Effect of substitutional elements on hydrogen absorption properties in Mm-based AB5 alloys
TL;DR: In this paper, the authors studied the hydrogen absorption isotherms for the CaCu5 hexagonal structured alloys MmNi3.4, Mm Ni3.8Al 0.368Mn0.5Fe0.4Co 0.333V0.333Al0.3Fe0,4Fe 0.5Co 0,5Fe 0,6Al 0,7Al 0 0,8Al0 0.4Fe0 0,4Co0.
Abstract: Hydrogen absorption isotherms for the CaCu5 hexagonal structured alloys MmNi3.8Al0.4Fe0.4Co0.4, MmNi3.5Al0.5Fe0.5Co0.5, MmNi3.4Mn0.4Al0.4Fe0.4Co0.4, MmNi3.368Mn0.333V0.333Al0.3Fe0.333Co0.333 and MmNi3Mn0.333V0.333Al0.333Fe0.333Co0.333Cu0.333 with Fe and Co in the mole ratio 1:1 have been obtained in the temperature and pressure ranges 30≤T/°C≤100 and 0.1≤P/bar≤30 using a high pressure unit based on the pressure reduction method. The powder X-ray diffractograms of the unannealed alloys show the formation of single phase. The lattice constants and the unit cell volume of these alloys increase with substitution of Mn, V, Cu, Fe, Al and Co at the Ni site in MmNi5. The hydrogen absorption isotherms show the presence of a single plateau region (α+β) in the temperature and pressure ranges studied. The hydrogen absorption studies show no marked change in the plateau slope due to the presence of Fe and Co in 1:1 mole ratio. The maximum hydrogen intake capacity (r=nH/nf.u.) is around 4.75 in MmNi3.8Al0.4Fe0.4Co0.4 at 30 °C and at 30 bar. The dependence of the thermodynamics of dissolved hydrogen in these alloy hydrides on the hydrogen concentration shows the different phase regions α, α+β and β seen in the hydrogen absorption isotherms. At any particular temperature investigated, the chemical potential of dissolved hydrogen in these alloy hydrides decreases with the substitution of Mn, V, Cu, Fe, Al and Co at the Ni site, which has been correlated with the increase in the volume of the unit cell of the alloys. The desorption isotherms of MmNi3.8Al0.4Fe0.4Co0.4 at 30 and 50 °C show that the hysteresis is very small with free energy loss per cycle about 0.4 kJ/mol H at 30 °C. The kinetics of hydrogen absorption at 30, 50, 75 and 100 °C have been studied for MmNi3.8Al0.4Fe0.4Co0.4. The different phases identified by both kinetic and thermodynamic studies confirm those seen in the hydrogen absorption isotherms. The average activation energies Ea in the α, (α+β) and β phases are found to be 0.38 eV, 0.32 eV and 0.054 eV, respectively. The diffusion coefficient at 303 K in MmNi3.8Al0.4Fe0.4Co0.4–H is about 2.55×10−10 cm2 s−1. The powder X-ray diffractograms of the alloy hydrides show that these alloys do not undergo any structural transformation upon hydrogenation.
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TL;DR: In this paper, the authors explored the technical issues surrounding the use of hydrogen storage, in conjunction with a PEM electrolyser and PEM fuel cell, to guarantee electricity supply when the energy source is intermittent, most typically solar photovoltaic.
Abstract: The use of intermittent renewable energy sources for power supply to off-grid electricity consumers depends on energy storage technology to guarantee continuous supply. Potential applications of storage-guaranteed systems range from small installations for remote telecoms, water-pumping and single dwellings, to farms and whole communities for whom grid connection is too expensive or otherwise infeasible, to industrial, military and humanitarian uses. In this paper we explore some of the technical issues surrounding the use of hydrogen storage, in conjunction with a PEM electrolyser and PEM fuel cell, to guarantee electricity supply when the energy source is intermittent, most typically solar photovoltaic. We advocate metal-hydride storage and compare its energy density to that of Li-ion battery storage, concluding that a significantly smaller package is possible with metal-hydride storage. A simple approach to match the output of a photovoltaic array to an electrolyser is presented. The properties required for the metal-hydride storage material to interface the electrolyser to the fuel cell are discussed in detail. It is concluded that relatively conventional Mischmetal-based AB5 alloys are suitable for this application.
