"There is plenty room at the bottom", as the visionary physics Nobel Prize laureate Richard Feynman proclaimed in as early as 1959, which refers to the unlimited boundaryless opportunities in the realm of now thriving nanoscience and nanotechnology. Well, the research in TongLab is right in the middle of this "plenty room at the bottom", focusing on unraveling and utilizing the novel chemical and physical properties of metal nanoparticles (MNPs) based nanomaterials for clean energy generation (fuel cells), environmental remedies (CO2 reduction), and controlling charge transfer through metal-ligand interfaces that is one of the key factors underlying nano-electronic or nano-optic devices. These novel functional properties, which are on longer spatial and smaller energetic scales as compared to atoms and molecules, can be varied by changing the MNP size (i.e., number of atoms), composition (i.e., multi-element), and/or chemical environment (i.e., ligand-protected, matrix-embedded, or structurally-encaged) and thus be optimized for real life applications. The real challenge, therefore also opportunity, is to achieve detailed fundamental understanding of the chemistries that govern these novel properties/functionalities. This is what the research in TongLab is all about. That is, we strive to disentangle the seemingly complex chemistry and physics of MNP materials at the most fundamental level so that their optimal applications that address many pressing societal issues that mankind is currently facing can be envisioned and developed.
The research in TongLab draws upon combined strengths of several fields including interfacial surface chemistry and electrochemistry, relevant wet synthetic chemistry, the rich chemistry of polyoxometallates (POM), modern physical characterization methods (NMR, IR, Raman, STM/AFM, etc.), and modern DFT (density functional theory) calculations. For electrocatalysis related to fuel cell applications, we focus on Pt-based bimetallic MNPs (Pt-Ru, Cu, Ni, Co) for methanol, ethanol, and formic acid oxidation, oxygen reduction, and CO2 reduction. For ligand stabilized MNPs, we target different metal core elements (Ag/Au/Cu as vs. Pt/Pd/Rh) and different stabilizing ligands (from CO to alkanethiol/selenol/tellurol to POM). Ag/Au/Cu and Pt/Pd/Rh are two different types of metals: the former are largely s-orbital coinage metals while the latter are typical d-orbital late transition metals. Thus the corresponding metal-ligand interfaces are expected to be chemically very different. For physical characterizations, we focus on developing and utilizing electrochemical (EC) methods and powerful, molecular level in situ spectroscopies such as EC-NMR, surface-enhanced IR (SEIRAS) and Raman (SERS and TERS), and EC STM/AFM.
Therefore, the researches in TongLab are inherently interdisciplinary, challenging but also full of fun of scientific discoveries. They offer uniquely broad opportunities for post-docs, graduate as well as undergraduate to be well trained and successful in the frontiers of modern nanochemistry and nanoscience, encompassing MNPs synthesis, surface chemistry and interfacial electrochemistry of the synthesized MNP materials, heterogeneous and electrocatalysis, in situ EC NMR, IR spectroscopy, Raman (SERS) spectroscopy, EC STM/AFM, and quantum chemistry, all directed towards achieving better fundamental understanding of the chemistries of the MNP materials for applications in clean energy generation, environmental remedies, and nano-electronic/optical devices.(1) YuYe J. Tong, "Unconventional Promoters of Catalytic Activity in Fuel Cell Electrocatalysis", Chem. Soc. Rev., 2012, 41, 8195-8209.
(2) Yuan Gao, Yangwei Liu, Ying Li, Oksana Zaluzhna, YuYe J. Tong, "Mechanistic Insights into the Brust–Schiffrin Synthesis of Organochalcogenolate-Stabilized Metal Nanoparticles", in "Functional Nanometer-Sized Clusters of Transition Metals: Synthesis, Properties and Applications", Eds. Wei Chen and Shaowei Chen, the RSC Smart Materials Series, 2014, 1-24.
