Insight into the mechanism of hydrogen permeation inhibition by cerium during electroplating: Enhanced kinetics of hydrogen desorption

In our previous work, we found that hydrogen permeation can be noticeably reduced during Ni–Cu electroplating by the addition of Ce salt to the plating solution. The mechanism of hydrogen permeation inhibition via Ce salt was further studied in the present work. Through the Iver–Pickering–Zamenzadeh (IPZ) model fitting of the kinetic of hydrogen evolution reaction, we found that the trace Ce salt that precipitated during electroplating could improve Tafel reaction kinetic parameters and reduce the strength of the Ni–H and Cu–H bonds due to its abundant d/f electrons and enough d/f orbitals. Meanwhile, Ce can provide electrons for the Heyrovsky reaction. These effects promoted surface electron migration and thus led to the desorption of adsorbed hydrogen atoms (H_ads) and the decreased diffusion of H_ads into the Ni–Cu coatings. The accuracy of the IPZ model fitting results was verified by hydrogen evolution rate experiments during the electroplating process. Hence, Ce salt can effectively inhibit hydrogen permeation and reduce the dehydrogenation annealing time, thereby showing great potential for energy saving and emission reduction in the electroplating industry.     

Effect of rare earth (RE) elements on V-based hydrogen storage alloys

In this work, the effect of RE additives on the properties of _{V55Ti22.5Cr16.1Fe6.4}${\mathrm{V}}_{55}{\mathrm{Ti}}_{22.5}{\mathrm{Cr}}_{16.1}{\mathrm{Fe}}_{6.4}$ alloy (RE=La$\mathrm{RE}=\mathrm{La}$, Pr, Ce and Nd, separately) was discussed. It was demonstrated that RE additives improve the activation property rather than kinetics during cycling, absorption capacity and the plateau pressure. Two phases, including BCC main phase and Ce second one, were found in Ce-containing alloy. It is inferred that RE element offers a route for hydrogen to enter the alloys more easily, which leads to the improvement of activation property of the alloys.     

Electrochemical performance of Ni-RE (RE = rare earth) as electrode material for hydrogen evolution reaction in alkaline medium

In this work, Ni-RE (RE = rare earth, La, Ce) materials were obtained by the solid state reaction using as Ni source: a) metal acetylacetonates and b) metal powders while rare earth element was added from acetylacetonates. These materials were synthesized for 3 h at different temperatures (800 °C or 900 °C, 1000 °C and 1200 °C) in order to evaluate their electrochemical performance on the Hydrogen Evolution Reaction (HER). The effects of the sintering temperature and the Ni source on the morphology, structure and particle size were evaluated and correlated with the displayed catalytic activity. The results showed that depending of the added rare earth element and Ni source the formed compounds varied from a mixture of oxides (NiO, CeO₂) and intermetallic compounds (LaNiO₃) at low annealing temperatures up to the formation of the NiO-CeO₂, NiO-LaNiO₃ and NiO-La₄Ni₃O₁₀ compounds at 1200 °C. From Scanning Electron Microscopy (SEM) results, it was observed that the agglomerates of Ni-RE electrode materials presented a more uniform shape (semispherical) and lower crystal sizes (0.2-2.0 μm) using acetylacetonate precursors than that obtained with Ni powders (5-50 μm). It was found that the individual organization of the nickel particles and their electrocatalytic activity is affected by diverse factors: a) the type of precursor used in the synthesis, b) the reaction temperature and c) the synergetic effect caused by the addition of the rare earth metal, which seems to be better for lanthanum than for cerium. The Tafel parameters of the stabilized Ni-RE electrodes revealed that the formation of Ni-La intermetallic compounds at low temperature favors the current densities on the HER. Thus a clear dependence of the electrocatalytic activity on the source of these Ni-RE materials was observed.     

Co catalysts modified by rare earths (La,Ce or Pr) for hydrogen production from ethanol

Co/MgAl₂O₄ catalysts modified with La, Pr or Ce were prepared, characterized by different techniques and tested in ethanol steam reforming reaction to produce hydrogen. The catalytic behavior at 650 °C depended on the nature of rare earth. The amount of carbon on promoted catalysts was significantly lower than that on unpromoted one. The Pr and La containing catalysts produced a high acetaldehyde selectivity which decreased the hydrogen production. The superior performance of the catalyst promoted with 7.8% Ce could be partially explained by a higher dispersion and a high reduction of Co species.     