115 citations
TL;DR: In this paper, the role of Mn in C14 Laves phase alloys for battery applications was studied by adjusting the Mn content in exchange with Ni and Cr in three series of C14 AB2 Laves Phase alloys.
Abstract: The role of Mn in C14 Laves phase alloys for battery applications was studied by adjusting the Mn content in exchange with Ni and Cr in three series of C14 AB2 Laves phase alloys. Additional B-modifiers, such as Sn, Co, and Al as a group, were also compared to Mn using AB2 MH alloys in a nickel metal hydride (NiMH) battery. In all cases, higher Mn content degraded the cycle life performance while marginally increasing the discharge capacity. Without the presence of other modifiers, such as Sn, Co, and Al, Mn proved to be detrimental to both charge retention and activation of Ti-based C14 Laves phase MH alloys. However, in combination with Sn, Co, and Al; Mn contributed positively to charge retention while activation remained at a manageable level. It has also been shown a lower Mn and higher Ni content improved the specific power and low temperature performance, whereas increasing Cr content at the expense of Mn improved cycle life and charge retention in a NiMH battery.
61 citations
TL;DR: In this paper, the effects of aluminum substitution to the structural, electrochemical, and gas phase hydrogen storage properties of C14-rich alloys were reported, including minor phases including C15 and TiNi, identified by X-ray diffraction analysis.
Abstract: The effects of aluminum substitution to the structural, electrochemical, and gas phase hydrogen storage properties of C14-rich alloys are reported. Minor phases, including C15 and TiNi, were identified by X-ray diffraction analysis. Entropy and enthalpy were estimated from equilibrium pressure at a fixed hydrogen concentration due to the large slope factor in pressure–concentration–temperature isotherms. The stability of hydrides from these materials, determined from the pressure–concentration isotherm equilibrium pressure and maximum storage capacities has a better correlation with the change in entropy than that in enthalpy. Alloys having smaller unit cell volume, relatively low hydride heat of formation, and relatively higher degree of disorder exhibit lower plateau pressure, higher storage capacity, and smaller hydrogen diffusion coefficient. Comparing to the Co substitution in the same base alloy, Al substitution makes better contribution to both bulk hydrogen transport and surface reaction. Substituting 0.4% Al and 1.5% Co to AB2 alloy is found to be the best combination in terms of general nickel metal hydride battery performance.
48 citations
TL;DR: In this article, a novel AB5-type, non-stoichiometric, lanthanum-rich MmNi3.03Si0.85Co0.60Mn0.31Al0.08 (Mm: Misch metal) hydrogen storage metal hydride alloy electrodes are prepared.
Abstract: The heat of hydride formation is a crucial parameter in characterizing a hydrogen storage alloy for battery applications. Novel AB5-type, non-stoichiometric, lanthanum-rich MmNi3.03Si0.85Co0.60Mn0.31Al0.08 (Mm: Misch metal) hydrogen storage metal hydride alloy electrodes are prepared. Electrochemical hydrogen absorption/desorption and electrochemical impedance measurements are carried out at various temperatures in conjunction with sintered nickel hydroxide positive electrodes. The specific capacity of the prepared metal hydride electrodes decreases from 283 mAh g−1 at 303 K to 213 mAh g−1 at 328 K. Electrochemical pressure–composition–temperature (PCT) isotherms are constructed from galvanostatic discharge curves and the change in enthalpy ( Δ H e ° ) and the change of entropy ( Δ S e ° ) of the metal hydride alloy electrodes are evaluated as −41.74 kJ mol−1 and 146.28 J mol−1 K−1, respectively. Kinetic parameters are obtained by fitting the electrochemical impedance spectrum performed at different temperatures. The charge-transfer resistance decreases with temperature, whereas exchange current density and diffusion coefficient parameters increase with temperature. It is concluded that the deterioration in capacity is due to enhanced surface activity at higher temperatures.
