Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session Y49: Modeling the Electrochemical Interface and Aqueous Solutions IIFocus Recordings Available
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Sponsoring Units: DCOMP Chair: Ismaila Dabo, Penn State Room: McCormick Place W-471B |
Friday, March 18, 2022 8:00AM - 8:36AM |
Y49.00001: Quantum–continuum simulation of underpotential deposition at electrified metal–solution interfaces Invited Speaker: Stephen Weitzner
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Friday, March 18, 2022 8:36AM - 8:48AM |
Y49.00002: Vapor-Liquid Interface in Ionic Fluids Nikhil Agrawal, Rui Wang One of the foremost unsolved problems in the field of electrolyte solution theory is the accurate calculation of interfacial properties in situations where spatially varying dielectric permittivity, large concentration gradients, and strong ion-ion correlations are prevalent. A solution to this problem has applications ranging from prediction of surface tension of water-air/oil interface to double-layer structure inside nanopores and highly charged surfaces, among many others. Currently, such problems are handled using a phenomenological approach, non-local density functional theory, or liquid-state theory. All these methods require approximations that have not been verified. Here, through the example of the vapor-liquid interface in ionic fluids, we demonstrate the application of a new theory within the Gaussian-fluctuation framework which can be non-perturbatively and self-consistently solved for interfaces with a large gradient in ionic strength. The theory systematically captures the anisotropic electrostatic interactions and the spatially varying ion correlation in the vicinity of the interface. We show results for the interfacial structure for both symmetric and asymmetric electrolytes. For symmetric salts, the surface tension predicted by our theory is quantitatively in agreement with the simulation data. Furthermore, our work also provides the first calculation of the concentration distribution and electrostatic potential profiles between vapor and liquid phases for asymmetric salts without any approximations. |
Friday, March 18, 2022 8:48AM - 9:00AM |
Y49.00003: Alkaline ORR Pathway on Spinel Electrocatalysts Revealed Through Joint Density-Functional Theory Colin R Bundschu The oxygen reduction reaction (ORR) features prominently and is of fundamental importance in the field of electrocatalysis, with direct applications to fuel cells. The alkaline ORR on metal oxide surfaces shows great promise to reduce/eliminate the need for costly platinum group metals (PGMs). This reaction is currently thought to proceed through the intermediates *OH, *O2, *OOH, and *O. We have investigated these intermediates using ab initio joint density-functional theory (JDFT) to describe the electrochemical interface. In particular, we studied the above intermediates on spinel Co3O4 and CoMn2O4. We find that the energies of the traditional intermediates do not agree with the observed experimental values of the ORR half-wave potential. However, splitting the reaction intermediates, hydrogenating the surface, and angling the adsorbates to form additional surface bonds significantly improves agreement with experiment. Given the agreement of this new reaction pathway with experimental data, we propose a new pathway for the alkaline ORR on spinel electrocatalyst materials. |
Friday, March 18, 2022 9:00AM - 9:12AM |
Y49.00004: Predicting the redox potentials of lithium polysulfides from first principles Cierra A Chandler, Ismaila Dabo Lithium-sulfur batteries are an attractive electrochemical option for electrochemical energy storage due to their high theoretical energy density, low toxicity, and moderate cost. Despite these interesting characteristics, lithium-sulfur batteries are limited by the loss of active cathode material (the shuttling effect), which causes self-discharge and reduces their Coulombic efficiency. In this work, we study polysulfide-electrolyte interactions from first principles to determine the charge-discharge response of lithium-sulfur batteries. Using semilocal density-functional theory with van der Waals correction and ab-initio molecular dynamics with explicit-implicit solvation models, the intrinsic charge-voltage response of polysulfide systems is calculated and compared to experimental data. This first-principles study reveals that the critical influence of solvation on the charge-voltage response and provides guiding principles for tuning the redox properties of solvated lithium polysulfides. |
Friday, March 18, 2022 9:12AM - 9:24AM |
Y49.00005: Predicting Solid-Liquid Interfaces with Joint Density Functional Theory (JDFT) harrison j gardner, Kendra L Letchworth-Weaver, Ravishankar Sundararaman, Tomas A Arias, Paul Fenter, Katherine Harmon Modeling the electrochemical interface offers a significant challenge due to the complexity of the liquid and the long length and time scales. Joint Density Functional Theory (JDFT), which is implemented in the open source software JDFTx, combines a classical continuum liquid model with quantum-mechanical density functional theory for an accurate and efficient description of solvent-solute interactions. While JDFT is a promising approach for describing the electrochemical interface, additional benchmarking has been required to demonstrate the robustness of the approximate functionals and determine areas of improvement to be addressed by development of novel functionals. Here we further test the accuracy of a universal solvent-electron coupling functional which was trained on three different solvents and multiple solute molecules to capture nonlocal effects such as van der Waals interactions. By computing the solvation energies of 240 solutes in water using both the universal and solvent-specific coupling functionals, we demonstrate that near-chemical accuracy is maintained for the test set as well as the training set. Furthermore, we explore the accuracy of JDFT for water at interfaces relative to X-ray reflectivity measurements and molecular dynamics simulations. |
Friday, March 18, 2022 9:24AM - 9:36AM |
