Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session V20: Energy Storage: Hydrogen Production and StorageFocus
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Sponsoring Units: GERA Chair: Rosa Cardenas, Rosa’s affiliation is the University of the Incarnate Word Room: LACC 308B |
Thursday, March 8, 2018 2:30PM - 2:42PM |
V20.00001: Water adsorption on clean and defective anatase TiO2(001) nanotube surfaces: a surface science approach Stephane Kenmoe, Oleg Lisovski, Sergei Piskunov, Dmitry Bocharov, Yuri zhukovskii, Eckhard Spohr Nanostructuring TiO2, e.g., by the formation of nanotubes (NTs) with large surface area is an efficient way to improve the photocatalytic performance of anatase TiO2. In this respect, TiO2 (001) NTs are promising candidates for hydrogen production via photocatalytic water splitting, as their visible-light-driven photocatalytic response can be tuned by N and S dopant atoms. As water is necessarily present in operando, it is essential to simulate not only the pure material but also the interface with at least a film of water molecules, together with its molecular and chemical dynamics. Using a 2D slab representation of the nanotube which takes into account the strain and partial curvature of the NT, we employ ab initio molecular dynamics simulations to study the adsorption of thin films of water ( 1ML and 2ML) on anatase TiO2 (001) nanotubes. The effect of anion doping on adsorption and surface chemistry is investigated by substituting O atoms by N and S impurities on the NT slab surface. While an S dopant weakens the interaction of the surface with water, which adsorbs molecularly, an N impurity renders the surface more reactive to water with a surface-assisted proton transfer taking place in the water film, and the formation of an OH- group and a NH2+ cation on the surface. |
Thursday, March 8, 2018 2:42PM - 2:54PM |
V20.00002: Highly Efficient Hydrogen Evolution by Self-Standing Nickel Phosphide-Based Hybrid Nanosheet Arrays Electrocatalyst Ishwar Mishra, Haiqing Zhou, Jingying Sun, Keshab Dahal, Zhensong Ren, Ran He, Shuo Chen, Zhifeng Ren Hydrogen evolution electrocatalyst made from earth-abundant elements for electrocatalytic water splitting is essential for sustainable and clean hydrogen economy. At present, how to make efficient catalysts with superior catalytic activity from cheap raw materials in large scale remains a great challenge. Here, we report a new nickel phosphide-based hybrid nanosheet arrays electrocatalyst, synthesized by a one-step phosphorization of commercial nickel (Ni) foam, for hydrogen evolution in water splitting. In acidic medium, the nickel phosphide nanosheet arrays exhibit very stable and fast hydrogen evolution kinetics with a relatively low overpotential of -61 mV and -121 mV to achieve current densities of -10 and -100 mA cm-2, respectively, with a Tafel slope of 51 mV dec-1, showing comparable performance to the most efficient non-noble metal based hydrogen evolution electrocatalysts reported so far. This robust electrocatalyst, made from commercially available materials, holds a potential for the industrialization of clean hydrogen energy. |
Thursday, March 8, 2018 2:54PM - 3:06PM |
V20.00003: One-step laser-induced hydrogen generation from graphite and coal in water Khomidkhodzha Kholikov, Dovletgeldi Seyitliyev, Byron Grant, Omer San, Ali Er A simple way of obtaining hydrogen gas from various ranks of coal, coke, and graphite using nanosecond laser pulses under different conditions such as water, air, and argon atmosphere is presented. Coal samples were initially characterized by scanning electron microscope (SEM), Fourier transform infrared (FTIR) spectroscopy, and calorimeter. It was observed that 532 nm laser pulses were more effective than 1064 nm pulses in gas generation and both were nonlinearly correlated with respect to the laser energy density. Gas chromatography measurements indicate that mainly hydrogen and carbon monoxide were generated. The hydrogen to carbon monoxide ratio shows that the highest efficiency rank was anthracite coal, with an average ratio of 1.4 due to its high fixed-carbon content and relatively high hydrocarbon amount. Graphite was used as a pure carbon source to study the possible reactions of gas yielded during the irradiation process. In addition, theoretical simulations using a standard finite difference method supported experimental observations. The possible mechanisms of gas generation were explained with chemical reactions. |
Thursday, March 8, 2018 3:06PM - 3:18PM |
