Hello, A yearly allocation for the LCRC cluster has been requested with the following updated information: Submitter/PI: Jeffrey Greeley Project Name: DFT_corrosion Division: CNM Project title: First principles studies of oxide/metal interface structures and reactivity for hydrogen evolution reaction and lithium oxide dissociation Associated funding: DOE-BES Other Systems: I have access to the CNM's cluster, carbon, as a staff member. Research staff nominally split about 30% of carbon's resources, but given the recent, rapid increases in the number of staff and postdocs, this resource has become substantially strained. Science: This project uses periodic, planewave Density Functional Theory (DFT) calculations, combined with atomistic thermodynamic models, to probe the particular reactive pathways that may be available at oxide/metal interfaces. Experimental results from the group of Nenad Markovic (ANL/MSD) have recently shown that the edges of 1-2 ML oxide nanoislands supported on Pt(111) and Au(111) have potentially unique catalytic properties for several electrochemical reactions of importance in fuel cells, including the Hydrogen Evolution (HER) and Oxygen Evolution reactions (OER). These interfaces also have the potential to facilitate Li2O/Li2O2 decomposition in Li-air batteries. Motivated by these results, we will investigate the effect of the nature and structure of the interface between simple, electrochemically deposited metal oxides and single crystal Pt(111) and Au(111) substrates. We expect that the computational results will provide enhanced understanding of the atomic struct ure of these oxide/metal interfaces and will help us to develop a fundamental picture of the reaction mechanisms and energetics that occur in these systems. Project description: Electrochemical surface studies on well-defined, single crystal metal and oxide surfaces have provided tremendous understanding of the fundamentals of chemistry and catalysis at interfaces in the past 20 years. 1,2 The applications of such systems are wide ranging, form fuel cells to solar fuels production. However, to our knowledge, very few studies have paid attentions to electrocatalytic processes at the interfaces between oxides and metals. Metals and oxides have dramatically different properties, structures, and affinities to reactive species, which bring potentially unique properties to electrocatalytic process at interfaces between these disparate classes of materials. Recent experimental work by Nenad Markovic’s group (ANL/MSD) has demonstrated that certain electrochemically deposited oxides (nickel, cobalt, iron, and manganese-based, with dimensions of ~10 nanometers) on Pt(111) can efficiently catalyze the hydrogen evolution reaction (HER) wi th activities never before seen on either metal or oxide catalysts in alkaline electrolytes.3 This work intends to provide atomic-scale insight into the localized structure and elementary catalytic reaction steps that underlie the reactivity trends observed experimentally. We will primarily focus on nickel, cobalt, iron, and manganese-based oxides on Pt(111) and Au(111) substrates. We will initially develop models of 1 and 2 ML thick metal oxide films on Pt(111). We will consider numerous structures with different oxidation states (the oxidation states are fixed by the number of O or OH atoms included in the model nanofilms), and the optimal structures and oxidation states as a function of the electrode potential will be determined by applying standard entropy corrections to the DFT-determined energies and referring the resulting energetics to the standard hydrogen electrode (SHE) potential scale. Once reliable, potential-dependent structural models have been determined, we will determine the thermodynamics and activation barriers for elementary catalytic reaction steps at the interfaces. The initial focus will be the kinetics and thermodynamics of the water dissociation step (the proposed rate-limiting step in the HER), and we will compare the energetics of this process at the oxide/metal interfaces with corresponding energetics on pure metal and oxide surfaces (see also discussion below). The study will also focus on lithium oxide (Li2O/Li2O2) decomposition, which is a particular challenge concerning the performance and stability of Li-air battery cathodes. While the formation of these oxidic species (termed “discharge” of the battery) is rapid and proceeds at voltages close to the appropriate equilibrium potential, the reverse process (decomposition of the oxidic species, or “charging” of the battery) suffers from significant kinetic inhibitions and requires large overpotentials. Most catalytic studies of Li-air focus, therefore, on finding catalytic electrode materials that facilitate oxide/peroxide decomposition and avoid fouling of the cathode due to excessive solid oxide/peroxide accumulation. Manganese oxide, to date, is one of the best cathode charging catalyst for Li-air battery and Pt(111) is very active for discharging reaction.4 The oxide/metal interfaces may therefore bring unique bifunctional properties to electrocatalytic process in Li-ai r battery. Using the oxide/metal interfacial models developed for the HER as a starting point, we will determine the thermodynamics and activation barriers for elementary reaction steps of Li2O/Li2O2 dissociation at the interfaces. The obtained atomistic understanding of the effect of the oxide/metal interfaces on the electrocatalytic chemistry of the HER and Li2O/Li2O2 dissociation that will be derived from these calculations will ultimately facilitate experimental efforts to design improved electrocatalysts for these and related reactions. The