Production of hydrogen via hydrolysis of hydrides in Mg–La system

Hydrogen generation via hydrolysis of 250 mg hydrogenated Mg₃La and La₂Mg₁₇ in 100 ml water has been investigated at 298 K. Hydrolysis reactions of hydrogenated Mg₃La and La₂Mg₁₇ obtained by induction melting and then hydrogenated at 298 K is found to be fast when they are immersed in water. The hydrolysis reaction of hydrogenated Mg₃La almost completes within 21 min with faster kinetics and higher yield than those obtained of hydrogenated La₂Mg₁₇. The hydrogen production rate is 43.8 ml min⁻¹ g⁻¹ of hydrogen in the first 20 min of reaction compared to a conversion yield of 88% for hydrogenated Mg₃La and 40.1 ml min⁻¹ g⁻¹ of hydrogen in the first 20 min of reaction for hydrogenated La2Mg17. It is related to the catalytic effect of LaH₃ formed during the hydriding process, accentuating corrosion of MgH₂ greatly. The experimental curves of hydrogen generation kinetics at room temperature are well fitted by the Avrami–Erofeev equation. The reaction mechanism of hydrogenated Mg₃La and La₂Mg₁₇ was also discussed.     

On the hydriding kinetics of the alloys La2Mg17 and La2−xCaxMg17

The hydriding kinetics of the alloys La₂Mg₁₇, La_1.8Ca_0.2Mg₁₇ and La_1.6Ca_0.4Mg₁₇ are studied using experimental data from previous papers [Khrussanova et al., J. Less-Common Metals86, 153 (1982); Khrussanova et al., Int. J. Hydrogen Energy10, 591 (1985)] and the kinetic equations proposed by Park and Lee [J. Less-Common Metals83, 39 (1982)] and Song and Lee [Int. J. Hydrogen Energy8, 363 (1983)]. It is established that at low values of the reacted fraction (0 < F < 0.4) hydrogen chemisorption on the alloy surface is the rate-controlling stage of the process, the partial substitution of calcium for lanthanum enhancing the activation energy of chemisorption from 16.6 kJ mol⁻¹ for La₂Mg₁₇ to 24.9 kJ mol⁻¹ for La_1.8Ca_0.2Mg₁₇. At higher F values hydriding is controlled by hydrogen diffusion through the hydride layer being formed. In this case the introduction of calcium facilitates the hydrogen diffusion by increasing the hydride/alloy interface.     

Hydrogenation and electrochemical studies of La–Mg–Ni alloys

La–Mg–Ni alloys are potential candidates for hydrogen storage materials. In this study, mechanical alloying with subsequent annealing under an argon atmosphere at 973 K for 0.5 h, were used to produce La_2-xMg_xNi₇ alloys (x = 0, 0.25, 0.5, 0.75, 1). Shaker type ball mill was used. An objective of the present study was to investigate an influence of amount of Mg in alloy on electrochemical, hydrogenation and dehydrogenation properties of La–Mg–Ni materials. X-ray diffraction analyses revealed formation of material with multi-phase structure. Obtained materials were studied by a conventional Sievert's type device at 303 K. It was observed that electrochemical discharge capacity and gaseous hydrogen storage capacity of La–Mg–Ni alloys increases with Mg content to reach maximum for La_1.5Mg_0.5Ni₇ alloy. Moreover, all of La–Mg–Ni alloys were characterized by improved hydrogen sorption kinetics in comparison to La–Ni alloy.     

