Influence of 2-(4-chlorophenyl)-2-oxoethyl benzoate on the hydrogen evolution and corrosion inhibition of 18 Ni 250 grade weld aged maraging steel in 1.0 M sulfuric acid medium

Electrochemical corrosion behavior and hydrogen evolution reaction of weld aged maraging steel have been investigated, in 1.0 M sulfuric acid solution containing different concentrations of 2-(4-chlorophenyl)-2-oxoethyl benzoate (CPOB). The data obtained from polarization technique showed that the corrosion current density (i_corr) and the hydrogen evolution rate decrease, indicating a decrease in the corrosion rate of weld aged maraging steel as well as an increase in the inhibition efficiency (η%) with the increase in inhibitor concentration. Changes in impedance parameters were indicative of adsorption of CPOB on the metal surface, leading to the formation of protective film. Both activation (E_a) and thermodynamic parameters (ΔG_ads⁰, ΔH_ads⁰ and ΔS_ads⁰) were calculated and discussed. The adsorption of CPOB on the weld aged maraging steel surface obeyed the Langmuir adsorption isotherm model. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) study confirmed the formation of an adsorbed protective film on the metal surface.     

Surface microstructure and performance of TiN monolayer film on titanium bipolar plate for PEMFC

The influence of bias voltage on surface microstructure of TiN films deposited on Ti substrate by multi-arc ion plating was systematically investigated. The TiN films were characterized using X-ray diffraction, scanning electron microscopy and atomic force microscopy. The corrosion resistance was tested by potentiodynamic polarization and electrochemical impedance spectroscopy at 70–80 °C in the simulated PEMFC cathode environment. The results show that the surface microstructure of TiN film depends strongly on the bias voltages. At the bias voltage of −100 V, TiN film shows the optimum surface microstructure with the lowest surface roughness R_z of 0.039 μm tested by AFM and relatively high compactness. The optimized TiN film exhibits excellent corrosion resistance with corrosion current density of 0.87 μA/cm² in a 0.5 M H₂SO₄ + 2 ppm HF solution at 80 °C with air and a low interfacial contact resistance (ICR) value of 3.0 mΩ cm² at a compaction force of 140 N/cm². These results support TiN as a promising coating material for Ti bipolar plates.     

Hydrogen generation during the corrosion of carbon steel in crotonic acid and using some organic surfactants to control hydrogen evolution

The purpose of this paper is to describe and evaluate the corrosion of carbon steel in crotonic acid for hydrogen production and using polysorbate 20 (NS), dioctyl sodium sulfosuccinate (AS) and benzalkonium chloride (CS) to control hydrogen evolution. Measurements were conducted in tested solutions using hydrogen evolution and electrochemical impedance spectroscopy (EIS) measurements and complemented by scan electron microscope (SEM) and energy dispersive X-ray (EDX) investigations. It is shown that the hydrogen generation rate obtained during the corrosion of carbon steel in crotonic acid increased with increase in acid concentration, temperature and immersion time. The addition of organic surfactants inhibits the hydrogen generation rate. The inhibition occurs through adsorption of organic surfactants on the metal surface. Adsorption processes followed the Langmuir isotherm. The order of effectiveness of the surfactants was AS > NS > CS. The values of activation energy (E_a) and heat of adsorption (Q_ads) were calculated and discussed.     

Electrochemical investigation on the corrosion and hydrogen evolution rate of mild steel in sulphuric acid solution

Corrosion and hydrogen evolution rate of mild steel alloy have been investigated using various electrochemical techniques. Mild steel was polarized vs. saturated calomel electrode (SCE) in naturally aerated 0.1 M H₂SO₄ solution containing three newly synthesized heterocyclic compounds in different concentrations. The data obtained from polarization technique showed that the corrosion current density, i_corr, and the hydrogen evolution rate decrease with increasing concentration of heterocyclic inhibitors in 0.1 M H₂SO₄ medium, indicating a decrease in the corrosion rate of mild steel as well as an increase in the inhibition efficiency (IE) of the newly synthesized inhibitors. The impedance measurements confirmed well the polarization behaviour. Increasing the temperature leads to an increase in corrosion or hydrogen evolution rate of the mild steel and a decrease of the total resistance value (R_T) or the relative thickness (1/C_T) of the film. The obtained results were confirmed by surface examination using scanning electron microscope.     

