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Title: Controlling Proton Delivery through Catalyst Structural Dynamics

 [1];  [2];  [2];  [2];  [2];  [2];  [2];  [2];  [2]
  1. Center for Molecular Electrocatalysis, Pacific Northwest National Laboratory, P.O. Box 999, K2-57 Richland WA 99352 USA; 221 Science Center, State University of New York at Fredonia, Fredonia NY 14063 USA
  2. Center for Molecular Electrocatalysis, Pacific Northwest National Laboratory, P.O. Box 999, K2-57 Richland WA 99352 USA
Publication Date:
Research Org.:
Energy Frontier Research Centers (EFRC) (United States). Center for Molecular Electrocatalysis (CME)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
DOE Contract Number:
Resource Type:
Journal Article
Resource Relation:
Journal Name: Angewandte Chemie (International Edition); Journal Volume: 55; Journal Issue: 43; Related Information: CME partners with Pacific Northwest National Laboratory (lead); University of Illinois, Urbana-Champaign; Pennsylvania State University; University of Washington; University of Wyoming
Country of Publication:
United States
catalysis (homogeneous), catalysis (heterogeneous), solar (fuels), bio-inspired, energy storage (including batteries and capacitors), hydrogen and fuel cells, charge transport, materials and chemistry by design, synthesis (novel materials)

