Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session D36: Invited Session: Materials for Energy: Predicting the Properties of Solid/Electrolyte Interfaces from First Principles |
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Sponsoring Units: DCOMP Chair: Giulia Galli, University of Chicago Room: 211 |
Monday, March 2, 2015 2:30PM - 3:06PM |
D36.00001: Electronic properties of semiconductor-water interfaces: Predictions from \textit{ab-initio} molecular dynamics and many-body perturbation theory Invited Speaker: Tuan Anh Pham Photoelectrochemical cells offer a promising avenue for hydrogen production from water and sunlight. The efficiency of these devices depends on the electronic structure of the interface between the photoelectrode and liquid water, including the alignment between the semiconductor band edges and the water redox potential. In this talk, we will present the results of first principles calculations of semiconductor-water interfaces that are obtained with a combination of density functional theory (DFT)-based molecular dynamics simulations and many-body perturbation theory (MBPT). First, we will discuss the development of an MBPT approach that is aimed at improving the efficiency and accuracy of existing methodologies while still being applicable to complex heterogeneous interfaces consisting of hundreds of atoms~[1,2]. We will then present studies of the electronic structure of liquid water and aqueous solutions using MBPT, which represent an essential step in establishing a quantitative framework for computing the energy alignment at semiconductor-water interfaces~[3-5]. Finally, using a combination of DFT-based molecular dynamics simulations and MBPT, we will describe the relationship between interfacial structure, electronic properties of semiconductors and their reactivity in aqueous solutions through a number of examples, including functionalized Si surfaces [6] and GaP/InP surfaces in contact with liquid water. \vspace{0.5cm} \\ $[1]$ H.-V. Nguyen, T. A. Pham, D. Rocca and G. Galli, Phys.~Rev.~B~\textbf{85}, 081101(R) (2012).\\ $[2]$ T. A. Pham, H.-V. Nguyen, D. Rocca and G. Galli, Phys.~Rev.~B~\textbf{87}, 155148 (2013).\\ $[3]$ T. A. Pham, C. Zhang, E. Schwegler and G. Galli, Phys.~Rev.~B~\textbf{89}, 060202(R) (2014).\\ $[4]$ D. Opalka, T. A. Pham, M. Sprik and G. Galli, J.~Chem.~Phys.~\textbf{141}, 034501 (2014).\\ $[5]$ C. Zhang, T. A. Pham, F. Gygi and G. Galli, J.~Chem.~Phys.~\textbf{138}, 181102 (2013).\\ $[6]$ T. A. Pham, D. Lee, E. Schwegler and G. Galli, J.~Am.~Chem.~Soc. in press (2014). [Preview Abstract] |
Monday, March 2, 2015 3:06PM - 3:42PM |
D36.00002: First-principles simulations of charge storage at electrochemical interfaces in supercapacitors Invited Speaker: Brandon Wood Supercapacitors store charge via polarization at the electrode-electrolyte interface. Many models of interfacial charge storage focus on the formation of the electric double layer (EDL) in the electrolyte, but it is often assumed that in the electrode, a shift in the Fermi level is the only notable response to interface polarization. In reality, the presence of the interface impacts the fundamental properties of both the electrode and the electrolyte, often in complex and nontrivial ways that are difficult to capture using simple models. I will discuss how including an applied bias potential in first-principles simulations allows one to directly simulate the process of charge storage at the electrode-electrolyte interface, and thereby to unravel the interplay between the electrode and the electrolyte. I will show how these more complex treatments lead to improved descriptions of intrinsic quantum and EDL capacitance contributions in graphene-based supercapacitors, which can be used to suggest engineering strategies for improved electrode materials. I will also discuss how combining theory with in operando X-ray spectroscopy can give insights into nanoscale chemical changes and mesoscale morphological changes in electrodes during charging. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under contract DE-AC52-07NA27344. [Preview Abstract] |
Monday, March 2, 2015 3:42PM - 4:18PM |
