Browsing by Author "Ashish Bhatnagar"

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A dual borohydride (Li and Na borohydride) catalyst/additive together with intermetallic FeTi for the optimization of the hydrogen sorption characteristics of Mg(NH2)2/2LiH
(Royal Society of Chemistry, 2019) Vivek Shukla; Ashish Bhatnagar; Sweta Singh; Pawan K. Soni; Satish K. Verma; T.P. Yadav; M.A. Shaz; O.N. Srivastava
The present study deals with the material tailoring of Mg(NH2)2-2LiH through dual borohydrides: the reactive LiBH4 and the non-reactive NaBH4. Furthermore, a pulverizer, as well as a catalyst FeTi, has been added in order to facilitate hydrogen sorption. Addition of LiBH4 to LiNH2 in a 1 : 3 molar ratio leads to the formation of Li4(BH4)(NH2)3 which also acts as a catalyst. However, the addition of NaBH4 doesn't lead to any compound formation but shows a catalytic effect. The onset dehydrogenation temperature of thermally treated Mg(NH2)2-2LiH/(Li4(BH4)(NH2)3-NaBH4) is 142 °C as against 196 °C for the basic material Mg(NH2)2-2LiH. However, with the FeTi catalyzed Mg(NH2)2-2LiH/(Li4(BH4)(NH2)3-NaBH4, it has been reduced to 120 °C. This is better than other similar amide/hydride composites where it is 149 °C (when the basic material is catalyzed with LiBH4). The FeTi catalyzed Mg(NH2)2-2LiH/(Li4(BH4)(NH2)3-NaBH4 sample shows better de/re-hydrogenation kinetics as it desorbs 3.9 ± 0.04 wt% and absorbs nearly 4.1 ± 0.04 wt% both within 30 min at 170 °C (with the H2 pressure being 0.1 MPa for desorption and 7 MPa for absorption). The eventual hydrogen storage capacity of Mg(NH2)2-2LiH/(Li4(BH4)(NH2)3-NaBH4 together with FeTi has been found to be ∼5.0 wt%. To make the effect of catalysts intelligible, we have put forward in a schematic way the role of Li and Na borohydrides with FeTi for improving the hydrogen sorption properties of Mg(NH2)2-2LiH. © 2019 The Royal Society of Chemistry.
A highly porous, light weight 3D sponge like graphene aerogel for electromagnetic interference shielding applications
(Royal Society of Chemistry, 2015) Sweta Singh; Prashant Tripathi; Ashish Bhatnagar; Ch. Ravi Prakash Patel; Avanish Pratap Singh; S.K. Dhawan; Bipin Kumar Gupta; O.N. Srivastava
Here we report the microwave shielding properties of a light weight three dimensional (3D) sponge like graphene aerogel (GA) derived from graphene oxide (GO). GA is a new exotic form of graphene nanosheet, which shows improved shielding features as compared to its pristine counterpart. The structural and microstructural characteristics of this new indigenous 3D sponge like graphene aerogel architecture have been probed by XRD, Raman, SEM and TEM/HRTEM. Furthermore, the porosity of this newly synthesized structure has been investigated by the Brunauer-Emmett-Teller (BET) method, which confirms the high surface area of ∼516 m2 g-1 with an average pore diameter of ∼2.5 nm. The high surface area and better porosity improve the EMI shielding effectiveness of GA. Simultaneously, the GA nanostructure also enhances the dielectric properties which provide a better alternative for EMI shielding materials as compared to GO. This engineered GA exhibits enhanced shielding effectiveness (∼20.0 dB at 0.20 g in a frequency region of 12.4 to 18.0 GHz) as compared to the conventional GO. Thus, the result of the EMI shielding of GA offers a new ingenious nanostructure which can be used as an EMI pollutant quencher for next-generation EMI shielding devices. © The Royal Society of Chemistry 2015.
