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Scholarly Interest Report
         
Thomas Senftle
Assistant Professor
Assistant Professor
 
e-mail:tsenftle@rice.edu
 
  • B.S. Chemical Engineering (2010) University of Notre Dame, South Bend, IN
  • Ph.D. Chemical Engineering (2015) Pennsylvania State University, State College, PA
 
Primary Department
   Department of Chemical and Biomolecular Engineering
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Department Affiliations
 
  • Department of Chemical and Biomolecular Engineering
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    Websites
     Google Scholar
     
    Research Areas
     1. Multi-physics Computational Modeling (ab initio and classical) 2. Metal-oxide Catalysis 3. Photo-catalysis 4. Lithium-ion Batteries 5. Reactive Force Field (ReaxFF) Development
     
    Research Interests 30-JAN-2018
     

    Combining Quantum and Classical Computational Approaches to Catalyst Design


    Research Objective. My laboratory will develop and apply a series of computational modeling tools for assessing complex, multi-component catalysts at both the electronic and atomistic level. Particular focus will be placed on developing fundamental structure-activity relationships informing the rational design of catalytic systems for efficient energy conversion, storage, and utilization.


    Background. Innovative catalytic systems will play an indispensable role shaping our energy and environmental future. Recent estimates suggest that improvements to catalytic processes in the chemical sector can lead to energy savings on the order of 13 EJ per year by 2050—roughly equivalent to the annual consumption of electricity in the US. Novel catalytic processes will also play a central role in improving the efficiency of low-carbon energy technologies, such as the utilization of fossil resources with fuel cells, or the electro-chemical processing of H2O and CO2 to produce fuels. Successful heterogeneous catalysts must feature complex surface morphologies (e.g., metal nanoclusters of varying size and composition on oxide supports, or functionalized semiconductor electrodes in equilibrium with multi-component electrolyte solutions), as multiple functionalities will be required to achieve conversion that is both active and selective. Simulation techniques based on quantum mechanics (QM), such as Kohn-Sham density functional theory (KS-DFT), have provided invaluable guidance for rational catalyst design. However, computational intensity relegates KS-DFT to small length scales (~102 atoms) that are inadequate for simultaneously modeling the interplay between all components in an intricate catalytic system. Conversely, classical interatomic potentials are able to reach significantly larger system sizes (~106 atoms), but are rarely employed in catalysis studies since they often require fixed atomic connectivity and are therefore unsuitable for modeling catalytic processes. Reactive force-fields, which have matured in the last decade, employ a formalism capable of describing bond formation and scission during a simulation. In particular, the ReaxFF potential has had success treating reactive events at chemically diverse interfaces separating solid, liquid, and gas phases, offering a unique opportunity for modeling catalysis at a scale and resolution that is not possible with  KS-DFT. QM calculations employing system models inspired by ReaxFF simulations can provide complementary electronic-level insight, and can be used to validate the required ReaxFF parameters. Thus, applying ReaxFF and QM in tandem is a powerful approach for modeling multi-component catalytic systems.


    My research program will develop an integrated QM/ReaxFF simulation workflow for assessing multi-component catalysts at both the electronic and atomistic level. This program will begin with three distinct research areas: (1) designing photocatalytic electrodes by characterizing the intricate interface between semiconductor surfaces and electrolyte solutions, (2) elucidating the role of strong metal-support interactions impacting the catalytic behavior of oxide-supported metal clusters, and (3) developing accelerated simulation methods tailored to the ReaxFF potential and QM cross-validation. Although initially focused on catalysis, the methods and expertise acquired from these projects will be readily extendable to many other research areas, such as the design of battery components, photo-voltaic cells, and novel materials. Continuous integration between theory and experiment through collaboration will be emphasized.


