Enhanced inhibition on hydrogen permeation during electrodeposition process by rare earth (RE = Ce) salt additive

High-strength steel parts are electroplated with corrosion-resistant coatings and then subjected to hydrogen removal annealing to prevent hydrogen embrittlement. This approach has become the standard in the industry. However, it is not beneficial to energy conservation and emission reduction. Herein, a rare earth salt (Ce salt) additive is determined to be efficient for inhibiting hydrogen permeation during electroplating process. A modified Devanathan-Stachurski method was applied to investigate the hydrogen permeation behavior. Results demonstrated that the hydrogen permeation during direct current (DC) and pulsed current (PC) electrodeposition was considerably inhibited by the Ce salt additive. The amount of permeated hydrogen increased in the following order: PC electrodeposition with Ce＜PC electrodeposition＜DC electrodeposition with Ce＜DC electrodeposition. Therefore, the environmentally friendly additive has great potential for energy saving and emission reduction in the electrodeposition or pickling industry.     

Influence of low tensile stress on the kinetics of hydrogen permeation and evolution behavior in alkaline environment

The hydrogen behavior the surface of X70 pipeline steel in alkaline environment after applying low tensile stress was investigated by electrochemical tests. It is found by hydrogen permeation tests that the steady-state hydrogen permeation current density (i_∞) and sub-surface hydrogen concentration (C₀) greatly increased, whereas apparent diffusivity (D) was almost unchanged after applying low tensile stress. LSV and EIS measurements indicated that the activity of hydrogen evolution reaction (HER) was improved by elastic tensile stress. The mechanism of stress enhanced the hydrogen embrittlement sensitivity was conducted by Iyer-Pickering-Zamanzadeh (IPZ) and surface effect model. The results demonstrated that the Volmer reaction was facilitated, and the Tafel reaction was restricted by the application of tensile stress. The activation energy obtained by the Arrhenius equation indicated that when the specimen suffered from tensile stress, the adsorption activation energy decreased, and the desorption activation energy increased, leading to the remarkable increase of C₀.     

Ni composite electrodes for hydrogen generation: Activation of Nb-based semiconductors

The hydrogen evolution reaction depends on the accumulation of electrons on the catalytic center to enable the two-electron processes involved in water reduction. This work reports on the modification of inexpensive nickel (Ni) composite electrodes with engineered semiconductor heterojunctions based on earth-abundant transition metals that show superior hydrogen generation activity in the presence of a non-toxic electrolyte (K₂CO₃). This is, small amounts of cobalt (Co) or copper (Cu) oxides can improve the reactivity of composite electrodes formed by deposition of titanium (Ti) or niobium (Nb) semiconductors onto Ni surfaces. In general, modified Nb-based semiconductors show better performance and their enhanced activity can be understood in terms of modified surface potentials upon formation of semiconductor-Ni heterojunctions. Photoelectrochemical activity can be detected in the presence of Cu oxides, where hydrogen generation onset potential is reduced under UV–Vis light irradiation. The study demonstrates that small composition changes can greatly affect the activity of Nb-based Ni composite electrodes, showing exciting new applications for Nb-based materials.     

Influence of Pt decoration on the hydrogen storage performance of cup-stacked carbon nanotubes: A DFT study

The hydrogen adsorption behaviour of cup-stacked carbon nanotubes (CSCNTs) decorated with the platinum atom at four positions of the conical graphene layer (CGL) is investigated using density functional theory. The optimization shows that the inside lower edge position (IL) results have the best hydrogen adsorption parameters among the four positions. The Pt–H₂ distance is 1.54 Å, the H–H bond length (l_H-H) is 1.942 Å, and the hydrogen adsorption energy (E_ads) is 1.51 eV. The hydrogen adsorption of CSCNTs decorated by Pt at the IL position also has larger E_ads and l_H-H than the Pt-doped planar graphene, Pt-doped single-wall carbon nanotubes and Pt-doped carbon nanocones. The Pt atom at the IL position has a more significant polarization effect on the adsorbed H₂, it has trends to convert H₂ into two separate H atoms. While the hydrogen adsorption behaviour at other positions belongs to the Kubas coordination, the l_H-H and the E_ads increased not significantly.     

