The Experts below are selected from a list of 318 Experts worldwide ranked by ideXlab platform
David S. Sholl - One of the best experts on this subject based on the ideXlab platform.
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examining the robustness of first principles calculations for metal hydride Reaction Thermodynamics by detection of metastable Reaction pathways
Physical Chemistry Chemical Physics, 2011Co-Authors: Ki Chul Kim, Anant D Kulkarni, Karl J Johnson, David S. ShollAbstract:First principles calculations have played a useful role in screening mixtures of complex metal hydrides to find systems suitable for H2storage applications. Standard methods for this task efficiently identify the lowest energy Reaction mechanisms among all possible Reactions involving collections of materials for which DFT calculations have been performed. The resulting mechanism can potentially differ from physical reality due to inaccuracies in the DFT functionals used, or due to other approximations made in estimating Reaction free energies. We introduce an efficient method to probe the robustness of DFT-based predictions that relies on identifying Reactions that are metastable relative to the lowest energy Reaction path predicted with DFT. An important conclusion of our calculations is that in many examples DFT cannot unambiguously predict a single Reaction mechanism for a well defined metal hydride mixture because two or more mechanisms have Reaction energies that differ by a small amount. Our approach is illustrated by analyzing a series of single step Reactions identified in our recent work that examined Reactions with a large database of solids [Kim et al., Phys. Chem. Chem. Phys. 2011, 13, 7218].
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large scale screening of metal hydrides for hydrogen storage from first principles calculations based on equilibrium Reaction Thermodynamics
Physical Chemistry Chemical Physics, 2011Co-Authors: Anant D Kulkarni, Karl J Johnson, David S. ShollAbstract:Systematic Thermodynamics calculations based on density functional theory-calculated energies for crystalline solids have been a useful complement to experimental studies of hydrogen storage in metal hydrides. We report the most comprehensive set of Thermodynamics calculations for mixtures of light metal hydrides to date by performing grand canonical linear programming screening on a database of 359 compounds, including 147 compounds not previously examined by us. This database is used to categorize the Reaction Thermodynamics of all mixtures containing any four non-H elements among Al, B, C, Ca, K, Li, Mg, N, Na, Sc, Si, Ti, and V. Reactions are categorized according to the amount of H2 that is released and the Reaction's enthalpy. This approach identifies 74 distinct single step Reactions having that a storage capacity >6 wt.% and zero temperature heats of Reaction 15 ≤ ΔU0 ≤ 75 kJ mol−1 H2. Many of these Reactions, however, are likely to be problematic experimentally because of the role of refractory compounds, B12H12-containing compounds, or carbon. The single most promising Reaction identified in this way involves LiNH2/LiH/KBH4, storing 7.48 wt.% H2 and having ΔU0 = 43.6 kJ mol−1 H2. We also examined the complete range of Reaction mixtures to identify multi-step Reactions with useful properties; this yielded 23 multi-step Reactions of potential interest.
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assessing nanoparticle size effects on metal hydride Thermodynamics using the wulff construction
Nanotechnology, 2009Co-Authors: Ki Chul Kim, Karl J Johnson, Bing Dai, David S. ShollAbstract:The Reaction Thermodynamics of metal hydrides are crucial to the use of these materials for reversible hydrogen storage. In addition to altering the kinetics of metal hydride Reactions, the use of nanoparticles can also change the overall Reaction Thermodynamics. We use density functional theory to predict the equilibrium crystal shapes of seven metals and their hydrides via the Wulff construction. These calculations allow the impact of nanoparticle size on the Thermodynamics of hydrogen release from these metal hydrides to be predicted. Specifically, we study the temperature required for the hydride to generate a H(2) pressure of 1 bar as a function of the radius of the nanoparticle. In most, but not all, cases the hydrogen release temperature increases slightly as the particle size is reduced.
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using first principles calculations to identify new destabilized metal hydride Reactions for reversible hydrogen storage
Physical Chemistry Chemical Physics, 2007Co-Authors: Sudhakar V Alapati, Karl J Johnson, David S. ShollAbstract:Hydrides of period 2 and 3 elements are promising candidates for hydrogen storage, but typically have heats of Reaction that are too high to be of use for fuel cell vehicles. Recent experimental work has focused on destabilizing metal hydrides through mixing metal hydrides with other compounds. A very large number of possible destabilized metal hydride Reaction schemes exist, but the thermodynamic data required to assess the enthalpies of these Reactions are not available in many cases. We have used density functional theory calculations to predict the Reaction enthalpies for more than 300 destabilization Reactions that have not previously been reported. The large majority of these Reactions are predicted not to be useful for reversible hydrogen storage, having calculated Reaction enthalpies that are either too high or too low, and hence these Reactions need not be investigated experimentally. Our calculations also identify multiple promising Reactions that have large enough hydrogen storage capacities to be useful in practical applications and have Reaction Thermodynamics that appear to be suitable for use in fuel cell vehicles and are therefore promising candidates for experimental work.
