Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session M38: Energy Storage and Conversion |
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Sponsoring Units: GERA Chair: Joseph Poon, University of Virginia Room: 347 |
Wednesday, March 20, 2013 8:00AM - 8:12AM |
M38.00001: Adsorbed Methane Film Properties in Nanoporous Carbon Monoliths YuChoong Soo, Nagaraju Chada, Matthew Beckner, Jimmy Romanos, Jacob Burress, Peter Pfeifer Carbon briquetting can increase methane storage capacity by reducing the useless void volume resulting in a better packing density. It is a robust and efficient space-filling form for an adsorbed natural gas vehicle storage tank. To optimize methane storage capacity, we studied three fabrication process parameters: carbon-to-binder ratio, compaction temperature, and pyrolysis temperature. We found that carbon-to-binder ratio and pyrolysis temperature both have large influences on monolith uptakes. We have been able to optimize these parameters for high methane storage. All monolith uptakes (up to 260 bar) were measured by a custom-built, volumetric, reservoir-type instrument. The saturated film density and the film thickness was determined using linear extrapolation on the high pressure excess adsorption isotherms. The saturated film density was also determined using the monolayer Ono-Kondo model. Film densities ranged from ca. 0.32 g/cm$^{3}$ - 0.37 g/cm$^{3}$.The Ono-Kondo model also determines the binding energy of methane. Binding energies were also determined from isosteric heats calculated from the Clausius-Clapeyron equation and compared with the Ono-Kondo model method. Binding energies from Ono-Kondo were ca. 7.8 kJ/mol - 10 kJ/mol. [Preview Abstract] |
Wednesday, March 20, 2013 8:12AM - 8:24AM |
M38.00002: Finite-Temperature Dihydrogen Adsorption/Desorption Thermodynamics on Metallo-Porphyrin Incorporated Graphene: Enthalpy versus Vibration Eui-Sup Lee, Sung-Jae Woo, Mina Yoon, Yong-Hyun Kim Gas adsorption is closely related to a variety of important physicochemical processes and technologies. Especially, hydrogen storage has been attracting much interest due to high energy density and the environmetally-friendly nature. Although a lot of theoretical studies have been carried out, the thermal vibration effect on hydrogen-sorbent interaction is relatively laking. Here we report the thermodynamics of H$_{\mathrm{2}}$ molecules adsorbed onto metallo-porphyrin-incoporated graphenes based on first-principles density-functional theory calculations. We found that the slow vibrations induced by weak binding tend to make the system more stable under finite temperature while the fast vibrations induced by strong binding disturb the adsorption. This tendency is expected to be universally found in various gas-sorbent systems. [Preview Abstract] |
Wednesday, March 20, 2013 8:24AM - 8:36AM |
M38.00003: Hydrogen Storage Investigation on Nanotube, Graphene and Organo-metallic Complexes Hong Zhang New materials and methods for storing hydrogen at high gravimetric and volumetric densities are required because of the widely use of hydrogen for clean fuel. With exceptionally high surface areas, porous materials based on carbon have recently emerged as some of the most promising candidate materials. Here I reviewed our former work on hydrogen storage based on several kinds of organometallic Complexes. Maximum capacities of the hydrogen storage in organometallic compounds consisting of Co and Ni atoms bound to C$_{\mathrm{m}}$H$_{\mathrm{m}}$ ring were found 3.48 wt {\%} and 3.49 wt {\%}, respectively; for the structures having a transition metal (TM) Co and Ni inserted in C$_{\mathrm{m}}$H$_{\mathrm{m}}$ ring, the maximum number of H$_{2}$ molecule bound to the inserted-type CoC$_{\mathrm{m}}$H$_{\mathrm{m}}$ and NiC$_{\mathrm{m}}$H$_{\mathrm{m}}$ complexes is three, and the largest hydrogen storage density is 5.13 wt {\%} and 3.49 wt {\%} for CoC$_{4}$H$_{4}$ and NiC$_{4}$H$_{4}$, Meanwhile, the ionic (C$_{4}$H$_{4}^{+}$ and C$_{5}$H$_{5}^{+})$ improves the capability of hydrogen storage and makes all H$_{2}$ adsorbed to the charged compounds in molecular form. With the CH$_{3}$ ligand bound to the compounds, the adsorption energy of H$_{2}$ decreases to an ideal range, and stability of the compounds are improved. At last, the hydrogen adsorption properties on the complex structures TiRH$_{7}$Si$_{8}$O$_{12}$ are investigated, and the kinetic stability when H$_{2}$ was added to organometallic compounds is also discussed by analyzing HOMO-LUMO gaps. Here we also mentioned our results of hydrogen storage based on nanotubes and graphene. [Preview Abstract] |
