CaNi5-based alloys and nanoconfined NaAlH4 for solid-state hydrogen storage

A simple mechanical ball-milling and annealing has been used to synthesize CaNi5-based alloys. Heat treatment at 800 ºC under vacuum results in the formation of a crystalline CaNi5 phase. CaNi4.9Al0.1 shows durability improvement by maintaining its initial hydrogen absorption capacity for 20 cycles performed at 85 ºC. NaAlH4 was confined within 2-3 nm pores in a carbon scaffold and shows significant improvement in the hydrogen desorption kinetics and thermodynamic properties compared to bulk NaAlH4

Hydrogen Storage Materials for Mobile and Stationary Applications: Current State of the Art

One of the limitations to the widespread use of hydrogen as an energy carrier is its storage in a safe and compact form. Herein, recent developments in effective high-capacity hydrogen storage materials are reviewed, with a special emphasis on light compounds, including those based on organic porous structures, boron, nitrogen, and aluminum. These elements and their related compounds hold the promise of high, reversible, and practical hydrogen storage capacity for mobile applications, including vehicles and portable power equipment, but also for the large scale and distributed storage of energy for stationary applications. Current understanding of the fundamental principles that govern the interaction of hydrogen with these light compounds is summarized, as well as basic strategies to meet practical targets of hydrogen uptake and release. The limitation of these strategies and current understanding is also discussed and new directions proposed

Physical and Electrical Property of TiO<sub>2</sub> Nanotube Arrays for Supercapacitors

TiO2 nanotube arrays (TiO2 NTAs) were prepared by anodization method. The as-prepared TiO2 NTAs were annealed at 450 °C for 3 h transforming amorphous TiO2 to anatase TiO2. The inner diameter and tube length of synthesized TiO2 NTAs are approximately 100 nm and 1.0 mm, respectively. Electric double-layer capacitor (EDLC) was fabricated using TiO2 NTAs as electrodes with 6 M KOH electrolyte. The internal resistance of the EDLC is relatively low (3.8 – 6.5 Ω) depending on the operating temperature. This work confirmed experimentally the use of TiO2 NTAs as EDLC electrodes.</jats:p

Effect of Aging Heat Treatment on Corrosion Behavior and Corrosion Kinetics of 17-4PH Stainless Steel in Artificial Saliva

The corrosion behavior of the sintered 17-4PH stainless steel samples aged at different conditions in artificial saliva was studied using the method of electrochemical and weight loss after exposure for various periods of time. The results showed that the samples aged at 480 °C for 1 h exhibited the highest corrosion resistance.The pitting corrosion was predominantly initiated from existing, isolated pores and further accelerated. The corrosion kinetics trend is found to be more consistent with a bimodal function form rather than the classical power-law function.</jats:p

Effect of Al and Mo substitution on the structural and hydrogen storage properties of CaNi5

A simple mechanical milling and annealing process has been used to synthesize CaNi5-based hydrogen storage alloys. Heat treatment at 800°C under vacuum results in theformation of a crystalline CaNi5 phase. Secondary phases, including Ca2Ni7 and MoeNi, areformed when substituting Mo for Ni. Replacement of Ni by Al or Mo leads to an increase inthe unit cell volume of the CaNi5 phase. The hydrogen storage capacity of all substitutedalloys is reduced and the plateau pressures are lower than those of pure CaNi5. Fairly flatplateau regions are retained for all compositions except the CaNi4.8Mo0.2 compositionwhere a Ca2Ni7 phase is dominant. The incorporation of Mo also causes slow sorptionkinetics for the CaNi4.9Mo0.1 alloy. CaNi4.9Al0.1 maintains its initial hydrogen absorptioncapacity for 20 cycles performed at 85°C but the other substituted alloys lose their capacityrapidly, especially the CaNi4.8Mo0.2 composition

Cycle life and hydrogen storage properties of mechanical alloyed Ca1-xZrxNi5-yCry; (x=0, 0.05 and y=0, 0.1)

CaNi5–based alloys have been synthesized by mechanical alloying followed by isothermal annealing. The formation of the CaNi5 structure occurred when the milled powders were heated at 800 °C under vacuum for 3 h. The abundance of CaNi5 phase in the alloys ranges from 60 to 70 wt.%. Replacement of Zr into the Ca site reduces the unit cell volume of CaNi5 whilst replacement of Cr into the Ni site slightly increases the unit cell volume. The hydrogen storage capacity of all substituted alloys is decreased and the hydrogen sorption plateau regions are narrowed compared to those of pure CaNi5. Substitution of Zr into the Ca site extinguishes the flat plateau region unlike replacement of Cr into the Ni site where a flat plateau is maintained. The reaction enthalpy ΔH for both absorption and desorption are directly proportional to the unit cell volume of the alloys. The hydrogen storage capacity of all alloys rapidly decays for the first 50 cycles at 85 °C followed by a more gradual decline after 50 further cycles. The hydrogen storage capacity of the alloys after 200 cycles is in the range of 65–75% of the initial capacity

First-order phase transition in the Li2B12H12 system

The thermal decomposition of anhydrous Pa[3 with combining macron] Li2B12H12 was studied in situ by high resolution synchrotron X-ray diffraction. A first-order phase transition can be observed at 355 °C where the unit cell volume expands by ca. 8.7%. The expanded β-Li2B12H12 polymorph simultaneously decomposes to a hydrogen poor γ-Li2B12H12−x phase. Expansion of the unit cell across the discontinuity is consistent with reorientational motion of B12H122− anions, and the presence of a frustrated Li+ lattice indicating Li ion conduction

Nanoconfinement degradation in NaAlH4/CMK-1

An ordered mesoporous carbon scaffold (CMK-1) has been synthesized and infiltrated with NaAlH4 nanoparticles by solvent- and melt-infiltration techniques. Small angle X-ray scattering (SAXS), powder X-ray diffraction (XRD), scanning electron microscopy (SEM), Transmission Electron Microscopy (TEM) and energy dispersive spectroscopy (EDS) are used to characterize the structure, composition and morphology before and after thermal treatment. This study illuminates some of the problems that can be associated with nanoconfinement of hydrogen storage materials including scaffold contamination, residual solvent contamination, sample morphology changes after heating, and other factors that can be detrimental to the application of these systems. Of particular interest is the expulsion of NaAlH4 decomposition products from the scaffold after heating beyond its melting point under vacuum. This results in the surface of mesoporous carbon particles having arrays of multi-micron-long Al filaments that are >100 nm in diameter