Carbon nanotubes for CO2 capture and conversion
(Elsevier, 2022) Satish Kumar Verma; Prashant Tripathi; Ashish Bhatnagar
It is now generally accepted that carbon emissions from the burning of fossil fuels and changes in land use are causing atmospheric CO2 levels to rise rapidly, resulting in an increase in the impact of greenhouse gases (GHGs) due to climate change. Carbon Capture and Storage and later on conversion to a valuable fuel by adsorption in carbon nanomaterials is an attractive approach to mitigate future global climate change and is generally accepted as a viable road to sustainable fossil fuel usage. Out of the various carbon nanomaterials, carbon nanotubes (CNT) are the front-running candidates owing to their classical performance as adsorbents. CNTs are pure carbon cylinders with a radius of a few nm and variable lengths (100nm to mm). CNTs are extraordinarily light and highly porous and very suitable for gas storage applications due to their high surface area. CNTs also have elevated conductivity (thermal and electrical) and are rich in chemistry. The properties mentioned above make them a competent candidate for CO2 adsorption and desorption, efficiently and selectively. This chapter will discuss the state-of-the-art CNTs used for carbon capture and prospects of the same. © 2023 Elsevier Inc. All rights reserved.
Catalytic characteristics of titanium-(IV)-isopropoxide (TTIP) on de/re-hydrogenation of wet ball-milled MgH2/Mg
(John Wiley and Sons Ltd, 2022) Sunita Kumari Pandey; Satish Kumar Verma; Ashish Bhatnagar; Thakur Prasad Yadav
Magnesium hydride (MgH2) has received much attention as a solid-state hydrogen storage material worldwide due to its high hydrogen storage capacity, good reversibility, and low cost. However, its practical application has been limited due to its high thermodynamic stability and slow kinetics. In the present work, we have employed a new type of catalyst, Titanium-tetra-isopropoxide (TTIP) (Ti(OC3H7)4), to catalyze MgH2. To disperse the catalyst evenly over the MgH2, the milling operation was conducted using tetrahydrofuran (THF) as a process control agent. Here, using THF as the process control agent during the wet ball milling along with TTIP of MgH2 itself used to improve the de/re-hydrogenation behavior of MgH2. A de/re-hydrogenation investigation demonstrates that MgH2 catalyzed by TTIP has better hydrogen storage properties (onset dehydrogenation temperature 210°C) than as-cast MgH2 (onset dehydrogenation temperature ~400°C). Furthermore, a remarkable catalytic behavior of TTIP on MgH2 was observed during de-/re-hydrogenation kinetics (absorb the hydrogen ~4.6 wt% within the 1.5 minutes at a temperature of 300°C under a hydrogen pressure of 20 atm and release the hydrogen of ∼4.98 wt% within 5 minutes at ∼300°C) due to formation of intermediate compound Mg1−xTixO, and it retains nearly constant hydrogen storage capacity (from 5.25 to 5.20 wt% in rehydrogenation and from 4.95 wt % to 4.95 wt% in dehydrogenation) up to 60 cycles of de/re-hydrogenation. The estimated desorption activation energy for MgH2-TTIP using Arrhenius equation is 77.67 kJ/mol. The reason for de/re-hydrogenation kinetics improvement of MgH2-TTIP can be seen in the mechanism. © 2022 John Wiley & Sons Ltd.
Catalytic effect of carbon nanostructures on the hydrogen storage properties of MgH2-NaAlH4 composite
(Elsevier Ltd, 2014) Ashish Bhatnagar; Sunita K. Pandey; Viney Dixit; Vivek Shukla; Rohit R. Shahi; M.A. Shaz; O.N. Srivastava
The present investigation describes the hydrogen storage properties of 2:1 molar ratio of MgH2-NaAlH4 composite. De/rehydrogenation study reveals that MgH2-NaAlH4 composite offers beneficial hydrogen storage characteristics as compared to pristine NaAlH4 and MgH2. To investigate the effect of carbon nanostructures (CNS) on the de/rehydrogenation behavior of MgH2-NaAlH4 composite, we have employed 2 wt.% CNS namely, single wall carbon nanotubes (SWCNT) and graphene nano sheets (GNS). It is found that the hydrogen storage behavior of composite gets improved by the addition of 2 wt.% CNS. In particular, catalytic effect of GNS + SWCNT improves the hydrogen storage behavior and cyclability of the composite. De/rehydrogenation experiments performed up to six cycles show loss of 1.50 wt.% and 0.84 wt.% hydrogen capacity in MgH2-NaAlH 4 catalyzed with 2 wt.% SWCNT and 2 wt.% GNS respectively. On the other hand, the loss of hydrogen capacity after six rehydrogenation cycles in GNS + SWCNT (1.5 + 0.5) wt.% catalyzed MgH2-NaAlH4 is diminished to 0.45 wt.%. © 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.