Wednesday, March 20, 2013 8:36AM - 8:48AM |
M38.00004: First-principles calculations of mass transport in magnesium borohydride Chao Yu, Vidvuds Ozolins Mg(BH$_{4}$)$_2$ is a hydrogen storage material which can decompose to release hydrogen in the following reaction: Mg(BH$_4$)$_{2(\mathrm{solid})}$ $\rightarrow \frac{1}{6}$MgB$_{12}$H$_{12(\mathrm{solid})}$ + $\frac{5}{6}$MgH$_{2(\mathrm{solid})} + \frac{13}{6}$H$_{2(\mathrm{gas})}$ $\rightarrow$ MgH$_{2(\mathrm{solid})}$ + 2B$_{(\mathrm{solid})}$ + 4H$_{2(\mathrm{gas})}$. However, experiments show that hydrogen release only occurs at temperatures above 300 $^{\circ}$C, which severely limits applications in mobile storage. Using density-functional theory calculations, we systematically study bulk diffusion of defects in the reactant Mg(BH$_{4}$)$_2$ and products MgB$_{12}$H$_{12}$ and MgH$_{2}$ during the first step of the solid-state dehydrogenation reaction. The defect concentrations and concentration gradients are calculated for a variety of defects, including charged vacancies and interstitials. We find that neutral [BH$_3$] vacancies have the highest bulk concentration and concentration gradient in Mg(BH$_{4}$)$_2$. The diffusion mechanism of [BH$_3$] vacancy in Mg(BH$_{4}$)$_2$ is studied using the nudged elastic band method. Our results shows that the calculated diffusion barrier for [BH$_3$] vacancies is $\approx. 2$~eV, suggesting that slow mass transport limits the kinetics of hydrogen desorption. [Preview Abstract] |
Wednesday, March 20, 2013 8:48AM - 9:00AM |
M38.00005: Effect of transition-metal additives on dehydrogenation kinetics of MgH$_2$ Anindya Roy, Anderson Janotti, Chris G. Van de Walle Using first-principles calculations based on hybrid density functional theory we study the (de)hydrogenation process in MgH$_2$, an important solid-state hydrogen storage material. This reaction proceeds through diffusion processes, mediated by native point defects such as vacancies and interstitials. Reducing the formation energy of relevant defects increases their concentrations, resulting in higher diffusion rates and an enhancement in kinetics. We investigate the formation energies of native point defects in MgH$_2$ and determine the position of the Fermi level in the band gap using the charge neutrality condition. The presence of transition-metal (TM) impurities (Ti, Fe, Co and Ni) causes the Fermi level to shift according to the position of the TM acceptor/donor levels in the band gap. This shift can bring down the formation energy of native defects. Our calculations predict that all of the TM additives, in either interstitial or substitutional configurations, may cause such a shift in the Fermi level and thus increase the concentration of the hydrogen vacancies that govern hydrogen diffusion. Our proposed mechanism explains the experimentally observed enhancement in the rate of dehydrogenation of MgH$_2$ upon addition of TM impurities. [Preview Abstract] |
Wednesday, March 20, 2013 9:00AM - 9:12AM |
M38.00006: Low-Energy Polymeric Phases of Alanates Huan Tran, Maximilian Amsler, Miguel Marques, Silvana Botti, Alexander Willand, Stefan Goedecker Low-energy structures of alanates are currently known to be described by patterns of isolated, nearly ideal tetrahedral [AlH$_4$] anions and metal cations. We discover that the novel polymeric motif recently proposed for LiAlH$_4$ plays a dominant role in a series of alanates, including LiAlH$_4$, NaAlH$_4$, KAlH$_4$, Mg(AlH$_4$)$_2$, Ca(AlH$_4$)$_2$ and Sr(AlH$_4$)$_2$. In particular, most of the low-energy structures discovered for the whole series are characterized by networks of corner-sharing [AlH$_6$] octahedra, forming wires and/or planes throughout the materials. Finally, for Mg(AlH$_4$)$_2$ and Sr(AlH$_4$)$_2$, we identify two polymeric phases to be lowest in energy at low temperatures. [Preview Abstract] |