Synthesis and characterization of porous HKUST-1 metal organic frameworks for hydrogen storage

Hydrogen storage capacity has been investigated on a copper-based metal organic framework named HKUST-1 with fine structural analyses. The crystalline structure of HKUST-1 MOF has been confirmed from the powder X-ray diffraction and the average particle diameter has been found about 15–20 μm identified by FE-SEM. Nitrogen adsorption isotherms show that HKUST-1 MOF has approximately type-I isotherm with a BET specific surface area of 1055 m²g⁻¹. Hydrogen adsorption study shows that this material can store 0.47 wt.% of H₂ at 303 K and 35 bar. The existence of Cu (II) in crystalline framework of HKUST-1 MOF has been confirmed by pre-edge XANES spectra. The sharp feature at 8985.8 eV in XANES spectra represents the dipole-allowed electron transition from 1s to 4p_xy. In addition, EXAFS spectra indicate that HKUST-1 MOF structure has the Cu–O bond distance of 1.95 Å with a coordination number of 4.2.     

Investigation on the corrosion and hydrogen evolution for AZ91D magnesium alloy in single and anion-containing oxalate solutions

Corrosion characterization of AZ91D alloy was studied in aqueous sodium oxalate solutions with various concentrations using different electrochemical techniques (open circuit potential, electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV)). The corrosion rate and consequently the rate and extent of hydrogen evolution were found to increase significantly with increasing oxalate anion concentration and temperature or with decreasing the pH of solution. Increasing additions of various anions over the lower concentration range (0.001-1.0 mM) in the blank oxalate solution increases to a varying extent the corrosion rate of the alloy and hence increases the hydrogen evolution rate and decreases surface film stability in the following order Cl⁻ > SO₄²⁻ > F⁻. On the other hand, addition of phosphate anion exhibits a reverse trend, where the active corrosion rate decreases with increasing PO₄³⁻ anion concentration, implying that this anion acts as a passivator for AZ91D alloy. The obtained electrochemical results are further confirmed by scanning electron microscopy (SEM) analysis.     

Effects of transition metal Ti and its compounds on hydrogen adsorption performance of Mg17Al12

Catalytic effects of Ti, Ti_n (n = 2–4), TiC, and TiO₂ clusters on hydrogenation of the Mg17Al12(110) surface were investigated by using density functional theory. The geometry structure, adsorption energy, dissociation barrier, density of state, electron density, and electron density difference were calculated. As a result, the adsorption energy and dissociation barrier of hydrogen on the Ti-containing Mg17Al12(110) surfaces were effectively improved as compared with the clean Mg17Al12(110) surface. Such as the adsorption energy of H(H2) on the Mg17Al12(110) surface was ?0.18 (?0.13) eV, while the related energy of H(H2) on the Mg17Al12(110)/TiO2 system was ?1.50 (?1.22) eV. In addition, H2 molecules could be spontaneously dissociated to H atoms on the Mg15Ti2Al12(110), Mg17Al12(110)/Ti3, and Mg17Al12(110)/TiO2 surfaces. The results of electronic structures indicated that the H s states principally hybridized with the Ti s and d states. The mechanism of Ti, Ti_n (n = 2–4), TiC, and TiO2 clusters on the promoted hydrogenation of Mg17Al12 was explained.     

Nanoscale cobalt doped carbon aerogel: microstructure and isosteric heat of hydrogen adsorption

The incorporation of nanoscale Co particles (with sizes from a few nanometres) into porous carbon aerogels (CAs) was investigated. Elemental maps of the nanoscale metal particles embedded within CA were obtained using energy filtered transmission electron microscopy. The microstructure of Co doped carbon aerogels was further investigated using small angle X-ray scattering and nitrogen adsorption at 77 K. The isosteric heat of adsorption (Qst) was investigated as a function of hydrogen uptake at temperatures from 77 K to 110 K over the pressure range of 0-0.25 MPa. The isosteric heat of adsorption at low H₂ concentration for Co doped CA (9.0 kJ mol⁻¹) was found to be higher than for pure CA (5.8 kJ mol⁻¹).     

Electrochemical polarization and corrosion behavior of Al–Zn–In based alloy in acidity and alkalinity solutions

The corrosion behavior of Al–5Zn–1Mg−0.02In−0.05Ti−0.1Si (wt %) alloy has been investigated in different pH solutions by cyclic polarization, self-corrosion and scanning electron microscopy. The results show that the alloy undergoes two types of corrosion, including pitting in acidic solutions, relative light pitting in neutral solutions and crystallographic corrosion in alkalinity solutions with a high possibility. The difference of ΔE = (E_pit − E_cor) are used as criterion for susceptibility to pitting and the hysteresis loop area as criterion for pitting propagation and repassivation of the alloy. The criterion is discussed. Corrosion morphologies of the alloy are in good agreement with corrosion parameters.     