Ruthenium-Imine catalyzed KBH4 hydrolysis as an efficient hydrogen production system

The present study focused on the increasing of hydrogen evolution through hydrolysis of potassium borohydride in the presence of Ruthenium complex catalyst. It is the first time to use the Ru-Imine complex catalyst in KBH₄ hydrolysis reaction to hydrogen evolution. The new Ru complex was synthesized from the tetradentate Imine ligand namely 4,4′-methylenebis (2,6-diethyl)aniline-3,5-di-tert-butylsalisylaldimine and Ru salt under the inert atmosphere. Ru-Imine complex was fully characterized by Elemental Analysis, Infrared Spectroscopy, Scanning Electron Microscope, X-Ray Diffraction Analysis, Brunauer-Emmett-Teller Surface Area Analysis and Transmission Electron Microscopy. By the synthesized Ru-Imine complex catalyst, the potassium borohydride hydrolysis reaction resulted in a lower energy barrier with 20,826 kJ/mol activation energy (Ea) for nth order kinetic model and 18,045 kJ/mol for Langmuir-Hinshelwood (L-H) kinetic model. According to the results Ru-complex was highly active and stable catalyst in KBH₄ hydrolysis reaction to hydrogen evolution with 45,466 mL H₂/g_cat.min and 76,815 mL H2/g_cat.min hydrogen generation rates at 30 °C and 50 °C respectively. Moreover Ru-Imine complex catalyst displayed 100% stability even at fifth recycle.     

Stacked nano rods of cobalt and nickel based metal organic frame work of 2–amino benzene dicarboxylic acid for photocatalytic hydrogen generation

Stacked nanorods of cobalt and nickel based hetero bimetallic organic frameworks (MOFs) of 2–amino benzene dicarboxylic acid are developed as photocatalyst for hydrogen evolution reaction. The ratio of metals in the catalyst is tuned to achieve a narrow band gap, and the MOF with optimized Ni to Co ratio of 1: 0.5 (1Ni0.5Co@NH₂BDC) exhibited the lowest band gap (2.2 eV) and electron–hole recombination rate. The catalyst exhibits enhanced photocatalytic activity for hydrogen evolution reaction due to the absorption of photons by 2–amino benzene dicarboxylic acid and excitation of electrons from HOMO to LUMO of the organic linker. The excited electrons relay to the cluster of the framework and reduce the protons gather around the cluster to hydrogen. The holes in the HOMO state are occupied by the electrons from the sacrificial agents and it supports the photocatalytic hydrogen evolution by avoiding electron–hole recombination. The stability of MOF catalyst in water splitting medium even with sacrificial agents confirms its competency with the state–of–the–art photocatalytic materials.     

Synergistic regulation of hydrogen adsorption/desorption via dual interfaces of Cu/Ni/Ni(OH)2 toward efficient hydrogen evolution reaction

Nickel-based catalysts have attracted tremendous attention as alternatives to precious metal-based catalysts for electrocatalytic hydrogen evolution reaction (HER) in virtue of their conspicuous advantages such as abundant reserves and high electrochemical activity. Nevertheless, a great challenge for Ni-based electrocatalyst is that nickel sites possess too strong adsorption for key intermediates H1, which severely suppresses the hydrogen-production activities. Herein, we report a hierarchical architecture Cu/Ni/Ni(OH)₂ consisting of dual interfaces as a high-efficient electrocatalyst for HER. The Cu nanowire backbone could provide geometric spaces for loading plenty of Ni sites and the formed Ni/Cu interface could effectively weakened the adsorption intensity of H1 intermediates on the catalyst surface. Moreover, the H1 adsorption could be further controlled to appropriate states by in-situ formed Ni(OH)₂/Ni interface, which simultaneously promotes water adsorption and activation, thus both Heyrovsky and Volmer steps in HER could be obviously accelerated. Experimental and theoretical results confirm that this interface structure can promote water dissociation and optimize H1 adsorption. Consequently, the Cu/Ni/Ni(OH)₂ electrocatalyst exhibits a low overpotential of 20 mV at 10 mA cm^?2 and an ultralow Tafel slope of 30 mV dec^?1 in 1.0 M KOH, surpassing those of reported transition-metal-based electrocatalysts and even the prevailing commercial Pt/C.     

