Surface coating with a high resistance to hydrogen entry under high-pressure hydrogen-gas environment

Development of a surface coating with high resistance to hydrogen entry under a high-pressure hydrogen-gas environment is presented. Two aluminum-based coatings were developed on the basis of preliminary tests: two-layer (alumina/Fe–Al) and three-layer (alumina/aluminum/Fe–Al) coatings, deposited onto cylindrical and pipe (Type 304 austenitic stainless steel) surfaces by immersion into a specially blended molten aluminum alloy. The coated specimens were exposed to hydrogen gas at 10–100 MPa at 270 °C for 200 h. Specimen hydrogen content was measured by thermal desorption analysis; hydrogen distributions were analyzed by secondary ion mass spectroscopy. Both coatings showed high hydrogen-entry resistance at 10 MPa. However, resistance of the two-layer coating clearly decreased with an increase in pressure. In contrast, the three-layer coating showed excellent hydrogen-entry resistance at a wide pressure range (10–100 MPa), achieved by the combined effect of alumina, aluminum, and Fe–Al layers.     

Producing hydrogen in an aqueous NaCl solution by the hydrolysis of metallic couples of low-grade magnesium scrap and noble metal net

As part of the trend toward an increasing fuel conscious economy, the automobile industry has increased the number of components that are produced from Mg alloy. Additionally, Mg alloy products have been widely adopted in the structure, outer shell and base seat of 3C (computer, communication, and consumer electronics) products. Therefore, from the manufacture to the end-of-life of Mg products, a very large amount of post-consumer Mg scrap is expected to be produced. This work presents a novel process for converting low-grade Mg scrap (LGMS) into H₂ and Mg(OH)₂. A molten LGMS bath at 580 °C in a semi-solid state was prepared. A platinum-coated Ti (Pt-Ti) net and 304 stainless steel (S.S.) net were used as metallic catalysts. A hot dipping process involved dipping the catalyst nets into the molten Mg scrap bath to obtain an Mg overlayer on the metallic net. The galvanic couple (LGMS/Pt-Ti net and LGMS/S.S. net) generated hydrogen in an NaCl solution (3.5 wt.%). The mean volume of hydrogen generated in 50 min was 28.2 ± 5.7 L as the catalyst was platinum-coated titanium and 16.1 ± 7.8 L was produced when the catalyst was stainless steel. On average, one gram of LGMS yielded approximately 1 L of H₂. Experimental results concerning the metallic catalysts reveal that the platinum-coated titanium and stainless steel can be reused at least five times with comparable H₂ yields. However, the performance of the catalysts gradually worsened as the number of recyclings increased.     

Enhanced sintering resistance of Fe2O3/CeO2 oxygen carrier for chemical looping hydrogen generation using core-shell structure

CeO₂-supported Fe₂O₃ is a satisfactory oxygen carrier for chemical looping hydrogen generation (CLHG). However, the sintering problem restrains its further improvement on redox reactivity and stability. In the present work, a core-shell-structured Fe₂O₃/CeO₂ (labeled Fe₂O₃@CeO₂) oxygen carrier prepared by the sol-gel method was studied in a fixed bed. The effect of the core-shell structure on the sintering resistance and redox performance was investigated with a homogenous composite sample of Fe₂O₃/CeO₂ as a reference. The results showed that the Fe₂O₃@CeO₂ exhibited much higher redox reactivity and stability than the Fe₂O₃/CeO₂ with no CO or CO₂ observed in the generated hydrogen, while the hydrogen yield for Fe₂O₃/CeO₂ decreased with redox cycles due to serious sintering. The satisfactory performance of Fe₂O₃@CeO₂ can be ascribed to its high sintering resistance, since the core-shell structure suppressed the outward migration of Fe cations from the bulk to the surface of the particles. On the other hand, the migration of Fe cations and their subsequent enrichment on the particle surface led to the serious sintering of Fe₂O₃/CeO₂. The crystallite size evolution of Fe₂O₃ and CeO₂ in redox cycles further demonstrated the higher sintering resistance of Fe₂O₃@CeO₂. Further, the particle size distribution (PSD) results indicated the agglomeration of Fe₂O₃/CeO₂ after cycles. In addition, the CeO₂ shell could facilitate the transport of oxygen ions between the iron oxide nanoparticle core and the shell surface. Therefore, the coating of nanoscale Fe₂O₃ with a CeO₂ shell did not reduce the redox reactivity and stability of Fe₂O₃@CeO₂, but rather promoted it, though less oxygen-ionic-conductive CeFeO₃ was generated.     

