Hydrogen production from ethanol steam reforming over core–shell structured NixOy–, FexOy–, and CoxOy–Pd catalysts

The present work focused on the investigation of the hydrogen generation through the ethanol steam reforming over the core–shell structured Ni_xO_y–, Fe_xO_y–, and Co_xO_y–Pd loaded Zeolite Y catalysts. The transmission electron microscopy (TEM) image of Ni_xO_y–Pd represented a very clear core–shell structure, but the other two catalysts, Co_xO_y– and Fe_xO_y–Pd, were irregular and non-uniform. The catalytic performances differed according to the added core metal and the support. The core–shell structured Co_xO_y–Pd/Zeolite Y provided a significantly higher reforming reactivity compared to the other catalysts. The H₂ production was maximized to 98% over Co_xO_y–Pd(50.0 wt%)/Zeolite Y at the conditions of reaction temperature 600 °C, CH₃CH₂OH:H₂O = 1:3, and GHSV (gas hourly space velocity) 8400 h⁻¹. In the mechanism that was suggested in this work, the cobalt component played an important role in the partial oxidation and the CO activation for acetaldehyde and CO₂ respectively, and eventually, cobalt increased the hydrogen yield and suppressed the CO generation.     

Cu/MnOx–CeO2 and Ni/MnOx–CeO2 catalysts for the water–gas shift reaction: Metal–support interaction

Monometallic copper and nickel catalysts supported on cerium-manganese mixed oxides are prepared, characterized and evaluated for the Water–Gas Shift (WGS) reaction. Active metal loading of 2.5 wt% and 7.5 wt% are used to impregnate MnO_x–CeO₂ supports with 30% and 50% Mn:Ce molar ratio. The structure of the samples strongly depends on both the active metal employed and the manganese content in the mixed support. For both Cu and Ni samples, the best catalytic behavior is found in samples supported on the MnO_x–CeO₂ oxides with 30% Mn:Ce molar ratio, as a result of the presence of Cu_xMn_yO₄ spinel-type phases in the case of copper catalysts and the presence of a NiMnO₃ mixed oxide with defect ilmenite structure in the case of nickel catalysts.     

Preparation and electrochemical properties of composite LaNix/Ni–S–Co alloy film

The composite LaNi_x/Ni–S–Co film with considerable stability and high HER activity (η₁₅₀ = 70 mV, 353 K) was obtained by molten salt electrolysis combined with aquatic electrodeposition. LaNi_x film was prepared by galvanostatic electrolysis at 100 mA cm⁻² under 1273 K. The results showed that the La³⁺ ions could be reduced on the nickel cathode and the LaNi_x film could form, i.e. La³⁺ + 3e + xNi = LaNi_x (x = 5 or 3) at ca. −0.6 V, which is much lower than that of the decomposition potential of lanthanum, due to the strong depolarization effect of nickel. Furthermore, compared with the traditional amorphous Ni–S film, the composite LaNi_x/Ni–S–Co film could absorb large amount of H atoms, which would be oxidized and avoid the dissolution of the Ni–S–Co film under the state of open-circuit effectively and increase the HER activity.     

A DMFC stack operating with hydrocarbon blend membranes and Pt–Ru–Sn–Ce/C and Pd–Co/C electrocatalysts

Direct methanol fuel cell (DMFC) stacks consisting of 5 cells and 20 cells were assembled with low-cost hydrocarbon blend membranes and new electrocatalysts with better methanol tolerance and stability. The hydrocarbon blend membranes consisting of an acidic polymer (sulfonated poly (ether ether ketone), SPEEK) and a basic polymer (polysulfone-2-amide-benzimidazole, PSf-ABIm) exhibited low methanol crossover, high conductivity, and good mechanical stability. The Pt–Ru–Sn–Ce/C anode catalyst exhibited better stability than the commercial PtRu/C catalyst, while the cathode catalyst Pd–Co/C showed better methanol tolerance than the commercial Pt/C catalyst. A maximum power of around 20 W was achieved with a DMFC stack consisting of 20 membrane-electrode assemblies (MEAs) fabricated with the above membranes and electrocatalysts. The results demonstrate the feasibility of utilizing these acid-base blend membranes and novel catalysts for DMFC applications.     