Inhibitive action of ferricyanide complex anion on both corrosion and passivation of zinc and zinc-nickel alloy in the alkaline solution

The corrosion of zinc and Zn-0.5Ni alloy in strong alkaline solution (7 M KOH) in the absence and presence of [Fe(CN)₆]³⁻ complex anion (1 × 10⁻³-1 × 10⁻² M) as inhibitor has been studied. Tafel plot, potentiodynamic, potentiostatic and electrochemical impedance spectroscopy (EIS) techniques were used, and complementary by EDX and SEM investigation. It is observed that, the corrosion current density (I_corr) decreases, and the inhibition efficiency (IE%) increases as the concentration of inhibitor is increased. The shift of breakdown potential to less positive direction, indicating that the reduction of oxide layer on the alloy surface occurs somewhat easier in the presence of [Fe(CN)₆]³⁻ complex anion. The impedance measurements have shown that the increase of the inhibitor concentration in the alkaline solution reduces the corrosion rate in the active region. Accordingly, addition of [Fe(CN)₆]³⁻ complex anion to KOH solution can be considered as an important criteria for a good battery anodes. This behavior is due to its high negative open-circuit potential, less corrosion rate and higher self-catalysis in the passive region compared with those in its absence.     

Surfactant based sol–gel approach to nanostructured LiFePO4 for high rate Li-ion batteries

Porous nanostructured LiFePO₄ powder with a narrow particle size distribution (100–300 nm) for high rate lithium-ion battery cathode application was obtained using an ethanol based sol–gel route employing lauric acid as a surfactant. The synthesized LiFePO₄ powders comprised of agglomerates of crystallites <65 nm in diameter exhibiting a specific surface area ranging from 8 m² g⁻¹ to 36 m² g⁻¹ depending on the absence or presence of the surfactant. The LiFePO₄ obtained using lauric acid resulted in a specific capacity of 123 mAh g⁻¹ and 157 mAh g⁻¹ at discharge rates of 10C and 1C with less than 0.08% fade per cycle, respectively. Structural and microstructural characterization were performed using X-ray diffraction (XRD), scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM) with energy dispersive X-ray (EDX) analysis while electronic conductivity and specific surface area were determined using four-point probe and N₂ adsorption techniques.     

Analysis of corrosion inhibition of Kleinhovia hospita plant extract aided by quantification of hydrogen evolution using a GLCM/SVM method

During a corrosion inhibition test, a combination of common electrochemical corrosion test methods with an in-situ quantification of H₂ evolution could provide a comprehensive analysis of the effectiveness of an organic inhibitor. This work analyzes the corrosion inhibition efficiency of Kleinhovia hospita plant extract on carbon steel specimens polarized in 1 M HCl, based on acquired H₂ bubbles images, by using gray level co-occurrence matrix (GLCM) and support vector machine (SVM) classification. A conformity was established between the classified-algorithm models and the corrosion test results obtained by potentiodynamic polarization test and electrochemical impedance spectroscopy. Hydrogen rate and corrosion rate show the same lowest trends at the addition of 3000 mg/L of KH extract. The inhibitor addition led to 99% of maximum inhibition efficiency. Based on the polarization data, KH extract is a mixed type inhibitor. Supported by Langmuir calculation for adsorption isotherm, a physisorption is stated as the main inhibition mechanism. The feature extraction using GLCM was able to distinguish changes in H₂ bubbles characteristics where the addition of inhibitor affected the corrosion rate. The GLCM/SVM method applied as a linear kernel function and showed 88% accuracy with d = 5 for image data testing. Remarkable changes in H₂ gas bubbles characteristic were observed in the specimen immersed in the solution with 3000 mg/L inhibitor addition, signified by 99% inhibition efficiency.     

Hydrogen storage on uncharged and positively charged Mg-decorated graphene

The storage of H₂ molecules was studied theoretically on charged and uncharged Mg decorated graphene surfaces using density-functional theory and by incorporating the van der Waals (vdW) interactions. We found that an increase in the number of Mg atoms and H₂ molecule increases the net interaction of the hydrogen molecule with the surface. The Mg-Gr⁺ has the hydrogen storage capacity of up to nine H₂ molecules, with the average adsorption energy of −0.134 eV/H₂. Also, we found that hydrogen molecules play an important role in the interaction between the graphene surface and the Mg atom. The charge density difference analysis showed that electron transfer occurs from H₂ molecules to Mg atom in uncharged system. However, the Bader charge analysis showed that the positive charges in the Mg-Gr⁺ and nH₂-Mg-Gr⁺ systems are concentrated on the Mg atom. When the number of H₂ molecules reaches more than 4, the charge transfer instead occurs from the Mg atom to H₂ molecules as well as to the graphene surface. This results in better interaction between the Mg atom and the Gr⁺ surface.     