Dongan Liu - One of the best experts on this subject based on the ideXlab platform.
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studies of the effects of ticl3 in libh4 cah2 ticl3 reversible hydrogen storage system
Journal of Alloys and Compounds, 2012Co-Authors: Dongan Liu, Jun Ni, Jun Yang, Andy DrewsAbstract:Abstract In the present study, the effects of TiCl 3 on desorption kinetics, absorption/desorption reversibility, and related phase transformation processes in LiBH 4 /CaH 2 /TiCl 3 hydrogen storage system was studied systematically by varying its concentration ( x = 0, 0.05, 0.15 and 0.25). The results show that LiCl forms during ball milling of 6LiBH 4 /CaH 2 / x TiCl 3 and that as temperature increases, o-LiBH 4 transforms into h-LiBH 4 , into which LiCl incorporates, forming solid solution of LiBH 4 ·LiCl, which melts above 280 °C. Molten LiBH 4 ·LiCl is more viscous than molten LiBH 4 , preventing the clustering of LiBH 4 and the accompanied agglomeration of CaH 2 , and thus preserving the nano-sized phase arrangement formed during ball milling. Above 350 °C, the molten solution LiBH 4 ·LiCl further reacts with CaH 2 , precipitating LiCl. The main hydrogen desorption Reaction is between molten LiBH 4 ·LiCl and CaH 2 and not between molten LiBH 4 and CaH 2 . This alters the hydrogen Reaction Thermodynamics and lowers the hydrogen desorption temperature. In addition, the solid–liquid nano-sized phase arrangement in the nano-composites improves the hydrogen Reaction kinetics. The reversible incorporation/precipitation of LiCl at the hydrogen Reaction temperature and during temperature cycling makes the 6LiBH 4 /CaH 2 /0.25TiCl 3 nano-composite a fully reversible hydrogen storage material. These four states of LiCl in LiBH 4 /CaH 2 /TiCl 3 system, i.e. “formed-solid solution-molten solution-precipitation”, are reported for the first time and the detailed study of this system is beneficial to further improve hydrogen storage property of complex hydrides.
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Studies of the effects of TiCl3 in LiBH4/CaH2/TiCl3 reversible hydrogen storage system
Journal of Alloys and Compounds, 2012Co-Authors: Dongan Liu, Jun Ni, Jun Yang, Andy DrewsAbstract:Abstract In the present study, the effects of TiCl 3 on desorption kinetics, absorption/desorption reversibility, and related phase transformation processes in LiBH 4 /CaH 2 /TiCl 3 hydrogen storage system was studied systematically by varying its concentration ( x = 0, 0.05, 0.15 and 0.25). The results show that LiCl forms during ball milling of 6LiBH 4 /CaH 2 / x TiCl 3 and that as temperature increases, o-LiBH 4 transforms into h-LiBH 4 , into which LiCl incorporates, forming solid solution of LiBH 4 ·LiCl, which melts above 280 °C. Molten LiBH 4 ·LiCl is more viscous than molten LiBH 4 , preventing the clustering of LiBH 4 and the accompanied agglomeration of CaH 2 , and thus preserving the nano-sized phase arrangement formed during ball milling. Above 350 °C, the molten solution LiBH 4 ·LiCl further reacts with CaH 2 , precipitating LiCl. The main hydrogen desorption Reaction is between molten LiBH 4 ·LiCl and CaH 2 and not between molten LiBH 4 and CaH 2 . This alters the hydrogen Reaction Thermodynamics and lowers the hydrogen desorption temperature. In addition, the solid–liquid nano-sized phase arrangement in the nano-composites improves the hydrogen Reaction kinetics. The reversible incorporation/precipitation of LiCl at the hydrogen Reaction temperature and during temperature cycling makes the 6LiBH 4 /CaH 2 /0.25TiCl 3 nano-composite a fully reversible hydrogen storage material. These four states of LiCl in LiBH 4 /CaH 2 /TiCl 3 system, i.e. “formed-solid solution-molten solution-precipitation”, are reported for the first time and the detailed study of this system is beneficial to further improve hydrogen storage property of complex hydrides.