Effect of Zr7Ni10 additive on hydrogen mobility in (TiCr1.8)1-xVx (x = 0.2, 0.4, 0.6, 0.8): An 1H NMR SFG study

In order to optimize hydrogen storage properties of bcc Ti–V–Cr alloys it was found that alloying with a few 4 at% of Zr₇Ni₁₀ results in acceleration the hydrogen sorption kinetics in the composite material. The novel intergranular phase plays a role of gate for hydrogen, leading parallel to its easy decrepitate, thus enhancing fast formation of Ti–V–Cr hydrides. Nevertheless, the question on how such a composite microstructure affects hydrogen mobility in the material is still open. Here we report on the results of the studies of hydrogen self-diffusion in hydrogenated (TiCr_1.8)_1-xV_x based alloys (x = 0.2, 0.4, 0.6 and 0.8) carried out using proton nuclear magnetic resonance diffusiometry in a static field gradient_. For all compounds the method has proved itself as a powerful tool to probe the microstructure of the multicomponent alloys with inhomogeneous element distribution in a few micrometer scale. It has been found that addition of Zr₇Ni₁₀ lowers the activation energy of hydrogen motion in (TiCr_1.8)_1-xV_x alloys and leads appear two different diffusion areas. They can be associated with a redistribution of elements within the intra-granular phase due to opposite substitution of Ti and Ni atoms during synthesis and blurring the boundaries between the intra-granular and inter-granular phases.     

Hydrogen production by iso-octane steam reforming over Cu catalysts supported on rare earth oxides (REOs)

The present work aims to investigate the steam reforming (SR) of liquid hydrocarbons toward hydrogen production, employing iso-octane as gasoline surrogate, over Cu catalysts supported on rare earth oxides (REOs). An extensive characterization study, involving X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and temperature-programmed reduction (TPR), is undertaken to correlate the structural, morphological and surface properties of catalysts with their reforming performance. Several parameters related to the effect of operation temperature (600–800 °C), steam/carbon ratio (1–3) and Cu loading (0–25 wt%) on the catalytic performance are investigated. The results reveal that the best performance is obtained over the Cu/CeO₂ catalysts at a steam/carbon ratio of 3; H₂ yields as high as ∼55% are obtained at the expense of CH₄ and higher hydrocarbons. Concerning the influence of oxide carries on reforming efficiency the following order, in terms of H₂ yield, is recorded: CeO₂ ? Nd₂O₃ > Gd₂O₃ > Sm₂O₃ ≈ Pr₆O₁₁ ≈ La₂O₃. However, a notable deterioration of Cu/CeO₂ catalyst is observed in long term stability tests, ascribed to carbon deposition and catalyst sintering.     

Effect of transition metal (Cu and Pt) doping/ co-doping on hydrogen gas sensing capability of graphene: A DFT study

Carbon nano-materials are found to demonstrate good hydrogen gas sensing capability and researchers are trying their modified derivatives for enhanced sensitivity. Studies have confirmed improvement in sensing performance of graphene when doped with N or Si or Sb. However, effect of the doping of graphene with transition metals of comparable size on its hydrogen sensing properties has not yet been studied. In the present study, we investigated the sensitivity of pristine graphene, Pt-doped graphene; Cu-doped graphene and Pt–Cu co-doped graphene surface towards hydrogen molecule adsorption utilizing density functional theory (DFT) by ab initio method. The adsorption energies for the optimized geometries have been calculated to probe the suitability and effectiveness of the modified graphene structures for Hydrogen sensing. In addition, the electronic properties for instance charge transfer analysis, band gap and density of states have also been taken into consideration. The reactivity of graphene surface for hydrogen adsorption was found to be greatly enhanced with Pt–Cu co-doped graphene surface as demonstrated by the adsorption energies and electronic properties.     

Influence of the ECAP and HEBM processes and the addition of Ni catalyst on the hydrogen storage properties of AZ31-x Ni (x=0,2,4) alloy