Li center clusters MLi4+ (M = C,Si, Ge) for dihydrogen storage

A density functional study of dihydrogen adsorption and storage capacity of reported stable clusters MLi₄⁺ (M = C, Si, Ge) has been performed at different levels. The cationic systems MLi₄⁺ (M = C, Si, Ge) can adsorb up to 12, 12, and 14 hydrogen molecules respectively with respective H₂ gravimetric uptake capacity of 37.82, 30.22, and 21.94 wt%. The interactions of MLi₄⁺ (M = C, Si, Ge) with H₂ molecules are analyzed by means of the bond critical points (bcp) in the quantum theory of atoms in molecules (QTAIM). The Gibbs free energy corrected adsorption energies indicate that the maximum adsorption of MLi₄⁺ (M = C, Si, Ge) are energetically favorable at low temperature or high pressure. Atom-centered density matrix propagation (ADMP) molecular dynamics simulations are performed at different temperatures. It can be found that MLi₄⁺ (M = C, Si, Ge) can bind 3, 6, and 4 hydrogen molecules with respective gravimetric densities of 13.20, 17.80, and 7.43 wt% at 200 K and 1atm. At room temperature, MLi₄⁺ (M = C, Si, Ge) can adsorb 3, 5, and 3 hydrogen molecules with gravimetric densities of 13.20, 15.29, and 5.68 wt%.     

Study of the dry methane reforming process using a rotating gliding arc reactor

Dry methane reforming (DMR) via rotating gliding arc (RGA) discharge, co-driven by a magnetic field and tangential flow, was investigated in this study. Optical emission spectroscopy (OES) was used to characterize the major active species (energetic electrons, radicals, ions, atoms and excited molecules) in the DMR chemical process. The influence of the operational conditions (applied voltage and CH₄/CO₂ ratio) on the basic spectroscopic parameters (electron excitation temperature, electron density and rotational temperature) was determined by spectroscopic methods. The rotational and electron excitation temperatures were approximately 1100–1200 K and 1.1–1.7 eV, respectively, indicating the non-thermal equilibrium characteristics of the RGA discharge. The electron density was approximately 5–20 × 10²¹ m⁻³ by fitting the line shape of H_α at 656 nm. The conversions of the reactants (CH₄ and CO₂) and the selectivities of the products (H₂, CO and C₂ hydrocarbon) were analyzed using a gas chromatograph (GC) under different energy inputs or feed gas proportions. The structure and morphology of carbon black produced during the chemical process was characterized by high-resolution transmission electron microscopy (HRTEM) and Raman spectroscopy, indicating the properties of electrical conductivity and high absorption capacity that can be useful for potential application.     

Enhanced hydrogen storage capacity of Pt-loaded CNT@MOF-5 hybrid composites

We report on an easy synthesis method for the preparation of a hybrid composite of Pt-loaded MWCNTs@MOF-5 [Zn₄O(benzene-1,4-dicarboxylate)₃] that greatly enhanced hydrogen storage capacity at room temperature. To prepare the composite, we first prepared Pt-loaded MWCNTs, which were then incorporated in-situ into the MOF-5 crystals. The obtained composite was characterized by various techniques such as powder X-ray diffractometry, optical microscopy, porosimetry by nitrogen adsorption, and hydrogen adsorption. The analyses confirmed that the product has a highly crystalline structure with a Langmuir specific surface area of over 2000 m²/g. The hybrid composite was shown to have a hydrogen storage capacity of 1.25 wt% at room temperature and 100 bar, and 1.89 wt% at cryogenic temperature and 1 bar. These H₂ storage capacities represent significant increases over those of virgin MOF-5s and Pt-loaded MWCNTs.     