Synthesis and electrochemistry of cubic rocksalt Li–Ni–Ti–O compounds in the phase diagram of LiNiO2–LiTiO2–Li[Li1/3Ti2/3]O2

On the basis of extreme similarity between the triangle phase diagrams of LiNiO₂–LiTiO₂–Li[Li_1/3Ti_2/3]O₂ and LiNiO₂–LiMnO₂–Li[Li_1/3Mn_2/3]O₂, new Li–Ni–Ti–O series with a nominal composition of Li_1+z/3Ni_1/2−z/2Ti_1/2+z/6O₂ (0 ≤ z ≤ 0.5) was designed and attempted to prepare via a spray-drying method. XRD identified that new Li–Ni–Ti–O compounds had cubic rocksalt structure, in which Li, Ni and Ti were evenly distributed on the octahedral sites in cubic closely packed lattice of oxygen ions. They can be considered as the solid solution between cubic LiNi_1/2Ti_1/2O₂ and Li[Li_1/3Ti_2/3]O₂ (high temperature form). Charge–discharge tests showed that Li–Ni–Ti–O compounds with appropriate compositions could display a considerable capacity (more than 80 mAh g⁻¹ for 0.2 ≤ z ≤ 0.27) at room temperature in the voltage range of 4.5–2.5 V and good electrochemical properties within respect to capacity (more than 150 mAh g⁻¹ for 0 ≤ z ≤ 0.27), cycleability and rate capability at an elevated temperature of 50 °C. These suggest that the disordered cubic structure in some cases may function as a good host structure for intercalation/deintercalation of Li⁺. A preliminary electrochemical comparison between Li_1+z/3Ni_1/2−z/2Ti_1/2+z/6O₂ (0 ≤ z ≤ 0.5) and Li_6/5Ni_2/5Ti_2/5O₂ indicated that charge–discharge mechanism based on Ni redox at the voltage of >3.0 V behaved somewhat differently, that is, Ni could be reduced to +2 in Li_1+z/3Ni_1/2−z/2Ti_1/2+z/6O₂ while +3 in Li_6/5Ni_2/5Ti_2/5O₂. Reduction of Ti⁴⁺ at a plateau of around 2.3 V could be clearly detected in Li_1+z/3Ni_1/2−z/2Ti_1/2+z/6O₂ with 0.27 ≤ z ≤ 0.5 at 50 °C after a deep charge associated with charge compensation from oxygen ion during initial cycle.     

Thermophysical properties and devitrification of SrO–La2O3–Al2O3–B2O3–SiO2-based glass sealant for solid oxide fuel/electrolyzer cells

Thermal behaviors and stability of glass/glass–ceramic-based sealant materials are critical issues for high temperature solid oxide fuel/electrolyzer cells. To understand the thermophysical properties and devitrification behavior of SrO–La₂O₃–Al₂O₃–B₂O₃–SiO₂ system, glasses were synthesized by quenching (25 − X)SrO–20La₂O₃–(7 + X)Al₂O₃–40B₂O₃–8SiO₂ oxides, where X was varied from 0.0 mol% to 10.0 mol% at 2.5 mol% interval. Thermal properties were characterized by dilatometry and differential scanning calorimetry (DSC). Microstructural studies were performed by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD). All the compositions have a glass transition temperature greater than 620 °C and a crystallization temperature greater than 826 °C. Also, all the glasses have a coefficient of thermal expansion (CTE) between 9.0 × 10⁻⁶ K⁻¹ and 14.5 × 10⁶ K⁻¹ after the first thermal cycle. La₂O₃ and B₂O₃ contribute to glass devitrification by forming crystalline LaBO₃. Al₂O₃ stabilizes the glasses by suppressing devitrification. Significant improvement in devitrification resistance is observed as X increases from 0.0 mol% to 10.0 mol%.     