Y49.00006: First-Principles Assessment of Alkali and Alkaline-Earth p-Block Ternary Oxides for Photocatalytic Water Splitting Nicole Hall Molecular hydrogen is a sustainable energy carrier of primary interest to draw down carbon dioxide emissions and accelerate the transition to renewable modes of energy production for transportation, commercial, and residential applications. Photocatalytic materials use solar energy to split water and generate hydrogen, emitting oxygen as the only byproduct; however, many of the known water-splitting photoactive semiconductors have limited solar-to-hydrogen conversion efficiency. We present a detailed investigation of 109 alkali and alkaline-earth p-block ternary oxides for use as efficient water-splitting photocatalysts. We screen these materials on the basis of their band gaps and band edges calculated at both the semilocal density-functional theory (DFT) and nonempirical DFT+U levels [1, 2]. Nonempirical Hubbard U parameters are determined from first principles for the O-2p states of each material [3, 4]. Our calculations support that the addition of alkali and alkaline-earth elements to p-block binary oxides shifts the band edges towards more cathodic potentials and decreases the electron effective mass of the oxide, thereby increasing the photocatalytic efficiency. Pourbaix diagrams are used to assess electrochemical stability under aqueous conditions and narrow down the candidate materials by considering their decomposition energy and their decomposition products. Using this screening protocol, 8 alkali and alkaline-earth p-block oxides show promise as water-splitting photocatalysts. |
Friday, March 18, 2022 9:36AM - 9:48AM |
Y49.00007: Polarizable embedding with a transferable H2O potential energy function Elvar Ö Jónsson Most commonly used interfaces between quantum mechanics and molecular mechanics (QM/MM) are based on the so-called electrostatic embedding scheme. There, an additional external potential term is included in the electronic structure calculation of the QM subsystem [1]. In this way the QM subsystem is polarized, whereas the charges of the MM subsystem remain static. This limits the applicability of the interface to the parameter set of the MM potential. For example, water potential functions based on fixed point charges are usually parameterized to reproduce a few thermally averaged properties of the liquid and may not be transferable to other systems such as at solid/liquid interfaces. The properties of the water molecule are strongly environment dependent as illustrated by the molecular dipole moment, which is 1.8 D in the gas phase but 3.1 D in ice Ih [2]. Polarizability must be taken into account in order to ensure transferability. An energy functional for describing mutual polarization between the QM and MM parts of the system is presented. A double SCF loop is introduced in order to arrive at a self-consistent solution for the total system. The resulting polarizable embedding QM/MM (PE-QM/MM) interface [3,4] couples KS-DFT with the single center multipole expansion (SCME) model describing H2O molecules. The SCME includes static dipole up to the hexadecapole moment tensor, as well as polarizable dipole and quadrupole moment tensors, resulting in a good description of small clusters, liquid and ice Ih [5,6]. A flexible boundary scheme has also been developed, a scattering adapted implementation of the FIRES approach (SAFIRES) [7]. Applications to dynamics simulations at solid/liquid interfaces will be presented, and a modified Poisson-Boltzmann distribution to describe the electric double layer at solid/ liquid interfaces in PE-QM/MM simulations will be discussed. |
Friday, March 18, 2022 9:48AM - 10:00AM |
Y49.00008: Quantum chemical study of correlated motion in salt/water electrolytes Rabi Khanal, Stephan Irle Aqueous electrolyte solutions are becoming increasingly important in energy devices such as capacitors and rechargeable ion batteries. The energy conversion process in such devices is linked to the effect of ions on the physical properties of aqueous solutions. Here, we have performed quantum chemical molecular dynamics (MD) simulations for aqueous solutions of KCl, NaCl, and MgCl2 at various concentrations from salt in water (SIW) to water in salt (WIS) conditions, using the density-functional tight-binding (DFTB) method. DFTB is a quantum chemical method that is well known for its good tradeoff between accuracy and computational efficiency. Comparisons with experimental data and published ab initio DFT results confirm that DFTB can be reasonably used to study the solvation shell of ions in an aqueous salt solution. We then proceeded to compute the time-dependent pair correlation function, also known as the Van Hove function. Our results predict a decay of the hydration shell and salt-dependent cation-water correlated motion, with Mg-O correlation lasting longer and Na-O decaying fastest. In the SIW case, the total Van Hove Function feature is dominated mainly by water-water correlation motion. In contrast, in the case of WIS, the water-water correlation is essentially lost. |
Friday, March 18, 2022 10:00AM - 10:12AM |
Y49.00009: Non-equilibrium Electrochemical Phase Diagrams with Automatic Differentiation Rachel Kurchin, Dhairya Gandhi, Venkat Viswanathan Reaction rate models are a vital tool to understand behavior of electrochemical systems. The Butler-Volmer model is a standard workhorse in the field, but especially at more extreme conditions (large currents, high overpotentials), it fails to capture realistic behavior. We have previously argued for the need to move towards more physical models such as Marcus-Hush-Chidsey, and also introduced an MHC variant that explicitly incorporates the electronic density of states of the solid side of a solid-electrolyte interface. In this talk, I will showcase a software package I developed that implements a variety of standard electrochemical rate models and allows the construction of multidimensional phase diagrams along axes of composition, current, temperature, or any other model parameter. This functionality relies critically on the automatic differentiation capabilities of the Julia Language to be able to smoothly and efficiently handle mathematically nontrivial model formulations in terms of integrals, inverse functions, etc. We will showcase the capabilities of this package to easily compare model types, fit to experimental data, and construct these phase diagrams. |
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