The objective of this project is to use a novel interdisciplinary approach, which draws diverse strengths from in situ EC-NMR, SEIRAS, SERS, interfacial electrochemistry, and DFT calculations, to investigate the physical and chemical properties of electrochemically-engineered nanoscale bimetallic surfaces in order to establish relationships between surface electronic/structural/dynamic properties and catalytic reactivity in real-world Pt-based bimetallic catalysts with many industrial applications. This project will provide unique insights into electronic structure –– reactivity relationships for real-world bimetallic catalysts and make significant contributions toward establishing a bridge between low-surface-area model and high-surface-area industrial catalysts, thereby furthering our understanding of surface science in general and bimetallic electrocatalysis in particular.
As pointed out above, our approach draws strengths from different fields. First, the materials-engineering and environment-controlling power of interfacial electrochemistry offers a truly elegant way to prepare nanoscale bimetallic surfaces via electroless or underpotential deposition (UPD), and electrolysis or electro-dissolution. The relatively mild electrochemical approach in preparing bimetallic surfaces can rival the widely-used vapor deposition technique used in UHV and wet impregnation methods used industrially, both of which involve procedures that are rigorous and often technically demanding. Second, EC-NMR possesses technical versatility and chemical specificity for in-situ investigations in general and the analytical strength of high-field solid-state NMR in investigating real-world supported nanoscale (gas phase) metal and alloy catalysts in particular. Third, SEIRAS and SERS are a well-established major research techniques of the surface/interface science community and can provide quick access to important information regarding the bond strength and geometry of molecular probes such as CO, NO, or other reaction intermediates. A combined in situ EC SEIRAS/SERS/NMR approach will provide new, mutually complementary information on the electronic/molecular structure of the bimetallic surfaces by combining bond strength/geometry (IR/Raman) and quantitative electronic/dynamic (NMR) results. Finally, detailed DFT calculations can deep our fundamental understanding of experimentally observed trends. We currently focus on developing more active, less cost, and more stable (ACS) Pt-based bimetallic electrocatalysts for methanol, ethanol, formic acide oxidation and oxygen and CO2 reductions.
Representative Recent Publications:
(1) De-Jun Chen, YuYe J. Tong, "Irrelevance of CO Poisoning in Methanol Oxidation Reaction on a PtRu Electrocatalyst", Angew. Chem. Int. Ed. 2015, 54, 9394 –9398.(3) Thomas C. Allision, YuYe J. Tong, "Application of the Condensed Fukui Function to Predict Reactivity in Core-Shell Transition Metal Nanoparticles", Electrochim. Acta, 2013, 101, 334-340.
(2) De-Jun Chen, Shi-Gang Sun, YuYe J. Tong, "On the chemistry of activating commercial carbon-supported PtRu electrocatalyst for methanol oxidation reaction", ChemComm. 2014, 50, 12963-12965.
(4) Dianne O. Atienza, Thomas C. Allison, YuYe J. Tong, "Spatially-Resolved Electronic Alterations as Seen by in situ 195Pt and 13C NMR in Ru@Pt and Au@Pt Core-Shell Nanoparticles", J. Phys. Chem. C 2012, 116, 26480-26486.
(5) Augusta M. Hofstead-Duffy, De-Jun Chen, Shi-Gang Sun, YuYe J. Tong, "Origin of the current peak of negative scan in the cyclic voltammetry of methanol electro-oxidation on Pt-based electrocatalysts: a revisit to the current ratio criterion", J. Mater. Chem. 2012, 22, 5205-5208.
(6) In-Su Park, Bolian Xu, Dianne O. Atienza, Augusta M. Hofstead-Duffy, Thomas C. Allison, and YuYe J. Tong, "Chemical State of Adsorbed Sulfur on Pt Nanoparticles", (Inside Cover Commun.) ChemPhysChem, 2011, 12, 747-752. Also see the highlights by the ChemistryViews: "Prevent Poisoning of Catalysts".
