Hydrogen Evolution Measurements Research Articles

Effects of Li on Microstructures, Mechanical, and Biocorrosion Properties of Biodegradable Mg94‐xZn2Y4Lix Alloys with Long Period Stacking Ordered Phase

Mg94‐xZn2Y4Lix alloys (at%) (x = 0, 1, 5, 9, 13) are designed to develop a novel, biodegradable magnesium alloy. Microstructures evolution and mechanical properties are evaluated by using OM, XRD, SEM, and tensile tests. The biocorrosion behaviors of the alloys are investigated by using hydrogen evolution and electrochemical measurements. The precipitation of 18R LPSO phase is facilitated by a little Li (<1 at%), while exceeded Li (>1 at%) inhibits the formation of 18R LPSO phase and favors the formation of (Mg,Zn)24Y5 eutectic phase. The grain size of α‐Mg phase is refined with 5 at% Li. Besides the optimal combined mechanical properties (UTS = 190 MPa, elongation = 3.1%), the as‐cast Mg89Zn2Y4Li5 alloy has the lowest corrosion rate and the highest biocorrosion resistance, which are desirable for use as a biomaterial.

Efficient photoelectrochemical hydrogen production over p-Si nanowire arrays coupled with molybdenum–sulfur clusters

p-Si nanowire (Si-NW) arrays are successfully decorated with molybdenum–sulfur (MS) clusters by a drop-casting method. The composited photocathode (MS/Si-NW) demonstrated an enhanced photoelectrochemical (PEC) hydrogen production performance, with a photocurrent density of −14.3 mA/cm2 at a potential of 0 V vs. RHE under the illumination of the red part of simulated solar light (λ > 590 nm, 27.3 mW/cm2). The photocathode also showed a good stability in the long-term photocatalytic hydrogen evolution measurement, and the Faradaic efficiency of hydrogen production was close to 100%. Additionally, the morphological, optical and wetting properties of the photoelectrodes were investigated in detail. On the basis of the results, it could be concluded that the enhanced PEC performance is attributed to the high surface area, low light reflection and good wetting property of Si-NW, together with a low overpotential for hydrogen evolution reaction (HER) of the molybdenum–sulfur clusters.

Corrosion resistance of biodegradable polymeric layer-by-layer coatings on magnesium alloy AZ31

Biocompatible polyelectrolyte multilayers (PEMs) and polysiloxane hybrid coatings were prepared to improve the corrosion resistance of biodegradable Mg alloy AZ31. The PEMs, which contained alternating poly(sodium 4-styrenesulfonate) (PSS) and poly(allylamine hydrochloride) (PAH), were first self-assembled on the surface of the AZ31 alloy substrate via electrostatic interactions, designated as (PAH/PSS)5/AZ31. Then, the (PAH/PSS)5/AZ31 samples were dipped into a methyltrimethoxysilane (MTMS) solution to fabricate the PMTMS films, designated as PMTMS/(PAH/PSS)5/AZ31. The surface morphologies, microstructures and chemical compositions of the films were investigated by FE-SEM, FTIR, XRD and XPS. Potentiodynamic polarization, electrochemical impedance spectroscopy and hydrogen evolution measurements demonstrated that the PMTMS/(PAH/PSS)5/AZ31 composite film significantly enhanced the corrosion resistance of the AZ31 alloy in Hank’s balanced salt solution (HBSS). The PAH and PSS films effectively improved the deposition of Ca-P compounds including Ca3(PO4)2 and hydroxyapatite (HA). Moreover, the corrosion mechanism of the composite coating was discussed. These coatings could be an alternative candidate coating for biodegradable Mg alloys.