Catalytic mechanism of TiO2 quantum dots on the de/re-hydrogenation characteristics of magnesium hydride
(Elsevier Ltd, 2021) Sunita Kumari Pandey; Ashish Bhatnagar; Vivek Shukla; Rashmi Kesarwani; Uday Deshpandey; Thakur Prasad Yadav
In the present study, the catalyst anatase titanium dioxide (TiO2) quantum dots (QDs) of size ∼ (2.50–4.00)nm was successfully synthesized by the hydrothermal method. The formation of TiO2: QDs has been established by UV–Vis spectroscopy and confirmed by transmission electron microscopy. Here, we report the catalytic action of TiO2:QDs on de/re-hydrogenation properties of magnesium hydride (MgH2/Mg). By catalyzing MgH2 through this catalyst, the onset desorption temperature of MgH2 gets reduced significantly from ∼360 °C (for ball-milled MgH2) to ∼260 °C. Moreover, the Mg-TiO2: QDs sample absorbed a significant amount of hydrogen up to ∼6.10 wt% in just 77sec at 280 °C. Improved rehydrogenation kinetics has been found even at lower temperatures by absorbing ∼5.30 wt% in 74 s at 225 °C and ∼5.0 wt% of hydrogen in 30 min at 100 °C. Based on structural,.microstructural, and XPS investigations, a feasible mechanism for improved hydrogen sorption and cyclic stability in MgH2 catalyzed with TiO2:QDs has been explained and discussed. To our knowledge, no studies have been carried out on the sorption of hydrogen in MgH2 catalyzed by TiO2:QDs. © 2021 Hydrogen Energy Publications LLC
Co-catalytic effect of carbon based nanostructures and TiO2 on sorption behavior of nanocrystalline MgH2
(American Scientific Publishers, 2014) Sunita K. Pandey; Ashish Bhatnagar; Rohit R. Shahi; T.P. Yadav; O.N. Srivastava
The aim of the present investigation is to explore the synergistic effect of TiO2–graphene nano sheets and TiO2- single wall carbon nanotubes on the sorption behaviour of MgH2. The nanocrystalline MgH2–TiO2 is synthesized by reactive ball-milling of MgH2 and TiO2 under 10 atm of hydrogen pressure. Temperature programmed desorption study reveals that the hydrogen desorption in TiO2 catalyzed MgH2 starts at ∼312 ºC. On the other hand, MgH2/TiO2 admixed with 2 wt% of SWCNT and MgH2/TiO2 admixed with 2 wt% of graphene starts to desorb hydrogen at ∼295 and ∼280 ºC respectively. The onset desorption temperature of MgH2/TiO2 is reduced by ∼17 ºC and ∼32 ºC by admixing 2 wt% of single wall carbon nanotubes and graphene nano sheets in MgH2/TiO2 respectively. © 2014 American Scientific Publishers. All rights reserved.
Curious Catalytic Characteristics of Al-Cu-Fe Quasicrystal for De/Rehydrogenation of MgH2
(American Chemical Society, 2017) Sunita Kumari Pandey; Ashish Bhatnagar; S.S. Mishra; T.P. Yadav; M.A. Shaz; O.N. Srivastava
The present study reports the curious catalytic action of a new class of catalyst, quasicrystal of Al65Cu20Fe15 on de/rehydrogenation properties of magnesium hydride (MgH2). Catalyzed through this catalyst, the onset desorption temperature of MgH2 gets reduced significantly from ∼345 °C (for ball-milled MgH2) to ∼215 °C. A more dramatic effect of the above catalyst has been observed on rehydrogenation. Here, 6.00 wt % of hydrogen storage capacity is observed in just 30 s at 250 °C. Improved rehydrogenation kinetics has been found even at lower temperatures of 200 and 150 °C by absorbing ∼5.50 and ∼5.40 wt % of H2, respectively, within 1 min and ∼5.00 wt % at 100 °C in 30 min. These are some of the lowest desorption temperatures and rehydrogenation kinetics obtained for MgH2 through any other known catalyst. The storage capacity of MgH2 catalyzed with the leached version of Al65Cu20Fe15 quasicrystalline alloy degrades negligibly even after 51 cycles of de/rehydrogenation. The feasible reason for catalytic action has been described and discussed on the basis of structural, microstructural, Fourier transform infrared, and X-ray photoelectron spectroscopic studies. © 2017 American Chemical Society.
