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Synthesis, characterization and hydrogen storage characteristics of ambient pressure dried carbon aerogel
(Elsevier Ltd, 2016) Sweta Singh; Ashish Bhatnagar; Viney Dixit; Vivek Shukla; M.A. Shaz; A.S.K. Sinha; O.N. Srivastava; V. Sekkar
The present communication deals with the hydrogen storage performance of ambient pressure dried pristine as well as platinum doped carbon aerogel (CA-0.10 Pt). These carbon aerogels (CAs) have been prepared from resorcinol-formaldehyde (R-F) through sol-gel synthesis route with sodium carbonate as a catalyst (C). The synthesis parameters adapted led to the formation of CA having preponderance of submicropores. Structural and microstructural characteristics of these carbon aerogels have been investigated through XRD, SEM, TEM, nitrogen adsorption and Raman spectroscopic techniques. Nitrogen adsorption and TEM studies confirm the large density of micropores with the majority of pores having sizes between 0.30 and 1.46 nm (submicropores). The hydrogen storage characteristics of as synthesized carbon aerogels have been investigated by monitoring the hydrogen ad/desorption curves. At room temperature and at pressure upto 22 atm the CA and CA-0.1 Pt have hydrogen storage capacity of 0.40 wt.% and 0.33 wt.% respectively. However, under the same pressure but at liquid nitrogen temperature CA and CA-0.10 Pt have hydrogen storage capacity of 5.65 wt.% and 5.15 wt.%. Feasible reasons for the high hydrogen storage capacities at liquid nitrogen temperature for the present CAs have been put forward. Copyright © 2016 Hydrogen Energy Publications, LLC.
Structural and hydrogenation studies of ZnO and Mg doped ZnO nanowires
(2012) Jai Singh; M.S.L. Hudson; S.K. Pandey; R.S. Tiwari; O.N. Srivastava
In this work, Mg doped zinc oxide (Mg xZn 1-xO, x = 5, 10 and 20 at. %) nanowires were successfully prepared by two step process. Initially, ZnO nanowires were grown by thermal evaporation of Zn powder under oxygen atmosphere. Mg powder was doped in as grown ZnO through solid state diffusion at low temperature. Energy dispersive x-ray spectroscopy (EDAX), transmission electron microscopy (TEM), X-ray diffraction (XRD) and UV-Visible absorption spectra analysis reveals that the Mg doping on ZnO nanowires induces lattice strain in ZnO. Rietveld analysis of XRD data confirms the wurtzite structure and a continuous compaction of the lattice (in particular, the c-axis parameter) as x increases. The hydrogenation properties of ZnO nanowires and Mg doped ZnO (Mg xZn 1-xO, x = 0, 5, 10 and 20 at. %) nanowires were studied. The hydrogenated samples were further investigated through XRD and Fourier transform infrared spectroscopy (FTIR). The hydrogen storage capacity of as grown ZnO nanowires has been estimated to be 0.57 wt. % H 2 at room temperature. However, the hydrogen storage capacity gets increased to ∼1 wt. % upon doping ZnO with 10 at. % Mg. Further increase in Mg concentration decreases the hydrogen storage capacity of ZnO nanowires. Thus for 20 at. % Mg doped ZnO; the hydrogen absorption capacity gets decreased from ∼1 wt. % to 0.74 wt. %. The mechanism of hydrogen storage in ZnO nanowires and Mg doped samples of ZnO has been discussed. © 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.