Investigation of the thermodynamic and kinetic properties of La–Fe–B system hydrogen-storage alloys

La–Fe–B hydrogen-storage alloys were prepared using a vacuum induction-quenching furnace with a rotating copper wheel. The thermodynamic and kinetic properties of the La–Fe–B hydrogen-storage alloys were investigated in this work. The P–C–I curves of the La–Fe–B alloys were measured over a H₂ pressure range of 10⁻³ MPa to 2.0 MPa at temperatures of 313, 328, 343 and 353 K. The P–C–I curves revealed that the maximum hydrogen-storage capacity of the alloys exceeded 1.23 wt% at a pressure of approximately 1.0 MPa and temperature of 313 K. The standard enthalpy of formation ΔH and standard entropy of formation ΔS for the alloys' hydrides, obtained according to the van't Hoff equation, were consistent with their application as anode materials in alkaline media. The alloys also exhibited good absorption/desorption kinetics at room temperature.     

Effect of rare earth elements on electrochemical properties of La–Mg–Ni-based hydrogen storage alloys

La_0.60R_0.20Mg_0.20(NiCoMnAl)_3.5 (R = La, Ce, Pr, Nd) alloys were prepared by inductive melting. Variations in phase structure and electrochemical properties due to partial replacement of La by Ce, Pr and Nd, were investigated. The alloys consist mainly of LaNi₅ phase, La₂Ni₇ phase and LaNi₃ phase as explored by XRD and SEM. The maximum discharge capacity decreases with Ce, Pr and Nd substitution for La. However, the cycling stability is improved by substituting Pr and Nd at La sites, capacity retention rate at the 100th cycle increases by 13.4% for the Nd-substituted alloy. The electrochemical kinetics measurements show that Ce and Pr substitution improves kinetics and thus ameliorates the high rate dischargeability (HRD) and low temperature dischargeability. The HRD at 1200 mA g⁻¹ increases from 22.1% to 61.3% and the capacity at 233 K mounts up from 90 mAh g⁻¹ to 220 mAh g⁻¹ for the Ce-substituted alloy.     

Synthesis and characterization of dense proton-conducting La1-xSrxScO3-α ceramics

Research into the synthesis of oxide materials exhibiting high ionic conductivity values allows these materials to be used for the fabrication of such high-temperature electrochemical devices as fuel cells, gas sensors, electrolyzers, etc. A focused interest in the physical and chemical properties of oxide proton conductors is driven by the phenomenon of proton transfer in those solids, where hydrogen is not a structural unit. LaScO₃-based materials are considered to be promising for high-temperature engineering due to their bulk conductivity at low temperatures, chemical resistance and mechanical strength as compared to widely-used proton-conducting cerate- and zirconate-based electrolytes. A series of experiments was performed to compare the properties of La_1-xSr_xScO_3-α (х = 0.05; 0.10) solid proton-conducting electrolytes synthesized using different methods. An alternative combustion method that does not apply nitrates as precursor materials is proposed. This method allowed ceramics with a density greater than 98% of theoretical to be obtained. A detailed qualitative and quantitative evaluation was performed at different synthesis stages using the methods of X-ray diffraction, scanning electron microscopy, X-ray fluorescent and atomic emission spectroscopy. The structure parameters of La_1-xSr_xScO_3-α were determined by full-profile Rietveld X-ray diffraction analysis. The thermal expansion and electrical conductivity of La_1-xSr_xScO_3-α (x = 0.05, 0.10) materials having various densities were studied in oxidizing and reducing atmospheres under changes in the temperature and humidity of the gas phase. The contribution of bulk and grain boundary conductivities was assessed using the impedance method. Both conductivities are established to exhibit the same activation energy for the materials with a density of 94–98% of the theoretical value. The high porosity of the materials (30%) is shown to adversely affect the total conductivity, with the bulk conductivity remaining almost at the same level. A bridge model based on semi-coherent boundaries is proposed for explaining a low grain boundary conductivity in proton electrolytes having a low-symmetry crystal lattice.     