In vitro Degradation of Pure Mg for Esophageal Stent in Artificial Saliva

Magnesium and its alloys as biodegradable implant materials can be potentially used in cardiovascular and orthopedic devices. However, few studies have focused on its application in esophageal stents. In this paper, time-lapse degradation characteristics of pure Mg were analyzed by scanning electron microscopy, energy dispersive spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy, hydrogen evolution, pH and electrochemical measurements after immersion in artificial saliva for different times. Results revealed that a dense degradation product film formed on samples, which mainly consisted of two kinds of layers: one was calcium phosphate compounds with different structures; the other was thin magnesium hydrate layer close to the substrate. Less pH increase and low degradation rate were observed in the first 5 days of immersion, which can be ascribed to the formation of a thicker and denser layer on the sample surface with increasing immersion time. And then there was an increase in degradation rate and pH values; the deposition layer remained almost intact after immersion for 6 and 8 days. After 10 days of immersion, the degradation rate and pH value remained stable, and the calcium phosphate layer was delaminated and the inner magnesium hydrate layer was exposed. This study indicated that pure Mg exhibited desirable degradation resistance in artificial saliva, which provided magnesium-based materials with the potential to be used as esophageal stents.

Experimental investigation and analysis of a novel photo-electrochemical hydrogen production cell with polymeric membrane photocathode

In this paper, a novel photo-electrochemical cell for hydrogen production is developed, tested and analyzed based on exergy method. As novelty, a membrane photo-electrode assembly (MPEA) is fabricated by electro-deposition of CuO/Cu2O semiconductor photo-catalysts on the cathode surface such that a polymeric membrane photocathode is formed. The reactor has a planar construction consisting of two half-cells separated by the MPEA with a total surface of 200 cm2. The MPEA is pre-doped with platinum electro-catalyst both at anode and cathode. Both dark-exposure and light-exposure tests using voltammetry clearly demonstrate the beneficial effect of the photocathode which enhances the rate of hydrogen production by increasing the current density and lowering the bias voltage. In addition, hydrogen evolution measurements confirm the cell functionality and allowed for efficiency determination. The experimental work is also used to validate a simple phenomenological model based on an electric equivalent diagram of the photo-electrochemical process which further is used to quantify the various kinds of irreversibility by evaluation of the exergy destructions.

Effect of <i>Catharanthus roseus</i> (<i>Vince rosea</i>) and Turmeric (<i>Curcuma longa</i>) Extracts as Green Corrosion Inhibitors for Mild Steel in 1 M HCl

The corrosion inhibition of mild steel by Catharanthus roseus (Vince rosea) and Turmeric (Curcuma longa) extracts as green inhibitors in 1 M HCl solutions has been investigated by using potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), hydrogen evolution measurements and scanning electron microscope (SEM) techniques. Results obtained show that these investigated compounds are good inhibitors and act as mixed type inhibitors. The inhibition efficiencies increase with increasing inhibitor concentration. The SEM results show the formation of protective film on the mild steel surface in the presence of Catharanthus roseus and Turmeric extracts. The results obtained from different tested techniques are in good agreement.

Effect of Precipitated Phases on Corrosion of Mg95.8Gd3Zn1Zr0.2 Alloy with Long-Period Stacking Ordered Structure

The microstructure of the precipitated phases of Mg95.8Gd3Zn1Zr0.2 alloys with long-period stacking ordered structure before and after heat treatment is discussed. The corrosion properties of the as-cast (F), solid-solution (T4) and aging-treated (T6) alloys in 1% NaCl solution are studied. The hydrogen evolution and electrochemical measurements display that the as-cast Mg95.8Gd3Zn1Zr0.2 alloy with the continuous network eutectic phase exhibits the greatest corrosion resistance, while T6 sample with some needle-like phases and the particle phases is the worst among the three alloys. It is proposed to be mainly related to the amount, composition, microstructure and distribution of the precipitated phases.

Enhancement in hydrogen evolution using Au-TiO2 hollow spheres with microbial devices modified with conjugated oligoelectrolytes.