Wednesday, March 20, 2013 9:12AM - 9:24AM |
M38.00007: Stability of transition metals on the Mg-terminated $MgB_2$ (0001) surface and their effects on hydrogen dissociation Yongli Wang, Chris Wolverton The re-hydrogenation of $MgB_2$ is a critical step in the reversibility of several key hydrogen storage reactions. Two main activated processes affect the kinetics of hydrogen absorption by $MgB_2$: the dissociation of the $H_2$ molecule and the diffusion of atomic H into the bulk. In order to have fast absorption kinetics both activated processes need to have a low barrier. Using first-principles calculations, we investigate the dissociation of $H_2$ on the Mg-terminated $MgB_2$ (0001) surfaces. We investigate both ideal surfaces as well as surfaces with vacancies, and transition-metal-dopants (TM=Sc$\sim$Zn,Y$\sim$Cd,Au,Pt). Our calculations show that the late TMs more favorably substitute for the Mg atoms in the outermost layer of the Mg-terminated surface, rather than for those in the sub-layers. We find the dissociation barrier for $H_2$ on the clean Mg-terminated $MgB_2$ (0001) surface is 0.46eV. The TM dopants have only a small effect on dissociation barrier when they are incorporated into the sub-layers. However, when doped in the outermost layer, we find examples of dopants that significantly decrease the activation barrier for the dissociation of $H_2$. We also investigate the diffusivity of H in $MgB_2$ and find strong anisotropy in the diffusion pathways. [Preview Abstract] |
Wednesday, March 20, 2013 9:24AM - 9:36AM |
M38.00008: Adsorbed Hydrogen Film Densities and Thicknesses Determined from Low-Temperature Hydrogen Sorption Experiments Jacob Burress, Elmar Dohnke, Matthew Beckner, Mark Lee, Carlos Wexler, Peter Pfeifer Hydrogen storage through physisorption has shown tremendous promise. Advancement of our understanding about hydrogen behavior in confined pores can lead to a development of new storage materials. For example, isosteric heat is used to determine the quality of a sorbent. Yet, Clausius-Clapeyron isosteric heat calculations are typically performed on excess adsorption, which leads to unphysical results. Absolute adsorption should be used for these calculations. To determine absolute adsorption from excess adsorption, the volume of the adsorbed film is needed. We have built a Sievert type instrument capable of temperatures from 10 K to 300 K and pressures up to 200 bar. Using this instrument to measure low temperature ($<$ 77 K) and high pressure ($>$ 100 bar) isotherms, experimental film density and volume have been determined from the linear decrease in excess H$_{2}$ as a function of bulk gas density. Additionally, some materials have shown H$_{2}$ uptakes higher than what their surface area predicts. One hypothesis is N$_{2}$, the standard gas to determine surface areas, is sterically forbidden to go into pores that H$_{2}$ can. Sub-critical H$_{2}$ isotherms have been measured to determine surface area available to the H$_{2}$ and comparisons are made to N$_{2}$ surface area. [Preview Abstract] |
Wednesday, March 20, 2013 9:36AM - 9:48AM |
M38.00009: Thermodynamics, kinetics, and catalytic effect of dehydrogenation from MgH2 stepped surfaces and nanocluster: a DFT study Jason Reich, LinLin Wang, Duane Johnson We detail the results of a Density Functional Theory (DFT) based study of hydrogen desorption, including thermodynamics and kinetics with(out) catalytic dopants, on stepped (110) rutile and nanocluster MgH$_{2}$. We investigate competing configurations (optimal surface and nanoparticle configurations) using simulated annealing with additional converged results at 0 K, necessary for finding the low-energy, doped MgH$_{2}$ nanostructures. Thermodynamics of hydrogen desorption from unique dopant sites will be shown, as well as activation energies using the Nudged Elastic Band algorithm. To compare to experiment, both stepped structures and nanoclusters are required to understanding and predict the effects of ball milling. We demonstrate how these model systems relate to the intermediary sized structures typically seen in ball milling experiments. [Preview Abstract] |