V20.00004: Models of the Hydrogen Evolution Reaction on Transition Metal Phosphide Catalyst Surface Hao Gao, Chenyang Li, Wan Wan, Tim Mueller The hydrogen evolution reaction (HER) constitutes half of the water splitting reaction, which allows for the production of H2 from renewable energy resources, and reducing the demand for fossil fuels. Transition metal phosphides (TMP) have emerged as promising HER catalysts made from earth-abundant materials. TMP surfaces have a variety of symmetrically distinct sites that may be catalytically active. Their hydrogen adsorption energy has been shown to strongly depend on the coverage of adsorbed hydrogen on these surfaces. However, the structure of hydrogen adsorbed on TMP surfaces is largely unknown, limiting our understanding of the catalytic properties of these surfaces. To address this problem, we used cluster expansions to determine the atomic-scale structure of hydrogen on four different TMP surfaces: FeP(011), Fe2P(100), CoP(101), and Co2P(101). For reference, we constructed a cluster expansion for hydrogen adsorption on the widely-studied Pt(111) surface. These cluster expansions allow us to identify the structure and energetics of adsorbed hydrogen as a function of temperature, applied potential, and hydrogen chemical potential. We also present the results of related kinetic models to better understand the catalytic properties of TMP surfaces. |
Thursday, March 8, 2018 3:18PM - 3:30PM |
V20.00005: First-principles Studies on the Stability and Activity of CoS2 Surfaces for Hydrogen Evolution Reaction Yanning Zhang, Shengwen Li
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Thursday, March 8, 2018 3:30PM - 3:42PM |
V20.00006: Effects of Nano-confinement in Mesoporous Silica on Hydrogen Dynamics in TiCl3-Doped NaAlH4 Studied using Quasi-Elastic Neutron Scattering Tabbetha Dobbins, Craig Brown, Madhusan Tyagi, Timothy Jenkins The dynamics of hydrogen in 4 mol % TiCl3-doped NaAlH4 which was then confined within the mesoporous SBA15 was studied using quasi-elastic neutron scattering (QENS) technique. Results show that a higher fraction of hydrogen is mobile within the nanoconfined systems relative to bulk TiCl3-doped NaAlH4. However, the overall motion of hydrogen was localized and the nanostructured Ti-doped NaAlH4 exhibited mobility than the bulk (not nanostructured) materials of the same composition. Data were collected on the Disc Chopper Spectrometer and the High Flux Backscattering Spectrometer. Approximately 70% of hydrogen atoms are mobile at 400K while participating in short-range dynamics which could be described by the rotation of a AlH4 tetrahedra. However, less than 10% hydrogen was mobile at higher temperatures of 420K and 450K, possibly because the higher temperatures lead the formation of hydride phases. |
Thursday, March 8, 2018 3:42PM - 3:54PM |
V20.00007: Mechanism of Water Splitting Catalysed by Co-intercalated Birnessite Studied by SCAN MetaGGA Jinliang Ning, Jianwei Sun, Yubo Zhang Designing cheap, efficient and robust catalysts facilitating the splitting of water into oxygen and hydrogen is a worthwhile goal for conversion of solar energy into chemical energy, which helps eliminate the fossil fuel dependence of mankind. Inspired by the outstanding water-splitting ability of a manganese-bearing biological system, photo-system II (PS-II), manganese-containing compounds has been one of the research focuses for oxygen evolution reaction (OER) catalysts. Recently, a ubiquitous manganese oxide mineral, birnessite, has shown impressive performance for OER when intercalated with Co atoms, due to its special 2D-layered structure1. To understand the mechanism of activity of Co intercalated birnessite for OER, we propose a first-principles study using the newly developed SCAN functional2 to clarify possible effects contributing to the adsorption energies and overpotentials. These contributions include confinement effect, water layer effect, and Co concentration effect. |
Thursday, March 8, 2018 3:54PM - 4:06PM |
V20.00008: Origin of Hydrogen Evolution in MoS2 Liping Yu, Qimin Yan, Adrienn Ruzsinszky Molybdenum disulfide (MoS2) is a promising nonprecious catalyst for catalyzing electrochemical hydrogen (H2) production from water. Previous studies have indicated that the edge sites and sulfur vacancies are the most-probable active sites for the hydrogen evolution reaction (HER). However, their microscopic origin remains elusive. In this talk, we will present a microscopic model explaining the variation in the free energy of H-absorption at different sites. The results are obtained from first principles calculations using SCAN meta-GGA functional. We find that the energy difference between the lowest unoccupied states and the H-associated anti-bonding states dominates the H-adsorption. The larger the difference, the stronger the H adsorption becomes. The guiding principles emerging from this understanding will be discussed for improving the HER in MoS2 and designing new HER catalyst. |
Thursday, March 8, 2018 4:06PM - 4:18PM |