Development and Demonstration of Air Stable rGO-EC@AB5 Type Hydrogenated Intermetallic Hybrid for Hydrogen Fuelled Devices
(Wiley-VCH Verlag, 2017) Ashish Bhatnagar; Bipin Kumar Gupta; Prashant Tripathi; Ayfer Veziroglu; Michael Sterlin Leo Hudson; Mohammad Abu Shaz; Onkar Nath Srivastava
Hydrogen is a promising alternative energy vector, but its use at an appropriate site requires storage, which is a crucial aspect. Hydrogen storage (HS) in the form of metal hydrides represents an attractive possibility, and is being investigated worldwide. La(Ni0.95Fe0.05)5 (LNF) has achieved significant attention as a HS media due to its suitable thermodynamics. However, its use as an effective storage material is hindered due to burning of hydrogenated LNF (LNFH) on exposure to air. The pristine LNFH catches fire rapidly on exposure to atmosphere. Here, a breakthrough strategy is demonstrated for design of hydrogenated air-stabilized hybrid material by encapsulating LNF inside reduced graphene oxide-ethyl cellulose. This novel hybrid material does not ignite upon exposure to air. This proposed hybrid material could be the ultimate choice for air-stable and safe storage for fuel cell/internal combustion engine-based vehicles. Further, the effectiveness of this hydrogen storage material is demonstrated for fuel cells. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Economical synthesis of highly efficient and tunable carbon aerogels for enhanced storage of CO2 emitted from energy sources
(John Wiley and Sons Ltd, 2021) Ashish Bhatnagar; Anant Prakash Pandey; M. Sterlin Leo Hudson; Pawan K. Soni; Satish K. Verma; Vivek Shukla; V. Sekkar; Manoj Tripathi; O.N. Srivastava
The present investigation reports the synthesis of Carbon Aerogel (CA) with varying pore size and surface area by changing the initial precursor that is, Resorcinol (R) and novel Catalyst (triethyl amine [TEA]) (C) ratio (R/C). The catalyst, TEA allows the gel to dry with negligible shrinkage. The R/C ratio has been kept 1000, 2000 and 3000. The CA with R/C = 1000 has the lowest pore size 1.93 nm, the highest surface area (369.14 m2/g) and the highest CO2 uptake of 24.40 wt.% (5.54 mmol/) at 40 atm CO2 pressure. The activated version of optimum CA (R/C = 1000) has been found to have an average pore diameter ~ 1.91 nm and CO2 uptake capacity of 29.56 wt% (6.71 mmol/g) at 25°C which is one of the highest CO2 storage capacity of CAs reported so far. Thus, the present manuscript put forward highly efficient and tunable CAs for enhanced CO2 storage. © 2020 John Wiley & Sons Ltd
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
Effect of TiO2 nanoparticles on the hydrogen sorption characteristics of magnesium hydride
(2013) Sunita K. Pandey; Ashish Bhatnagar; Rohit R. Shahi; M. Sterlin Leo Hudson; Milind K. Singh; O.N. Srivastava
The present paper explores the enhancement in hydrogen sorption behavior of MgH2 with TiO2 nanoparticles. The catalytic effect of TiO2 nanoparticles with different sizes (7, 25, 50, 100 and 250 nm) were used for improving the sorption characteristics of MgH2. The MgH2 catalyzed with 50 nm of TiO2 exhibited the optimum catalytic effect for hydrogen sorption behavior. The desorption temperature of MgH2 catalyzed through 50 nm TiO2 was found to be 310 )C. This is 80 )C lower as compared to MgH2 having a desorption temperature of 390 )C. It was noticed that the dehydrogenated MgH2 catalyzed with 50 nm TiO2 reabsorbed 5.1 wt% of H2 within 6 minutes at temperature and pressure of 250 )C and 50 atm, respectively. The 50 nm TiO2 catalyst lowered the absorption activation energy of MgH2 from ̃92 to ̃52.7 kJ mol-1. Copyright © 2013 American Scientific Publishers All rights reserved.