An isolated MNP containing hundreds or thousands of metal atoms which forms a small enough geometric 3-dimension confinement of electrons leading to resolvable discrete electronic energy levels, as opposed to the quasi-continuum of band structures in its bulk counterpart. Such MNP are the fundamental building blocks for many nanostructured materials expected to show unprecedented physical and chemical properties which are inaccessible using existing materials. This project is directed toward investigation of local electronic/structural properties of ligand-protected MNPs as a function of size, number of excess electrons that the MNP carries (i.e., electric potential), and inter-MNP spacing in MNP superlattices. The research aims to provide critical data for understanding the physics and chemistry of these systems, in particular the bonding interactions between the metal surface and the ligand. Such an understanding is crucial for the ultimate rational design of novel nanostructured materials which will be the basis for many future technological applications, for instance, molecular electronics, biosensing, and MNP assisted radiotherapy.
Currently, our research focuses on two primary objectives. The first is to explore and develop systematically heavier chalcogen (Se and Te) interfacial chemistry in monolayer-protected MPNs for using them as alternative anchoring elements to the prevailingly used sulfur (S) for attaching organic molecular wires to metal surfaces. The second is to investigate how such interfacial chemistry can be used advantageously to control charge transfer/transport (CT) through a single MPN or MPN assemblies in enabling MPN-based novel applications in nano-devices. To achieve these two objectives, the research will entail (1) synthesizing MPNs of different metal elements (Au, Ag, Cu, Pt, and Pd), different sizes (1 to 5 nm), different organic backbones (alkyl and aryl) and lengths (C6, C8, and C12), and different anchoring heavier chalcogen elements (Se and Te); (2) in situ electrochemical (EC) spectroscopic (NMR/IR/Raman) characterizations of the afore-synthesized MPNs, which will be guided and assisted by targeted DFT calculations for better mechanistic understanding of the interface; and (3) comparative mechanistic investigations of CT through MPN assemblies (using EC redox chemistry measurements) and through individual MPNs (using EC scanning tunneling microscopic measurements).Representative Recent Publications:
(1) Ying Li, Oksana Zaluzhna, Bolian Xu, Yuan Gao✝ , Jacob M. Modest✝, YuYe J. Tong, "Mechanistic insights into the Brust-Schiffrin two-phase synthesis of organo-chalcogenate-protected metal nanoparticles", J. Am. Chem. Soc., 2011, 133, 2092-2095.
(2) Ying Li, Oksana Zaluzhna, YuYe J. Tong, "Critical Role of Water and Structure of Inverse Micelles in the Brust-Schiffrin Synthesis of Metal Nanoparticles", Langmuir 2011, 27, 7366-7370.
(3) Oksana Zaluzhna, Ying Li, Chris Zangmeister, Thomas C. Allison, YuYe J. Tong, "Mechanistic insights on the one-phase vs. two-phase Brust-Schiffrin method synthesis of Au nanoparticles with diactyl-diselenide", Chem. Comm. 2012, 48, 362-364.
(4) Ying Li, Oksana Zaluzhna, Chris Zangmeister, Thomas C. Allison, YuYe J. Tong, "Different Mechanisms Govern the Two-Phase Brust-Schiffrin Dialkyl-Ditelluride Syntheses of Ag and Au Nanoparticles", J. Am. Chem. Soc., 2012, 134, 1990-1992.
(5) Oksana Zaluzhna, Ying Li, Thomas C. Allison, YuYe J. Tong, "Inverse-Micelle-Encapsulated Water-Enabled Bond Breaking of Dialkye-Diselenide/Disulfide: a Critical Step for Synthesizing High-Quality Au Nanoparticles", J. Am. Chem. Soc., 2012, 134, 17991-17996.
