Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session D34: Solar Fuels, Biofuels, and PEC |
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Sponsoring Units: GERA Chair: Sue Carter, University of California, San Diego Room: 704 |
Monday, March 3, 2014 2:30PM - 2:42PM |
D34.00001: High-throughput characterization for solar fuels materials discovery Slobodan Mitrovic, Natalie Becerra, Earl Cornell, Dan Guevarra, Joel Haber, Jian Jin, Ryan Jones, Kevin Kan, Martin Marcin, Paul Newhouse, Edwin Soedarmadji, Santosh Suram, Chengxiang Xiang, John Gregoire In this talk I will present the status of the High-Throughput Experimentation (HTE) project of the Joint Center for Artificial Photosynthesis (JCAP). JCAP is an Energy Innovation Hub of the U.S. Department of Energy with a mandate to deliver a solar fuel generator based on an integrated photoelectrochemical cell (PEC). However, efficient and commercially viable catalysts or light absorbers for the PEC do not exist. The mission of HTE is to provide the accelerated discovery through combinatorial synthesis and rapid screening of material properties. The HTE pipeline also features high-throughput material characterization using x-ray diffraction and x-ray photoemission spectroscopy (XPS). In this talk I present the currently operating pipeline and focus on our combinatorial XPS efforts to build the largest free database of spectra from mixed-metal oxides, nitrides, sulfides and alloys. [Preview Abstract] |
Monday, March 3, 2014 2:42PM - 2:54PM |
D34.00002: The effect of surfactant on the formation and combustion of methane hydrates Jeffrey Botimer, Peter Taborek, Sunny Karnani, Derek Dunn-Rankin Methane hydrates are an abundant and globally distributed fuel source that has potential to play an important role in the worlds energy economy. We have used optical imaging to study the effects of surfactant on the kinetics of formation and the combustion of methane hydrates. We grow hydrates from liquid water in methane gas at 275K and 1000psi. The hydrate growth front propagates into the vapor rather than into the liquid. We have investigated the effect of wetting properties of the substrate on the growth of the hydrate. The combustion of hydrates is complicated by the requirement of draining away the melting water during combustion. The surfactant complicates the combustion process further because it inhibits the drainage of water. We have investigated this process as a function of surfactant concentrations and ambient pressure. [Preview Abstract] |
Monday, March 3, 2014 2:54PM - 3:06PM |
D34.00003: Properties of Solar Thermal Fuels by Accurate Quantum Monte Carlo Calculations Kayahan Saritas, Can Ataca, Jeffrey C. Grossman Efficient utilization of the sun as a renewable and clean energy source is one of the major goals of this century due to increasing energy demand and environmental impact. Solar thermal fuels are materials that capture and store the sun's energy in the form of chemical bonds, which can then be released as heat on demand and charged again. Previous work on solar thermal fuels faced challenges related to the cyclability of the fuel over time, as well as the need for higher energy densities. Recently, it was shown that by templating photoswitches onto carbon nanostructures, both high energy density as well as high stability can be achieved. In this work, we explore alternative molecules to azobenzene in such a nano-templated system. We employ the highly accurate quantum Monte Carlo (QMC) method to predict the energy storage potential for each molecule. Our calculations show that in many cases the level of accuracy provided by density functional theory (DFT) is sufficient. However, in some cases, such as dihydroazulene, the drastic change in conjugation upon light absorption causes the DFT predictions to be inconsistent and incorrect. For this case, we compare our QMC results for the geometric structure, band gap and reaction enthalpy with different DFT functionals. [Preview Abstract] |
Monday, March 3, 2014 3:06PM - 3:18PM |
D34.00004: Synergy between cellulolytic enzymes during the biodegradation of cellulose microfibrils measured using angle-scanning surface plasmon resonance (SPR) imaging Adam Raegen, Alexander Dion, Kyle Reiter, Anthony Clarke, Jacek Lipkowski, John Dutcher The use of cellulosic ethanol, a promising emerging energy source, is limited by the energy intensive and costly step of first converting the cellulose fibers into their constituent glucose monomers. Industrial processes mimic those that occur in nature, using mixtures or ``cocktails'' of different classes of cellulolytic enzymes derived from fungi. Despite several decades of investigation, the molecular mechanisms for enzyme synergy remain poorly understood. To gain additional insight, we have used a custom angle-scanning surface plasmon resonance (SPR) imaging apparatus to obtain a sensitive measure of enzymatic degradation. By implementing a novel SPR data analysis procedure, we have been able to track the thickness and roughness of laterally heterogeneous cellulose microfibril-coated substrates as enzymatic degradation proceeds. This has allowed us to measure the synergistic actions of the different enzymes, providing data that are directly relevant to the cellulosic ethanol industry. [Preview Abstract] |