Effects of nano size mischmetal and its oxide on improving the hydrogen sorption behaviour of MgH2
(2013) T. Sadhasivam; M. Sterlin Leo Hudson; Sunita K. Pandey; Ashish Bhatnagar; Milind K. Singh; K. Gurunathan; O.N. Srivastava
This paper reports the catalytic effects of mischmetal (Mm) and mischmetal oxide (Mm-oxide) on improving the dehydrogenation and rehydrogenation behaviour of magnesium hydride (MgH2). It has been found that 5 wt.% is the optimum catalyst (Mm/Mm-oxide) concentration for MgH2. The Mm and Mm-oxide catalyzed MgH2 exhibits hydrogen desorption at significantly lower temperature and also fast rehydrogenation kinetics compared to ball-milled MgH2 under identical conditions of temperature and pressure. The onset desorption temperature for MgH2 catalyzed with Mm and Mm-oxide are 323 C and 305 C, respectively. Whereas the onset desorption temperature for the ball-milled MgH2 is 381 C. Thus, there is a lowering of onset desorption temperature by 58 C for Mm and by 76 C for Mm-oxide. The dehydrogenation activation energy of Mm-oxide catalyzed MgH 2 is 66 kJ/mol. It is 35 kJ/mol lower than ball-milled MgH 2. Additionally, the Mm-oxide catalyzed dehydrogenated Mg exhibits faster rehydrogenation kinetics. It has been noticed that in the first 10 min, the Mm-oxide catalyzed Mg (dehydrogenated MgH2) has absorbed up to 4.75 wt.% H2 at 315 C under 15 atmosphere hydrogen pressure. The activation energy determined for the rehydrogenation of Mm-oxide catalyzed Mg is ∼62 kJ/mol, whereas that for the ball-milled Mg alone is ∼91 kJ/mol. Thus, there is a decrease in absorption activation energy by ∼29 kJ/mol for the Mm-oxide catalyzed Mg. In addition, Mm-oxide is the native mixture of CeO2 and La2O3 which makes the duo a better catalyst than CeO2, which is known to be an effective catalyst for MgH2. This takes place due to the synergistic effect of CeO 2 and La2O3. It can thus be said that Mm-oxide is an effective catalyst for improving the hydrogen sorption behaviour of MgH2. © 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights.
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.
Enhanced hydrogen properties of MgH2 by Fe nanoparticles loaded hollow carbon spheres
(Elsevier Ltd, 2023) Pawan K. Soni; Ashish Bhatnagar; M.A. Shaz
In the present investigation, we have reported the synergistic effect of Fe nanoparticles and hollow carbon spheres composite on the hydrogen storage properties of MgH2. The onset desorption temperature for MgH2 catalyzed with hollow carbon spheres and Fe nanoparticle (MgH2-Fe-HCS) system has been observed to be 225.9 °C with a hydrogen storage capacity of 5.60 wt %. It could be able to absorb 5.60 wt % hydrogen within 55 s and desorb 5.50 wt % hydrogen within 12 min under 20 atm H2 pressure at 300 °C. The desorption activation energy of MgH2-Fe-HCS has been found to be 84.9 kJ/mol, whereas the desorption activation energies for as received MgH2, Hollow carbon sphere catalyzed MgH2 and Fe catalyzed MgH2 are found to be 130 kJ/mol, 103 kJ/mol, and 94.2 kJ/mol respectively. MgH2-Fe-HCS composite lowered the change in enthalpy of hydrogen desorption from MgH2 by 20.02 kJ/mol as compared to pristine MgH2. MgH2-Fe-HCS shows better cyclability up to 24 cycles of hydrogenation and dehydrogenation of MgH2. The mechanism for the better catalytic action of Fe and HCS on MgH2 has also been discussed. © 2023 Hydrogen Energy Publications LLC
Enhanced hydrogen sorption in a Li-Mg-N-H system by the synergistic role of Li4(NH2)3BH4 and ZrFe2
(Royal Society of Chemistry, 2017) Vivek Shukla; Ashish Bhatnagar; Pawan K. Soni; Alok K. Vishwakarma; M.A. Shaz; T.P. Yadav; O.N. Srivastava
