution processes at the steel surface.

Abstract: Binary Mg-Ca and ternary Mg-Ca-Zn alloys are a new group of magnesium materials, which can be used in many goods. Among others, biomedical applications of these alloys mainly involved surgical implants in the form of plates or screws. In order to improve mechanical properties and corrosion resistance of Mg-based alloys with Ca and Zn addition in as-cast state a plastic deformation was applied by using the KOBO extrusion method. The microstructure studies conducted by scanning microscopy show that the structure of the alloys after the plastic deformation exhibits banding character and the bands are oriented in the direction of an extrusion. A significant increase of mechanical properties was observed for MgCa5Zn1 alloy. After the plastic deformation, the corrosion potential determined for the MgCa5 and MgCa5Zn1 alloy is shifted into the positive direction, which may suggest the increase of corrosion resistance. Moreover, the MgCa5 alloy in as-cast state was completely dissolved after 288 h of immersion in Ringer’s solution. A volume of hydrogen evolution for the same alloy after plastic deformation showed a value of 35 ml/cm².

Abstract: In this work, a novel and facile sequential cation-exchanging strategy was developed to synthesize phosphorus doped g-C₃N₄ nanotubes, and resulted nanotubes were composed of small nanorods with length of several hundred nanometers by oriented aggregation. As obtained products exhibit greatly enhanced photocatalytic hydrogen evolution with rate of 4.59 mmol h^-1 g^-1, which is 16 times higher than that of the bulk g-C₃N₄ under visible light irradiation. Mechanism investigation reveals that the superior photocatalytic property could be attributed to its improved visible light absorbance, well suppressed charges recombination and nanostructural construction.

Abstract: Nickel foam-based Ni-Mo alloy electrodes, Ni+Mo composite electrodes and Ni+Mo/Ni-Mo composite alloy electrodes were prepared by eletrodeposition, and the electrocatalytic characteristics for hydrogen evolution reaction (HER) in 30wt% KOH solution were investigated by cathode polarization curve and electrochemical impedance spectroscopy (EIS). The experimental results show that in comparison with nickel foam electrodes, these electrodes exhibit a lower overpotential, a higher exchange current density and a larger real surface area for HER. At 30°C and current density of 200 mA/cm², the overpotentials of foam Ni electrodes, nickel foam-based Ni-Mo alloy electrodes, Ni+Mo composite electrodes, Ni+Mo/Ni-Mo electrodes are respectively 506, 252, 336, 202 mV. The nickel foam-based Ni+Mo/Ni-Mo composite alloy electrode had the highest HER electrocatalytic activity.

Abstract: The amorphous-nanocrystal Ni-Mo deposits were obtained by electrodeposition in alkaline nickel carbonate solution. X-ray diffraction (XRD), scanning electron microscopy (SEM) and modern technologies were used to describe the content, microstructure and morphology of the deposits. The electrochemical characteristics of Ni-Mo deposits were electrolyzed in 33°C, 7 mol/L NaOH electrolytic solutions. The results showed that when I was 100 mA·cm⁻², the hydrogen evolution potential of Ni-Mo_21.76 was lower than amorphous Ni-Mo_26.36 and 250mV lower than the nanocrystal Ni cathode. And the Ni-Mo deposits with more amorphous phase content would be in lower hydrogen evolution overpotential, a higher exchange current density, and a better electrolytic stability. These due to the amorphous combined with nanocrystal, lager contact surface and binding energy of Ni-Mo structure.

Abstract: In this study, we can fabricate Cu₂O on F-doped SnO₂ coated glass (FTO) substrates as photocathode for hydrogen evolution reaction by electro-deposition techniques. Cyclic voltammetry as a new deposition method was studied to fabricate Cu₂O photocathode in a mixed solution of Cu (NO₃)₂ and KNO₃ under a condition of low temperature and without pH value adjustment. Amperometry as a previous method was used to compare for Cu₂O electrode fabrication under the situation of pH adjustment and higher temperature condition. A photocurrent from hydrogen evolution reaction was performed by keep potential at-0.2 V in 0.1 M Na₂SO₄ under visible irradiation comparing with both fabricated method. The Cu₂O photocathode from cyclic voltammetry deposition method presents photoelectrocatalytic activity higher than that of amperometry deposition method with the optimum conditions. This electro-deposition technique represents the excellent method with simple, fast and low cost of Cu₂O photocathode fabrication for photoelectrochemical hydrogen evolution reaction.

Abstract: This paper presents the corrosion behavior of the composite Mg-10wt.% bio-glass (45S5) with different concentration of Zn. Bio-glass (BG) was added to the composite in order to improve bioactivity behavior of magnesium. The composite was fabricated by mixing, compacting followed by sintering. Composites was compacted at 550 MPa and sintered at 450°C under an argon atmosphere. Corrosion behavior was investigated by the immersion test. Sintered samples were immersed in 0.9 % NaCI solution and monitored by hydrogen evolution and XRD analysis. The results showed that hydrogen evolution rate decreased with addition of Zn content. The microstructure and phase analysis were observed by optical microscope, scanning electron microscope and x-ray diffraction.

Abstract: The corrosion behaviour of AM60 magnesium alloy containing 1.88 wt.% Cd in 0.1 M NaCl solution was investigated by weight loss and hydrogen evolution measurements. The microstructure was evaluated using EPMA. Cd was observed to have an even distribution, hence, no new phase was formed. The corrosion resistance was enhanced by the addition of Cd. The rate of corrosion reduced by a factor of 1.5 times that of AM60 alloy. The microstructure played a crucial role as the presence of defects in the alloys initiated and accelerated corrosion.