Enhanced hydrogen generation from Al-water reaction mediated by metal salts

Hydrogen generation by the reaction of micrometer-aluminum powder with water at room temperature is hard to proceed due to the inhibition of alumina layer. In this study, a novel strategy of metal salts mediated Al-water reaction was proposed for more efficient and practical hydrogen generation. The effects of metal salt composition and dosage, and water injection rate and volume on hydrogen generation were investigated. The hydrogen yield of 230.0 mL was achieved in the Al/Ni/Cu/H₂O system within 600 s under the following conditions: 0.24 g aluminum with the molar ratio of Al, Ni and Cu at 10:1:1 and 2 mL water at the injection rate of 2 mL/min, which was equivalent to 70.4% of the theoretical hydrogen yield. Based on the morphology, element composition, crystal structure and electrochemical test results of the obtained composites after reaction, the mechanism of hydrogen production by metal salts mediated Al-water reaction was proposed.     

Hydrogen production by aluminum corrosion in hydrochloric acid and using inhibitors to control hydrogen evolution

This study reports on the systematic assessment of hydrogen (H₂) production by corrosion of aluminum alloy (AA) in hydrochloric acid (HCl) at different temperature. Rare earth inhibitors, lanthanum (La) and cerium (Ce) have been applied to control the H₂ production process. The production process is based on electrochemical reaction of aluminum (anodic reaction) in the HCl solution, which has a high concentration of hydrogen ions (H⁺), the H⁺ ions are reduced and H₂ is evolved. Preliminary results showed that an increase in temperature of working solution produced an increase of the H₂ production rate. The H₂ production rate increases because acid can prevent aluminum passivation during H₂ evolution. The rare earth inhibitors La and Ce control the H₂ evolution, especially, when using mixture of both inhibitors. This result demonstrates a synergistic effect between the La and the Ce inhibitors. X-ray diffraction studies were performed on the surface structure before and after immersion, and a scanning electron microscope (SEM) was used to study the morphology of the AA.     

Highly active Ni/CeO2 for the steam reforming of acetic acid using CTAB as surfactant template

A series of CTAB-templated Ni/Ce catalysts were synthesized by adding CTAB during the hydrothermal synthesis of ceria to improve the pore structure of catalysts. Their catalytic performance was evaluated in the steam reforming of acetic acid and the effects of CTAB concentration on the porous structures, reducibilities, morphology, and activity of catalysts were studied. The catalysts were characterized by BET, XRD, H₂-TPR, XPS, HRTEM, in-situ DRIFTS, DTG, FTIR, and temperature-programmed reaction to elucidate the structure-activity relationship of the catalyst. The results showed that owing to the CTAB assistance, a high surface area of ceria could be achieved, which induced a better Ni dispersion with a smaller Ni size, strengthened the interaction between Ni and CeO₂, and promoted the reducibility of Ni, obtaining higher activity and lower methane yield than Ni/Ce. Among these prepared samples, Ni/Ce–C6 showed the highest surface area and the best catalytic performance with a hydrogen yield of up to 82.5% even at a low temperature (550 °C). Owing to the stronger Ni-ceria interaction of Ni/Ce–C6, the lattice oxygen in ceria migrates easily to the Ni surface, interacts with the reaction intermediates, and thus improves the CO₂/CO ratio in the products. Much more CO and CO₂ and less CH₄ were observed over Ni/Ce–C6 during the temperature-programmed reaction, indicating its high activity. In-situ DRFITS characterization demonstrated that the two types of catalysts had similar reaction intermediates but various adsorption and conversion abilities toward the acetic acid. More reaction intermediates were adsorbed at low temperatures and a higher conversion was obtained over Ni/Ce–C6 owing to its better Ni dispersion. The CTAB assistance inhibited the formation of amorphous carbon but facilitated the formation of graphitic carbon at ～637 °C which did not induce catalyst deactivation.     

