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Research Programs


Introduction

Solar-to-Chemical Energy Conversions
Energy-Synthesis Heterogeneous Catalysis

Fabrication of Catalytic Nanomachines

▪ Instrumentation

 

 
 

Introduction


 
 

   

    The ultimate goal of our research program is to develop high-performance catalysts to respond to the current energy crisis. Our principal strategy is to precisely control the architecture and composition of the materials at the nanoscale by the means of wet chemistry and vapor-phase deposition techniques. The projects are categorized into two directions: sunlight-driven photocatalysis and energy-synthesis heterogeneous catalysis. The photocatalysis studies aim to establish new synthetic strategies of nano-photocatalysts for optimizing solar-to-chemical energy conversions. We focus on sunlight-driven water splitting and carbon dioxide photoreduction. The heterogeneous catalysis studies aim to improve the stability, activity, and selectivity of heterogeneous catalysts for important industrial-type catalytic reactions. The target reactions include syngas reactions, biomass reactions, and low-temperature PEM fuel cell reactions. We also perform thorough in-situ catalytic studies over our materials via lab-based and synchrotron-based techniques. The in-situ studies of the evolution of catalysts under the reaction conditions are crucial to understand the catalytic behaviors.

 

 
 

Solar-to-Chemical Energy Conversions


 
 

 

    Solid-state photoelectrocatalytic (PEC) systems generally consist of a semiconductor (SC) and co-catalysts. The SC absorbs sunlight and separates photon-generated electron/hole pairs, while the co-catalytic sites promote the desired charge-transfer redox reactions. There are several fundamental requirements for PECs to provide adequate performance. First, the bandgap of the absorber must be greater than or equal to the thermodynamic energy required to drive the reduction and oxidation half reactions, plus the overpotential required for each. In addition to the bandgap requirement, energetics of the semiconductor surface band edges must be such that the electrons in the conduction band possess an electrochemical potential energy greater than that needed to reduce the reductant and the holes at the valence band posses an energy less than that needed to oxidize the oxidant. Third, the SC must be stable under operating conditions. Unfortunately, only few of the known cost-effective materials meet all the requirements. Overcoming this limitation is a major motivation for the projects of this direction..

 

To design a nanocomposite photocatalytic system
   

    Traditionally there are two basic configurations for PEC systems: photoelectrode systems and particle systems. We focus on particle-PEC systems and further engineer these systems on the nanometer scale. The overwhelming advantages of the nano-PECs arise from their small dimensions. The nanoparticle size can be chosen such that the diameter is much smaller than the diffusion length to minimize the energy losses due to the electron/hole recombination. The decreased photon absorption in a single particle can be overcome by simply increasing the number of particles available to absorb light. In the nano-PEC system, the overpotential required for the half reactions can be surmounted by increasing the surface kinetic energy through addition of oxidation and reduction nanoparticle co-catalysts to the SC surface, thereby maximizing the efficiency.

 

To develop high-surface-area photocatalyst film system for visible-light driven water splitting

    We also concentrate on developing new synthetic strategies by integrating sol-gel chemistry and vapor-phase deposition for high-surface-area semiconductor films with diverse compositions. Ultimately, the target is to utilize these synthetic strategies for developing photocatalyst films for visible-light-driven water splitting.

 

 

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Energy-Related Heterogeneous Catalysis


 
 

 

    Metals and metal-oxides are two major components applied in heterogeneous catalysts. It is generally believed that the performance of a catalyst is largely affected by the heterojunction interfaces between metals and metal oxides. Therefore, it is very important to be able to control the interfaces  in a catalyst for optimizing the performance.

 

To create well-defined nanoparticle based heterojunctions for heterogeneous catalysis

 

    The aim here is to develop new-type nanoparticle-based catalysts of well-controlled heterojunctions. This new-type catalyst is achieved by manipulating the assembly of well-shaped nanoparticles. The interfaces of these catalysts are designed to optimize the stabilities, activities, and selectivities for important industrial-type catalytic reactions. We mainly focus on energy-synthesis reactions including syngas reactions, biomass reactions, and low-temperature PEM fuel cell reactions. These 2-D and 3-D nanoparticle-based catalysts are explored by synchrotron-based and lab-based in-situ analytical techniques. The information learned here is expected to further optimize the catalytic performance of the catalysts.

 

 

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Fabrication of Catalytic Nanomachines


 
 

 

    Drug and molecule delivery has been an attractive topic in nanoscience for decades. In most of the conventional designs, the nanoparticles only served as a carrier and the motion of the carriers were driven by external energy sources, such as a strong external magnetic field. In our design, we synthesize nanosized heterostructural carriers with well-controlled structures, which allow us to control catalytic behaviors of our nanomachines. Thus, the motion of our nanomachine carriers is driven by decomposing fuels around the carriers without any external energy source.
 

 
 

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Instrumentation


 
 

 

    Transmission electron microscopes (TEM), scanning electron microscopes (SEM), gas chromatography (GC), mass spectrometry, potentiostats, solar simulator, X-ray photoelectron spectroscopy (XPS), atomic force microscope (AFM), X-ray diffraction spectrometer (XRD), porosimiters, nuclear magnetic resonance (NMR), UV-Vis and IR spectrometer, confocal microscopy, thermogravimetric analysis and differential scanning calorimetry (TGA/DSC), zeta potential measurements, dynamic light scattering, in-situ synchrotron-based XPS, extended X-ray absorption fine structure (EXAFS), and Transmission X-ray Microscopy (TXM).

 

 
 

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