Objective:Although photoelectrochemical (PEC) water splitting heralds the emergence of the hydrogen economy, the need for external bias and low efficiency stymies the widespread application of this technology. By coupling water splitting (in a PEC cell) to a microbial fuel cell (MFC) using Escherichia coli as the biocatalyst, this work aims to successfully demonstrate a sustainable hybrid PEC–MFC platform functioning solely by biocatalysis and solar energy, at zero bias. Through further chemical modification of the photo-anode (in the PEC cell) and biofilm (in the MFC), the performance of the hybrid system is expected to improve in terms of the photocurrent generated and hydrogen evolved.Methods:The hybrid system constitutes the interconnected PEC cell with the MFC. Both PEC cell and MFC are typical two-chambered systems housing the anode and cathode. Au-TiO2 hollow spheres and conjugated oligoelectrolytes were synthesised chemically and introduced to the PEC cell and MFC, respectively. Hydrogen evolution measurements were performed in triplicates.Results:The hybrid PEC–MFC platform generated a photocurrent density of 0.35 mA/cm2 (~70× enhancement) as compared with the stand-alone P25 standard PEC cell (0.005 mA/cm2) under one-sun illumination (100 mW/cm2) at zero bias (0 V vs. Pt). This increase in photocurrent density was accompanied by continuous H2 production. No H2 was observed in the P25 standard PEC cell whereas H2 evolution rate was ~3.4 μmol/h in the hybrid system. The remarkable performance is attributed to the chemical modification of E. coli through the incorporation of novel conjugated oligoelectrolytes in the MFC as well as the lower recombination rate and higher photoabsorption capabilities in the Au-TiO2 hollow spheres electrode.Conclusions:The combined strategy of photo-anode modification in PEC cells and chemically modified MFCs shows great promise for future exploitation of such synergistic effects between MFCs and semiconductor-based PEC water splitting.

Corrosion resistance of flaky aluminum pigment coated with cerium oxides/hydroxides in chloride and acidic electrolytes

The objective of this study was to enhance the corrosion resistance of lamellar aluminum pigment through surface treatment by cerium oxides/hydroxides. The surface composition of the pigments was studied by energy-dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). The corrosion resistance of the pigment was evaluated by conventional hydrogen evolution measurements in acidic solution and electrochemical impedance spectroscopy (EIS) in 3.5% NaCl solution. Results showed that the Ce-rich coating composed of Ce2O3 and CeO2 was precipitated on the pigment surface after immersion in the cerium solution. The corrosion resistance of pigment was significantly enhanced after modification with cerium layer.

Synthesis, characterization and study of methyl 3-(2-oxo-2H-1,4-benzoxazin-3-yl) propanoate as new corrosion inhibitor for carbon steel in 1M H2SO4 solution

A new benzoxazin derivative, namely methyl 3-(2-oxo-2H-1,4-benzoxazin-3-yl) propanoate (1,4-MBXP), was synthesized under mild conditions from 2-aminophenols and dimethyl-2-oxoglutarate. The prepared compound was identified by FT-IR, 1H NMR, 13C NMR spectroscopies, elementary analysis and MS. Its inhibitive action against the corrosion of carbon steel in 1M H2SO4 solution was investigated by weight-loss and hydrogen evolution measurements. 1,4-MBXP is a good corrosion inhibitor and its inhibition efficiency increases with the increase of concentration to attain 75.08 % at 180 ppm. The temperature effect on the corrosion behaviour of carbon steel in 1M H2SO4 with and without the inhibitor at 180 ppm was studied in the temperature range from 298 to 338 K. The synergistic action caused by iodide ions on the corrosion inhibition of carbon steel in 1M H2SO4 by 1,4-MBXP at 180 ppm was studied using weight methods at 298 K. The inhibition efficiency synergistically increased on addition of potassium iodide.

Corrosion product layers on magnesium alloys AZ31 and AZ61: Surface chemistry and protective ability

This paper studies the chemical composition of the corrosion product layers formed on magnesium alloys AZ31 and AZ61 following immersion in 0.6M NaCl, with a view to better understanding their protective action. Relative differences in the chemical nature of the layers were quantified by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), energy dispersive analysis of X-ray (EDX) and low-angle X-ray diffraction (XRD). Corrosion behavior was investigated by Electrochemical Impedance Spectroscopy (EIS) and hydrogen evolution measurement. An inhibitive effect from the corrosion product layers was observed from EIS, principally in the case of AZ31, as confirmed by hydrogen evolution tests. A link was found between carbonate enrichment observed by XPS in the surface of the corrosion product layer, concomitant with the increase in the protective properties observed by EIS.