Andy Drews - One of the best experts on this subject based on the ideXlab platform.
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studies of the effects of ticl3 in libh4 cah2 ticl3 reversible hydrogen storage system
Journal of Alloys and Compounds, 2012Co-Authors: Dongan Liu, Jun Ni, Jun Yang, Andy DrewsAbstract:Abstract In the present study, the effects of TiCl 3 on desorption kinetics, absorption/desorption reversibility, and related phase transformation processes in LiBH 4 /CaH 2 /TiCl 3 hydrogen storage system was studied systematically by varying its concentration ( x = 0, 0.05, 0.15 and 0.25). The results show that LiCl forms during ball milling of 6LiBH 4 /CaH 2 / x TiCl 3 and that as temperature increases, o-LiBH 4 transforms into h-LiBH 4 , into which LiCl incorporates, forming solid solution of LiBH 4 ·LiCl, which melts above 280 °C. Molten LiBH 4 ·LiCl is more viscous than molten LiBH 4 , preventing the clustering of LiBH 4 and the accompanied agglomeration of CaH 2 , and thus preserving the nano-sized phase arrangement formed during ball milling. Above 350 °C, the molten solution LiBH 4 ·LiCl further reacts with CaH 2 , precipitating LiCl. The main hydrogen desorption Reaction is between molten LiBH 4 ·LiCl and CaH 2 and not between molten LiBH 4 and CaH 2 . This alters the hydrogen Reaction Thermodynamics and lowers the hydrogen desorption temperature. In addition, the solid–liquid nano-sized phase arrangement in the nano-composites improves the hydrogen Reaction kinetics. The reversible incorporation/precipitation of LiCl at the hydrogen Reaction temperature and during temperature cycling makes the 6LiBH 4 /CaH 2 /0.25TiCl 3 nano-composite a fully reversible hydrogen storage material. These four states of LiCl in LiBH 4 /CaH 2 /TiCl 3 system, i.e. “formed-solid solution-molten solution-precipitation”, are reported for the first time and the detailed study of this system is beneficial to further improve hydrogen storage property of complex hydrides.
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Studies of the effects of TiCl3 in LiBH4/CaH2/TiCl3 reversible hydrogen storage system
Journal of Alloys and Compounds, 2012Co-Authors: Dongan Liu, Jun Ni, Jun Yang, Andy DrewsAbstract:Abstract In the present study, the effects of TiCl 3 on desorption kinetics, absorption/desorption reversibility, and related phase transformation processes in LiBH 4 /CaH 2 /TiCl 3 hydrogen storage system was studied systematically by varying its concentration ( x = 0, 0.05, 0.15 and 0.25). The results show that LiCl forms during ball milling of 6LiBH 4 /CaH 2 / x TiCl 3 and that as temperature increases, o-LiBH 4 transforms into h-LiBH 4 , into which LiCl incorporates, forming solid solution of LiBH 4 ·LiCl, which melts above 280 °C. Molten LiBH 4 ·LiCl is more viscous than molten LiBH 4 , preventing the clustering of LiBH 4 and the accompanied agglomeration of CaH 2 , and thus preserving the nano-sized phase arrangement formed during ball milling. Above 350 °C, the molten solution LiBH 4 ·LiCl further reacts with CaH 2 , precipitating LiCl. The main hydrogen desorption Reaction is between molten LiBH 4 ·LiCl and CaH 2 and not between molten LiBH 4 and CaH 2 . This alters the hydrogen Reaction Thermodynamics and lowers the hydrogen desorption temperature. In addition, the solid–liquid nano-sized phase arrangement in the nano-composites improves the hydrogen Reaction kinetics. The reversible incorporation/precipitation of LiCl at the hydrogen Reaction temperature and during temperature cycling makes the 6LiBH 4 /CaH 2 /0.25TiCl 3 nano-composite a fully reversible hydrogen storage material. These four states of LiCl in LiBH 4 /CaH 2 /TiCl 3 system, i.e. “formed-solid solution-molten solution-precipitation”, are reported for the first time and the detailed study of this system is beneficial to further improve hydrogen storage property of complex hydrides.
Ki Chul Kim - One of the best experts on this subject based on the ideXlab platform.
