NIU Department of
Chemistry & Biochemistry
Where the study of matter...matters!
Assistant Professor
Office: Faraday West 412
Phone: (815) 753-6357
txu@niu.edu
Postdoctoral Research Associate, Argonne National Laboratory, 2004-2006
Research Associate, Texas A&M University, 2003-2004
Ph.D., University of Alabama, 2003
B.S., East China University of Science and Technology, 1995
Curriculum Vitae (pdf)
Inorganic-organic hybrid interfaces and nanomaterials for applications in sensors, energy storage and conversion, solid-state lighting, and molecular electronics.
Xu Group Homepage
Enhanced Electron Transport in Dye-Sensitized Solar Cells Using Short ZnO Nanotips on A Rough Metal Anode. Yang, Z.; Xu, T.; Yasuo, I.; Welp, U.; Kwok, W. K. (Accepted) J. Phys. Chem. C
Hydrogen spillover enhanced hydriding kinetics of palladium-doped lithium nitride to lithium imide. Lin, C.; Xu, T.; Yu, J.; Ge, Q.; Xiao, Z. (2009) J. Phys. Chem. C, 113: 8513-8517.
An in situ electrical study on primary hydrogen spillover from nanocatalysts to amorphous carbon support. Lin, C.; Yang, Z.; Xu, T.; Zhao, Y. (2008) Appl. Phys. Lett., 93: 233110.
Direct mass determination of hydrogen uptake using a quartz crystal microbalance. Kulchytskyy, I.; Kocanda, M. G.; Xu, T. (2007) Appl. Phys. Lett., 91: 113507.
Self-assembled monolayer-enhanced hydrogen sensing with ultrathin palladium films. Xu, T.; Zach, M. P.; Xiao, Z. L.; Rosenmann, D.; Welp, U.; Kwok, W. K.; Crabtree, G. W. (2005) Appl. Phys. Lett., 86: 203104.
A spectroscopic study of hexadecylquinolinium tricyanoquinodimethanide as a monolayer and in bulk. Xu, T.; Szulczewski, G. J.; Morris, T.; Amaresh, R.; Gao, Y.; Street, S. C.; Kispert, L.; Metzger, R. M. (2002) J. Phys. Chem. B, 106: 10374-10381.
Periodic holes with 10 nm diameter produced by grazing Ar+ milling of the barrier layer in hexagonally ordered nanoporous alumina. Xu, T.; Zangari, G.; Metzger, R. M. (2002) Nano Lett., 2: 37-41.
Rectification by a monolayer of hexadecylquinolinium tricyanoquinodimethanide between gold electrodes. Xu, T.; Peterson, I. R.; Lakshmikantham, M. V.; Metzger, R. M. (2001) Angew. Chem. Int. Ed., 40: 1749-1752.
Electrical rectification by a monolayer of hexadecylquinolinium tricyanoquinodimethanide measured between macroscopic gold electrodes. Metzger, R. M.; Xu, T.; Peterson, I. R. (2001) J. Phys. Chem. B, 105: 7280-7290.
As the global climate change becomes more and more evident with each passing decade, cutting greenhouse gas emissions from energy production, storage, and utilization must be our top priority in order to minimize future climate changes. From the viewpoint of materials science, the research in energy is closely related to the interfacial transfers of electron/hole, ions and/or atoms, to facilitating the wanted transfers and to suppressing the unwanted transfers. Therefore, the study of physical and chemical properties at interfaces becomes exceptionally desirable in order to explore and fundamentally understand the electrical, optical and chemical phenomena occurring at various hybrid interfaces at nanometer scale. Research in our group is focused on the syntheses, characterizations, modifications, and applications of a variety of hybrid interfaces for clean energy applications including gas sensors, hydrogen storage, solar cells, catalysis, Li-ion battery and molecular electronics.
For gas sensor research, as an example illustrated in Figure 1, we used gas-induced changes in the electrical transport properties of a percolating nanocluster-like palladium thin film on a self-assembled organic monolayer to rapidly detect hydrogen and other gaseous species.
Figure 1. Schematic drawing of a nanopalladium thin film/organic monolayer assembly used in the rapid detection of hydrogen. Conductivity is low in the absence of hydrogen, but higher when hydrogen is present.
For hydrogen storage materials, one of our research interests is to fundamentally understand the kinetics and thermodynamics associated with the diffusion of hydrogen adatoms across the nanoscale interfaces between nanocatalysts and storage materials. This phenomenon is often termed as hydrogen spillover and is believed to be an effective approach to suppress the activation energy during hydriding and dehydriding processes. We have used an in-situ electrical method to rapidly probe hydrogen spillover from nanocatalyst to amorphous carbon. We also established a piezoelectric nanogravimetric system for measuring hydrogen mass uptake in thin film materials. Different from any existing bulk gravimetric or volumetric system, our thin film nanogravimetric system allows us to conveniently establish a well-controlled interface between catalyst and storing material. Meanwhile, we are also working on improving the hydriding kinetics of bulk storage materials including metal hydrides and adsorbents with large surface area through hydrogen spillover. For example, we demonstrated the enhanced hydriding kinetics in palladium-doped lithium nitride as illustrated in Figure 2.
Figure 2. Schematic elucidation of hydrogen spillover-enhanced hydriding in complex metal hydride-based hydrogen storage materials.
For solar cell research, one of our research interests is in the field of dye-sensitized solar cells (DSSCs). We explore new nanoarchitectured electrode designs that can bring new basic sciences to enhance the interfacial electron transport in DSSCs. For example, we recently demonstrated that the fill factor and open circuit voltage of ZnO-based DSSCs can be significantly improved by using a Zn-microtip|ZnO-nanotip core-shell hierarchy nano-architecture (shown in Figure 3) as the anode in a DSSC.
Figure 3. Zn-microtip|ZnO-nanotip core-shell hierarchy nano-architecture as anode in dye-sensitized solar cells.
Through our close and active collaborations with researchers at Argonne National Laboratory and National Renewable Energy Laboratory, students in our group will use a variety of cutting-edge techniques, including atomic force microscopy, scanning electron microscopy, UHV thin-film sputter systems, thermal evaporation, photo/electron-beam lithography, electrical transport measurement systems, electrochemical measurement system, advanced photon source (APS at Argonne) to explore the fundamental science at nanoscale hybrid interfaces and to synthesize the corresponding materials for clean energy applications.