High performance of Mg–La mixed oxides supported Ni catalysts for dry reforming of methane: The effect of crystal structure

A series of mixed Mg–La oxide supports with various Mg²⁺/La³⁺ mole ratios were prepared via co-precipitation of Mg and La nitrates, and then impregnated to form 5 wt.% Ni catalysts. The as-prepared catalysts were evaluated in DRM reaction for 200 h and characterized by means of in situ DRIFTS, XRD, TEM, CO₂-TPD, XPS, and TGA. It was found that the interaction of suitable amount of MgO with La₂O₃ stabilized cubic La₂O₃ species in catalysts, which has high basicity to adsorb CO₂ forming monoclinic La₂O₂CO₃ (Ia) species in DRM reaction. The introduction of MgO also created surface oxygen ions (i.e. O^–). Both monoclinic La₂O₂CO₃ (Ia) and surface oxygen species are able to oxidize and remove deposited carbon, keeping the Ni catalyst at high activity and stability. Low Mg²⁺/La³⁺ ratios generated hexagonal La₂O₃ and La₂O₂CO₃ (II) in DRM reaction. The hexagonal La₂O₂CO₃ (II) did not play significant role in carbon removal so that the catalysts deactivated fast.     

Function of Al on the cycling behavior of the La–Mg–Ni–Co-type alloy electrodes

The cycling behavior of the _{La0.7Mg0.3Ni2.65-xCo0.75Mn0.1Alx}${\mathrm{La}}_{0.7}{\mathrm{Mg}}_{0.3}{\mathrm{Ni}}_{2.65-x}{\mathrm{Co}}_{0.75}{\mathrm{Mn}}_{0.1}{\mathrm{Al}}_x$(x=0,0.3)$(x=0,0.3)$ alloy electrodes was systematically investigated by XRD, SEM, EIS, XPS and AES measurements, and the function of Al in the La–Mg–Ni-based alloys and the reasons for the improvement of the cycling stability of the alloy electrode with Al were discussed. Results show that the cycling behavior of the _{La0.7Mg0.3Ni2.35Co0.75Mn0.1Al0.3}${\mathrm{La}}_{0.7}{\mathrm{Mg}}_{0.3}{\mathrm{Ni}}_{2.35}{\mathrm{Co}}_{0.75}{\mathrm{Mn}}_{0.1}{\mathrm{Al}}_{0.3}$ alloy electrode can be divided into three stages, i.e., the pulverization and Mg oxidation stage, the Mg oxidation and La and/or Al oxidation stage, and the La and Al oxidation and Al oxide film protection stage. The improvement of the cycling stability of the alloy electrode with Al can be ascribed to two factors. One is the decrease in the pulverization of the alloy particles during charge/discharge cycling due to the alloy with Al undergoes a smaller cell volume expansion and contraction. The other is the increase in the anti-oxidation/corrosion due to the formation of a dense Al oxide film during cycling, which is believed to be the most important reason for the improvement of the cycling stability of the La–Mg–Ni–Co–Mn–Al-type alloy electrodes.     

Effect of Mo–Ni treatment on electrochemical kinetics of La–Mg–Ni-based hydrogen storage alloys

In order to improve kinetic properties of La–Mg–Ni-based hydrogen storage alloys, Mo–Ni treatment was applied to La_0.88Mg_0.12Ni_2.95Mn_0.10Co_0.55Al_0.10 alloy powders. FESEM results showed that after Mo–Ni treatment some network-shaped substance with nano-size formed on the surface of the alloy particles. The EDS results revealed increase in Ni content and emerge of Mo element. EIS and Linear polarization showed that charge-transfer resistance decreased and exchange current density increased for the treated alloy electrode, and the high rate dischargeability (HRD) was consequently improved. HRD at 1500 mA/g increased from 22.5% to 39.5%. Mo- and Ni-single treatments were performed compared with the Mo–Ni treatment, and the results showed that the single treatment improved HRD slightly, far less than the Mo–Ni treatment.     

