Browsing by Author "Sumita Srivastava"

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Hydrogenation behaviour with regard to storage capacity, kinetics, stability and thermodynamic behaviour of hydrogen storage composite alloys, LaNi5/La2Ni7, LaNi3
(Elsevier BV, 1999) Sumita Srivastava; O.N. Srivastava
The present study deals with investigations into the composite hydrogen storage materials LaNi5/La2Ni7, LaNi3, for improved hydrogenation characteristics. To achieve this goal, extensive investigations were carried out to study the effect of the presence of secondary phases on the main phase LaNi5, with reference to hydrogenation behaviour, including incubation time, p-c isotherms, desorption kinetics, hysteresis factor, cyclic stability and thermodynamic behaviour. Alloys were synthesized through melt-casting with varying concentrations of secondary phases like La2Ni7, LaNi3, Ni (minor phases), i.e. 55%, 30%, 5% and 0%, using a special technique of pellet encapsulation. Structural characterization using the XRD technique confirmed the formation of secondary phases together with major phase LaNi5. Microstructural evaluations through SEM revealed that secondary phases suppressed pulverization. Investigations on the hydrogenation behaviour of these alloys showed that the presence of secondary phases in small quantities resulted in a much lower incubation time (lower by 63%), in comparison to singular LaNi5 alloy. The hydrogen storage capacity and desorption kinetics did not decrease for minor concentrations of secondary phases, but a decrease was found for the alloys having higher concentrations of secondary phases. The hysteresis factor has also been found to be less for the multiphasic alloy. The cyclic stability test with regard to storage capacity degradation, showed a higher stability of the alloy having a small concentration of secondary phases. Thermodynamic parameters have been found to be: ΔH (change in enthalpy), -9.05 and -7.03 kcal mol , and ΔS (change in entropy), 31.92 and 23.64 cal mol-1 K-1, for the alloys with 5% and 0% secondary concentrations. © 1999 Elsevier Science S.A. All rights reserved.
Investigations of synthesis and characterization of MmNi4.3Al0.3Mn0.4 and MmNi4.0Al0.3Mn0.4Si0.3, hydrogen storage materials through thermal and spin melting processes
(Elsevier Ltd, 1998) Sumita Srivastava; O.N. Srivastava
The present study deals with investigations on the synthesis and characterization of negative electrode material for high energy density Ni-MH battery. The hydrogen storage material (MH) has been synthesized through thermal and spin melting techniques. A comparative study of materials synthesized by these two techniques with emphasis on the characteristics relevant to battery electrode applications has been carried out. In the present study, the modified composition of AB5-type corresponds to the spin as well as thermal melted versions of MmNi4.3Al0.3Mn0.4 and MmNi4.0Al0.3Mn0.4Si0.3. Structural characterization has revealed that, whereas for the spin melted MmNi4.3Al0.3Mn0.4 the dominant growth is perpendicular to the c-axis, it is parallel to the c-axis for MmNi4.0Al0.3Mn0.4Si0.3. The hydrogenation behaviour of these materials has been monitored through P-C-T and kinetic curves. Attempts have been made to establish a correlation between the structure and hydrogenation behaviour. The spin melted material (MmNi4.3Al0.3Mn0.4) exhibits reduced pulverization and hence is expected to have increased cycle life. This version of the material also exhibits higher storage capacity, faster kinetics and faster activation as compared to the conventionally prepared bulk form. The bulk version of the alloy with silicon has been found to undergo easy activation (2nd cycle) as compared to the bulk version of the alloy without silicon (6th cycle). The spin melted version of the material with silicon leads to smaller (finer) particle size material compared to the alloy form without silicon. © 1997 International Association for Hydrogen Energy.
Investigations on synthesis, characterization and hydrogenation behaviour of the spin- and thermal-melted versions of LaNi5 - xSix (x = 0.1, 0.3, 0.5) hydrogen storage materials
(Elsevier BV, 1998) Sumita Srivastava; O.N. Srivastava
The present study deals with investigations on the synthesis and characterisation of negative electrode material for high energy density Ni-MH battery. The hydrogen storage material (MH) has been synthesised through normal casting and melt-spinning techniques. In LaNi5/MmNi5 family various substitutions like Al, Mn, Co have been studied. The substitution of metalloid like Si is known to be very helpful in improving several hydrogenation properties. In the present study, the Si substituted versions of AB5-type storage materials typified by LaNi5 - xSix (x = 0.1,0.3,0.5) have been investigated. A comparison between the present material and the conventional AB5-type material MmNi4.3Al0.3Mn0.4 has also been made which has been previously studied. The main features revealed by XRD characterisations are the existence of the free Ni and Si together with AB5 material for all the three compositions. These free Ni and Si were found to disappear and yield, giving rise to a singular material after hydrogenation. The melt-spun version of the material was found to grow invariably in a direction perpendicular to the c-axis. The kinetics and activation process was better for the melt-spun version of the LaNi4.7Si0.3 alloy than its thermally-melted counterpart (bulk) as well as to the alloy MmNi4.3Al0.3Mn0.4. For example, the kinetics of the melt-spun version of LaNi4.7Si0.3 is 60% faster than its bulk version and 70% faster than the melt-spun version of MmNi4.3Al0.3Mn0.4. Similarly, the melt-spun version of the alloy LaNi4.7Si0.3 gets activated in the 2nd cycle itself where as the alloy MmNi4.3Al0.3Mn0.4 attains this stage only in the 6th cycle. © 1998 Elsevier Science S.A.