Citation Formats

Cardenas, Allan Jay P., Ginovska, Bojana, Kumar, Neeraj, Hou, Jianbo, Raugei, Simone, Helm, Monte L., Appel, Aaron M., Bullock, R. Morris, and O'Hagan, Molly. Controlling Proton Delivery through Catalyst Structural Dynamics. United States: N. p., 2016. Web. doi:10.1002/anie.201607460.
Cardenas, Allan Jay P., Ginovska, Bojana, Kumar, Neeraj, Hou, Jianbo, Raugei, Simone, Helm, Monte L., Appel, Aaron M., Bullock, R. Morris, & O'Hagan, Molly. Controlling Proton Delivery through Catalyst Structural Dynamics. United States. doi:10.1002/anie.201607460.
Cardenas, Allan Jay P., Ginovska, Bojana, Kumar, Neeraj, Hou, Jianbo, Raugei, Simone, Helm, Monte L., Appel, Aaron M., Bullock, R. Morris, and O'Hagan, Molly. 2016. "Controlling Proton Delivery through Catalyst Structural Dynamics". United States. doi:10.1002/anie.201607460.
title = {Controlling Proton Delivery through Catalyst Structural Dynamics},
author = {Cardenas, Allan Jay P. and Ginovska, Bojana and Kumar, Neeraj and Hou, Jianbo and Raugei, Simone and Helm, Monte L. and Appel, Aaron M. and Bullock, R. Morris and O'Hagan, Molly},
abstractNote = {},
doi = {10.1002/anie.201607460},
journal = {Angewandte Chemie (International Edition)},
number = 43,
volume = 55,
place = {United States},
year = 2016,
month = 9
  • The fastest synthetic molecular catalysts for production and oxidation of H2 emulate components of the active site of natural hydrogenases. The role of controlled structural dynamics is recognized as a critical component in the catalytic performance of many enzymes, including hydrogenases, but is largely neglected in the design of synthetic molecular cata-lysts. In this work, the impact of controlling structural dynamics on the rate of production of H2 was studied for a series of [Ni(PPh2NC6H4-R2)2]2+ catalysts including R = n-hexyl, n-decyl, n-tetradecyl, n-octadecyl, phenyl, or cyclohexyl. A strong correlation was observed between the ligand structural dynamics and the rates ofmore » electrocatalytic hydrogen production in acetonitrile, acetonitrile-water, and protic ionic liquid-water mixtures. Specifically, the turnover frequencies correlate inversely with the rates of ring inversion of the amine-containing ligand, as this dynamic process dictates the positioning of the proton relay in the second coordination sphere and therefore governs protonation at either catalytically productive or non-productive sites. This study demonstrates that the dynamic processes involved in proton delivery can be controlled through modifications of the outer coordination sphere of the catalyst, similar to the role of the protein architecture in many enzymes. The present work provides new mechanistic insight into the large rate enhancements observed in aqueous protic ionic liquid media for the [Ni(PPh2NR2)]2+ family of catalysts. The incorporation of controlled structural dynamics as a design parameter to modulate proton delivery in molecular catalysts has enabled H2 production rates that are up to three orders of magnitude faster than the [Ni(PPh2NPh2)]2+complex. The observed turnover frequencies are up to 106 s-1 in acetonitrile-water, and over 107 s-1 in protic ionic liquid-water mixtures, with a minimal increase in overpotential. This material is based upon work supported as part of the Center for Molecular Electrocatalysis, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, and was performed in part using the Molecular Science Computing Facility (MSCF) in the William R. Wiley Environmental Molecular Sciences Laboratory, a DOE national scientific user facility located at Pacific Northwest National Laboratory (PNNL). PNNL is operated by Battelle for DOE.« less
  • The p-n junction can be regarded as the most important electronic structure that is responsible for the ubiquity of semiconductor microelectronics today. Efforts to continually scale down the size of electronic components is guiding research to explore the use of nanomaterials synthesized from a bottom-up approach - group-IV semiconductor nanowires being one such material. However, Au-catalyzed synthesis of Si/Si1-x-Gex semiconductor nanowire heterojunctions using the commonly-used vapor-liquid-solid (VLS) growth technique results in diffuse heterojunction interfaces [1], leading to doubts of producing compositionally-sharp p-n junctions using this approach. However, we have recently reported the ability to increase Ge-Si nanowire heterojunction abruptness bymore » VLS synthesis from a Au(1-x)Ga(x) catalyst alloy as shown by EDX analysis in an SEM [2]. In this work, we have extended the use of a AuGa catalyst alloy to produce more compositionally abrupt p-n junction interfaces compared to using pure Au as directly measured by atom probe tomography. As shown in Figure 1(a-b), individual Ge-Si heterostructured nanowires were grown vertically atop Ge(111) microposts. Direct growth on the microposts provides a facile approach to nanowire analysis which circumvents the need to use FIB-based sample preparation techniques. Both nanowires grown from pure Au and a AuGa catalyst alloy were analyzed. The corresponding 3D APT reconstruction of an individual heterostructured nanowire is shown in Figure 1(c) with the corresponding materials labeled. A 1-dimensional composition profile along the analysis direction in Figure 1(d) confirms an increase in heterojunction abruptness for nanowires grown from AuGa (~10nm) compared to nanowires grown from pure Au (~65nm). Analysis of the P distribution within the Si region (Figure 1(e)) indicates that P reaches a constant distribution over approximately 10nm when incorporated through the AuGa catalyst, whereas it continually increases over 100’s of nanometers when incorporated through pure Au. The apparent lower overall P concentration within the nanowire grown from the AuGa alloy suggests that the solubility of P in the alloy is lower compared to pure Au. The ability to controllably increase nanowire p-n junction abruptness is important for nanowire applications as solar cells and tunneling field effect transistors where an increase in device performance is expected from shaper p-n junction interfaces. [1] T.E. Clark et al., Nano Lett. 8 (2008) 1246. [2] D.E. Perea et al., Nano Lett. 11 (2011) 3117. [3] The research was supported through the user program at both the Center for Integrated Nanotechnologies at Los Alamos National Laboratory and the Environmental Molecular Sciences Laboratory at Pacific Northwest National Laboratory.« less
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  • Intense, single-cycle terahertz (THz) pulses are powerful tools to understand and control material properties through low-energy resonances, such as phonons. Combining this with optical second harmonic generation (SHG) makes it possible to observe the resulting ultrafast structural changes with surface sensitivity. This makes SHG an ideal method to probe phonon dynamics in topological insulators (TI), materials with unique surface transport properties. Here, we resonantly excite a phonon mode in the TI Bi 2Se 3with THz pulses and use SHG to separate the resulting symmetry changes at the surface from the bulk. Furthermore, we coherently control the lattice vibrations with amore » pair of THz pulses. Lastly, our work demonstrates a versatile, table-top tool to probe and control phonon dynamics in a range of systems, particularly at surfaces and interfaces.« less