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a review on design strategies for metal hydrides with enhanced Reaction Thermodynamics for hydrogen storage applications
International Journal of Energy Research, 2018Co-Authors: Ki Chul KimAbstract:Summary Hydrogen is an alternative clean energy carrier that can replace current fossil fuels for vehicular applications. Thus, it is important to develop a method that would enable a high density of hydrogen to be stored safely under the operating conditions of polymer electrolyte membrane fuel cells. Even though metal hydrides are regarded as promising candidates that can safely store a high density of hydrogen, their stable nature makes it difficult for them to release hydrogen at mild temperatures in the range of 50 to 150°C. In this review, 3 primary strategies, namely, introduction of appropriate dopants, particle size control, and design of novel reactant mixtures based on high-throughput screening methods, are briefly described with the aim of evaluating the potential of metal hydrides for hydrogen storage applications. The review suggests that successful development of promising hydrogen storage systems will depend on collaborative introduction of these 3 primary design strategies through the combined utilization of experimental and computational techniques to overcome the major challenges associated with the Reaction Thermodynamics of metal hydrides.
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validation of the Reaction Thermodynamics associated with nasc bh4 4 from first principles calculations detecting metastable paths and identifying the minimum free energy path
Journal of Chemical Physics, 2012Co-Authors: Ki Chul KimAbstract:A critical drawback with first-principles thermodynamic calculations is the absence of the vibrational and entropic contributions to the prediction of Reaction mechanisms, which could conclusively show that the predicted Reaction mechanism might be not the most stable Reaction path. This study focused on providing an answer to this problem by examining possible metastable paths for five reactant mixtures whose Reaction mechanisms were previously predicted using first-principles thermodynamic calculations. The aim of this study was to find a minimum free energy path among all the possible paths of each reactant mixture. This effort provided the clear conclusion that the original Reaction paths predicted from first-principles thermodynamic calculations were the most stable Reaction paths at an appropriate H2 pressure range for all cases. An additional examination associated with density functional theory uncertainty suggests how the ambiguity of Reaction mechanisms predicted based on thermodynamic calculati...
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examining the robustness of first principles calculations for metal hydride Reaction Thermodynamics by detection of metastable Reaction pathways
Physical Chemistry Chemical Physics, 2011Co-Authors: Ki Chul Kim, Anant D Kulkarni, Karl J Johnson, David S. ShollAbstract:First principles calculations have played a useful role in screening mixtures of complex metal hydrides to find systems suitable for H2storage applications. Standard methods for this task efficiently identify the lowest energy Reaction mechanisms among all possible Reactions involving collections of materials for which DFT calculations have been performed. The resulting mechanism can potentially differ from physical reality due to inaccuracies in the DFT functionals used, or due to other approximations made in estimating Reaction free energies. We introduce an efficient method to probe the robustness of DFT-based predictions that relies on identifying Reactions that are metastable relative to the lowest energy Reaction path predicted with DFT. An important conclusion of our calculations is that in many examples DFT cannot unambiguously predict a single Reaction mechanism for a well defined metal hydride mixture because two or more mechanisms have Reaction energies that differ by a small amount. Our approach is illustrated by analyzing a series of single step Reactions identified in our recent work that examined Reactions with a large database of solids [Kim et al., Phys. Chem. Chem. Phys. 2011, 13, 7218].
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assessing nanoparticle size effects on metal hydride Thermodynamics using the wulff construction
Nanotechnology, 2009Co-Authors: Ki Chul Kim, Karl J Johnson, Bing Dai, David S. ShollAbstract:The Reaction Thermodynamics of metal hydrides are crucial to the use of these materials for reversible hydrogen storage. In addition to altering the kinetics of metal hydride Reactions, the use of nanoparticles can also change the overall Reaction Thermodynamics. We use density functional theory to predict the equilibrium crystal shapes of seven metals and their hydrides via the Wulff construction. These calculations allow the impact of nanoparticle size on the Thermodynamics of hydrogen release from these metal hydrides to be predicted. Specifically, we study the temperature required for the hydride to generate a H(2) pressure of 1 bar as a function of the radius of the nanoparticle. In most, but not all, cases the hydrogen release temperature increases slightly as the particle size is reduced.
Karl J Johnson - One of the best experts on this subject based on the ideXlab platform.