Laminar burning velocities and flame characteristics of CO–H2–CO2–O2 mixtures

Laminar burning velocities of CO–H₂–CO₂–O₂ flames were measured by using the outwardly spherical propagating flame method. The effect of large fraction of hydrogen and CO₂ on flame radiation, chemical reaction, and intrinsic flame instability were investigated. Results show that the laminar burning velocities of CO–H₂–CO₂–O₂ mixtures increase with the increase of hydrogen fraction and decrease with the increase of CO₂ fraction. The effect of hydrogen fraction on laminar burning velocity is weakened with the increase of CO₂ fraction. The Davis et al. syngas mechanism can be used to calculate the syngas oxyfuel combustion at low hydrogen and CO₂ fraction but needs to be revised and validated by additional experimental data for the high hydrogen and CO₂ fraction. The radiation of syngas oxyfuel flame is much stronger than that of syngas–air and hydrocarbons–air flame due to the existence of large amount of CO₂ in the flame. The CO₂ acts as an inhibitor in the reaction process of syngas oxyfuel combustion due to the competition of the reactions of H + O₂ = O + OH, CO + OH = CO₂ + H and H + O₂(+M) = HO₂(+M) on H radical. Flame cellular structure is promoted with the increase of hydrogen fraction and is suppressed with the increase of CO₂ fraction due to the combination effect of hydrodynamic and thermal-diffusive instability.     

Hydrogen storage properties of Li–Ca–N–H system with different molar ratios of LiNH2/CaH2

In this work, dehydrogenation and rehydrogenation of three LiNH₂/CaH₂ samples with LiNH₂/CaH₂ molar ratio of 2/1, 3/1 and 4/1 were systematically investigated. Remarkable differences were observed in the temperature dependence of hydrogen desorption and subsequent absorption. LiNH₂/CaH₂ in a molar ratio of 2/1 transforms to ternary imide Li₂Ca(NH)₂ after desorbing about 4.5 wt.% H₂ at 350 °C. And it has a reversible hydrogen storage capacity of 2.7 wt.% at 200 °C. As for the LiNH₂/CaH₂ mixture in a molar ratio of 4/1, it transforms to a new compound with a composition of Li₄CaN₄H₆ after being dehydrogenated at 350 °C. The rehydrogenation of both LiCa(NH)₂ and Li₄CaN₄H₆ gives LiNH₂, LiH and the solid solution of 2CaNH–Ca(NH₂)₂.     

Tunable microstructure,de-/hydrogenation kinetics and thermodynamics performance of Mg–Ni–La–Ti–H systems

In the light of positive effects of rare earth and transition metals on the hydrogen absorption/desorption properties of magnesium, the Mg20La–5TiH₂, Mg20Ni–5TiH₂ and Mg10Ni10La–5TiH₂ composites have been prepared in this work to ameliorate the de-/hydrogenation kinetics and thermodynamic performance. The results indicate that the as-prepared composites are mainly composed of Mg, Mg₂Ni/LaH₃ and TiH₂ phases after activation, and LaH₃ and TiH₂ are stable during de-/hydrogenation cycles. The morphology observations give evidences that LaH₃ with size about ~20 nm and Mg₂Ni with size about ~1 μm are uniformly distributed in the composites. It is noted that the de-/hydriding kinetics of the as-prepared composites are significantly improved after internal and surface modification, of which the Mg10Ni10La–5TiH₂ composite can desorb as high as 5.66 wt% hydrogen within 3 min at 623 K. Moreover, the thermodynamic properties of the experimental composites have also been investigated and discussed according to the pressure-composition isothermal curves and corresponding calculation by Van't Hoff equation. The improved hydrogen storage properties of the as-prepared composites are mainly attributed to the uniformly distributed LaH₃, Mg₂Ni and TiH₂ phases, which provide a large amount of phase boundaries, diffusion paths and nucleation sites for de-/hydrogenation reactions.     