The present investigation describes the synergistic role of Li4(BH4)(NH2)3 and ZrFe2 in the hydrogen storage behaviour of a Li-Mg-N-H hydride system. The onset desorption temperature of ZrFe2-catalysed Mg(NH2)2-LiH-Li4(BH4)(NH2)3 is ∼122°C, which is 83°C, 63°C, and 28°C lower than that of thermally treated 2LiNH2-1MgH2, 2LiNH2-1MgH2-4 wt%ZrFe2, and 2LiNH2-1MgH2-0.1LiBH4 composites, respectively. Native Mg(NH2)2-LiH-Li4(BH4)(NH2)3 absorbed only 2.78 wt% of H2 within 30 min. On the other hand, the ZrFe2-catalysed Mg(NH2)2-LiH-Li4(BH4)(NH2)3 sample absorbed 3.70 wt% of hydrogen within 30 min and 5 wt% of H2 in 6 h at 180°C and 7 MPa H2 pressure. Mg(NH2)2-LiH-Li4(BH4)(NH2)3 catalyzed with ZrFe2 shows negligible degradation of the storage capacity even after repeated cycles of de/rehydrogenation. The effect of ZrFe2 and Li4(BH4)(NH2)3 on a Mg(NH2)2/LiH composite has been described and discussed with the help of structural (X-ray diffraction), microstructural (electron microscopy), and vibrational modes of molecules through FTIR studies. The present results suggest that an optimum catalysis may originate from the synergistic action of an in situ formed quaternary hydride (Li4(BH4)(NH2)3) and an intermetallic-like ZrFe2, which acts as a pulverizer cum catalyst. © the Owner Societies 2017.
Enhanced hydrogenation characteristics of Li-Mg-N-H system catalyzed with TiO2 nanoparticles; a mechanistic approach
(Elsevier Ltd, 2017) Rohit R. Shahi; Rajesh K. Mishra; Vivek Shukla; Ashish Bhatnagar; O.N. Srivastava
The report describes the effect of TiO2 nano particles on the hydrogenation characteristics of promising Li-Mg-N-H hydrogen storage system. The effect of different particle size of TiO2 (200, 25 and 7 nm) on de/re-hydrogenation characteristics of Mg(NH2)2/LiH mixture has been investigated. Desorption kinetics of Li-Mg-N-H system with 25 nm TiO2 gets enhanced upto ∼25% as compared to the pristine material kinetics at 453 K (180 °C). The report also deals mechanistic approach for hydrogen release from Li-Mg-N-H system in the presence of TiO2 nanoparticles through XPS analysis of catalyzed sample at various stages of reaction. The XPS analysis confirms that during dehydrogenation nitrogen atom present in Li-Mg-N-H system share their lone pair electrons to Ti (present in TiO2) and provides an alternate decomposition path which has lower activation energy for dehydrogenation. © 2017 Hydrogen Energy Publications LLC
Enhancement in hydrogen sorption behaviour of MgH2 catalyzed by graphene quantum dots
(Elsevier Ltd, 2024) Rashmi Kesarwani; Ashish Bhatnagar; Satish K. Verma; M. Sterlin Leo Hudson; M.A. Shaz
The present investigation reports the synthesis of graphene quantum dots (GQDs) by the microwave-assisted green synthesis method, and its catalytic effect in improving the hydrogen storage behaviour of magnesium hydride (MgH2). Transmission electron microscopy, UV–Vis, Raman, FTIR and XRD analysis was done to characterize the samples. It has been observed that the as-synthesized GQDs are in the size range of 3–12 nm. The catalytic activity of GQDs on improving the de/re-hydrogenation kinetics of MgH2 has been investigated with different additive concentrations. It has been observed that there is an improvement in the hydrogen sorption characteristics of ball-milled MgH2 when 7 wt.% GQDs was employed. The onset dehydrogenation temperature of 7 wt.% GQDs admixed ball milled MgH2 (7 % GQDs-MgH2) was observed at 300 ᵒC, which is 60 ᵒC lower than that of additive free ball-milled MgH2 under identical condition. Furthermore, the 7 % GQDs-MgH2 sample reabsorbs nearly 5 wt.% hydrogen in 2.5 min at 300 ᵒC and 15 atm hydrogen pressure. The GQDs catalyzed MgH2 sample exhibit good de/re-hydrogenation cyclic stability. No significant loss in hydrogen capacity was noticed even after 25 de-/re-hydrogenation cycles. From the Van't Hoff plot, the formation enthalpy of 7 % GQDs-MgH2 was estimated to be 58 kJmol-1. © 2024 Hydrogen Energy Publications LLC