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examining the robustness of first principles calculations for metal hydride Reaction Thermodynamics by detection of metastable Reaction pathways
Physical Chemistry Chemical Physics, 2011Co-Authors: Ki Chul Kim, Anant D Kulkarni, Karl J Johnson, David S. ShollAbstract:First principles calculations have played a useful role in screening mixtures of complex metal hydrides to find systems suitable for H2storage applications. Standard methods for this task efficiently identify the lowest energy Reaction mechanisms among all possible Reactions involving collections of materials for which DFT calculations have been performed. The resulting mechanism can potentially differ from physical reality due to inaccuracies in the DFT functionals used, or due to other approximations made in estimating Reaction free energies. We introduce an efficient method to probe the robustness of DFT-based predictions that relies on identifying Reactions that are metastable relative to the lowest energy Reaction path predicted with DFT. An important conclusion of our calculations is that in many examples DFT cannot unambiguously predict a single Reaction mechanism for a well defined metal hydride mixture because two or more mechanisms have Reaction energies that differ by a small amount. Our approach is illustrated by analyzing a series of single step Reactions identified in our recent work that examined Reactions with a large database of solids [Kim et al., Phys. Chem. Chem. Phys. 2011, 13, 7218].
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large scale screening of metal hydrides for hydrogen storage from first principles calculations based on equilibrium Reaction Thermodynamics
Physical Chemistry Chemical Physics, 2011Co-Authors: Anant D Kulkarni, Karl J Johnson, David S. ShollAbstract:Systematic Thermodynamics calculations based on density functional theory-calculated energies for crystalline solids have been a useful complement to experimental studies of hydrogen storage in metal hydrides. We report the most comprehensive set of Thermodynamics calculations for mixtures of light metal hydrides to date by performing grand canonical linear programming screening on a database of 359 compounds, including 147 compounds not previously examined by us. This database is used to categorize the Reaction Thermodynamics of all mixtures containing any four non-H elements among Al, B, C, Ca, K, Li, Mg, N, Na, Sc, Si, Ti, and V. Reactions are categorized according to the amount of H2 that is released and the Reaction's enthalpy. This approach identifies 74 distinct single step Reactions having that a storage capacity >6 wt.% and zero temperature heats of Reaction 15 ≤ ΔU0 ≤ 75 kJ mol−1 H2. Many of these Reactions, however, are likely to be problematic experimentally because of the role of refractory compounds, B12H12-containing compounds, or carbon. The single most promising Reaction identified in this way involves LiNH2/LiH/KBH4, storing 7.48 wt.% H2 and having ΔU0 = 43.6 kJ mol−1 H2. We also examined the complete range of Reaction mixtures to identify multi-step Reactions with useful properties; this yielded 23 multi-step Reactions of potential interest.
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assessing nanoparticle size effects on metal hydride Thermodynamics using the wulff construction
Nanotechnology, 2009Co-Authors: Ki Chul Kim, Karl J Johnson, Bing Dai, David S. ShollAbstract:The Reaction Thermodynamics of metal hydrides are crucial to the use of these materials for reversible hydrogen storage. In addition to altering the kinetics of metal hydride Reactions, the use of nanoparticles can also change the overall Reaction Thermodynamics. We use density functional theory to predict the equilibrium crystal shapes of seven metals and their hydrides via the Wulff construction. These calculations allow the impact of nanoparticle size on the Thermodynamics of hydrogen release from these metal hydrides to be predicted. Specifically, we study the temperature required for the hydride to generate a H(2) pressure of 1 bar as a function of the radius of the nanoparticle. In most, but not all, cases the hydrogen release temperature increases slightly as the particle size is reduced.
-
using first principles calculations to identify new destabilized metal hydride Reactions for reversible hydrogen storage
Physical Chemistry Chemical Physics, 2007Co-Authors: Sudhakar V Alapati, Karl J Johnson, David S. ShollAbstract:Hydrides of period 2 and 3 elements are promising candidates for hydrogen storage, but typically have heats of Reaction that are too high to be of use for fuel cell vehicles. Recent experimental work has focused on destabilizing metal hydrides through mixing metal hydrides with other compounds. A very large number of possible destabilized metal hydride Reaction schemes exist, but the thermodynamic data required to assess the enthalpies of these Reactions are not available in many cases. We have used density functional theory calculations to predict the Reaction enthalpies for more than 300 destabilization Reactions that have not previously been reported. The large majority of these Reactions are predicted not to be useful for reversible hydrogen storage, having calculated Reaction enthalpies that are either too high or too low, and hence these Reactions need not be investigated experimentally. Our calculations also identify multiple promising Reactions that have large enough hydrogen storage capacities to be useful in practical applications and have Reaction Thermodynamics that appear to be suitable for use in fuel cell vehicles and are therefore promising candidates for experimental work.