Ni–Fe–B catalysts for NaBH4 hydrolysis

A series of Ni–Fe–B catalysts with different Fe/(Fe + Ni) molar ratios, used for the hydrolysis of NaBH₄, were prepared by chemical reduction of NiCl₂ and FeCl₃ mixed solution with NaBH₄. The measurements revealed that the catalysts with the molar ratio of Fe/(Fe + Ni) (30%) exhibited the highest catalytic activity, and the optimal reduction temperature is 348 K. In addition, the effects of the concentration of NaBH₄, NaOH and the hydrolytic temperature of NaBH₄ were discussed in detail. The results show that the reaction rate of hydrolysis first rises up and then goes down subsequently with the increase of NaBH₄ concentration, as well as the concentration of NaOH. The activation energy of the hydrolysis for Ni–Fe–B catalysts is fitted to 57 kJ/mol. The maximum value of hydrogen generation is 2910 ml/(min g) at 298 K.     

Ce–K-promoted Co–Mo/Al2O3 catalysts for the water gas shift reaction

The effect of doping traditional Co–Mo/Al₂O₃ catalysts with Ce and K on their catalytic activity for the water gas shift reaction in coke oven gas was investigated. Doped Co–Mo/Al₂O₃ catalysts were prepared by adding different amounts of Ce and K (CeO₂, K₂O, and CeO₂–K₂O ∼10 wt%) by a wetness impregnation method and characterized by BET specific surface area measurements and scanning electron microscopy (SEM). The characterization results reveal that CeO₂ addition mainly produced an electronic effect and aided to disperse the active ingredient. At the same time, the synergistic effect between Ce and K contributed to the catalytic activity. Activity tests showed that Ce–K-promoted Co–Mo/Al₂O₃ catalysts exhibited greater activity and selectivity than Co–Mo–Ce/Al₂O₃ catalysts and Co–Mo–K/Al₂O₃ catalysts. The maximum promotion of the water gas shift reaction was observed when 3.0 wt% CeO₂ and 6.0 wt% K₂O were added.     

Experimental vapour–liquid equilibrium data of HI–H2O–I2 mixtures for hydrogen production by Sulphur–Iodine thermochemical cycle

The Sulphur–Iodine thermochemical cycle for hydrogen production has been investigated by ENEA in the framework of the Italian TEPSI Project whose main objective is the realization of an integrated loop plant at a laboratory scale. For the design of the separation–purification equipments, the study of vapour–liquid equilibrium characterization of the ternary HI–H₂O–I₂ system is considered a key factor. The aim of the present work is to provide new experimental isobaric vapour–liquid equilibrium data for this system by ebulliometry varying both temperature and solution composition. The temperature range has been extended up to about 144 °C, the iodine concentration range from 0.2%w/w to 90%w/w while HI weight fraction varies from 4%w/w to 67%w/w in the liquid phase. Most of the data obtained in this work are in good agreement with other experimental data retrieved from literature, which have been recorded in similar operative conditions but acquired by different procedures.     

Production of hydrogen by methane catalytic decomposition over Ni–Cu–Fe/Al2O3 catalyst

Catalysts with high nickel concentrations 75%Ni–12%Cu/Al₂O₃, 70%Ni–10%Cu–10%Fe/Al₂O₃ were prepared by mechanochemical activation and their catalytic properties were studied in methane decomposition. It was shown that modification of the 75%Ni–12%Cu/Al₂O₃ catalyst with iron made it possible to increase optimal operating temperatures to 700–750 °C while maintaining excellent catalyst stability. The formation of finely dispersed Ni–Cu–Fe alloy particles makes the catalysts stable and capable of operating at 700–750 °C in methane decomposition to hydrogen and carbon nanofibers. The yield of carbon nanofibers on the modified 70%Ni–10%Cu–10%Fe/Al₂O₃ catalyst at 700–750 °C was 150–160 g/g. The developed hydrogen production method is also efficient when natural gas is used as the feedstock. An installation with a rotating reactor was developed for production of hydrogen and carbon nanofibers from natural gas. It was shown that the 70%Ni–10%Cu–10%Fe/Al₂O₃ catalyst could operate in this installation for a prolonged period of time. The hydrogen concentration at the reactor outlet exceeded 70 mol%.     