Study on hydrogen generation and cornstalk degradation by redox coupling of non-noble metal Fe3+/Fe2+

Environmental application of cornstalk and production of hydrogen from biomass are two vital research topics. Herein, a low-cost easy preparing strategy was proposed for trying to give a solution. Non-noble metal of Fe ion was used as an oxidizing agent and electron stockpile carrier for degrading cornstalk and providing e^? to the cathode. Using proton exchange electrolysis technique, it can realize H₂ production with a Faraday Efficiency of 94.65%. Different influence factors including temperature, electrolytic potential and electrolytic current density were studied. To the degradation products, the preliminary analyses by SEM, FT-IR, GC-MS and 2D HSQC NMR were given. The results demonstrate that Fe³⁺/Fe²⁺-cornstalk electrolytic system could give a new pathway for environmental application of cornstalk and production of hydrogen.     

Influence of surface martensite layer on hydrogen embrittlement of Fe-Mn-C-Mo steels in wet H2S environment

This study investigated the effect of thermally induced surface martensite layer on hydrogen embrittlement of Fe-16Mn-0.4C-2Mo (wt.%) (16Mn) and Fe-25Mn-0.4C-2Mo (wt.%) (25Mn) steels through slow strain rate stress corrosion cracking testing and proof ring testing in wet H₂S environment. The 16Mn steel had a surface layer of less than 150 μm in depth containing ε-martensite, α′-martensite and austenitic twins. The martensite layer is found to reduce the hydrogen embrittlement resistance of the steel. In comparison, the 25Mn steel developed a full α′-martensite surface layer, which exhibited practically nil effect on the hydrogen embrittlement resistance of the steel. The ε-martensite provides much larger interface areas with the mechanical twins of the austenite in the 16Mn steel than the α′-martensite/austenite interfaces in the 25Mn steel. These interfaces are hydrogen trapping sites and are prone to initiate surface cracks, as observed in the scanning electron microscope. The formation of the cracks is attributed to hydrogen concentration at the ε-martensite and austenitic twin interfaces, which accelerates material fracture.     

Fast response of hydrogen sensor using palladium nanocube-TiO2 nanofiber composites

In this work, we investigated the properties of resistivity type hydrogen (H₂) sensor for monitoring in H₂ gas. The H₂ sensor was made of Pd nanocube (NCs) and TiO₂ nanofiber (NFs) composites. The Pd NCs was synthesized by seed-mediated growth and TiO₂ nanofiber was synthesized via electrospinning method. The two nanomaterials are then converted into nanocomposites by ultrasonication process. Pd NCs-TiO₂ NFs composite was characterized by scanning electron microscope (SEM) and high resolution transmission electron microscope (HRTEM). The H₂ sensing properties including the response/recovery time, the response value and linearity of the synthesized samples were investigated toward to various H₂ concentrations (0.6, 0.8 and 1%). The response of H₂ sensor is S = 40.8% and the response/recovery time are 25/1 s with 0.6% at working temperature of 150 °C. Moreover, the H₂ sensor has excellent cross-selectivity for H₂ compared to ethanol, nitrogen dioxide and isopropyl alcohol.     

Activating Fe2O3 using K2CO3-containing ethanol solution for corn stalk chemical looping gasification to produce hydrogen

Alkaline organic liquid waste was introduced to activate Fe₂O₃ and provide sufficient steam to boost biomass chemical looping gasification (CLG) for H₂ production. Experiments under different excess oxygen ratios, temperatures, and alkali contents were performed to investigate the reaction characteristics of alkaline organic waste - biomass CLG. The highest H₂ yield of 1.71 L and carbon conversion rate of 83.8% were obtained at the excess oxygen ratio of 0.2, the alkali concentration of 6%, and the reaction temperature of 800 °C. Moreover, the kinetic and thermodynamic analysis under the optimized condition have cast light on the fundamental understanding of alkaline organic liquid waste - biomass CLG. Results demonstrate that this novel approach has the potential to enhance energy conversion.     