     
    Research Interests 30-JAN-2018
     

    Multi-Physics Simulation of Complex Semiconductor/Electrolyte Interfaces


    Background. Effective, affordable solar energy conversion devices will require the discovery of novel materials that are both efficient and inexpensive. There is an emerging interest in photoelectrochemical devices that employ electrodes capable of harvesting photons while at the same time providing active surface sites for heterogeneous catalysis. To design such electrodes, one must have a fundamental understanding of interactions occurring between the electrode and the reactive electrolyte environment it is exposed to during operation. Adsorption of species from the electrolyte solution can induce the formation of dipole layers, surface reconstructions, and distinct phases, which in turn will affect the alignment of electronic energy levels at the electrode/electrolyte interface. These alignments determine the thermodynamics of photo-excited electron transfer between the electrode and species residing in the electrolyte (i.e., either reactants or homogeneous co-catalysts), and consequently determine which reaction steps can occur spontaneously. One can therefore control electrode reactivity by altering the alignment of these energy levels. Reaction paths can be further tuned by decorating the semiconductor surface with metal nanoclusters or organic functional groups, offering many design opportunities. The ability to model multi-component surface structures with atomic resolution is therefore crucial to the rational design of advanced photochemical electrodes.


    Research Approach. Simulations utilizing density functional theory (DFT) and reactive force fields (ReaxFF) will be used to assess the structural evolution of catalytically active photoelectrode surfaces under reaction conditions. DFT calculations, employing the formalism of ab initio thermodynamics, will be used to predict stable surface structures on electrode materials that show promise for use as either anode or cathode components in photoelectrochemical cells, such as Si, TiO2, Cu2O, ZnO, and InP. Subsequent QM calculations will assess the interaction between identified surface structures and species from the electrolyte solution, such as water molecules, hydroxides, protons, homogeneous co-catalysts, and other intermediates likely to be present in the cell. Although providing valuable electronic-level insight, DFT calculations will be limited to idealized surface models, and as such the ReaxFF potential will be used to model dynamic surface/electrolyte interactions occurring at scales beyond the computational reach of DFT. The necessary empirical parameters of the ReaxFF potential will be trained against the initially acquired DFT data sets. Monte Carlo (MC) simulations will be employed to predict thermodynamic effects leading to phase formation at the surface, and reactive molecular dynamics (RMD) will be used to assess reaction kinetics. Once both thermodynamic and kinetic influences impacting overall surface morphology are understood, electronic structure methods will be applied to elucidate the electronic structure of excited states that are accessible to photo-excited electrons involved in possible catalytic mechanisms. This approach will reveal how the dynamic interplay between the surface and the electrolyte affects charge transfer across the solid/liquid interface during catalytic operation.    


    Outcomes. Insight gained from these calculations will help pin-point synthesis approaches and operating conditions that will maximize photoelectrode performance, as well as offer guidance in the search for new electrode materials. The methodologies developed in this project will be extendable to a diverse range of electrochemical interfaces, providing the community with new tools for investigating structural influences on charge transfer dynamics with atomistic-scale resolution.   


     
    Research Interests 30-JAN-2018
     

    Unraveling the Role of Metal-Support Interactions in Catalysis


    Background. Synergistic interactions that occur in oxide-supported metal catalysts can lead to emergent behavior that is absent in the parent metal and support materials. The causes underpinning these interactions are complex, often resulting from the simultaneous action of multiple independent phenomena. Charge can be transferred between the oxide and the supported metal, leading to altered occupations in frontier orbitals responsible for activating species from the gas phase. Distinct mixed phases also can form at the cluster/support boundary, where the formation of such phases will be influenced by synthesis, pre-treatment, and reaction conditions. The reactivity of the surface will be dependent on the coverage of intermediate species, which can reside on, and migrate between, sites located on the cluster, support, or interface. The surface may also incorporate atoms from the reaction environment, leading to entirely different phases with unique adsorption sites (e.g., metal carbide or hydride phases formed when the surface is exposed to a hydrocarbon environment). In addition to inducing phase formation, support and adsorbate interactions will impact metal atom mobility and cluster sintering rates. This will determine the size distribution of metal clusters, which is linked to overall activity and selectivity. While difficult to unravel, understanding the interplay of such phenomena is essential for optimizing metal-oxide catalysts.


