Research Area of Nick Wu Group:
Nanomaterials | Nano-patterns | Photocatalysts & Photoelectrochemical cells | Sensors | Batteries, Supercapacitors and Solid Oxide Fuel Cells


Low-Dimensional Nanomaterials
    We are working on the synthesis and characterization of low-dimensional nanomaterials such as nanoparticles, nanowires, nanotubes and thin films. We strive to synthesize such nanomaterials with controllable size, shape, microstructure and electronic structure by electrospinning, sol-gel, hydrothermal processing and other wet chemical processing, as well as chemical/physical vapor deposition. We attempt to utilize the nanomaterials to build sensors, lab-on-chips, photoelectrochemical cells and other energy conversion and storage devices.
    Nanoscale energy transfer and charge transfer processes governs the performance of materials and devices such as photocatalysts and photoelectrochemical cells, solar cells, supercapacitors, electrochemical and optical biosensors as well as solid oxide fuel cells. We strive to gain new insight into the charge transfer and energy transfer processes at the nanoscale and utilize nanotechnology to mediate the energy transfer and charge transfer processes in materials and devices. We study the size- and/or shape-dependent energy transfer and charge transfer processes. In addition, we study how surface plasmons affect the energy transfer and charge transfer processes in metal-semiconductor or semiconductor-semiconductor systems. The outcome of this effort will provide the guidelines for designing new materials and devices.

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Dispersed TiO2 nanobelts Energy transfer from a quantum dot to a Au nanoparticle

Nano-lithography and Micro-fabriction
    Large-area-ordered two dimensional (2D) or 3D nanopatterns such as nanohole arrays and nanorod arrays have extensive applications in photonic crystals, biosensors, catalysts and solar energy devices. Future sucess of 2D/3D nanopatterns depends on the availability of cost-effective, scale-up patterning methods. Commomly used patterning techniques such as photolithography, electron beam lithography, and focused ion beam (FIB) lithography have limitation in fabrication of 2D/3D nanostructures. It is very difficult for the photolithography method to generate the features less than 100 nm. The e-beam and FIB techniques are limited by their low throughput in creating large-area nanoscale patterns. We strive to develop a facile approach for cost-effective, high throughput fabrication of large-area nanoscale patterns. For example, we are developing large-area nano-array patterns by nanosphere lithography or by block co-polymer template. We combine nano-lithography with micro-fabrication technology to create hierarchical structures. We create optical and electrochemical biosensors, lab-on-chips, as well as energy conversion and storage devices with 2D or 3D nanopatterns.

Nanoscale gold dot pattern Nanoscale “honeycomb”: nano-well array

Biosensors, Chemisensors and Lab-on-Chips
    Chemical sensors and biosensors attract increasing attention. It remains a challenge to improve the performance of sensors in terms of selectivity, sensitivity, response time, and reliability. We strive to utilize nanotechnology and nanomaterials to fabricate high-performance chemical sensors and biosensors. One of our goals is to make nanostructured sensors to detect trace chemical species or even single biological molecules. We attempt to achieve small size, easy integration into devices, and low cost. We work on electrochemical sensors and surface plasmon resonance (SPR)-enhanced fluorescent sensors and surface-enhanced Raman scattering (SERS) sensors. In particular, we attempt to integrate sensors with microfluidic modules to create lab-on-chips (LOCs) for real-world sample applications. We are interested in portable devices, especially point-of-care (POC) tools, which are used to detect DNA, proteins, pathogens, anticancer drugs and heavy metals.
    Understanding the inherent sensing mechanism and the chemical and physical process involved in sensing is the prerequisite for design of sensors. It is necessary to perform in parallel the classical electrochemical, the catalytic and surface analytical studies on sensors. In particular, we are performing an in-situ study on single molecular events, local electric and ionic transport in sensors on the nanoscale under the sensing environment. We are exploring the correlation of the sensing properties with the crystal structure, the chemical structure and the electronic structure of materials. We are also studying the interaction of chemical species with the surface of sensing materials

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Aptamer-based SERS biosensor DNA biosensor Lab-on-chip