An investigation of the effect of hydrogen on ductile fracture using a unit cell model

The effect of hydrogen on the ductility of metals is studied by incorporating the hydrogen diffusion process and the hydrogen enhanced localized plasticity (HELP) into a finite element program. A series of unit cell analyses are conducted under various stress states and the loading speed resulting in a steady state hydrogen distribution is determined. The evolution of the local stress and deformation states results in hydrogen redistribution in the material, which in turn changes the material's flow property due to the HELP effect. It is found that localized plastic deformation plays a major role in increasing the hydrogen concentration due to the newly generated trapping sites. The HELP effect promotes material failure by accelerating void growth, which is affected by the macroscopic stress state subjected by the material unit characterized by the stress triaxiality and the Lode parameter. For a constant Lode parameter, the effect of HELP on void growth and failure strain reduction increases with the stress triaxiality. For a constant stress triaxiality, the effect of HELP is highest when the Lode parameter is near 0. As the Lode parameter increases towards 1 or decreases towards −1, the HELP effect gradually diminishes.     

3D cohesive modelling of hydrogen embrittlement in the heat affected zone of an X70 pipeline steel

A three-dimensional finite cohesive element approach has been developed and applied in order to simulate the crack initiation of hydrogen-induced fracture. A single edge notched tension specimen of an X70 weld heat affected zone was simulated. The results were compared to similar two-dimensional plane strain model and the cohesive parameters were calibrated to fit the experimental results. The three dimensional simulations gave higher values in terms of opening stress at the stress peak, plastic strain levels at the crack tip and hydrogen lattice concentration when compared with two-dimensional simulations under the same global net section stress levels. Nevertheless a higher cohesive strength was needed for the 2D model for the onset of crack propagation. The best fit to the experimental data were obtained for a cohesive strength of 1840 MPa and 1620 MPa for the 2D and 3D simulation respectively. The critical opening was assigned to 0.3 mm for both models. The threshold stress intensities K_IC,HE were 142 MPa√m and 146 MPa√m for the 2D and 3D models, respectively.     

Establishment of an in-situ small punch test method for characterizing hydrogen embrittlement behaviors under hydrogen gas environments and new influencing factor

The hydrogen embrittlement (HE) behaviors of structural materials used to handle hydrogen must be tested at their use environments. In this study, an in-situ small punch (SP) test method was established to characterize HE behaviors of SA372 and STS304 steels under hydrogen gas environments at high pressures and low temperatures. In addition, a new influencing factor, relative reduction of thickness (RRT) was proposed to quantify the HE sensitivity of structural steels. Under 10 MPa H₂ gas environment, load-displacement curves obtained and fractographic morphologies of the recovered specimens were analyzed to investigate the HE behaviors based on punch velocity and test temperature. When the HE sensitivity was evaluated by RRT, STS304 steel appeared to be vulnerable to HE as compared to SA372 steel across the tested temperature range. As a result, it was found that in-situ SP test and RRT can be used to quantify the HE sensitivity for structural materials screening regardless of test environments.     

In situ measurement of plasticity accompanying hydrogen induced cracking in a polycrystalline AlZnMg alloy

Hydrogen induced single crack propagation is studied in an embrittled aluminum alloy. Hydrogen is introduced into the system by electrochemical reactions in an acidic aqueous medium. After hydrogen charging, tensile tests are performed in air, on notched samples, with a microtensile machine under an optical microscope. A high magnification of × 2000 is used to follow the single crack initiation and propagation. Digital Image Correlation gives the displacement field on the surface with a spatial resolution of approximately 1 μm. It enables the determination of the position of the crack tip and the local velocity at a sub-grain scale. The von Mises strain is calculated and provides a precise measure of the local plastic field that accompanies crack propagation. In addition to the primary plasticity which is emitted from the crack tip or its immediate neighborhood in the form of two intense slip bands, a secondary plastic zone that spreads over several microns ahead of the tip is sytematically found. The characteristics of the plastic zone are measured, together with the velocity and the applied stress intensity factor. In addition, different fracture mechanisms are found on the fracture surface. In particular there are transitions in the fracture mode from intergranular smooth to transgranular parallel to the grain boundary plane. The local fracture mechanisms, in the vicinity of the surface, are linked to the local velocities and plastic deformations. Surprisingly no strong velocity/plasticity correlations are found while the velocities are scattered over a wide range, which is interpreted as a strong polycrystalline effect.     

One-step water splitting and NaHCO3 reduction into hydrogen storage material of formate with Fe as the reductant under hydrothermal conditions

In this paper, we give an overview of recent advances in the production of formic acid, as a hydrogen carrier, from CO₂ and water by using the earth-abundant metal of Fe as the reductant under hydrothermal conditions, which mainly includes: 1) hydrogen production from water with Fe; 2) reduction of HCO₃^– to formic acid in the presence and absence of catalysts; 3) proposed reaction mechanisms. The novel options under this study are mainly the use of water as a hydrogen source with metal Fe as a reductant, and the formed Fe_xO_y as an auto-catalyst. Such a process possesses several benefits: (i) water acts not only as a hydrogen source but also as an environmentally benign solvent; (ii) there are no hydrogen requirements, including pumps or storage, because hydrogen is derived from water and reacts with CO₂in situ; (iii) no exotic catalysts or harsh reagents are used; and (iv) the method is simple and highly efficient. This technology can provide a one-step, sustainable and highly efficient way to reduce CO₂ into formic acid using the hydrogen directly from water.     