Raman spectroscopic observation of dehydrogenation in ball-milled LiNH2–LiBH4–MgH2 nanoparticles

In situ Raman spectroscopy was used to monitor the dehydrogenation of ball-milled mixtures of LiNH₂–LiBH₄–MgH₂ nanoparticles. The as-milled powders were found to contain a mixture of Li₄BN₃H₁₀ and Mg(NH₂)₂, with no evidence of residual LiNH₂ or LiBH₄. It was observed that the dehydrogenation of both of Li₄BN₃H₁₀ and Mg(NH₂)₂ begins at 353 K. The Mg(NH₂)₂ was completely consumed by 415 K, while Li₄BN₃H₁₀ persisted and continued to release hydrogen up to 453 K. At higher temperatures Li₄BN₃H₁₀ melts and reacts with MgH₂ to form Li₂Mg(NH)₂ and hydrogen gas. Cycling studies of the ball-milled mixture at 423 K and 8 MPa (80 bar) found that during rehydrogenation of Li₄BN₃H₁₀ Raman spectral modes reappear, indicating partial reversal of the Li₄BN₃H₁₀ to Li₂Mg(NH)₂ transformation.     

Ni–SiO2 and Ni–Fe–SiO2 catalysts for methane decomposition to prepare hydrogen and carbon filaments

Active and stable Ni–Fe–SiO₂ catalysts prepared by sol–gel method were employed for direct decomposition of undiluted methane to produce hydrogen and carbon filaments at 823 K and 923 K. The results indicated that the lifetime of Ni–Fe–SiO₂ catalysts was much longer than Ni–SiO₂ catalyst at a higher reaction temperature such as 923 K, however, a reverse trend was shown when methane decomposition took place at a lower reaction temperature such as 823 K. XRD studies suggested that iron atoms had entered into the Ni lattice and Ni–Fe alloy was formed in Ni–Fe–SiO₂ catalysts. The structure of the carbon filaments generated over Ni–SiO₂ and Ni–Fe–SiO₂ was quite different. TEM studies showed that “multi-walled” carbon filaments were formed over 75%Ni–25%SiO₂ catalyst, while “bamboo-shaped” carbon filaments generated over 35%Ni–40%Fe–25%SiO₂ catalysts at 923 K. Raman spectra of the generated carbons demonstrated that the graphitic order of the “multi-walled” carbon filaments was lower than that of the “bamboo-shaped” carbon filaments.     

Superior low-temperature hydrogen release from the ball-milled NH3BH3–LiNH2–LiBH4 composite

In the present study, we employed a multi-component combination strategy to constitute an AB/LiNH₂/LiBH₄ composite system. Our study found that mechanically milling the AB/LiNH₂/LiBH₄ mixture in a 1:1:1 molar ratio resulted in the formation of LiNH₂BH₃ (LiAB) and new crystalline phase(s). A spectral study of the post-milled and the relevant samples suggests that the new phase(s) is likely ammoniate(s) with a formula of Li_2−x(NH₃)(NH₂BH₃)_1−x(BH₄) (0 < x < 1). The decomposition behaviors of the Li_2−x(NH₃)(NH₂BH₃)_1−x(BH₄)/xLiAB composite were examined using thermal analysis and volumetric method in a wide temperature range. It was found that the composite exhibited advantageous dehydrogenation properties over LiAB and LiAB·NH₃ at moderate temperatures. For example, it can release ∼7.1 wt% H₂ of purity at temperature as low as 60 °C, with both the dehydrogenation rate and extent far exceeding that of LiAB and LiAB·NH₃. A selectively deuterated composite sample has been prepared and examined to gain insight into the dehydrogenation mechanism of the Li_2−x(NH₃)(NH₂BH₃)_1−x(BH₄)/xLiAB composite. It was found that the LiBH₄ component does not participate in the dehydrogenation reaction at moderate temperatures, but plays a key role in strengthening the coordination of NH₃. This is believed to be a major mechanistic reason for the favorable dehydrogenation property of the composite at moderate temperatures.     