Monday, March 3, 2014 3:18PM - 3:30PM |
D34.00005: First-principles quantum-mechanical investigations of biomass conversion at the liquid-solid interfaces Hongli Dang, Wenhua Xue, Yingdi Liu, Friederike Jentoft, Daniel Resasco, Sanwu Wang We report first-principles density-functional calculations and \textit{ab initio} molecular dynamics (MD) simulations for the reactions involving furfural, which is an important intermediate in biomass conversion, at the catalytic liquid-solid interfaces. The different dynamic processes of furfural at the water-Cu(111) and water-Pd(111) interfaces suggest different catalytic reaction mechanisms for the conversion of furfural. Simulations for the dynamic processes with and without hydrogen demonstrate the importance of the liquid-solid interface as well as the presence of hydrogen in possible catalytic reactions including hydrogenation and decarbonylation of furfural. [Preview Abstract] |
Monday, March 3, 2014 3:30PM - 3:42PM |
D34.00006: Fundamental efficiency limit for solar thermal fuels David A. Strubbe, Yun Liu, Jeffrey C. Grossman Solar thermal fuels (STFs) are an unconventional paradigm for solar energy conversion and storage which is attracting renewed attention: a material absorbs sunlight and stores the energy chemically via an induced structural change, which can later be reversed to release the energy as heat. An example is the azobenzene molecule which has a cis-trans photoisomerization with these properties, and can be tuned by chemical substitution and attachment to templates such as carbon nanotubes. By analogy to the Shockley-Queisser limit for photovoltaics (PV), we analyze the maximum attainable efficiency for STFs. The below-gap, above-gap, and recombination losses are similar to PV, but there are additional considerations about further losses, quantum yield, photostationary state, and interrelation with the storage lifetime, another key performance metric for STFs. We show constraints on feasible potential-energy surfaces for STFs, and compare to ab initio calculations and experimental measurements of the properties of STF materials. [Preview Abstract] |
Monday, March 3, 2014 3:42PM - 3:54PM |
D34.00007: Energy-Efficient Bioalcohol Recovery by Gel Stripping Rutvik Godbole, Lan Ma, Ronald Hedden Design of energy-efficient processes for recovering butanol and ethanol from dilute fermentations is a key challenge facing the biofuels industry due to the high energy consumption of traditional multi-stage distillation processes. Gel stripping is an alternative purification process by which a dilute alcohol is stripped from the fermentation product by passing it through a packed bed containing particles of a selectively absorbent polymeric gel material. The gel must be selective for the alcohol, while swelling to a reasonable degree in dilute alcohol-water mixtures. To accelerate materials optimization, a combinatorial approach is taken to screen a matrix of copolymer gels having orthogonal gradients in crosslinker concentration and hydrophilicity. Using a combination of swelling in pure solvents, the selectivity and distribution coefficients of alcohols in the gels can be predicted based upon multi-component extensions of Flory-Rehner theory. Predictions can be validated by measuring swelling in water/alcohol mixtures and conducting h HPLC analysis of the external liquid. 95{\%}$+$ removal of butanol from dilute aqueous solutions has been demonstrated, and a mathematical model of the unsteady-state gel stripping process has been developed. [Preview Abstract] |
Monday, March 3, 2014 3:54PM - 4:06PM |
D34.00008: Ab initio molecular dynamics simulations for the role of hydrogen in catalytic reactions of furfural on Pd(111) Wenhua Xue, Hongli Dang, Yingdi Liu, Friederike Jentoft, Daniel Resasco, Sanwu Wang In the study of catalytic reactions of biomass, furfural conversion over metal catalysts with the presence of hydrogen has attracted wide attention. We report \textit{ab initio} molecular dynamics simulations for furfural and hydrogen on the Pd(111) surface at finite temperatures. The simulations demonstrate that the presence of hydrogen is important in promoting furfural conversion. In particular, hydrogen molecules dissociate rapidly on the Pd(111) surface. As a result of such dissociation, atomic hydrogen participates in the reactions with furfural. The simulations also provide detailed information about the possible reactions of hydrogen with furfural. [Preview Abstract] |