English

The effect of cantaloupe juice and seed extracts on corrosion of cast iron in 1.0 M hydrochloric acid (HCl) solution using hydrogen evolution measurements (HEM) and mass loss measurements (MLM) were investigated. Cantaloupe extracts inhibited the corrosion of cast iron in 1.0 M HCl solution. The inhibition efficiency increased with concentration of the extracts. The adsorption of the inhibitor molecules on cast iron surface was in accordance to Langmuir adsorption isotherms. In absence of inhibitors, the corrosion rate of cast iron increases with HCl concentration. The fractional reaction order observed in HCl solution indicates the formation of intermediates through the dissolution process or multiple steps mechanism of cast iron dissolution in HCl solution.   Key words: Cantaloupe (Cucumis melo), corrosion, cast iron, HCl concentrations, adsorption isotherm.

Correlation between electrochemical impedance measurements and corrosion rate of magnesium investigated by real-time hydrogen measurement and optical imaging

The corrosion behaviour of magnesium in chloride-containing aqueous environment was investigated by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) performed simultaneously with real-time hydrogen evolution measurements and optical imaging of the corroding surface. The potentiodynamic investigation revealed substantial deviations from linearity in close proximity of the corrosion potential. In particular, differences in the slope of the current/potential curves were observed for small polarizations above or below the corrosion potential. These observations, suggest that the usual method based on the use of the Stern–Geary equation to convert a value of resistance into a value of corrosion current is inadequate. Nonetheless, a very good correlation between values of resistances estimated by EIS and corrosion currents obtained from real-time hydrogen measurement was found. Real-time hydrogen measurement also enabled, for the first time, direct measurement of an ‘apparent’ Stern–Geary coefficient for magnesium. In order to rationalize the complex behaviours experimentally observed, an electrical model for the corroding magnesium surface is presented.

Significantly improved corrosion resistance of heat-treated Mg–Al–Gd alloy containing profuse needle-like precipitates within grains

Microstructural evolution of a new Mg–Al–Gd alloy during heat treatment and its corrosion behavior in 1wt.% NaCl solution were investigated by morphological observation, hydrogen evolution and electrochemical measurements. The microstructure of the as-cast alloy mainly consists of α-Mg, network-like Mg5Gd and polygonal Al2Gd phases, while a considerable part of Mg5Gd ones dissolve after T4 treatment. After T6 treatment, profuse micro-sized needle-like precipitates including crossed Mg5Gd-type and parallel Mg12ZnY-type ones appear and occupy different grains. These precipitates, resulting in homogeneous corrosion, continuous and compact oxidation film on the surface, have significantly improved the corrosion resistance of the Mg alloy.

Effect of Cadmium Addition on the Galvanic Corrosion of AM60 Magnesium Alloy in 0.1 M Sodium Chloride Solution

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.

Enhanced Corrosion Resistance of AZ91 Alloy Produced by Semisolid Metal Processing

Rheocast AZ91 magnesium alloy was evaluated in terms of microstructure and corrosion resistance. Rheocasting leads to a globular microstructure of α-Mg spheres separated by an interconnected β-Mg17Al12 (β-phase) network. Findings revealed that early stages of corrosion were located at the center of α-Mg globules and more importantly at α-Mg/β-phase interfaces due to galvanic coupling as predicted from surface potential maps. Electrochemical, hydrogen evolution and weight loss measurements demonstrated the superior corrosion resistance of the rheocast alloy. This was attributed to an improved barrier effect of the β-Mg17Al12 phase and, possibly, to a smaller area fraction of Al-(Mn,Fe) inclusions. For long immersion times, only small attacked areas were observed which corresponded to randomly corroded α-Mg globules.