Insight into enhanced hydrogen evolution of single-atom Cu1/TiO2 catalysts from first principles

Developing efficient catalysts of low-cost transition metals for hydrogen production is of great importance but remains a huge challenge. Motivated by the idea of engineering local atomic configuration, we propose to focus on single metal atom confined in the lattice oxygen environment, as a class of non-Pt catalysts for hydrogen production. By first principles calculations, we study the characteristics and mechanism of hydrogen evolution reaction of single-atom Cu supported on anatase TiO₂ catalysts, Cu₁/TiO₂. Cu preferentially sits on the bridge-centre site between two 2-fold coordinated O atoms (O_2c) on the surface. Cu and coordinated O_2c function as copper oxide species (-Cu-O-) in the reaction. The reaction starts with two isolated H respectively positioned on Cu and O_2c, proceeds with a transfer of H from O_2c to Cu, and eventually forms a H₂ molecule. The free energy profiles indicate that Cu₁/TiO₂ exhibits excellent hydrogen evolution activity even better than Pt and MoS₂. This study not only shows that single-atom Cu₁/TiO₂ is an excellent hydrogen evolution catalyst, but also expands the understanding of oxide species in single-atom catalysis and proposes an engineering local atomic configuration strategy for optimizing the design of single-atom catalysts for enhanced hydrogen production.     

Hydrogen production by aqueous phase reforming of phenol derived from lignin pyrolysis over NiCe/ZSM-5 catalysts

Incipient wetness impregnation was used to synthesized the NiCe/ZSM-5 catalysts with different ratio of Ni:Ce, and CeO₂ was added as an assistant in the synthesis process. The physicochemical properties of the prepared catalysts were characterized by Transmission electron microscopy (TEM), X-ray diffraction (XRD), N₂-Sorption, H₂ temperature programmed reduction (H₂-TPR), X-ray photoelectron spectroscopy (XPS), Fourier Transform infrared Spectroscopy (FTIR) and ultraviolet–visible diffuse reflectance spectra (UV–Vis DR). The catalytic activities of the obtained catalysts were tested by using the reaction of aqueous phase reforming of phenol to produce hydrogen. Adding appropriate doze of Ce to the catalysts can increase the dispersion of nickel on the ZSM-5 support. The results showed that hydrogen selectivity was higher over 8Ni8Ce/ZSM-5 than using 8Ni/ZSM-5 as aqueous phase reforming catalysts. The content of carbon monoxide in the products after reaction over different catalysts was very low. However, the dispersion of carbon dioxide and hydrocarbons was significantly different over the two catalysts.     

Production of hydrogen and nanofibrous carbon by selective catalytic decomposition of propane

The process of production of highly concentrated CO_x-free hydrogen and nanofibrous carbon (NFC) by catalytic propane decomposition on Ni and Ni–Cu catalysts (different in active phase composition) at relatively low temperatures (400–700 °C) was investigated. The bimetallic Ni–Cu catalysts showed significantly higher propane conversion and longer lifetime than monometallic Ni catalyst. The Ni (50 wt.%)–Cu (40 wt.%)/SiO₂ catalyst exhibited the best activity and selectivity at 600 °C. Total hydrogen yield of 60.8 mol H₂/g_cat (during 24 h time on stream) and the total H₂:CH₄ ratio of 8.4 were obtained during propane decomposition under these optimal conditions. The possible reaction scheme of propane decomposition over Ni-based catalysts and the reasons of increasing the selectivity of hydrogen are discussed.     

The theoretical study of the bimetallic Ni/Pd,Ni/Pt and Pt/Pd catalysts for hydrogen spillover on penta-graphene

The catalytic property of the bimetallic Ni/Pd, Ni/Pt and Pt/Pd particles for hydrogen spillover on penta-graphene (PG) are studied by using the first-principles and kinetic Monte Carlo (KMC) calculations. The bimetallic Ni/Pd, Ni/Pt and Pt/Pd particles can be stably decorated on PG surface with binding energies in the range of 4.15–5.52 eV. The adsorption enthalpies of H₂ molecules on bimetallic particles are in the range of ?11.56–?15.35 kcal/mol. The H atom can migrate from the bimetallic particles to PG with the migration barriers range from 0.67 to 0.95 eV. The KMC simulations show that the hydrogen spillover reactions can occur at a suitable temperature (260–361 K), which meet DOE target for onboard hydrogen storage systems applied to light-duty vehicles. In the study, the highest occupied molecular orbital and electric field analysis shows that the bimetal mixing can reduce the hydrogen adsorption enthalpy, and thereby reduce the H migration barrier, which displays a synergistic effect for hydrogen spillover.     