Catalytic Application of Carbon-based Nanostructured Materials on Hydrogen Sorption Behavior of Light Metal Hydrides
(wiley, 2013) Rohit R. Shahi; O.N. Srivastava
The development of hydrogen storage materials with favorable thermodynamics (e.g., kinetics, desorption/adsorption temperature) has attracted considerable attention in recent years. Alanates, amide-hydride mixtures and magnesium hydride are the candidates with the most potential storage material due to their high hydrogen storage capacity and good reversibility, but each has its own limitations (e.g., high desorption temperature and sluggish kinetics). Carbon has many allotropes such as graphite, activated carbon, fullerenes, carbon nanotubes, and the most recent, graphene, etc. These have novel properties which are useful in many new innovative applications. Several recent investigations have also demonstrated the benefi cial effect of carbon materials as catalyst for enhancing sorption behavior of different light hydrogen storage materials. Carbon with a small curvature radius exhibits prominent "catalytic" effect for light metal and complex hydrides. The reduction in curvature radius of carbon nanostructures enhances the electron affi nity and interaction of carbon with hydrogen because the hydrogen release/combination energy has been changed, and consequently, the de-/rehydrogenation kinetics of the material is improved. In this chapter, we will highlight the current advances (including our recent works) in the hydrogen sorption enhancement of metal and complex hydrides by incorporating carbon nanomaterials as a catalyst. There will be a particular emphasis on carbon nanotubes, carbon nanofi bers and graphene employed as a catalyst for the aforesaid hydrogen storage materials. © 2014 Scrivener Publishing LLC. All rights reserved.
Effect of graphene templated fluorides of Ce and La on the de/rehydrogenation behavior of MgH2
(Elsevier Ltd, 2017) Pawan K. Soni; Ashish Bhatnagar; M.A. Shaz; O.N. Srivastava
The present investigation describes the hydrogen storage properties of MgH2 ball milled with different additives i.e. graphene templated rare earth metal (La and Ce) fluorides, CeF4 and LaF3. MgH2 ball milled with graphene templated CeF4 (MgH2:CeF4@Gr) has onset desorption temperature of 245 °C, which is 50 °C, 52 °C and 75 °C lower than MgH2 ball milled with LaF3 templated graphene, CeF4 and LaF3 respectively. CeF4@Gr also shows the superior effect amongst all additives during rehydrogenation where MgH2:CeF4@Gr absorbs 5.50 wt% within 2.50 min at 300 °C under 15 atm H2 pressure. Dual tuning effect, i.e. lowering of thermodynamic (62.77 kJ/mol H2: lower from 74 kJ/mol for pristine MgH2) and kinetics barrier (93.01 kJ/mol) has been observed for MgH2:CeF4@Gr. Additionally, MgH2 ball milled with CeF4@Gr shows good reversibility up to 24 cycles of de/rehydrogenation. The feasible working mechanism of CeF4@Gr as additive for MgH2 has been studied in detail with the help of Transmission Electron Microscope (TEM), Fourier Transform Infrared Spectroscopy (FTIR) and X-ray Diffraction characterizations (XRD). © 2017 Hydrogen Energy Publications LLC
On the synthesis, characterization and hydrogen storage behavior of ZrFe2 catalyzed Li-Mg-N-H hydrogen storage material
(Elsevier Ltd, 2015) Vivek Shukla; Ashish Bhatnagar; Sunita K. Pandey; Rohit R. Shahi; T.P. Yadav; M.A. Shaz; O.N. Srivastava
The present study deals with the use of ZrFe2 for the formation of pure phase of hydrogen storage material Mg(NH2)2/LiH. Since ZrFe2 is harder than the starting material LiNH2 and MgH2, pulverization effect produced by ZrFe2 assists in the synthesis of pure phase. The formation of pure Mg(NH2)2/LiH has been examined by XRD and confirmed by FTIR. The catalytic effect of ZrFe2 has been found to improve significantly the de/rehydrogenation characteristic of Mg(NH2)2/LiH. The ZrFe2 catalyzed Mg(NH2)2/LiH shows good recyclability. The activation energy of ZrFe2 catalyzed Mg(NH2)2/LiH was found to be 74.80 kJ/mol which is better than several other reported studies using different catalysts. Based on experimental results, a viable mechanism for dehydrogenation of Mg(NH2)2 in the presence of ZrFe2 has also been proposed. © 2015 Hydrogen Energy Publications, LLC.