Polytypism of La–Ni phases in multicomponent AB5 type hydride electrode alloys

The microstructure of multi-component AB₅ type alloy Ml(NiCoAl)₅ (Ml, Lanthanum riched misch rare earth metal) has been characterized using transmission electron microscopy, high resolution electron microscopy and energy dispersive spectrum analysis. The intermetallic phases Ml₅(NiCoAl)₁₉ of Ce₅Ni₁₉ (hexagonal 2H) type and Ml₂(NiCoAl)₇ phase of La₂Ni₇ type with two kinds of polytypes (modifications) are found for the first time to exist as equilibrium phases in stoichiometric Ml–Ni–Co–Al alloys after arc melting. All of the polytypes existing in the multicomponent alloys keep well-defined orientation relationship with the AB₅ type matrix expressed as the [0−10]_CaCu5||[0−10]_polytype and (001)_CaCu5||(001)_polytype. The misfit dislocations at the interfaces between polytypes structure and parent alloy matrix were clearly observed in high resolution electron microscopy (HREM) image. The possible reasons, which cause the formation of the polytypes and the effect of the polytypes on the hydrogen absorbing/desorbing properties for the multicomponent alloys are discussed.     

Ni/La2O3 and Ni/MgO–La2O3 catalysts for the decomposition of NH3 into hydrogen

The decomposition of NH₃ for hydrogen production was studied using Ni/La₂O₃ catalysts at varying compositions and temperatures prepared via surfactant-templated synthesis to elucidate the influence of catalyst active metal content, support composition and calcination temperature on the catalytic activity. The catalytic performance of all samples was studied between 300 and 600 °C under atmospheric pressure. The catalytic activity of the sample were as follows: 10Ni/La₂O₃-450 > 10Ni/La₂O₃-550 > 10Ni/La₂O₃-650 ≈ 10Ni/La₂O₃-750 ≈ 10Ni/La₂O₃-850. The excellent activity (100%) of 10Ni/La₂O₃-450 could be due to the high surface area, basicity strength and concentration of surface oxygen species of the catalyst as evidenced by BET, CO₂-TPD and XPS. In addition, to adjust the activity of the catalyst support, the molar ratios of Mg and La were varied (1:1, 3:1, 5:1, 7:1 and 9:1). The 5Ni/5MgLa (5:1 M ratio) was found to be the most active (100%) relative to other Ni/MgLa formulations. Furthermore, the Ni content in the Ni/5MgLa sample was adjusted between 10 and 40 wt%. Increasing the Ni content of the catalysts increased NH₃ conversion with the 40 wt% Ni formulation demonstrating complete NH₃ conversion at 600 °C and a high gas hourly space velocities (GHSV) (30,000 mL∙h⁻¹∙g_cat⁻¹).     

Effect of boron additive on electrochemical cycling life of La–Mg–Ni alloys prepared by casting and rapid quenching

In order to improve the electrochemical performances of La–Mg–Ni system (PuNi₃-type) hydrogen storage alloy, a trace of B was added in La₂Mg(Ni_0.85Co_0.15)₉ alloy. La₂Mg(Ni_0.85Co_0.15)₉B_x${}_x$ (x=0,0.05,0.1,0.15,0.2$x=0,0.05,0.1,0.15,0.2$) hydrogen storage alloys were prepared by casting and rapid quenching. The electrochemical charging-discharging cycling lives and microstructures of the as-cast and quenched alloys were measured and analyzed. The effects of B additive on the microstructures and cycling lives of as-cast and quenched alloys were investigated in detail. The results show that the as-cast and quenched alloys are composed of the (La, Mg)Ni₃ phase (PuNi₃ structure), the LaNi₅ phase and the LaNi₂ phase. A trace of the Ni₂B phase exists in the as-cast alloys containing B. The Ni₂B phase in the alloys containing B nearly disappears after rapid quenching and the relative ratio of each phase in the alloys changes with the variety of the quenching rate. The addition of B obviously enhances the charging-discharging cycling stabilities of the as-cast and quenched alloys. When B content x$x$ increases from 0 to 0.2, the cycling lives of the as-cast and quenched at 20 m/s alloys were increased from 72 to 94 cycles and from 86 to 104 cycles, respectively.     

