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A yearly allocation for the LCRC cluster has been requested with the
following updated information:
Submitter/PI: John J. Low
Project Name: DFT_NiOxHy_on_Pt3Ni
Division: APS
Project title: First principles studies of stability and reactivity of Ni (hydr)oxide films on Pt3Ni(111) surface in alkaline environments.
Associated funding: DOE, Office of Basic Energy Science
Other Systems: Carbon (CNM-ANL), Carter (Purdue)
Science: This project will employ Density Functional Theory (DFT) plus Hubbard U and van der Waals corrections, and ab inito molecular dynamics, combined with atomistic thermodynamic models and computational hydrogen electrode, to study the structures and catalytic activity of the three phase boundaries (TPB) between monolayer Ni (hydroxy)oxide films, close-packed Pt3Ni alloy substrates and aqueous bulk phases under hydrogen evolution reaction (HER) conditions in alkaline solution; additional work will focus on probing electrode potential probe based on energy level alignment technique, including electrode potential effect in thermodynamic and kinetic analysis and exploring possible way to achieve electrode potential control. The relevant films, i.e. Ni (hydroxy)oxide films on Pt(111) surface, which can be synthesized using standard electrochemical techniques, have been investigated experimentally in the group of Nenad Markovic (ANL-MSD) and have been shown to exhibit bifunc
tional catalytic properties for hydrogen evolution and other electrocatalytic reactions. To understand the bi-functional mechanisms, we have performed an extensive series of studies on the electrochemical phase diagrams/pourbaix of monolayer Ni-(hydroxy)oxide films on Pt(111) and the TPB at the film edges at different potential. The kinetic studies have shown that water dissociation, a key step in alkaline HER, is significantly accelerated at the TPB edges. Based on this understanding, we have extended the effort to probe the alloy effect of the substrate in the last proposal. The results have shown that the TPB edge of Ni-(hydroxy)oxide films on Pt3Ni may have similar promotion effects toward water dissociation of that on Pt(111) substrate. Due to limitation of core hours, however, the kinetic analyses so far are only performed few a few extra water molecules at TPB edges, instead of aqueous phase introduced by filling the vacuum space in supercell. In the present proposal,
in addition to including the salvation effect to generalize the understanding of the water dissociation kinetics, we will rigorously probe the electrode potential during HER, include electrode potential effect in the thermodynamic and kinetic analysis and explore a rigorous way to achieve control. We anticipate that the realistic electrode potential and its variation may have a substantial impact on both the thermodynamics and kinetics, and the present study may reveal the true chemistry at the film-electrode-liquid-water TPB edges.
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 years1-2. The applications of such systems are wide-ranging, from fuel cells to solar fuels production. However, very few studies have rigorously probed the fundamentals of electrocatalytic processes at the interface between oxide/hydr(oxy)oxide films, metal or alloy substrates, and bulk solution phases. Metals and oxides have dramatically different structures, properties, and affinities to reactive species, which bring potentially unique properties to electrocatalytic process at interfaces between these disparate classes of materials. Experimental results by Nenad Markovic’s group (ANL/MSD) have demonstrated that certain electrochemically deposited (hydroxy)oxides (nickel, cobalt, iron, and manganese-based, deposited as islands with diameters of 5-10
nanometers) on Pt(111) can efficiently catalyze the hydrogen evolution reaction (HER) with activities never before seen on either metal or oxide catalysts in alkaline electrolytes3. The bi-functional mechanisms behind have begun to be understood through our recent work. To study the generality of the understanding, we have extended our study from Pt substrate to Pt3Ni substrate to evaluate the alloy effect. Indeed, some Pt alloys have shown higher electrocatalytic activity than Pt itself. Investigation of alloy substrates is thus a natural extension of the work on pure Pt substrates and may provide an extra variable to tune the activity of water dissociation and hydrogen evolution reactions at three phase interfaces. And the results also show the monolayer Ni-(hydroxy)oxide/Pt3Ni is a promising bi-functional electrocatalyst. We note that, though basic thermodynamic and kinetic analyses make this systems very interesting, a few realistic effects (e.g. solvation effect and ele
ctrochemical double layer) have not been included in the studied yet, which in some instances, yield completely unexpected physical and catalytic properties. To evaluate the influence of true electrocatalytic environment, we will conduct a more careful study by considering explicit solvent effect and electrode potential. As there is still no experiment on these combined systems, the true chemistry predicted from the present study could provide a blueprint for the future search for and preparation of catalysts with higher activity.
In the previous proposal cycles, we have developed a new technique for highly accurately describe the stability of (hydroxy)oxides, and have found that using water reference, van der Waals correction and optimized Hubbard U together, the formation energy of (hydroxy)oxides can be predicted highly accurately, i.e. the standard deviation with respect the experiment values could be around 0.04 eV. This accuracy has never been reached by standard DFT calculations in previous studies, and has strong implication for the application on the extended systems. For example, we have used this technique to study the structural evolution of Ni-(hydroxy)oxides films deposited on Pt(111) substrates, and the bi-functional mechanism of the NiOH-Pt-H2O TPB. The experimental confirmation of the predicted film structures and the clarification of the bi-functional mechanism not only only a big step forward towards the accurate identification and prediction of a variety of oxide/electrode interfaci
al structure-properties relationship, but also provides the foundation for the rational design and control of ‘targeted active phases’.
In the last proposal cycle, we have applied the same methodology to screen the electrode potential-dependent structures of monolayer Ni-(hydroxy)oxides films deposited on Pt3Ni(111) substrates. Based on it, we have generated TPB models at HER potential region, and obtained basic water dissociation kinetics therein. In order to investigate on the influence of water on the thermodynamics and kinetics at the TPB, we have included a few extra water molecules at TPB, we also have started the AIMD simulation of liquid water on well-defined Pt(111) surface to accumulate fundamental knowledge.