Studies on the de/re-hydrogenation characteristic of Mg(NH 2) 2/LiH mixture admixed with carbon nanofibres
(2012) Rohit R. Shahi; Himanshu Raghubanshi; M.A. Shaz; O.N. Srivastava
The effect of carbon nanofibres (CNFs) on the de/re-hydrogenation characteristics of 1:2 magnesium amide (Mg(NH 2) 2) and lithium hydride (LiH) mixture is investigated. It is found that the desorption as well as absorption characteristic of the 1:2 Mg(NH 2) 2/LiH mixture is improved with admixing of different shaped (planar and helical) CNFs separately. The different shaped CNFs were synthesized through catalytic decomposition of acetylene gas over LaNi 5 alloy. The synthesized CNFs contain Ni-metal nano particles. Among two different types of nanofibres namely planar carbon nanofibres (PCNFs) and helical carbon nanofibres (HCNFs), the later was found to act as a better catalyst. The decomposition temperature of the pristine Mg(NH 2) 2/LiH mixture is ∼250 °C, reduced to 150 and 140 °C for the PCNF and HCNF admixed Mg(NH 2) 2/LiH mixture respectively. The activation energy for dehydrogenation reaction was found to ∼97.2 kJ/mol, which is further reduced to ∼67 and ∼65 kJ/mol for the PCNF and HCNF admixed Mg(NH 2) 2/LiH mixture respectively. The lowering of decomposition temperature and enhancement in desorption kinetics, with admixing of different shaped CNFs are described and discussed. © 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.
Hydrogen storage properties of carbon aerogel synthesized by ambient pressure drying using new catalyst triethylamine
(Elsevier Ltd, 2020) Anant Prakash Pandey; Ashish Bhatnagar; Vivek Shukla; Pawan K. Soni; Sweta Singh; Satish K. Verma; M. Shaneeth; V. Sekkar; O.N. Srivastava
In this paper, we report here the hydrogen storage capacity of activated carbon aerogel synthesized by ambient pressure drying using a new catalyst. The carbon aerogel (CA) has been synthesized by the sol-gel method using resorcinol (R) and formaldehyde (F). For drying of RF wet gel instead of expensive and unsafe supercritical process, we have used ambient pressure drying. To avoid shrinkage which may occur due to this mode of drying, instead of usual catalyst (C): Na2CO3, organic catalyst triethylamine (TEA), which is known to be a condensing agent has been used. In order to find out the effect of change of R/C ratio on hydrogen sorption, three different R/C namely CA 1000, CA 2000, and CA 3000 were taken. Structural and microstructural details have been studied employing XRD, SEM, TEM, nitrogen adsorption, FTIR, and Raman spectroscopy. TEM and nitrogen adsorption studies have revealed that aerogel with R/C 1000 exhibits a higher degree of micropore density. The hydrogen storage capacities for all R/C ratios have been determined. It has been found that carbon aerogel (CA) with R/C = 1000, exhibits the highest hydrogen adsorption capacity out of the three aerogels. At liquid nitrogen temperature, the hydrogen storage capacity of aerogel with R/C = 1000 for the as-synthesized and activated carbons have been found to be 4.00 wt % and 4.80 wt %. A viable reason for the occurrence of high hydrogen storage capacity at liquid nitrogen temperature for aerogel with R/C = 1000 has been put forward. © 2020 Hydrogen Energy Publications LLC
Effects of Ti-based catalysts and synergistic effect of SWCNTs-TiF 3 on hydrogen uptake and release from MgH2
(Elsevier Ltd, 2014) Rohit R. Shahi; Ashish Bhatnagar; Sunita K. Pandey; Viney Dixit; O.N. Srivastava
The present investigations are focused on the effect of different Ti-based catalysts (Ti, TiO2, TiCl3 and TiF3) on de/re-hydrogenation characteristics of nanocrystalline MgH2. Desorption temperature of milled MgH2 lowers from 380 to 350, 340, 310 and 260 °C with the addition of Ti, TiO2, TiCl3 and TiF3 respectively. The rehydrogenation characteristics are also improved through the deployment of Ti-based catalysts. Among all Ti based additives, TiF3 is found to be the most effective catalyst for hydrogen sorption from nano MgH2. The better catalytic effect of TiF3 over other Ti-based catalyst can be explained on the basis of temperature programmed reduction (TPR) studies. TPR experiments performed for different Ti additives, reveals that there is no oxidation/reduction reaction below 400 °C except for TiF3. The TPR profile of TiF3 shows some oxidation/reduction reaction exhibits at 200 °C. In order to further improve the sorption characteristics and cyclability of TiF3 catalyzed nano MgH2, we have investigated the effect of SWCNTs in MgH2+TiF3 sample. De/rehydrogenation characteristics reveal the synergistic effect of SWCNTs and TiF3 in MgH 2+TiF3 sample. The details of the improvement in sorption behavior of MgH2-TiF3 in presence of SWCNTs are described and discussed. © 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.