Effect of Y element on cyclic stability of A2B7 -type La–Y–Ni-based hydrogen storage alloy

The La_3-xY_xNi_9.7Mn_0.5Al_0.3 (x = 1, 1.5, 1.75, 2, 2.25, 2.5) alloys were prepared by magnetic suspension induction melting method and annealed at 1273 K for 24 h. The alloys were tested using electrochemical measurements, X-ray diffraction (XRD) and scanning electron microscope with energy-dispersive X-ray diffraction spectroscope (SEM-EDS). With the increase of Y content, the main phase of the alloys changed from Gd₂Co₇ phase to Ce₂Ni₇ phase, and Ce₂Ni₇ phase increased gradually. The maximum discharge capacity of alloys increased from 279.3 mA h/g (x = 1) to 383.8 mA h/g (x = 2.5). The high-rate dischargeabilitiy at the discharge current density of 1200 mA/g increased from 56.98% (x = 1) to 83.76% (x = 2.5). The maximum capacity retention rate first increased from 50.13% (x = 1) to 69.43% (x = 2), and then decreased to 21.35% (x = 2.5). The results showed that the structural stability of the alloys was improved due to the increase of Y content. However, with the increase of Y content, the corrosion, pulverization, and the dissolution of Al element aggravated, which deteriorated the cyclic stability of the alloy electrodes.     

Improved polarization behaviour of nanostructured La0.65Sr0.3MnO3 cathode with engineered morphology

We report a simple synthesis of La_0.65Sr_0.3MnO₃ nanorods (LSM-R) through hydrothermal reaction followed by calcination at high temperature (700–850 °C). Thermogravimetric analysis and XRD study reveals that 850 °C is adequate for phase pure LSM-R formation. The microstructure of the powder has been clinically studied using FESEM and TEM. It is observed that the intermediate hydrothermal treatment plays key role in formation of such nanorods. Different bulk properties of LSM-R like sinteractivity, CTE, density, electrical conductivity etc. have been comprehensively studied. A maximum electrical conductivity of around 250 S/cm at 800 °C is obtained when LSM-R specimen is sintered at 1200 °C/2 h. The cathodic polarization of such LSM-R is measured using impedance analysis. It is observed that polarization value initially decreases attains minimum and then starts to increase with increase in cathode sintering temperature and dwelling time. A minimum cathodic polarization value of 0.32 Ω/cm² at 800 °C is obtained at an optimized cathode sintering condition of 1000 °C/2 h.     

Synthesis and hydrogenation properties of Mg–La–Ni–H system by reactive mechanical alloying

We have synthesized Mg–30 mass%LaNi_2.28 composite material and investigated its hydrogenation behaviour. The reactive mechanical alloying process of the mixture of Mg and LaNi_2.28 was studied. It is found that a composite of _MgH2${\mathrm{MgH}}_2$, _La4H12.9${\mathrm{La}}_4{\mathrm{H}}_{12.9}$ and _Mg2NiH4${\mathrm{Mg}}_2{\mathrm{NiH}}_4$ formed after 80 h ball-milling under 3.0 MPa hydrogen. Scanning electron microscopic analysis indicated that these new phases are distributed homogeneously. This composite shows excellent hydriding properties even at moderate temperature. Under 3.0 MPa hydrogen pressure it absorbed more than 80% of its full capacity in the temperature range of 473–553 K within less than 1 min. The maximum hydrogen absorption capacity at 553 K is 5.4 mass%. The enhanced hydriding properties could be attributed to the fine and uniform particles and a synergeticly catalytic effect generated by mechanical milling.     