Wednesday, March 20, 2013 9:48AM - 10:00AM |
M38.00010: Measurements of Increased Enthalpies of Adsorption for Boron-Doped Activated Carbons Andrew Gillespie, Matthew Beckner, Nagaraju Chada, Joseph Schaeperkoetter, Anupam Singh, Mark Lee, Carlos Wexler, Jacob Burress, Peter Pfeifer Boron-doping of activated carbons has been shown to increase the enthalpies of adsorption for hydrogen as compared to their respective undoped precursors ($>$10kJ/mol compared to ca. 5kJ/mol). This has brought significant interest to boron-doped carbons for their potential to improve hydrogen storage. Boron-doped activated carbons have been produced using a process involving the deposition of decaborane (B$_{10}$H$_{14}$) and high-temperature annealing resulting in boron contents up to 15\%. In this talk, we will present a systematic study of the effect that boron content has on the samples' structure, hydrogen sorption, and surface chemistry. Measurements have shown a significant increase in the areal hydrogen excess adsorption and binding energy. Experimental enthalpies of adsorption will be presented for comparison to theoretical predictions. Additionally, samples have been characterized by thermal gravimetric analysis, gas chromatography-mass spectroscopy, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. TGA and GC-MS results investigated the decomposition of the decaborane in the carbon. Boron-carbon bonds are shown in the FTIR and XPS spectra, indicating that boron has been incorporated into the carbon matrix. [Preview Abstract] |
Wednesday, March 20, 2013 10:00AM - 10:12AM |
M38.00011: Bulk Diffusion via a ``kick-out'' method for Lithium in the decomposition reaction LiAlH4/Li3AlH6 Biljana Rolih, Vidvuds Ozolins In the pursuit to find a practical system for hydrogen storage, complex metal hydrides have long been considered as viable candidates due to their high hydrogen content. However, some of the challenges faced with these types of systems are poor thermodynamics or kinetics. The underlying mechanisms, and their limiting processes, for the decomposition of these materials need to be understood. From experimental work on the decomposition of hydrogen storage materials, it has been suggested that bulk diffusion of metal species is the bottleneck for hydrogen release. In this work is the dehydrogenation we investigated the system $ LiAlH_4 \longrightarrow LiAlH_6 $ with favorable hydrogen release (5.3 wt \%), at moderate temperatures. Using first-principles density functional theory we found the defects facilitating mass transport by calculating individual formation energies, highest concentrations, and activation barriers for defect mobility. The mass transport of Lithium is found to be mediated by a ``kick-out'' mechanism. The results are used to further our understanding of the fundamental mechanism of mass transport and evaluate the possibility of kinetics as the limiting process in this reaction. [Preview Abstract] |
Wednesday, March 20, 2013 10:12AM - 10:24AM |
M38.00012: Gold Nanoparticle Enhancement for Polymer Electrolyte Membrane (PEM) Fuel Cell Cheng Pan, Sisi Qin, Miriam Rafailovich PEM fuel cell is one of the most promising future alternative energy sources. However, its relatively low power output has prevented it from many practical applications. Marvrikakis et al have predicted that gold nanoparticles that are platelet shaped andhave direct contact to the substrate to be the perfect catalysts. In our experiment, hydrophobic, thiol-functionalized gold nanoparticles were synthesized through two-phase method developed by Brust et al. When particle solution is spread at the air water interface, EXAFS spectroscopy indicate that some of the gold atoms are removed, as the water displaces the hydrophobic thiol chains from the particle surface, resulting in platelet shaped particles. Furthermore, after these nanoparticles are spread on the surface of water in a Langmuir-Blodgett trough where surface pressure can be applied to compress them, they form LB film consisting of one or more monolayers. This LB film can then be deposited onto a solid surface, such as the Nafion membrane where the particle surface can make direct contact with electrodes and take effect. We also find that there is an optimal surface pressure for forming gold nanoparticles monolayer to achieve the highest enhancement of output power. [Preview Abstract] |