initial development of structural models for the oxide/metal interface, as described very briefly above, will follow a two-pronged strategy. One approach will be applied to nickel, cobalt, and iron oxide clusters and will involve building up cluster models of the various oxides on Pt(111). A 2√3 ×5 Pt(111) rectangular unit cell will be employed for this purpose, and clusters that are two monolayers high (the approximate height suggested by STM and crystal truncation rod X-ray experiments) will be generated. The XPS results suggest that the stoichiometry of the nickel and cobalt oxide clusters is similar and likely involves a hydroxyl group. We will therefore focus on clusters of this stoichiometry (for example, Ni(OH)2). The iron oxide clusters appear to have a combination of both oxygen and hydroxyl groups, and we will incorporate this result into our model development, thus focus on for example FeO(OH). A second class of oxide/metal models will involve building up ~2 monolayers of bulk-like oxide structures (e.g., NiO and FeO) on the Pt(111) surface; these structures are thought to be more favorable at higher electrode potentials and will cover approximately half of the Pt(111) surface unit cell. As with the cluster models, we will optimize the positions of hydroxyl groups near the oxide surfaces, initially focusing on O/OH ratios of approximately unity. As these models are developed, we will compare them to our current and future experimental results, refining them as necessary to identify realistic structures. As oxide/metal structures are developed and optimized, we will begin calculations of HER thermodynamics and kinetics near the oxide/metal interfaces. An important step in the HER in alkaline solutions is the dissociation of water to yield adsorbed H* and OH*. Although we anticipate that the most likely dissociation point for water will be at the oxide/metal interface (with the H atoms spilling on to platinum and the OH groups moving to the oxides), we will also consider dissociation on the uncovered portion of the Pt(111) surface and on the oxides themselves. In addition, the similar thermodynamically and kinetically approach will be applied to Li2O/Li2O2 dissociation. We will determine the most stable site for Li2O/Li2O2 to form on the oxide, Pt(111) and at the interface. The barrier energy of the initial step to dissociate Li2O to yield LiO* and O* and to dissociate Li2O2 to yield Li2O and O or to yield OLiO and Li will be calculated. We will consider the dissociation not only at the most stable site Li2O and Li2O2 to form, but at all three points; on oxide, on Pt(111) and at the interfaces. The ultimate goal of these analyses will be to understand how changes in the nature of the oxide/metal interfaces affect trends in HER and Li2O/Li2O2 dissociation activity. These computational studies will be performed in collaboration with Nenad Markovic (ANL/MSD). The computational requirements of the proposed research will be substantial. Test calculations with VASP code have indicated that full convergence of model oxide clusters on the 2√3 ×5 unit cells require approximately 48 hours per total geometric optimization on 32 cores on computer clusters similar to Fusion. For each elemental oxide considered (four in total), we will need to consider a significant number of different stoichiometries and configurations; we tentatively estimate that the total number of resulting optimizations will be ~50 per oxide, yielding a requirement of ~310,000 core hours. To determine barriers for water dissociation and Li2O/Li2O2 dissociation on these oxide/metal combinations, we anticipate needing to run approximately 6 Nudged Elastic Band calculations per oxide for water dissociation and approximately 14 Nudged Elastic Band calculations per oxide for Li2O/Li2O2 dissociation. Such calculations often require three times of the compute time of si mple structural optimizations, yielding an additional requirement of ~340,000 core hours. We are therefore requesting a total compute time of ~650,000 core hours. (1) Markovic, N. M.; Ross, P. N. Surface Science Reports 2002, 45, 117-229. (2) Kolb, D. M. Surface Science 2002, 500, 722-740. (3) Markovic, N. M. in preparation. (4) Lu, Y.-C.; Gasteiger, H. A.; Crumlin, E.; McGuire, J. R.; Shao-Horn, Y. Journal of The Electrochemical Society 2010, 157, A1016-A1025. Project URL: Current FY Hours Used: undetermined amount New FY Requested allocation: 650000 Q1: 162500 Q2: 162500 Q3: 162500 Q4: 162500 Justification: The computational requirements of the proposed research will be substantial. Test calculations with VASP code have indicated that full convergence of model oxide clusters on the 2√3 ×5 unit cells require approximately 48 hours per total geometric optimization on 32 cores on computer clusters similar to Fusion. For each elemental oxide considered (four in total), we will need to consider a significant number of different stoichiometries and configurations; we tentatively estimate that the total number of resulting optimizations will be ~50 per oxide, yielding a requirement of ~310,000 core hours. To determine barriers for water dissociation and Li2O/Li2O2 dissociation on these oxide/metal combinations, we anticipate needing to run approximately 6 Nudged Elastic Band calculations per oxide for water dissociation and approximately 14 Nudged Elastic Band calculations per oxide for Li2O/Li2O2 dissociation. Such calculations often require three times of the co mpute time of simple structural optimizations, yielding an additional requirement of ~340,000 core hours. We are therefore requesting a total compute time of ~650,000 core hours. Thank You, The LCRC Accounts System