The pH Dependence of Magnesium Dissolution and Hydrogen Evolution during Anodic Polarization

The dissolution of magnesium (Mg) has been investigated with an electrochemical flow cell coupled to downstream analysis. The setup allows for polarization experiments and simultaneous determination of the amount of dissolved magnesium ions via inductively coupled plasma - mass spectroscopy (ICP-MS). Additionally, Mg dissolution was compared to hydrogen evolution measurements in the flow cell and also in standard beakers. Experiments were performed in unbuffered NaCl and in buffered solutions of various pH to determine the influence of the pH on surface film stability and Mg dissolution. In borate buffer (pH 10.5), Mg(OH)2 was found to be more stable than in unbuffered electrolyte. In the flow cell, the negative difference effect (NDE) was absent for low anodic polarization currents in a neutral buffered solution, whilst high anodic polarization currents and unbuffered electrolytes favored its existence. In beaker experiments, strong NDE was observed in a pH 10.5 buffer, and also in pH 7 and 3 buffers, but only at higher applied currents where the buffering capacity was locally overwhelmed. These observations validate the importance of the pH in near surface regions with respect to the stability of Mg-surface films and subsequent NDE.

Effect of a small addition of zinc and manganese to Mg–Ca based alloys on degradation behavior in physiological media

The corrosion of a low-alloy Mg–Ca system was observed in typical physiological media. The specimens were divided into three groups of alloys: binary (Mg–Ca), ternary (Mg–Ca–Zn and Mg–Ca–Mn), and quaternary (Mg–Zn–Mn–Ca). The corrosion of the Mg–Ca based alloys in Tas simulated physiological media was investigated through a potentiodynamic polarization test and a hydrogen evolution measurement test for biomedical applications. An addition of Zn from 0.5 to 1wt.% in the Mg–1Ca shifted the corrosion potential toward a more positive zone and lowered the corrosion current. On the other hand, an increased amount of Mn from 0.5 to 1wt.% shifted the corrosion potential toward a more positive zone but increased the corrosion current. The observed microstructure indicated that the distributions of the intermetallic phase and the precipitate played a significant role in the ternary and quaternary alloys. Furthermore, a passive layer on the surface of the Mg alloys that contained Mn assisted in decreasing the current exchange between the environment and the alloys. The quaternary Mg–0.5Ca–0.25Zn–0.25Mn alloy exhibited the lowest hydrogen evolution rate at 0.262cc/cm2/day. However, an increase in the alloying ratio to Mg–1Ca–0.5Zn–0.5Mn resulted in an increase in the hydrogen evolution rate to 0.752cc/cm2/day.

Coupling of a scanning flow cell with online electrochemical mass spectrometry for screening of reaction selectivity

In this work the online coupling of a miniaturized electrochemical scanning flow cell (SFC) to a mass spectrometer is introduced. The system is designed for the determination of reaction products in dependence of the applied potential and/or current regime as well as fast and automated change of the sample. The reaction products evaporate through a hydrophobic PTFE membrane into a small vacuum probe, which is positioned only 50-100 μm away from the electrode surface. The probe is implemented into the SFC and directly connected to the mass spectrometer. This unique configuration enables fast parameter screening for complex electrochemical reactions, including investigation of operation conditions, composition of electrolyte, and material composition. The technical developments of the system are validated by initial measurements of hydrogen evolution during water electrolysis and electrochemical reduction of CO2 to various products, showcasing the high potential for systematic combinatorial screening by this approach.

Influence of Ca2+in Deicing Salt on the Corrosion Behavior of AM50 Magnesium Alloy

To lower the freezing point of deicing salt, calcium chloride (CaCl2) is commonly used. The influence of the presence and absence of the deicing salt ingredient Ca2+ on the corrosion behavior of die-cast AM50 magnesium alloy was investigated using an electrolyte close to the deicing salt composition with and without Ca2+ addition. The goal of the work was to point out the differences in the corrosion mechanism with and with-out Ca2+ addition by electrochemical investigations, H2 evolution, and weight-loss characterization. Under polarizing conditions the resulting current densities are significantly lower in the presence of Ca2+. Electrochemical impedance spectroscopy (EIS) measurements up to 4.5 h showed an increasing polarization resistance, RP, with time, and after 4.5 h, a breakdown of RP values in the presence of Ca2+ combined with the appearance of an inductive loop. Mass-gain, mass-loss, and hydrogen evolution measurements confirmed the inhibiting behavior in the presence of Ca2+ up to 1 day. Durin...