In the present cycle, we will focus on the influence of liquid water and electrode potential on the thermodynamics and kinetic at TPB. The TPB models developed in the last proposal cycle is composed by 1 nm NiOH ribbons deposited on Pt3Ni(111)-(8x4) substrate. To investigate the influence of liquid water on the thermodynamics and kinetics, we will fill the vacuum space based on water density. We will conduct geometry optimization to find local minimum, perform AIMD simulation to find more realistic water-electrode interfaces, and meta-dynamics simulation to calculate free energy barriers. Technically, we will firstly heat the systems up to 400 K to obtain liquid phase, then we will perform canonical ensemble (NVT) simulation with time up to 10 ps. We will cool the systems down to 0 k again every 1-2 ps during the simulation to find the most stable geometry. Then, it will be used as the starting point in the meta-dynamics simulation. We will probe the 1s core level of the bulk
water during the simulation and deduce the electrode potential by aligning it with the 1s core level of reference bulk water with ice structure. We will use the obtained electrode potential to correct thermodynamics and kinetic obtained from meta-dynamics simulation.
We will to compare the water dissociation properties for different (hydroxy)oxide films on both pure Pt and alloy substrates. If the hypothesis that H produced from water dissociation moves to metal sites is correct, then the thermodynamics and kinetics of water splitting will be substantially different on the different metal substrates. In combining with the influence of substrates to the thermodynamics and kinetics of hydrogen evolution (2H→H2), this could provide significant additional information that would be of use in further searching for and optimizing bifunctional catalysts, by tuning the films and substrates.
The present proposal requires time consuming ab initio molecular dynamics (AIMD) simulation. Spin-polarized calculations with the VASP code have shown that an ionic step could reach convergence with about 10 electronic steps. One electronic step requires about 300 second for the magnetic TPB model NiOH/Pt3Ni(111)-(8x4) with around 100 water molecules using 1 node of 16-cores Intel Xeon-E5-2670 (about 12 core hours per ionic step). For a typical AIMD simulation, we usually run with 1 fs per ionic step, and with 10 ps (10,000 steps) in total to reach equilibrium (120, 000 core hours per simulation). We will cool down the system every 2ps, which require another 5,000 steps (60, 000 core hours). We need to run AIMD simulation with two different initial water configurations, which require 360,000 core hours in total. After obtaining the most stable geometry, we will run meta-dynamics simulations with difference collective variables (~20) with 1 ps per simulations (240,000 core hou
rs). For the standard DFT calculations and core-level calculations, we need to run another 10,000 ionic steps with 120,000 core hours. So, we require 720,000 core hours in total.
The models of fully two dimensional hydroxide films on Pt(111), which were developed in previous proposal cycles, have been published in Nature Materials3. The newly developed scheme towards first-principles based prediction of highly accurate electrochemical Pourbiax diagrams has been published in the Journal of Physical Chemistry C,4 the magnetic properties of monolayer films has been published on Applied Physics Letters,5 the proposed general strategy towards controlling the structural evolution of the ultra-thin film/electrode interfaces, and the understanding of the bi-functionial mechanism of electrocatalyst NiOH/Pt111, which are generated from previous proposal cycles, could be the interest of the broad community and two papers are in preparation. The present study, a new thrust based on previous studies, not only would provide new insight towards the complex electrochemical interface, but also may suggest new materials for electrocatalytic application.
We will also be evauluating OpenMX to model electrified Pt/H2O interfaces. This will involve short blue moon trajectories to evaluate free energies along the reaction coordinate of the ORR and HER reactions as a function of applied voltages. This study will involve about 80,000 core-hours.
References
1.Markovic, N. M.; Ross, P. N., Surface science studies of model fuel cell electrocatalysts. Surface Science Reports 2002, 45, 121-229.
2.Kolb, D. M., An atomistic view of electrochemistry. Surf. Sci. 2002, 500, 722-740.
3.Subbaraman, R.; Tripkovic, D.; Chang, K. C.; Strmcnik, D.; Paulikas, A. P.; Hirunsit, P.; Chan, M.; Greeley, J.; Stamenkovic, V.; Markovic, N. M., Trends in activity for the water electrolyser reactions on 3d M(Ni,Co,Fe,Mn) hydr(oxy)oxide catalysts. Nature Materials 2012, 11, 550-557.
4.Zeng, Z.; Chan, M. K. Y.; Zhao, Z.-J.; Kubal, J.; Fan, D.; Greeley, J., Towards First Principles-Based Prediction of Highly Accurate Electrochemical Pourbaix Diagrams. J. Phys. Chem. C 2015, 119, 18177-18187.
5.Di, N.; Kubal, J.; Zeng, Z.; Greeley, J.; Maroun, F.; Allongue, P., Influence of controlled surface oxidation on the magnetic anisotropy of Co ultrathin films. Appl. Phys. Lett. 2015, 106, 122405.
Industry partnership:
Project URL:
Current FY Hours Used: undetermined amount
New FY Requested allocation: 800000
Q1: 200000
Q2: 200000
Q3: 200000
Q4: 200000
Justification: VASP does has have significant limitations on its parallel scaling. It will scale out to a number of cores equal to the number of atoms times the number of k-points. The Pt/H2O bilayer models involve ~500 atoms and at least two k-points. VASP should scale well out to a thousand cores for this system.
OpenMX has been shown to scale out to 10,000 cores on the K supercomputer.
We have been beta testing the GPU version of VASP (VASP_GPU). We expect that the release candidate version of VASP_GPU should be three times faster than the non-GPU version. This will give significant improvement in performance of the VASP simulations.
Storage requirements:
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