44 citations
TL;DR: In this article, the performance of metal hydride based cooling system (MHCS) is evaluated by characterizing intermetallic hydrides to determine their suitability in MHCS, and the effect of compositional changes on the variation of these parameters due to the variation in pressure concentration isotherm properties (storage capacity, plateau slope, hysteresis effect, etc.) was studied.
Abstract: The La0.9Ce0.1Ni5, La0.8Ce0.2Ni5, LaNi4.7Al0.3 and LaNi4.6Al0.4 intermetallic hydrides were characterised to determine their suitability in metal hydride based cooling system (MHCS). The performance of the MHCS depends on the driving potential, and rate and amount of hydrogen transfer between coupled metal hydride (MH) beds. Therefore, the effect of compositional changes on the variation of these parameters due to the variation in pressure – concentration isotherm (PCI) properties (storage capacity, plateau slope, hysteresis effect, etc.) of metal hydrides employed was studied. Compared to other possible MH pairs, La0.9Ce0.1Ni5 – LaNi4.7Al0.3 hydride pair exhibited high driving potential and transferrable amount of hydrogen, during cooling and regeneration processes, thereby better MHCS performance. In addition, the effect of change in hydrogen concentration (due to hydrogen transfer between coupled MH beds) on reaction enthalpy (ΔH) consequently on MHCS performance was found significant.
37 citations
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TL;DR: A key to pharmaceutical and medicinal chemistry literature and training of literature chemists are discussed in the Advances series as mentioned in this paper, with the focus on the training of chemistry chemists, which is a subject of great interest to the literature chemist.
Abstract: NUMBERS 16 and 17 in the Advances series have made their appearance. The titles are: "A Key to Pharmaceutical and Medicinal Chemistry Literature" and "Training of literature Chemists." The first is a collection of papers presented before the Divisions of Chemical Literature and Medicinal Chemistry; the second consists of papers given before a joint meeting of the Divisions of Chemical Education and Chemical Literature. Glancing at the titles of subjects covered to date in the Advances series, it becomes evident that a substantial literature is being built by literature chemists, largely through the divisions in the AMERICAN CHEMICAL SOCIETY. Number 4, "Searching the Chemical Literature," has been reprinted several times and frequently is referred to as the "bible" of literature chemists. Number 10, "Literature Resources for Chemical Process Industries," is in much demand. Nomenclature is a subject of direct importance to the literature chemist, and Number 8, entitled "Chemical Nomenclature," and ...
3,188 citations
TL;DR: In this paper, the structural and electrochemical properties of the La0.7Mg0.3(Ni0.85Co0.15)x (x=3.15, 3.30), 3.65,3.50, and 3.80) hydrogen storage electrode alloys have been studied systematically.
Abstract: In this paper, the structural and electrochemical properties of the La0.7Mg0.3(Ni0.85Co0.15)x (x=3.15, 3.30, 3.50, 3.65, 3.80) hydrogen storage electrode alloys have been studied systematically. From the XRD analyses, each alloy of this series is composed of the LaNi3 phase and the LaNi5 phase, and the phase abundance of each phase varies with the degree of non-stoichiometry x and determines the hydrogen absorption capacity of the alloy. The electrochemical studies show that as x increases the maximum discharge capacity first increases from 365.7 mAh/g (x=3.15) to 398.4 mAh/g (x=3.50) and then decreases to 328.5 mAh/g (x=3.80). Moreover, as x increases from 3.15 to 3.80, the high rate dischargeability (HRD), the exchange current density (I0), the limiting current density (IL) and the diffusion coefficient (D), of the alloy electrodes all increase first and then decrease.