Mechanisms of hydrides’ nucleation and the effect of hydrogen pressure induced driving force on de-/hydrogenation kinetics of Mg-based nanocrystalline alloys

Aiming to gain insight on the hydrogen storage properties of Mg-based alloys, partial hydrogenation and hydrogen pressure related de-/hydrogenation kinetics of Mg–Ni–La alloys have been investigated. The results indicate that the phase boundaries, such as Mg/Mg₂Ni and Mg/Mg₁₇La₂, distributed within the eutectics can act as preferential nucleation sites for β-MgH₂ and apparently promote the hydrogenation process. For bulk alloy, it is observed that the hydrogenation region gradually grows from the fine Mg–Ni–La eutectic to primary Mg region with the extension of reaction time. After high-energy ball milling, the nanocrystalline powders with crystallite size of 12～20 nm exhibit ameliorated hydrogen absorption/desorption performance, which can absorb 2.58 wt% H₂ at 368 K within 50 min and begin to desorb hydrogen from ～508 K. On the other side, variation of hydrogen pressure induced driving force significantly affects the reaction kinetics. As the hydrogenation/dehydrogenation driving forces increase, the hydrogen absorption/desorption kinetics is markedly accelerated. The dehydrogenation mechanisms have also been revealed by fitting different theoretical kinetics models, which demonstrate that the rate-limiting steps change obviously with the variation of driving forces.     

Enhanced hydrogen production over incorporated Cu and Ni into titania photocatalyst in glycerol-based photoelectrochemical cell: Effect of total metal loading and calcination temperature

The solar driven hydrogen production was successfully investigated in a glycerol-based photoelectrochemical cell (PEC) over nanostructured TiO₂ supported bimetallic Cu and Ni by adjusting total metal loading (5, 10, and 15 mol%) and calcination temperature (400, 450, 500, and 600 °C). The effects of the mentioned parameters on physicochemical and photoelectrochemical properties of prepared Cu–Ni/TiO₂ photoanodes were explored by using different characterization techniques. The hydrogen evolution was experimentally found to be affected total metal loading and calcination temperature. The calcined photocatalyst with the total metal loading of 5 mol% at 450 °C was identified as the most efficient photocatalyst by producing maximum accumulative hydrogen of 694.84 μmol. A high performance of this photocatalyst is mainly attributed to its proper particle size and great ratio of Ti³⁺:Ti⁴⁺ and Cu⁺:Cu²⁺ in TiO₂ matrix. These better physicochemical properties enhanced charge carrier separation, which retarded the charge recombination and enhanced the transportation of photo-induced electrons at the photoelectrode/electrolyte interface. The intermediates from photooxidation of glycerol were verified using high performance liquid chromatography, indicating a partial oxidation of glycerol with selective pathway in KOH (1 M) solution. This work demonstrates that optimization Cu–Ni/TiO₂ photoanode has the practical potential in PEC cell to generate hydrogen from solar and biomass energy.     

Vanadium carbide coating as hydrogen permeation barrier: A DFT study

Density functional calculations are used to investigate hydrogen (H) behaviors in vanadium carbide (VC). Molecular H₂ dissociation, atomic H diffusion and penetration are analyzed using the transition state theory. H₂ prefers to be close to the surface as physical adsorption, providing an environment conducive for further dissociation, and dissociates into atomic H adsorbed at the top C atom sites with co-adsorption state. The dissociation rate on the surface is mainly limited by the temperature-controlled activation energy barrier. The adsorptivity of atomic H by the surface tends to decrease as increasing of H coverage. For atomic H penetration through the surface, a significantly endothermic energy barrier and the low diffusion prefactor suggest that the main resistant effect of H permeation takes place at the surface. Energetic, vibrational, electronic consequences, and quantum effects on the H behaviors are discussed thoroughly. Our theoretical investigation indicates VC is a promising hydrogen permeation barrier.     