In this work, the hydrogen sorption properties of AZ31 magnesium alloys with various additions of nickel (Ni) (i.e., Ni (X = 0, 2, 4) wt.%) were investigated. Cast ingots with different AZ31/Ni_P compositions were fabricated using a gravitating mechanical stir casting (GMSC) method. Two different processes, namely, equal channel angular pressing (ECAP) and high energy ball milling (HEBM) were performed to improve its hydrogen storage properties. The particle size of the sample powders were measured by laser diffraction analysis. The microstructures, powder morphologies, and phase transformation were characterized by optical microscopy (OM), scanning electron microscopy (SEM) and x-ray diffraction (XRD) analysis. The hydrogen sorption kinetics were measured by a Sievert's type apparatus. The results showing the impact of the ECAP and HEBM processes on the hydrogen storage properties were compared. The AZ31-4 Ni ECAP processed sample showed a maximum hydrogen storage capacity of 7.0 wt.% at 2322 s with complete desorption of all the hydrogen in less than 5 min at a temperature of 375 °C. On the other hand, the pure AZ31 alloy which was treated with the HEBM process showed the maximum hydrogen capacity of 6.5 wt.% at 2393 s with desorption of all the hydrogen within 6 min. In addition, the activation energy, as illustrated by the Kissinger plot, revealed that the activation energy of the ECAP processed AZ31-4 Ni was 104.73 (KJ/mol), obviously lower than the material processed by HEBM and pure MgH₂.     

Fabrications and evaluations of hydrogen permeation on Al2O3/CeO2/graphene (ACG) composites membrane by Hot Press Sintering (HPS)

Ceramic membrane has high permeation rate of hydrogen and chemical stability. Al₂O₃ indicates stable at high temperature and a relatively large surface area. In addition, Al₂O₃ of porous is used as hydrogen separation membranes support, because of the high hydrogen permeability based on Knudsen diffusion mechanism.     

A two-stage hydrogen compressor based on (La,Ce,Nd,Pr)Ni5 intermetallics obtained by low energy mechanical alloying – Low temperature annealing treatment

La_0.67Ce_0.19Nd_0.08Pr_0.06Ni₅ was synthesized by low energy mechanical alloying. The AB₅ was milled up to completion stage to reach the final composition and appropriate particle size distribution and microstructure characteristics. Crystallite size, strain and sorption properties of as-milled samples were evaluated. After milling, La_0.67Ce_0.19Nd_0.08Pr_0.06Ni₅ and previously obtained LaNi₅ were annealed at 600 °C for 24 h. An improvement in both microstructural and hydrogen sorption properties was found. Equilibrium hydrogen sorption properties were obtained and quantified in the 25–90 °C range. From these results, a two-stage hydrogen compressor was proposed. In the first stage, hydrogen is absorbed by LaNi₅ at 575 kPa and 25 °C and desorbed at 1365 kPa and 90 °C. In the second stage, this fluid is absorbed by La_0.67Ce_0.19Nd_0.08Pr_0.06Ni₅ at 745 kPa and 25 °C and desorbed at 2100 kPa and 90 °C. As a result, a global compression ratio of 3.65 is reached using this scheme.     

Effect of B-site Al substitution on hydrogen production of La0.4Sr0.6Mn1-xAlx (x=0.4, 0.5 and 0.6) perovskite oxides

Thermochemical water splitting using perovskite oxides as redox materials is one of the important way to use solar energy to produce green hydrogen. Thus, it is hence important to discover new materials that can be used for this purpose. In this regard, we focused on Al-substituted La_0.4Sr_0.6Mn_1-xAl_xO₃ (x = 0.4, 0.5 and 0.6) perovskite oxides, namely as La_0.4Sr_0.6Mn_0.6Al_0.4 (LSMA4664), La_0.4Sr_0.6Mn_0.5Al_0.5 (LSMA4655), and La_0.4Sr_0.6Mn_0.4Al_0.6 (LSMA4646) which have been successfully synthesized. Herein, synthesized LSMA4664, LSMA4655, and LSMA4646 were subjected to three consecutive thermochemical cycles in order to determine their oxygen capacity, hydrogen capacity, re-oxidation capability and structural stability following three cycles. Thermochemical cycles were carried out at 1400 °C for reduction and 800 °C for the oxidation reaction. LSMA4646 exhibited the highest O₂ production capacity with 275 μmol/g among the other perovskites employed in the study. Moreover, LSMA4646 has also the highest H₂ production, 144 μmol/g, with 90% of re-oxidation capability by the end of three thermochemical water splitting cycles. On the other hand, LSMA4664 has the lowest H₂ production and only kept approximately one-third of its hydrogen production capacity by the end of cycles. Thus, the current study provides insight that the increase in the Al-substitution enhances both oxygen and hydrogen production capacity. Besides, increasing the Al amount increases the structural stability during the redox reactions, the re-oxidation capability was also increased from 38% to 89% after thermochemical cycles.