Synthesis and characterization of Pd0.5NixSe(0.5−x) electrocatalysts for oxygen reduction reaction in acid media

Pd_0.5Ni_xSe_(0.5−x) electrocatalysts with different chemical composition, X = 0.25, 0.35, 0.45, were synthesized by a NaBH₄ reduction of PdCl₂, NiCl₂ and SeO in a THF solution and evaluated for the oxygen reduction reaction (ORR) in acid media by electrochemical techniques of rotating disk electrode (RDE) and rotating ring-disk electrode (RRDE). The electrocatalysts were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and CO adsorption/stripping. The relation of Se to Ni in the samples has a profound effect on the nature of the cathode catalytic activity toward the oxygen reduction process, enhanced as the Se content in the electrocatalysts was reduced. Electrochemical results show that the ORR takes place by a multi-electron charge transfer process (n = 4e⁻) with the formation of less than 1% of hydrogen peroxide. The enhanced activity was attributed to the high active surface area deduced from CO adsorption/stripping analysis. The research activities are reported within the focus on the activity-stability of the bimetallic chalcogenides electrocatalysts.     

Electrochemical catalytic activities of nanoporous palladium rods for methanol electro-oxidation

A novel electrocatalyst, nanoporous palladium (npPd) rods can be facilely fabricated by dealloying a binary Al₈₀Pd₂₀ alloy in a 5 wt.% HCl aqueous solution under free corrosion conditions. The microstructure of these nanoporous palladium rods has been characterized using scanning electron microscopy and transmission electron microscopy. The results show that each Pd rod is several microns in length and several hundred nanometers in diameter. Moreover, all the rods exhibit a typical three-dimensional bicontinuous interpenetrating ligament-channel structure with length scale of 15-20 nm. The electrochemical experiments demonstrate that these peculiar nanoporous palladium rods (mixed with Vulcan XC-72 carbon powders to form a npPd/C catalyst) reveal a superior electrocatalytic performance toward methanol oxidation in the alkaline media. In addition, the electrocatalytic activity obviously depends on the metal loading on the electrode and will reach to the highest level (223.52 mA mg⁻¹) when applying 0.4 mg cm⁻² metal loading on the electrode. Moreover, a competing adsorption mechanism should exist when performing methanol oxidation on the surface of npPd rods, and the electro-oxidation reaction is a diffusion-controlled electrochemical process. Due to the advantages of simplicity and high efficiency in the mass production, the npPd rods can act as a promising candidate for the anode catalyst for direct methanol fuel cells (DMFCs).     

Zeolitic imidazolate framework-8 modified cathode promotes microbial electrosynthesis from carbon dioxide

Microbial electrosynthesis (MES) is an electrochemical reduction technology through which microorganisms attached to a cathode are driven by electricity to reduce carbon dioxide (CO₂) into industrial chemicals. However, the limited contact time with biocatalysts affects the performance of MES because of low CO₂ solubility. In this study, zeolitic imidazolate framework-8 (ZIF-8) particles with different pore diameters modified cathodes were prepared. Results showed that the ZIF-8 modified electrode obtained the maximum acetate production rate (0.13 g L^?1 d^?1), which was 1.4 times that of bare CF, and the accumulated acetate concentration reached 4.04 ± 0.1 g L^?1 within 30 days. Brunauer–Emmett–Teller test and CO₂ adsorption characteristic evaluation indicated that ZIF-8 had a high specific surface area and an excellent CO₂ adsorption capacity. Scanning electron microscopy and microbial community analysis revealed that ZIF-8 modified electrodes were beneficial to biofilm formation and increased the enrichment of Acetobacterium and Arcobacter. Therefore, CO₂-adsorbing materials modified electrodes are effective in improving the performance of MES.     

Quantitative study of the kinetics of hydrogen evolution reaction on aluminum surface and the influence of chloride ion

The behaviors and kinetics of hydrogen evolution reaction (HER) on pure aluminum with passive film in the presence and absence of chloride ion are quantitatively investigated by using the tip generation/substrate collection mode of scanning electrochemical microscopy (SECM) with dual Al/Pt ultramicroelectrode (UME) as tip electrode and Pt UME as substrate electrode. The standard rate constants k⁰ and transfer coefficients α_H of HER in ClO₄⁻- and Cl⁻-containing solution are 6.9 × 10⁻⁷ cm/s and 0.22, 7.1 × 10⁻⁶ cm/s and 0.19, respectively. Results show that the kinetic of HER is slow and the destruction of Cl⁻ on passive film can significantly promote the HER on Al surface. Moreover, these α_H far less than commonly used 0.5 in corrosion research, can explain the great difference between theoretical Tafel slopes and experimental results. Besides, the existence of current plateau in Al electrode explains the large difference in corrosion potential during parallel testing.