Highly sensitive hydrogen sensor based on a new suspended structure of cross-stacked multiwall carbon nanotube sheet

In this research, we proposed a highly sensitive hydrogen sensor based on a new suspended structure of cross-stacked multiwall carbon nanotube (MWCNT) sheet. MWCNT sheet is a kind of CNT film which has a super-high CNT alignment and can be easily prepared by drawing from the spinnable CNT array in large scales. By stacking the sheets onto an electrode with a 1 × 1 cm hole in mutually perpendicular directions, sensors with suspended cross-stacked structure were realized. Afterwards, a two-side Pd functionalization was introduced. The effects of suspended structure, cross-stacked structure and two-side Pd functionalization were investigated respectively. It was observed that the sample with 2 + 1 layers of cross-stacked MWCNT sheet and two-side 3 nm Pd deposition showed the best gas sensing performance with a relative resistance change of 35.30% at 4% H₂. This result indicates that the proposed sensor is one of the best among all reported MWCNT based hydrogen sensors. The method demonstrated in this research gives a potential solution for the mass production of CNT-based sensors with high sensitivity and reliability.     

In situ synthesis by organometallic method of vulcan supported PdNi nanostructures for hydrogen evolution reaction in alkaline solution

Pd and Pd-based catalysts for hydrogen production remain the best alternative to Pt substitution because of similarities in their electronic structure and more abundant reserves. In this work, it was carried out the in-situ synthesis of Pd_xNi_1-x/C electrode materials (x = 0, 30, 50, 70 and 100 wt%) by the displacement of ligands from organometallic compounds followed by an annealing process at 300 °C in Ar atmosphere. The electrocatalytic performance of these materials was evaluated on the hydrogen evolution reaction in alkaline medium (1 M KOH). The results showed that annealing process, after the synthesis of stabilized nanostructures by organometallic method, did not affect the particle size (4.27 ± 1.14 to 4.62 ± 1.59 nm) and dispersion (25.75–27.07%) of the alloyed nanostructures. The modification of Pd electronic features with low Ni amount facilitates the adsorption of the hydrogen on the bimetallic active surface of the catalysts. The PdNi alloys, especially Pd₇₀Ni₃₀/C, tend to display the overpotential of HER to more positive values in comparison with Pd/C catalysts. This behavior is clearly correlated with an improvement by the synergistic effect between the components, which in turn enhance the electrochemical surface area (ECSA) and the real area. Either the hydrogen adsorption resistance and charge transfer resistance are dependent of the Ni amount, due to Ni influences ion/atom recombination or hydrogen desorption.     

In situ tuning of band gap of Sn doped composite for sustained photocatalytic hydrogen generation under visible light irradiation

The significance of Sn dopant on the photocatalytic performance of Iron/Titanium nanocomposite towards photocatalytic hydrogen generation by water splitting reaction is investigated. Iron/Titanium nanocomposite modified by Sn⁴⁺ dopant acts as a suitable photocatalyst for induced visible light absorption facilitating pronounced charge separation efficiency. Various characterization techniques reveal the heterojunction formation of hematite Fe₂O₃ with anatase - rutile mixed phase of TiO₂ employing Sn doping, where Sn⁴⁺ dopant accomplishes the phase transformation of anatase to rutile, entering into the TiO₂ lattice. This extended the lifetime of photogenerated charge carriers and enhanced the quantum efficiency of the photocatalyst. The band gap of the nanocomposite is tuned to ~2.4 eV, favoring visible light absorption. A hydrogen generation activity of 1102.8 μmol, approximately five times higher than the lone system (216.5 μmol) is achieved for the 5% Sn doped system for an average of 5 h. Heterojunctions of hematite with anatase-rutile mixed phase, generated as a consequence of tin doping facilitated the enhanced hydrogen generation activity of photocatalyst.     