Photocatalysts and Photoelectrochemical Cells
    Photocatalysis generally involves three processes: (i) generation of electrons and holes by photoexcitation; (ii) migration of the photogenerated charge carriers to the surface and subsequent reduction/oxidization of the adsorbed reactants directly by electrons/holes or by reactive oxygen species (ROS); and (iii) recombination of the photogenerated electron-hole pairs. Desired photocatalysts are expected to promote Process (i) and (ii) in the meanwhile to suppress Process (iii). We attempt to gain fundamental understanding of the effects of the chemical composition, electronic structure, crystal structure and morphology of nanomaterials on the three processes in photocatalysis. In particular, we attempt to clarify the correlation of band structure with Process (i), (ii) and (iii). On the other hand, we strive to understand the underlying mechanisms of plasmon-enhanced solar energy harvesting. Recently we discovered an unprecedented plasmon-induced charge separation mechanism: plasmon-induced resonance energy transfer (PIRET) from a metal to a semiconductor.
    Currently, the primary energy source is supplied by fossil fuels. It is essential to increase the energy conversion/utilization efficiency and to reduce the pollutant emission of power generation. Photocatalysts and PECs are emerging as a potential hydrogen production and CO2 conversion technologies. By harnessing solar energy, the H2 generation process is less energy-consuming than the conventional methods. Also, H2 generation by photoelectrochemical cells will significantly reduce the release of pollutants to the ecological system. We are developing photocatalysts and photoelectrochemical cells (PECs) for solar fuel generation and environmental remediation. In particular, we incorporate plasmonic nanostructures into semiconductors to develop plasmonic photocatalysts/PECs.
    We are exploring to mitigate or remove the environmental pollutants such as heavy metals, small molecule toxins and pathogens by utilizing photocatalysts and photoelectrochemical cells.
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Solar water splitting by a plasmonic photoelectrochemical cell (Nat. Comm. 4, 2013) Hematite nanorod array as "optical fibers" (Nat. Comm. 4 (2013), 2651) Photocurrent enhancement in a plasmonic photoanode (Nat. Comm. 4 (2013), 2651)

Batteries, Supercapacitors and Solid Oxide Fuel Cells
    Safety concerns regarding commercial lithium-ion batteries are ever growing due to the use of highly volatile and flammable organic solvent-based electrolytes. In addition, the energy density and the long-term durability need to be further improved. One of my goals is to develop all-solid-state batteries.  We develop new ceramics and polymers with improved ionic conductivities; and then we incorporate the nanostructured ceramic material into a polymer matrix to develop ceramic-polymer composite electrolytes. We explore how to suppress the lithium dendrite formation at the lithium metal electrode/electrolyte interface. We also develop new electrode materials to improve the energy density and the power density of all-solid-state batteries. But our research is not limited to all-solid-state batteries. We exploit new avenues to develop high-performance lithium-metal batteries and lithium-sulfur batteries.
    Currently commercial supercapacitors are carbon-based electrochemical double-layer capacitance (EDLC) devices, which have excellent cyclic stability and long service lifetime. However, the energy density of carbon-based EDLC supercapacitors is typically 3~5 Wh/kg. Such low energy-density cannot fulfill the need of energy storage devices for vehicles, wind-farms and solar power plants. We strive to develop supercapacitors that have both high energy density and high power density. One of viable solutions is to develop carbon-metal oxide composites as supercapacitor electrodes. In addition, both EDLC and pseudo-capacitance can be simultaneously generated in a single supercapacitor to form a hybrid supercapacitor.
    Conventional solid oxide fuel cells (SOFCs) use yttria-stabilized zirconia (YSZ) electrolyte.  However, its conductivity characteristics require an operating temperature of over 900°C.  Reduction of the operating temperature of SOFCs to <800°C is one of the main goals of current SOFC research programs.  The challenge is that the electrochemical reaction becomes considerably slower as temperature is reduced. Due to the high activation energy of the oxygen reduction reaction, whose polarization resistance increases rapidly with decreasing temperature, the cathode requires particular attention when the operating temperature is reduced. The cathode performance depends on the electronic/ionic conductivity of the electrode, gas transport through electrode porosity, and the electrocatalytic activity at the three-phase boundary (TPB) areas among the gas, the electrolyte and the cathodes. We strive to improve the cathode performance by developing new materials and/or optimization of electrode architecture/microstructure.
   In addition, we are investigating the effects of trace impurities on the performance of SOFC anodes that are operated in coal-derived syngas. We are identifying the elements that have the most detrimental effects. We seek to establish the fundamental mechanism of the interaction of impurities with the anode by electrochemical studies and microstructural analysis. The knowledge obtained will lead to maximization of the power density of SOFC and improvement of the reliability of SOFC anode operated in the syngas environment.

Hierarchical carbon-MnO2 core-shell nano-cables for supercapacitor electrode LSCF-LDC composite nano-fibers for SOFC cathode



Prof. Junying Zhang
Electronic structure
Metal oxides


Last Updated 11/08/2013