139 citations
TL;DR: In this paper, the magnetic properties of the hydrides were determined and compared with the original compounds and it was shown that the magnetic moment per Fe atom is much larger in hydride phases.
Abstract: X-ray diffraction studies of the hydrogen absorption in several YFe and CeFe intermetallic compounds showed that no structural changes occur upon hydrogen absorption in Y6Fe23, YFe3, YFe2. The lattice constants of the hydrides were found to be appreciably larger than those of the pure intermetallic compounds. The magnetic properties of the hydrides were determined and compared with the original compounds. In all cases the magnetic moment per Fe atom proved to be much larger in the hydride phases. Hydrogen absorption can lead to a decrease as well as to an increase of the magnetic ordering temperature (Tc). These changes in Tc could adequately be explained in terms of the observed increases in lattice constant and the data available for the pressure derivative of Tc of these compounds.
89 citations
TL;DR: In this paper, the authors studied the hydrogen absorption-desorption characteristics of multicomponent alloys such as MmNi5−xAl(Mn)y−zMz and MnNi5 −xMnyM2.
Abstract: In order to reduce the large hysteresis effect in MmNi hydrides (Mm misch metal) we studied the hydrogen absorption-desorption characteristics of multicomponent alloys such as MmNi5−xAl(Mn)y−zMz and MmNi5−xAl(Mn)yM2 (M = Co, Cr, Cu, Nb, Ti, V, Zr; x = 0.3 − 0.5; y = 0.3 − 0.5; z = 0.05 − 0.1). The substitution or addition of the element M eliminates the large hysteresis effect that occurs during an absorption-desorption cycle. The hysteresis factor (equal to In( P a P d )) for MmNi4.7Al0.3M0.1 hydrides decreased for additives M in the following order: Zr > Co > Cr > Ti,V > Cu. Investigations of the effects of cycling showed that spalling occurred more rapidly for MmNi4.5Mn0.5 than for MmNi4.5Mn0.5Zr0.005 and MmNi4.5Mn0.5Zr0.1.
75 citations
TL;DR: The hydrogen absorption and desorption characteristics of mischmetal (Mm)-nickel-aluminum alloys were investigated in this paper, where the same hexagonal structure as LaNi5 and MmNi5 was found to react readily with hydrogen to form the hydrides MnNi4.5Al0.75 Al0.5A10.
Abstract: The hydrogen absorption and desorption characteristics of mischmetal (Mm)-nickel-aluminum alloys were investigated. MmNi5−xAlx (x = 0.25 −0.5) have been found to have the same hexagonal structure as LaNi5 and MmNi5, and they reacted readily with hydrogen to form the hydrides MmNi4.75 Al0.25H5.4, MmNi4.65Al0.35H 5.3H5.3 and MmNi4.5Al0.5H4.9 (hydrogen content: 1.3,1.2 and 1.2 wt.%, respectively) under 60 atm hydrogen pressure at room temperature. The dissociation pressures of these hydrides were dependent on the aluminum content (aluminum partially substitutes for nickel) and the value of log Pbecame lower than the value for MmNi5 hydride as x increased. The enthalpy change on hydride formation as determined from the dissociation isotherms for the MmNi4.5Al0.5-H system was − 5.5 kcal (mol H2)−1; this value was smaller than those for LaNi5 and MmNi5. The dissociation pressure at 30 °C was 3 atm and was nearly the same as that of LaNi5. The desorption rate of hydrogen for MmNi4.5Al0.5 was larger than those for LaNi5 and MmNi5) and a value of 2.1 – 4.3 kcal mol−1 was obtained for the apparent activation energy of hydrogen desorption. For MmNi4.5Al0.5 the hydrogen absorption-desorption cycle was repeated 30 times, but no variation in the hydrogen absorption-desorption capacity was observed. The hydride of MmNi4.5A10.5 proved to be suitable for use as a stationary hydrogen storage material.
64 citations