Experimental and first principle studies on hydrogen desorption behavior of graphene nanofibre catalyzed MgH2
(Elsevier Ltd, 2017) Milind K. Singh; Ashish Bhatnagar; Sunita K. Pandey; P.C. Mishra; O.N. Srivastava
With the combination of experiment and first-principles theory, we have evaluated and explored the catalytic effects of graphitic nanofibres for hydrogen desorption behaviour in magnesium hydride. Helical form of graphene nanofibres (HGNF) have larger surface area, curved configuration and high density of graphene layers resulting in large quantity of exposed carbon sheet edges. Therefore they are found to considerably improve hydrogen desorption from MgH2at lower temperatures compared to graphene (onset desorption temperature of MgH2catalyzed by HGNF is 45 °C lower as compared to MgH2catalyzed by graphene). Using density functional theory, we find that graphene sheet edges, both the zigzag and armchair type, can weaken Mg[sbnd]H bonds in magnesium hydride. When the MgH2is catalyzed with higher electronegative and reactive graphene edge of graphene, the electron transfer occurs from Mg to carbon, due to which MgH2is dissociated into hydrogen and Mg[sbnd]H component. The Mg gets bonded with the graphene edge carbon atoms in the form of C[sbnd]Mg[sbnd]H and C[sbnd]H bonds. In the as formed C[sbnd]Mg[sbnd]H, the graphene edges “grab” more electronic charge as compared to the normal charge donation of Mg to H. This leads to the weakening of the Mg[sbnd]H bond, causing hydrogen to desorbs at lower temperatures. © 2016 Hydrogen Energy Publications LLC
Fe3O4@graphene as a superior catalyst for hydrogen de/absorption from/in MgH2/Mg
(Royal Society of Chemistry, 2016) Ashish Bhatnagar; Sunita K. Pandey; Alok K. Vishwakarma; Sweta Singh; Vivek Shukla; Pawan K. Soni; M.A. Shaz; O.N. Srivastava
The present investigation describes the hydrogen sorption (de/absorption) behavior of MgH2 catalyzed by graphene sheet templated Fe3O4 nanoparticles (Fe3O4@GS). Hydrogen sorption studies reveal that MgH2 catalyzed by Fe3O4@GS (MgH2:Fe3O4@GS) offers improved hydrogen storage behavior as compared to stand-alone MgH2 catalyzed by graphene sheets (GS) (MgH2:GS) or Fe3O4 nanoparticles (MgH2:Fe3O4). The MgH2:Fe3O4@GS has an onset desorption temperature of ∼262 °C (∼142 °C lower than pristine MgH2), while MgH2:GS and MgH2:Fe3O4 have onset desorption temperatures of ∼275 °C and ∼298 °C respectively. In contrast to this, MgH2:GS absorbs 4.40 wt% and MgH2:Fe3O4 absorbs 5.50 wt% in 2.50 minutes at 290 °C under 15 atm hydrogen pressure. On the other hand, MgH2:Fe3O4@GS absorbs 6.20 wt% hydrogen in 2.50 minutes (which is considerably higher than recently studied catalyzed MgH2 systems) under identical temperature and pressure conditions. The MgH2 catalyzed with Fe3O4@GS shows negligible degradation of the storage capacity even after 25 cycles. Additionally, the desorption activation energy for MgH2:Fe3O4@GS has been found to be 90.53 kJ mol-1 (which is considerably lower as compared to metal/metal oxide catalyzed MgH2 and fluorographene catalyzed MgH2). The formation enthalpy for MgH2:Fe3O4@GS is 60.62 kJ per mole of H2 (13.44 kJ mol-1 lower than bulk MgH2). The catalytic effect of Fe3O4@GS has been described and discussed with the help of structural (X-ray diffraction (XRD)), micro structural (electron microscopy) and Raman spectroscopic studies. © 2016 The Royal Society of Chemistry.