    Research Approach. Combined quantum and classical simulation methods will be used to characterize metal/support interactions leading to emergent catalytic behavior. Research efforts will begin by applying density functional theory (DFT) to screen for metal/oxide pairs that exhibit strong interactions via charge transfer, which then can be used to tune reactivity toward either oxidation or reduction catalysis based on the direction of charge transfer. Initial results have identified key computational descriptors that can be used to predict the interaction strength between a particular metal/oxide pair: namely, the energy required to reduce the oxide support by forming an oxygen vacancy, and the energy required to oxidize the supported metal by forming its most stable oxide. Intuitively, charge transfer is pronounced between reducible oxide supports (e.g., TiO2 and CeO2) and metals that are readily oxidized (e.g., Ir and Fe). While these descriptors provide initial guidance, explicit account of the reaction environment is essential for building a complete account of the cluster/support interaction, as spectator species can also induce charge transfer. This effect is particularly important for catalysis under wet conditions, as the dissociative adsorption of water leads to charge reorganization in response to adsorbed protons and hydroxyl groups. For this reason, we will assess the impact of the reactive environment with reactive molecular dynamics simulations, where ReaxFF parameters will be developed based on data sets populated with DFT adsorption energies and reaction barriers. This analysis will provide valuable information regarding site reactivity, species coverage, and phase formation, which can be used to generate models for use in electronic structure calculations that are representative of the catalyst surface in operando.


    Outcomes. The developed methodology for employing ReaxFF in tandem with electronic structure calculations represents a new approach for unraveling concomitant electronic- and atomistic-level effects. Insight gained from this methodology will lead to concrete optimization principles informing the rational design of oxide-supported metal catalysts.  In particular, this work will identify key computational descriptors that can be used to select metal/support pairs with interaction characteristics that are tailored specifically to the operating environment of a target application. These methods will also be useful for studying phase formation processes that impact the performance of other multi-component systems, such as battery and fuel cell electrodes.  


     
    Teaching Areas
     Thermodynamics
     
    Selected Publications
     Refereed articles
     

    Fantauzzi, Donato; Krick Calderón, Sandra; Mueller, Jonathan E; Grabau, Mathias; Papp, Christian; Steinrück, Hans-Peter; Senftle, Thomas P; van Duin, Adri CT; Jacob, Timo; "Growth of Stable Surface Oxides on Pt (111) at Near-Ambient Pressures." Angewandte Chemie International Edition, 56 (2017) : 2594-2598.

     
     

    Fantauzzi, Donato; Krick Calderón, Sandra; Mueller, Jonathan E; Grabau, Mathias; Papp, Christian; Steinrück, Hans-Peter; Senftle, Thomas P; van Duin, Adri CT; Jacob, Timo; "Growth of Stable Surface Oxides on Pt (111) at Near-Ambient Pressures." Angewandte Chemie International Edition, 56 (2017) : 2594-2598.

     
     

    Senftle, Thomas P; Carter, Emily A; "The holy grail: chemistry enabling an economically viable CO2 capture, utilization, and storage strategy." Accounts of chemical research, 50 (2017) : 472-475.

     
     

    Senftle, Thomas P; Carter, Emily A; "Theoretical Determination of Band Edge Alignments at the WaterCuInS2 (112) Semiconductor Interface." Langmuir, 33 (2017) : 9479-9489.

     
     

    Senftle, Thomas P; Lessio, Martina; Carter, Emily A; "The Role of Surface-Bound Dihydropyridine Analogues in Pyridine-Catalyzed CO2 Reduction over Semiconductor Photoelectrodes." ACS central science, 3 (2017) : 968-974.

     
    Presentations
     Conference abstracts
     

    "The role of surface-bound dihydropyridine analogs in pyridine-catalyzed CO2 reduction over semiconductor photoelectrodes." 2017 AIChE Annual Meeting, Minneapolis. (10/31/2017) With Emily A. Carter

     
     Invited Talks
     

    "Pyridine Co-catalysis impacting CO2 reduction over semiconductor photoelectrodes." ACS 253rd National Meeting, San Francisco. (4/2/2017) With Emily A. Carter

     
     Posters
     

    "The Holy Grail: Chemistry enabling an economically viable CO2 capture, utilization, and storage strategy." ACS 253rd National Meeting, San Francisco. (4/2/2017) With Emily A. Carter