Fabrication of highly porous Pt coated nanostructured Cu-foam modified copper electrode and its enhanced catalytic ability for hydrogen evolution reaction

The nanoporous copper foam was prepared by electrochemical reduction of copper ion at the copper substrate. The as-prepared substrate was used as three-dimensional templates for preparation of Pt coated nanostructured Cu-foam by galvanic replacement of Cu with platinum by simply immersing the prepared nanoporous copper foam in a K₂PtCl₆ aqueous solution. The structure and nature of the fabricated Pt coated nanostructured Cu-foam was characterized by scanning electron microscopy and energy dispersive X-ray spectrometry. Pt coated nanostructured Cu-foam modified copper electrode exhibited remarkable electrocatalytic activity for the hydrogen evolution reaction. The effect of electrodeposition time during Cu-foam formation on the kinetic constants for hydrogen evolution reaction was comparatively investigated.     

Syntheses of alkali-metal carbazolides for hydrogen storage

Metalorganic hydrides are a new class of hydrogen storage materials. Replacing the H of N–H or O–H functional groups using metal hydrides have been recently reported, which substantially improved the dehydrogenation properties of heteroaromatic organic hydrides by lowering their enthalpies of dehydrogenation (ΔH_d), enabling dehydrogenation at much lower temperatures. Among the reported metalorganic hydrides, lithium carbazolide and sodium carbazolide appear to be the most attractive hydrogen storage/delivery material owing to its high hydrogen capacity (>6.0 wt%) and ideal ΔH_d. Nevertheless, the interaction of carbazole and corresponding metal hydride to form metallo-carbazolide is a multistep process involving intensive ball milling and high temperature treatment, where the interaction was not investigated in detail. In this paper, both alkali metal hydrides and amides were employed to react with carbazole to synthesize corresponding carbazolides, aiming to broaden and optimize the synthetic method and understand the reaction mechanism. Our experimental results showed that around one equivalent of H₂ or NH₃ could be released from the reactions of carbazole and corresponding hydrides or amides, respectively. Instrumental spectroscopic analyses proved that metallo-carbazolides were successfully synthesized from all precursors. It is found that the alkali metal amides (i.e., LiNH₂ and NaNH₂) with stronger Lewis basicities as metal precursors could synthesize the metallo-carbazolides under milder conditions. Furthermore, quasi in situ nuclear magnetic resonance results revealed that alkali metal could replace H (H–N) gradually, donating more electrons to carbazole ring. Additionally, the solubilized alkali cation may unselectively interact with π-electron of aromatic systems of both carbazole molecules and carbazolide anions via electrostatic cation-π interactions.     

Application of a deep eutectic solvent to prepare nanocrystalline Ni and Ni/TiO2 coatings as electrocatalysts for the hydrogen evolution reaction

The paper reports the electrochemical deposition of nanocrystalline nickel and composite nickel-titania films as effective electrocatalysts for the hydrogen evolution reaction. To produce the composite Ni/TiO₂ electrodeposits, a plating bath based on a deep eutectic solvent, a novel kind of ionic liquids, was used for the first time. The electrolyte contained ethaline (a eutectic mixture of choline chloride and ethylene glycol), 1 M NiCl₂⋅6H₂O and the addition of extra water (3, 6, 9 mol dm⁻³). Titania dispersed phase was introduced into the electrolyte as nanopowder Degussa P 25 (0–10 g dm⁻³). It was shown that the introduction of extra water to the plating bath allowed appreciably increasing the content of TiO₂ phase in the coating (from ca. 2 to 10 wt%). The effects of electrolysis conditions on the TiO₂ content in the coatings, surface morphology and microstructure were determined. The results of voltammetry measurements showed that the Ni and composite Ni/TiO₂ coatings electrodeposited from the plating electrolyte based on a deep eutectic solvent exhibit improved electrocatalytic properties towards the hydrogen evolution reaction as compared with deposits obtained from commonly used aqueous electrolytes. The mechanism of the hydrogen evolution reaction on the Ni and composite Ni/TiO₂ coatings is a combination of Volmer-Heyrovsky reactions. The introduction of TiO₂ particles into the nickel matrix results in the acceleration of the hydrogen evolution reaction. An improved catalytic activity of Ni/TiO₂ composites towards the hydrogen evolution reaction can be associated with the presence of titanium-containing redox couples on the surface.