Wednesday, March 20, 2013 10:24AM - 10:36AM |
M38.00013: Density Functional Theory Study of Oxygen Reduction Reaction Mechanism on Pt$_3$Ti(111) Surface Shyam Kattel, Zhiyao Duan, Guofeng Wang Density functional theory (DFT) calculations are performed to explain the ORR mechanism on Pt segregated Pt$_{3}$Ti(111) surface. The possible ORR mechanism is elucidated by calculating the activation energies of all ORR elementary reaction steps. Our preliminary results predict that the ORR proceeds via a H$_{2}$O$_{2}$ dissociation mechanism with coverage dependent kinetics. At high coverage, the rate determining step (RDS) is protonation of adsorbed O$_{2}$ to form OOH. The energy barrier for this process is 0.20 eV which is lower than the energy barrier for RDS on pure Pt(111) surface. These findings suggest that modified PtTi(111) surface has better ORR activity in comparison to pure Pt(111) surface. Furthermore, we have studied the corrosion behavior of Pt$_{3}$Ti(111) surface by evaluating the electrochemical potential shift for clean and oxygenated surface. The computations predict enhanced stability of Pt$_{3}$Ti(111) surface against surface Pt dissolution in comparison to Pt dissolution from pure Pt(111) surface. [Preview Abstract] |
Wednesday, March 20, 2013 10:36AM - 10:48AM |
M38.00014: Neutron Scattering Studies of Destabilized Lithium Borohydride Nina Verdal, Terrence Udovic, John Rush, Alexander Skripov One of the most promising materials for hydrogen storage is lithium borohydride, LiBH$_{\mathrm{4}}$, due to its high hydrogen mass fraction. However, applications require destabilization of the material in order to reduce the temperature and pressure required for hydrogen cycling. One possible avenue for destabilization has been via the use of mixed crystals, for example, LiI and LiBH$_{\mathrm{4}}$, in which the relatively large iodide anion expands the crystal lattice of bulk LiBH$_{\mathrm{4}}$. Here we present neutron scattering results comparing BH$_{\mathrm{4}}^{\mathrm{-}}$ anion reorientational dynamics for bulk LiBH$_{\mathrm{4}}$ and the destabilized LiI-LiBH$_{\mathrm{4}}$ system. Quasielastic neutron scattering spectroscopy shows that at temperatures below room temperature, the reorientational dynamics for hexagonal LiI-LiBH$_{\mathrm{4}}$ is very similar to that of the high-temperature (380 K and above) hexagonal phase of LiBH$_{\mathrm{4}}$ instead of its low-temperature orthorhombic phase, which exhibits different dynamics. This is consistent with the behavior found using NMR spectroscopy. [Preview Abstract] |
Wednesday, March 20, 2013 10:48AM - 11:00AM |
M38.00015: Predicting hydrogen and methane adsorption in carbon nanopores for energy storage Yungok Ihm, James Morris, Valentino Cooper There are increasing demands for alternate fuels for transportation, which requires safe, high energy density, lightweight storage materials. Experimental measurements and theoretical predictions show relatively low hydrogen storage capacities in various porous materials, limiting hydrogen as a viable alternative for automobiles. In this work, we use a continuum model based on van der Waals density functional (vdW-DF) calculations to elucidate the role that long-range interactions play in the hydrogen adsorption properties of model slit nanopores in carbon. The proper treatment of long-range interactions gives an optimal pore size for hydrogen storage of 8-9 {\AA} (larger than previously predicted). Remarkably, we find a peak hydrogen density close to that of liquid H$_{2}$ at ambient temperatures, in agreement with recent experimental results on pore-size dependent adsorption in nanoporous carbon. We then show that such nanopores would be better suited to storing methane, possibly providing an alternative to fill the gap between the capacity required by DOE goals and that attainable with current hydrogen storage technology. [Preview Abstract] |
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