Structures and properties of Mg–La–Ni ternary hydrogen storage alloys by microwave-assisted activation synthesis

It is a challenge to prepare a material meeting two conflicting criteria – absorbing hydrogen strongly enough to reach a stable thermodynamic state and desorbing hydrogen at moderate temperature with a fast reaction rate. With the guide of the Mg–La–Ni phase diagram, microwave sintering (MS) was successfully applied to preparing Mg–La–Ni ternary hydrogen storage alloys from the powder mixture of Mg, La and Ni. Their phase structures, morphologies and hydrogen absorption and desorption (A/D) properties have been studied by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), pressure-composition-isotherm (PCI) and differential scanning calorimetry (DSC). The metal hydride of 70 Mg–9.72 La–20.28 Ni (wt pct) has the best comprehensive hydriding and dehydriding (H/D) properties, which can absorb 4.1 wt.% H₂ in 600 s and desorb 3.9 wt.% H₂ in 1500 s at 573 K. The DSC results reveal its onset temperatures of hydrogen A/D are the lowest among all the samples, which are 671.4 and 600.9 K. Its activation energy of dehydriding reaction is 113.5 kJ/mol H₂, which is the smallest among all the samples. Also, Chou model was used to analyze the reaction kinetic mechanism.     

Composition dependent microstructure evolution,activation and de-/hydrogenation properties of Mg–Ni–La alloys

In this work, in order to elucidate the effect of different alloying elements on the microstructure, activation and the de-/hydrogenation kinetics performance, the Mg–20La, Mg–20Ni and Mg–10Ni–10La (wt.%) alloys have been prepared by near equilibrium solidification combined with high-energy ball milling treatment to realize the internal optimization as well as particle refinement. The results show that the microstructures of the prepared alloys are significantly refined by forming different types and sizes of intermetallic compounds. Meanwhile, the effects of LaH₃ and Mg₂Ni within the activated samples on de-/hydrogenation kinetics are also discussed. It is observed that the alloy containing LaH₃ preserves stable hydrogenation behavior between 573 and 623 K, while the hydrogenation properties of the alloy containing Mg₂Ni is susceptible to temperature. A preferable hydrogenation performance is observed in Mg–10Ni–10La alloy, which can absorb as high as 5.86 wt% hydrogen within 15 min at 623 K and 3.0 MPa hydrogen pressure. Moreover, the desorption kinetics and the desorption activation energies are evaluated to illustrate the mechanism based on improved dehydrogenation performance. The addition of proper alloying elements Ni and La in combination with reasonable processing is an effective strategy to improve the de-/hydrogenation performance of Mg-based alloys.     

La Spezia电站的4号锅炉

La Spezia电站的扩建,将使其成为意大利发电量最大的电站之一。已经运行的1号及2号机组系CE型的强制循环锅炉,合计容量为65万瓩。拟扩建的容量为120万瓩,包括两套60万瓩的单元机组,扩建后的电站总容量为185万瓩。     

Hydrogen production from oxidative steam reforming of ethanol over Ir catalysts supported on Ce–La solid solution

The Ce_1?xLa_xO_2?δ solid solution (CL) supported Ir (nIr/CL, n = 2, 5 and 10 wt.%) catalysts are studied for H₂ production from ethanol oxidative steam reforming (OSR). The Ir dispersion, surface area, oxygen vacancy density and carbon deposition resistance of nIr/CL catalysts are greatly enhanced compared with Ir/CeO₂. Among the tested catalysts, 5%Ir/CL shows the best catalytic performance, exhibiting >99.9% ethanol conversion at 400 °C with H₂ yield rate of 323 μmol·g_cata^?1·s^?1 and no obvious carbon deposition after used. The 5%Ir/CL catalyst contains the highest amount of reducible interface Ce⁴⁺, leading to a strong interaction with surface Ir species at the metal-support interface during the OSR reaction. The strong interaction induces Ir to be well dispersed on the CL support, and is associated with more redox-active sites (interface Ce⁴⁺/Ce³⁺), to guarantee high activity.