Dopant effect on hydrogen generation in two-step water splitting with CeO2–ZrO2–MOx reactive ceramics

The role played by the dopant in the H₂-generation step of two-step water splitting has been investigated with CeO₂–ZrO₂–MO_x (M = Mg, Ca, Sr, Ba, Sc, Y, Lu, La, Nd, Sm, Eu, Gd, Dy, Tm, Tb and Pr). The relationship between ionic radius, valence of the dopant, and oxidation ratio was investigated for its effect on H₂ yield. The oxidation ratio increases with an increase in the ionic radii. This tendency increases with an increase in the ionic valence (divalent < trivalent < tetravalent). This suggests that the surface process affects the chemical equilibrium of the reaction. The ionic conductivity measured by AC impedance spectroscopy showed that the increase in ionic conductivity speeds the reaction rate of H₂ generation. This indicates that a bulk diffusion process is the rate-determining step of H₂-generation reaction.     

Concentration measurements in lithium/polymer–electrolyte/lithium cells during cycling

We report on in situ and ex situ concentration measurements in lithium/polymer–electrolyte/lithium cells during cycling. We have used three different methods which give complementary results, in good agreement with theoretical predictions and previous concentration measurements by Raman confocal microspectroscopy. Our methods allow to obtain concentration maps in the electrolyte, in particular, when dendrites are observed: from these measurements, we can correlate the onset of dendritic growth with local concentration gradients.     

Phase separation characteristics of the Bunsen reaction when using HIx solution (HI–I2–H2O) in the sulfur–iodine hydrogen production process

To continuously operate an integrated sulfur–iodine (SI) hydrogen production process, the HI_x solution (HI–I₂–H₂O) could be recycled from the HI decomposition section as a reactant in the Bunsen reaction section. In this study, the temperature, iodine content and water content were varied to identify the phase separation characteristics of products from the Bunsen reaction using the HI_x solution with SO₂. Increasing the temperature increased the volume of the H₂SO₄ phase solution and decreased the impurity content in each phase. Increasing the iodine feed concentration somewhat decreased the volume of the H₂SO₄ phase solution, although the density difference between the phases increased. The amount of H₂SO₄ that separated into the H₂SO₄ phase was very small under most of these conditions, which significantly hindered the continuous operation of the integrated SI process. The feed of additional water in the separation step was suggested to improve the separation performance of the H₂SO₄ phase solution while minimizing side reactions.     

Processing analysis of the ternary LiNH2–MgH2–LiBH4 system for hydrogen storage

In this article, we investigate the ternary LiNH₂–MgH₂–LiBH₄ hydrogen storage system by adopting various processing reaction pathways. The stoichiometric ratio of LiNH₂:MgH₂:LiBH₄ is kept constant with a 2:1:1 molar ratio. All samples are prepared using solid-state mechano-chemical synthesis with a constant rotational speed, but with varying milling duration. Furthermore, the order of addition of parent compounds as well as the crystallite size of MgH₂ are varied before milling. All samples are intimate mixtures of Li–B–N–H quaternary hydride phase with MgH₂, as evidenced by XRD and FTIR measurements. It is found that the samples with MgH₂ crystallite sizes of approximately 10 nm exhibit lower initial hydrogen release at a temperature of 150 °C. Furthermore, it is observed that the crystallite size of Li–B–N–H has a significant effect on the amount of hydrogen release with an optimum size of 28 nm. The as-synthesized hydrides exhibit two main hydrogen release temperatures, one around 160 °C and the other around 300 °C. The main hydrogen release temperature is reduced from 310 °C to 270 °C, while hydrogen is first reversibly released at temperatures as low as 150 °C with a total hydrogen capacity of ∼6 wt.%. Detailed thermal, capacity, structural and microstructural properties are discussed and correlated with the activation energies of these materials.