Monday, March 3, 2014 4:06PM - 4:18PM |
D34.00009: Tin Nitride as an Earth Abundant Photoanode for Water Splitting Christopher Caskey, Ming Ma, Vladan Stephanovic, Stephan Laney, David Ginley, Ryan Richards, Wilson Smith, Andriy Zakutayev Photoelectrochemical (PEC) water splitting--the conversion of water to hydrogen and oxygen using light--is an attractive route to the chemical storage of solar energy. We demonstrate that spinel tin nitride (Sn$_{3}$N$_{4}$) has conduction and valence bands that straddle the redox potentials of water and we study it as a photoannode material. Sn$_{3}$N$_{4}$ thin films have been grown on glass at ambient temperature by reactive sputtering of tin in a nitrogen atmosphere. The resulting materials were n-type semiconductors. Carrier concentration, carrier mobility, work function, and optical properties were measured. Results indicate that tin nitride has a band gap of $\sim$ 1.7 eV aligned around water's redox potentials. GW-corrected DFT-surface calculations that take into account water surface dipole interactions are consistent with experiment. Early PEC devices were made from Sn$_{3}$N$_{4}$ on fluorinated tin oxide with cobalt oxide catalysts and show a small but promising photoresponse ($\sim$ 0.1 mA/cm$^{2}$ at 1.23 V vs. RHE) under AM 1.5 illumination in 0.1 M potassium phosphate (pH= 7.25). Further work will focus on increasing the photocurrent in tin nitride devices by increasing film quality and identifying the proper catalyst. [Preview Abstract] |
Monday, March 3, 2014 4:18PM - 4:30PM |
D34.00010: First-principles interpretation of core-level spectroscopy of photoelectrochemical materials and processes Sri Chaitanya Das Pemmaraju, David Prendergast We present two case studies of first-principles theoretical methods applied in conjunction with experimental core-level spectroscopy measurements to investigate the electronic structure and dynamical processes in molecular and interfacial systems relevant to photoelectrochemical (PEC) technologies. In the first [1], we study the core-level and valence spectroscopies of two zinc(II)-porphyrin based Donor-pi-Acceptor (D-p-A) [2] dyes using the occupancy-constrained excited electron and core-hole (XCH) [3] approach and time-dependent density functional theory (TDDFT) simulations. In the second, we use constrained DFT and TDDFT to interpret measured transient core-level shifts in time-resolved femtosecond x-ray photoelectron spectroscopy, investigating the dynamics of the electron injection process from a N3 dye molecule chemisorbed onto a ZnO substrate. These studies illustrate the utility of first-principles methods in guiding the design of better PEC materials. References: [1] Zegkinoglou, I et al, J. Phys. Chem. C, J. Phys. Chem. C, 2013, 117, 13357 [2] Yella, A. et al, Science 2011, 334, 629. [3] Prendergast, D and Galli, G; Phys. Rev. Lett. 2006, 96, 215502. [Preview Abstract] |
Monday, March 3, 2014 4:30PM - 4:42PM |
D34.00011: ABSTRACT WITHDRAWN |
Monday, March 3, 2014 4:42PM - 4:54PM |
D34.00012: Opto-electronic properties of Ta$_3$N$_5$: a joint experimental and theoretical study Juliana Morbec, Dario Rocca, Blaise Pinaud, Thomas Jaramillo, Giulia Galli Tantalum nitride (Ta$_3$N$_5$) is considered a promising material for use in photoelectrochemical cells, due to its suitable band gap for visible light absorption and favorable band-edge positions for water splitting. However, Ta$_3$N$_5$ films have been recently shown to exhibit low photocurrent (i.e. less than 50\% of the theoretical limit). We report a joint experimental and ab initio theoretical study of the opto-electronic properties of Ta$_3$N$_5$, aimed at understanding possible reasons for the limited photocurrent. Our experimental optical spectra of films with different thicknesses show two absorption edges at 2.1 and 2.5 eV. To provide an interpretation of these features, we performed ab initio calculations, at several levels of theory, of the electronic band structure and optical absorption spectra of Ta$_3$N$_5$. We employed density functional theory with semi-local (PBE/LDA) and hybrid (PBE0/HSE06) functionals and many body perturbation theory at the G$_0$W$_0$ level, and we obtained optical spectra by solving the Bethe-Salpeter equation within density matrix perturbation theory. [Preview Abstract] |