Ternary transition metal alloy FeCoNi nanoparticles on graphene as new catalyst for hydrogen sorption in MgH2
(Elsevier Ltd, 2020) Sweta Singh; Ashish Bhatnagar; Vivek Shukla; Alok K. Vishwakarma; Pawan K. Soni; Satish K. Verma; M.A. Shaz; A.S.K. Sinha; O.N. Srivastava
The present investigation deals with the synthesis of ternary transition metal alloy nanoparticles of FeCoNi and graphene templated FeCoNi (FeCoNi@GS) by one-pot reflux method and there use as a catalyst for hydrogen sorption in MgH2. It has been found that the MgH2 catalyzed by FeCoNi@GS (MgH2: FeCoNi@GS) has the onset desorption temperature of ~255 °C which is 25 °C and 100 °C lower than MgH2 catalyzed by FeCoNi (MgH2: FeCoNi) (onset desorption temperature 280 °C) and the ball-milled (B.M) MgH2 (onset desorption temperature 355 °C) respectively. Also MgH2: FeCoNi@GS shows enhanced kinetics by absorbing 6.01 wt% within just 1.65 min at 290 °C under 15 atm of hydrogen pressure. This is much-improved sorption as compared to MgH2: FeCoNi and B.M MgH2 for which hydrogen absorption is 4.41 wt% and 1.45 wt% respectively, under the similar condition of temperature, pressure and time. More importantly, the formation enthalpy of MgH2: FeCoNi@GS is 58.86 kJ/mol which is 19.26 kJ/mol lower than B.M: MgH2 (78.12 kJ/mol). Excellent cyclic stability has also been found for MgH2: FeCoNi@GS even up to 24 cycles where it shows only negligible change from 6.26 wt% to 6.24 wt%. A feasible catalytic mechanism of FeCoNi@GS on MgH2 has been put forward based on X-ray diffraction (XRD), Raman spectroscopy, Fourier Transform Infrared Spectroscopy (FTIR), X-Ray Photoelectron Spectroscopy (XPS), and microstructural (electron microscopic) studies. © 2019 Hydrogen Energy Publications LLC
One step high pressure mechanochemical synthesis of reversible alanates NaAlH4 and KAlH4
(Elsevier Ltd, 2015) D. Pukazhselvan; Duncan Paul Fagg; O.N. Srivastava
The present study suggests high pressure mechanochemical treatment is a better strategy for The synthesis of performance enhanced reversible alanates. The reactants NaH/KH + Al along with catalysts (TiCl3, TiF3 and TiO2) milled under 100 bar hydrogen pressure for 30 h effectively transforms to products (NaAlH4 and KAlH4) in a single step. The as-synthesized NaAlH4 and KAlH4 samples release hydrogen at The temperatures of ∼100 °C and 215 °C, respectively. The stability of The KAlH4 phase can be further reduced by extending The high pressure mechanochemical reaction time to 80 h. The XRD and TEM analysis of The residues observed after extracting The NaAlH4 from The TiCl3 catalyzed material confirms The presence of Ti-Al alloy and highly dispersed NaCl nanoparticles. Catalytic activity is therefore attributed to mechano-chemical activation which involves catalytically active species (for e.g. Ti-Al) and defects/vacancies/strain in The system. © 2015 Hydrogen Energy Publications, LLC.

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