Polyoxometalates (POMs) are discrete, nanoscale (0.6 -2.5 nm) molecular oxygen-metal clusters containing early transition metal cations M (=V, Nb, Ta, Mo, or W) in an oxygen-coordinated octahedra, MO6. By sharing edges and corners, these octahedra usually form a highly symmetrical structure of general formula XmMxOyn-, where X (=B, Si, Ge, P(V), As(V), and some other elements) are the so-called heteroatoms. The unique primary structures of POM result in many "value-adding" properties advantageous to processing that distinguish POMs from metallic oxides and conventional compounds. These include diverse molecular composition and aesthetically appealing geometric shape, redox reversibility and tunable redox potentials, strong acidity, high solubility, and good structural and thermal stability. Thus, POM chemistry is of fundamental importance for its current and future practical applications that spread over diverse fields such as catalysis, chemical/biological sensing, corrosion inhibition, geochemistry, and environmental chemistry as well as clinical chemistry. Among many current focuses of POM chemistry, POM-metal surface bonding is of particular interest because it lies at the heart of POM surface chemistry–a relatively young yet very technologically relevant subfield of POM chemistry that encompasses, among others, new heterogeneous catalysts for industrial oxidation of hydrocarbons, new electrocatalysts for hydrogen production and oxygen reduction in fuel cell applications, new electron transfer mediators for chemical sensors, and new corrosion inhibitors for replacing the still widely-used yet toxic chromate inhibitors.
Despite all these very promising technologically-related importances, the fundamentals of the POM surface chemistry are still far from well-understood, in particular, POM-metal bonding, a key surface chemical property that governs the formation of strongly adsorbed adlayers on metal (electrode) surfaces. Few detailed mechanistic investigations are available in the literature. Answers to many questions are still very evasive. For instance, how does the POM bind to the metal surface? how does the POM-metal bonding depend on the type of underlying metal and that of POM? how are the chemical properties of POMs modified through POM-metal bonding while their overall primary structure is retained? and what are the key factors that make adsorbed POMs more active and that influence the stability of the POM-metal bonding? just to name a few. Aiming to answer these questions mechanistically drives the research in this project. We focus on unraveling the chemistry of POMs chemisorption on electrode surfaces by employing conventional EC methods, in situ EC NMR/infrared/Raman spectroscopies to investigate metal-POM bonding interaction as a function of local chemical environment and of electrode potential. The potential societal impacts of this project are numerous.Representative Recent Publications:
(1) Georgeta. L. Lica, Kevin. P. Brown, Y. Y. Tong, "Interactions between Keggin-Type Lacunary Polyoxometalates and Ag Nanoparticles: A Surface-Enhanced Raman Scattering Spectroscopic Investigation", J. Cluster Sci., 2006, 17, 349-359.
(2) Thomas Hsu-Yao, Kevin P. Browne, Nicole Honesty, YuYe J. Tong, "Polyoxometalate-Stabilized Pt Nanoparticles and Their Electrocatalytic Activities", Phys. Chem. Chem. Phys., 2011, 13; 7433-7438.
Enhancing mass detection sensitivity is a constant challenge for applying solid-state NMR to surface, interface, and nanoscience, not to mention incorporating electrochemistry with NMR. New venues, such as low-temperature preamplifier system, microcoil and toroidal detection, stripline probe, polarization transfer, as well as coupling NMR with other sensitive techniques, are being explored along the progress of above research projects.
We are also developing in situ IR/Raman/MS spectroelectrochemistry, EC STM/AFM, EC quartz microbalance methods to expand our capability to investigate dynamic aspect of small organic molecules oxidation and oxygen reduction reactions on Pt-based electrocatalysts surfaces.Representative Recent Publications:
(1) Long Huang, Eric G. Sorte, Shi-Gang Sun, YuYe J. Tong, "A straightforward implementation of in situ solution electrochemical 13C NMR spectroscopyfor studying reactions on commercial electrocatalysts: ethanol oxidation", ChemComm. 2015, 51, 8086-8088..
(2) De-Jun Chen, YuYe J. Tong, "In situ Raman Spectroscopic Measurement of Near-Surface Proton Concentration Changes during Electrochemical Reactions",ChemComm. 2015, 51, 5683-5686.
(3) Ying Li, Brian S. Zelakiewicz, Thomas C. Allison, YuYe J. Tong, "Measuring Level Alignment at the Metal-Molecule Interface by in situ Electrochemical 13C NMR",ChemPhysChem 2015, 16, 747-751.
Research & etc. > 1. Research Opportunities: TongLab is a place for willing students to be challenged, well trained, and become highly successful >