On the synthesis and characterization of some new AB5 type MmNi4.3Al0.3Mn0.4, LaNi5-xSix (x = 0.1, 0.3, 0.5) and Mg-x wt% CFMmNi5-y wt% Si hydrogen storage materials
(Elsevier Science Ltd, 2000) Sumita Srivastava; S.S. Sai Raman; B.K. Singh; O.N. Srivastava
The viability and feasibility of AB5 type hydrides - MmNi4.3Al0.3Mn0.4, LaNi5-xSix and Mg-x wt% CFMmNi5-y wt% - as hydrogen storage materials were investigated. The hydrides were synthesized through normal casting and melt spinning techniques. The melt-spun version was superior over the bulk version with regards to the kinetics and activation process. Si substitution resulted in faster absorption and desorption kinetics and improved activation.
Recent developments in state-of-the-art hydrogen energy technologies – Review of hydrogen storage materials
(Elsevier Ltd, 2023) Rupali Nagar; Sumita Srivastava; Sterlin Leo Hudson; Sandra L. Amaya; Ashish Tanna; Meenu Sharma; Ramesh Achayalingam; Sanjiv Sonkaria; Varsha Khare; Sesha S. Srinivasan
Hydrogen energy has been assessed as a clean and renewable energy source for future energy demand. For harnessing hydrogen energy to its fullest potential, storage is a key parameter. It is well known that important hydrogen storage characteristics are operating pressure-temperature of hydrogen, hydrogen storage capacity, hydrogen absorption-desorption kinetics and heat transfer in the hydride bed. Each application needs specific properties. Every class of hydrogen storage materials has a different set of hydrogenation characteristics. Hence, it is required to understand the properties of all hydrogen storage materials. The present review is focused on the state-of–the–art hydrogen storage materials including metal hydrides, magnesium-based materials, complex hydride systems, carbonaceous materials, metal organic frameworks, perovskites and materials and processes based on artificial intelligence. In each category of materials’ discovery, hydrogen storage mechanism and reaction, crystal structure and recent progress have been discussed in detail. Together with the fundamental synthesis process, latest techniques of material tailoring like nanostructuring, nanoconfinement, catalyzing, alloying and functionalization have also been discussed. Hydrogen energy research has a promising potential to replace fossil fuels from energy uses, especially from automobile sector. In this context, efforts initiated worldwide for clean hydrogen production and its use via fuel cell in vehicles is much awaiting steps towards sustainable energy demand. © 2023 The Author(s)
Synthesis, characterization and hydrogenation behaviour of composite hydrogen storage alloys, LaNi5/La2Ni7, LaNi3
(Elsevier BV, 1999) Sumita Srivastava; O.N. Srivastava
The present study deals with investigations on the composite hydrogen storage materials LaNi5/La2Ni7, LaNi3, for efficient, high energy density Ni-MH batteries. To achieve this goal extensive investigations were carried out to study the effect of presence of secondary phases on the main phase LaNi5 with reference to hydrogenation behaviour and structural-microstructural characterizations using XRD, TEM and SEM techniques. Alloys were synthesized through melt-casting with varying concentrations of secondary phases like La2Ni7, LaNi3, Ni (minor phases), i.e., 55%, 30%, 5% and 0% by a special technique of pellet encapsulation. Structural characterizations using the XRD technique confirmed the formation of secondary phases together with the major phase LaNi5. The diffraction patterns after hydrogenation did not exhibit secondary phase diffraction peaks, instead the resulting phase was found to be single phasic, exhibiting LaNi5 like diffraction patterns with an unusual intensity distribution. TEM investigations showed the presence of two types of modulated phases; one of which corresponds to a≈1.5o, c≈co and the other to a≈1.3ao, c≈co, together with the parent phase (LaNi5), in the as-synthesized and hydrogenated/dehydrogenated versions, corresponding to alloy with secondary phase concentration upto 30%, (ao and Co being lattice constants of the parent LaNi5 structure). The signature of the modulated phases were not present in XRD patterns, but could be seen in the selected area electron diffraction patterns, suggesting that modulation has taken place in local areas of the basal plane, due to ordering of hydrogen atoms. These modulated unit cells can be modeled in terms of the original lattice of LaNi5, by inserting and ordering of hydrogen atoms at viable interstitial sites. Micro structural evaluations through SEM revealed that secondary phases suppressed pulverization. Investigations of the hydrogenation behaviour of these alloys showed that hydrogen storage capacity and desorption kinetics did not decrease for minor concentrations of secondary phases, but a decrease was found for the alloys having higher concentrations of secondary phases. Similar results were obtained for alloy MmNi5, where secondary phases corresponded to Mm2Ni7 and MmNi. © 1999 Elsevier Science S.A. All rights reserved.