In situ growth of MoS2 on carbon nanofibers with enhanced electrochemical catalytic activity for the hydrogen evolution

Developing an effective and facile method to achieve mass production of MoS₂ nanostructures with abundant of edges may be the feasible way to meet the increasing demand for hydrogen evolution electrocatalysts. We developed a facile glucose-assisted hydrothermal method to in-situ grow MoS₂ nanosheets on the commercial carbon nanofibers (CNFs). The controlled growth of MoS₂ on CNFs (MoS₂@CNFs) is leveraged to reveal mass ratio- and structure-dependent catalytic activity in the hydrogen evolution reaction (HER). Due to the unique shell structure, abundant edges of the MoS₂ layer are exposed as active site, as well as the underlying CNFs effectively improves the conductivity, the resulting MoS₂@CNFs hybrid exhibited high electrocatalytic activity in HER. The catalyst demonstrated the lowest overpotential of 52 mV, the highest current density of 101.49 mA cm^?2 at ～200 mV overpotential and the smallest Tafel slope of 49 mV/decade, suggesting the Volmer–Heyrovsky mechanism for the MoS₂-catalyzed HER.     

In situ synthesis of V2O3@Ni as an efficient hybrid catalyst for the hydrogen evolution reaction in alkaline and neutral media

The exploration of cheap and efficient electrodes for hydrogen evolution reactions (HER) is extremely challenging. Herein, we report a newly-designed V₂O₃@Ni hybrid grown in situ on nickel foam as an efficient HER catalyst. The nickel foam not only promoted the electron transfer rate as a supporting substrate, but also worked as the source of Ni to enhance the integration of catalyst components with abundant active sites. Moreover, benefitting from the synergistic effect of the interface between V₂O₃ and Ni, which accelerated the entire electrochemical kinetics and facilitated the electron transfer, the in situ V₂O₃@Ni hybrid catalysts afforded a small overpotential of 47 mV and 100 mV at a current density of 10 mA cm^?2 in 1.0 M KOH and 1.0 M PBS, respectively, and with excellent long-term stability. In addition, this research provides a new route for the fabrication of noble-metal-free electrocatalysts with excellent HER performance over a broad range of pH values.     

3D simulation of hydrogen distributions affected by a passive auto-catalytic recombiner in an oxygen-starved condition

In this paper, we simulated the change in hydrogen behavior according to a Passive Autocatalytic Recombiner (PAR) under oxygen depletion conditions and compared the results with the THAI project experimental results. In order to reduce calculation cost, we calculated the hydrogen-oxygen bonding reaction in the catalyst region through correlation equations of the hydrogen removal rate according to the PAR type, and we did not consider the shape of the catalyst with a relatively small size and the detailed hydrogen-oxygen bonding reaction. The hydrogen concentration at the PAR inlet and outlet, mixed gas temperature, flow rate at PAR inlet, pressure and total hydrogen removal rate were similar to the experimental results and analysis values in all cases and the reduction in the hydrogen removal rate agreed well under oxygen depletion conditions. However, after the hydrogen injection was stopped, errors of the hydrogen concentration and flow rate at the PAR inlet increased as the buoyancy decreased because the high temperature of the catalyst was not taken into account.     

Optimization of hydrogen production from three reforming approaches of glycerol via using supercritical water with in situ CO2 separation

A pathway for hydrogen production from supercritical water reforming of glycerol integrated with in situ CO₂ removal was proposed and analyzed. The thermodynamic analysis carried out by the minimizing Gibbs free energy method of three glycerol reforming processes for hydrogen production was investigated in terms of equilibrium compositions and energy consumption using AspenPlus™ simulator. The effect of operating condition, i.e., temperature, pressure, steam to glycerol (S/G) ratio, calcium oxide to glycerol (CaO/G) ratio, air to glycerol (A/G) ratio, and nickel oxide to glycerol (NiO/G) ratio on the hydrogen production was investigated. The optimum operating conditions under maximum H₂ production were predicted at 450 °C (only steam reforming), 400 °C (for autothermal reforming and chemical looping reforming), 240 atm, S/G ratio of 40, CaO/G ratio of 2.5, A/G ratio of 1 (for autothermal reforming), and NiO/G ratio of 1 (for chemical looping reforming). Compared to three reforming processes, the steam reforming obtained the highest hydrogen purity and yield. Moreover, it was found that only autothermal reforming and chemical looping reforming were possible to operate under the thermal self-sufficient condition, which the hydrogen purity of chemical looping reforming (92.14%) was higher than that of autothermal reforming (52.98%). Under both the maximum H₂ production and thermal self-sufficient conditions, the amount of CO was found below 50 ppm for all reforming processes.