V20.00009: Gettering of Hydrogen and Methane from a Helium Gas Mixture using SAES St 175 ® Getters Rosa Cardenas, Kenneth Stewart, Donald Cowgill An approach developed previously using commercially available SAES St 172® getters was successfully implemented with titanium based SAES St 172® getters to accurately quantify the helium content in a gas mixture. The gas mixture contained mostly hydrogen with small fractions of methane and helium. The approach used allows for multiple measurements to be made quickly with accuracy better than 1%. Both H2 and CH4 were removed simultaneously from the mixture using two SAES St 175® getters operating at different temperatures. A capacitance manometer was then used to measure the remaining He. Optimum performance was achieved by operating one getter at 500°C to decompose the methane, and the second at 100°C to remove the hydrogen. This gettering approach is also useful for quantifying the He-3 in mixtures that include tritium, tritiated methane, and helium-3. |
Thursday, March 8, 2018 4:18PM - 4:30PM |
V20.00010: Defect Properties of Alkaline-Earth Hydrides for Hydrogen Energy Applications Andrew Rowberg, Leigh Weston, Chris Van de Walle Heavy alkaline-earth hydrides (AeH2; Ae = Ca, Sr, Ba) are thermally stable materials that have demonstrated good conductivity of hydride ions over a broad temperature range. However, experimental studies have not conclusively determined the dominant mechanisms for hydride ion transport in these materials. To better understand these mechanisms and, in the process, move these materials closer to applications, we conduct first-principles calculations based on density functional theory with a hybrid functional. We characterize the bulk electronic and structural properties of CaH2, SrH2, and BaH2, focusing specifically on the correlation between native point defect properties and high ionic conductivity. We calculate low migration barriers for hydrogen vacancy-mediated conductivity, particularly for vacancies in the positive charge state; this suggests processing conditions should aim to increase the concentration of positively charged hydrogen vacancies. We show that doping these hydrides with certain alkali metals can lower the formation energies of such defects, justifying experimental reports of improved conductivity in doped alkaline-earth hydrides and guiding development of materials with superior properties. |
Thursday, March 8, 2018 4:30PM - 4:42PM |
V20.00011: Evidence of Molecular Hydrogen Trapped between MXene Layers Naresh Osti, Michael Naguib, Madhusudan Tyagi, Yury Gogotsi, Alexander Kolesnikov, Eugene Mamontov MXenes are two-dimensional (2D) transition metal carbides, nitrides and carbonitrides. They possess a variety of different properties including a rare combination of hydrophilicity and conductivity which make MXenes promising materials in a broad range of applications. Even though the MXenes have been explored for hydrogen evolution in hydrogen evolution reaction catalysis, none of the previous studies have detected presence of molecular hydrogen in MXene. Here, using inelastic and elastic neutron-scattering techniques, we find evidence of molecular hydrogen in MXene. Inelastic neutron scattering spectra at 5 K show a peak at 14.6 meV, providing a clear indication of presence of para hydrogen in MXene annealed at 110 oC, and synthesized using 48 % HF. Temperature increase leads to a decrease in the peak intensity with an increase in the peak width due to enhancement on the mobility of the hydrogen molecules in confinement. Presence of molecular hydrogen is further confirmed from the observed mobility of hydrogen in the temperature range of 10-35 K, as captured in a temperature scan of neutron elastic intensity measurements. The role of etching conditions, ion intercalation, and annealing temperature on the removal of the molecular hydrogen trapped in the MXene will be discussed. |
Thursday, March 8, 2018 4:42PM - 5:18PM |
V20.00012: Elucidating the Impact of Polyelectrolyte Dynamics on the Reactivity of Novel Redox-Active Polymers for a New type of Size-Exclusion Flow Battery Invited Speaker: Joaquin Rodriguez-Lopez Soluble Redox-Active Polymers (RAPs)[1] and Colloids (RACs)[2] are a new class of materials for energy storage in fluid dispersions for a novel concept in size-exclusion flow batteries.[3] Despite RAPs displaying excellent charge storage properties, their complex electrochemical reactive pathways are just becoming elucidated. RAPs and RACs rely on intra-particle electron transfer to yield quantitative charge accessibility and high rate in order to achieve full electrolysis.[4] Charge mobility via inter-pendant electron hopping combines with their polyelectrolyte nature to exhibit a rich electrochemical behavior that is strongly modulated by specific and non-specific interactions with the electrolyte. In this talk, I will highlight the impact of several variables on the electrochemical signatures created by RAPs and RACs. |
Thursday, March 8, 2018 5:18PM - 5:30PM |
V20.00013: Abstract Withdrawn |
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