D36.00003: Ab initio joint density-functional theory of solvated electrodes, with model and explicit solvation Invited Speaker: Tomas Arias First-principles guided design of improved electrochemical systems has the potential for great societal impact by making non-fossil-fuel systems economically viable. Potential applications include improvements in fuel-cells, solar-fuel systems (``artificial photosynthesis''), supercapacitors and batteries. Economical fuel-cell systems would enable zero-carbon footprint transportation, solar-fuel systems would directly convert sunlight and water into hydrogen fuel for such fuel-cell vehicles, supercapacitors would enable nearly full recovery of energy lost during vehicle braking thus extending electric vehicle range and acceptance, and economical high-capacity batteries would be central to mitigating the indeterminacy of renewable resources such as wind and solar. Central to the operation of all of the above electrochemical systems is the \emph{electrode-electrolyte interface}, whose underlying physics is quite rich, yet remains remarkably poorly understood. The essential underlying technical challenge to the first principles studies which could explore this physics is the need to properly represent {\em simultaneously both} the interaction between electron-transfer events at the electrode, which demand a quantum mechanical description, {\em and} multiscale phenomena in the liquid environment such as the electrochemical double layer (ECDL) and its associated shielding, which demand a statistical description. A direct \emph{ab initio} approach to this challenge would, in principle, require statistical sampling and thousands of repetitions of already computationally demanding quantum mechanical calculations. This talk will begin with a brief review of a recent advance, joint density-functional theory (JDFT), which allows for a fully rigorous and, in principle, exact representation of the thermodynamic equilibrium between a system described at the quantum-mechanical level and a liquid environment, \emph{but without the need for costly sampling}\footnote{S.~Petrosyan, A.A.~Rigos and T.A.~Arias, {\em J. Phys. Chem.} {\bf B 109}, 15436 (2005).}$^,$\footnote{S.A.~Petrosyan, Jean-Francois Briere, David Roundy and T.A.~Arias, {\em Phys. Rev.} {\bf B 75}, 205105 (2007).}. We then shall demonstrate how this approach applies in the electrochemical context and how it is needed for realistic description of solvated electrode systems\footnote{Kendra Letchworth-Weaver and T.A. Arias, {\em Phys. Rev.} {\bf B 86}, 075140 (2012).}, and how simple ``implicit'' polarized continuum methods fail radically in this context. Finally, we shall present a series of results relevant to battery, supercapacitor, and solar-fuel systems, one of which has led to a recent invention disclosure for improving battery cycle lifetimes. [Preview Abstract] |
Monday, March 2, 2015 4:18PM - 4:54PM |
D36.00004: Link between photocatalytic water splitting efficiency and surface acidity in GaN and SrTiO3 Invited Speaker: Marivi Fernandez-Serra |
Monday, March 2, 2015 4:54PM - 5:30PM |
D36.00005: First-Principles Approach to Energy Level Alignment at Aqueous Semiconductor Interfaces Invited Speaker: Mark Hybertsen We have developed a first principles method to calculate the energy level alignment between semiconductor band edges and reference energy levels at aqueous interfaces [1, 2]. This alignment is fundamental to understand the electrochemical characteristics of any semiconductor electrode in general and the potential for photocatalytic activity in particular. For example, in the search for new photo-catalytic materials, viable candidates must demonstrate both efficient absorption of the solar spectrum and an appropriate alignment of the band edge levels in the semiconductor to the redox levels for the target reactions. In our approach, the interface-specific contribution to the electrostatic step across the interface is evaluated using density functional theory (DFT) based molecular dynamics to sample the physical interface structure and the corresponding change in the electrostatic potential at the interface. The reference electronic levels in the semiconductor and in the water are calculated using the GW approach, which naturally corrects for errors inherent in the use of Kohn-Sham energy eigenvalues to approximate the electronic excitation energies in each material. Taken together, our calculations provide the alignment of the semiconductor valence band edge to the centroid of the highest occupied 1b$_{1}$ level in water. The known relationship of the 1b$_{1}$ level to the normal hydrogen electrode completes the connection to electrochemical levels. We discuss specific results for GaN, ZnO, and TiO$_{2}$. The effect of interface structural motifs, such as different degrees of water dissociation, and of dynamical characteristics, will be presented together with available experimental data.\\[4pt] [1] N. Kharche, et al., Phys. Rev. Lett. 113, 176802 (2014).\\[0pt] [2] Research done in collaboration with N. Kharche, J. Lyons and J. T. Muckerman. [Preview Abstract] |
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