Monday, March 3, 2014 4:54PM - 5:06PM |
D34.00013: Transient performance modeling of photoelectrochemical cells incorporating nano-structured photoanodes Sophia Haussener, Mikael Dumortier Photoelectrochemical processes constitute a viable route for renewable hydrogen production. Several practical systems that provide separated product streams of hydrogen and oxygen follow the design guidelines established in the fuel cell community and have been demonstrated. We developed a transient 1D numerical model of a photoelectrochemical fuel cell-based device, which incorporates a complex, nano-structured photoanode. The model accounted for radiation transport, charge carrier transport, species transport, fluid flow and electrochemical reactions. We investigated the transient performance under varying illumination, species mix and phases, and examined different types of nanostructured photoanodes, i.e. based on carbon-paper infiltrated with photoactive particles or carbon nanotubes uniformly covered by photoactive layers. Our model predicted the operational-dependent and experimentally observed four regimes of the transient photocurrent: anodic overshoot at illumination start, current increase, current decrease, and cathodic undershoot. The numerical results supported the hypothesis that the transient behavior of the photocurrent at startup was dominated by the low initial concentration of hydrogen and oxygen. The validated model developed provides a useful tool for system design and operational guidelines to avoid these regimes and keep the device at a stable operation and at a maximum efficiency. [Preview Abstract] |
Monday, March 3, 2014 5:06PM - 5:18PM |
D34.00014: Visible-light absorption in 2D covalent triazine framework: enhanced by interlayer coupling and pore size increasing Xue Jiang, Jijun Zhao Compared with traditional bulk materials, two-dimensional (2D) crystals have some intrinsic advantages as photocatalysis owing to the limited thickness and large surface area. So far, many monolayer materials have been shown to be potential photocatalysis for water splitting from both theoretical calculations and experiments; while most of them are inorganic materials. In contrast, g-carbon nitride, as a starting successful case, motivates us to explore 2D organic semiconductors, which have not yet well investigated. Using first principles calculations, we predicted a family of 2D covalent triazine framework (CTF) as a promising visible-light-driven photocatalyst by studying their electronic structures, work function, CBM/VBM position, and optical absorption spectra. Moreover, we found that multilayer CTF have much better visible-light adsorption than a single layer induced by the interlayer coupling. In addition, controlled construction of such CTF from suitable organic subunit pave the way for connection between the optical energy gap of CTF and pore size. The insights from our study not only enrich the family of organic semiconductor photocatalyst, but also are very helpful in designing and assembling CTF subunits for optimal performance. [Preview Abstract] |
Monday, March 3, 2014 5:18PM - 5:30PM |
D34.00015: Role of oxometallic complex on OH dissociation during water oxidation: A microscopic insight from DFT study Mukul Kabir, Soumyajit Sarkar, Martha Greenblatt, Tanusri Saha-Dasgupta The uncatalyzed atomic dissociation of water requires breaking strong O$-$H bond with enthalpy 494 KJ/mol, which necessitates understanding and designing appropriate catalysts. Here we employ transition state theory within quantum chemical density functional theory to understand the role of metal-oxide inorganic complexes to the OH$\rightarrow$ O + H process, the most important reaction in water oxidation. We study the effect of (a) chemical bonding in different M$_4$O$_4$ (M = Mn, Co) cubane complexes, (b) heterocubane geometry containing Ca, in addition to transition metal ion, (c) dimensionality by considering both three dimensional and two dimensional geometry of the oxometallic unit, and (d) connectivity between two oxometallic cubane units, corner shared versus edge shared geometry. Analysis of our density function theory based calculations singles out a robust microscopic quantity among various plausible and competing factors, which elucidates the important role of metal-oxygen covalency at the oxidized site. The M$-$O bonding strength inversely determines the strength of the O$-$H bond, and thus the energy required for OH dissociation. This provides one with an important microscopic design principle for metal-oxide complex catalyst responsible for water oxidation. [Preview Abstract] |
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