The growing need for clean and renewable energy has motivated the development of deployable systems to harvest and store earth's abundant solar energy resources. One promising approach is to collect and store solar energy within chemical bonds by forming fuels such as hydrogen and alcohols (solar fuels). This approach is similar to that of the natural photosynthetic process and thus has been dubbed "artificial photosynthesis." An example of this process is by utilizing the semiconductor as both the light absorber as well as the catalyst to split water into H2 and O2. The ultimate goal of these efforts is to develop a standalone photoelectrochemical cell in which water reduction and oxidation reactions occur efficiently under photo induced bias (ideally 1 sun), precluding the introduction of external electricity. In order to achieve this goal, the integration of stable light absorbing materials and effective catalysts to enhance the interfacial kinetics and fundamental mechanistic understanding of this coupled water splitting system still necessitate further explorations. In my lab, the majority of research focuses on two areas of solar energy conversion: 1) Development of light absorber-catalyst artificial photosynthesis assembles; 2) Understanding the electron and energy transfer mechanism in light harvesting systems
Areas of Specialization
Inorganic Chemistry, Renewable Energy
Research
Research Focus
The growing need for clean and renewable energy has motivated the development of deployable systems to harvest and store earth's abundant solar energy resources. One promising approach is to collect and store solar energy within chemical bonds by forming fuels such as hydrogen and alcohols (solar fuels). This approach is similar to that of the natural photosynthestic process and thus has been dubbed "artificial photosynthesis." An example of this process is by utilizing the semiconductor as both the light absorber as well as the catalyst to split water into H2 and O2. The ultimate goal of these efforts is to develop a standalone photoelectrochemical cell in which water reduction and oxidation reactions occur efficiently under photo induced bias (ideally 1 sun), precluding the introduction of external electricity. In order to achieve this goal, the integration of stable light absorbing materials and effective catalysts to enhance the interfacial kinetics and fundamental mechanistic understanding of this coupled water splitting system still necessitate further explorations. In my lab, the majority of research focuses on two areas of solar energy conversion described below.
Development of Light Absorber-Catalyst Artificial Photosynthesis Assembles
Semiconductor electrodes that have been modified by molecular catalysts have been investigated extensively with various polymeric backbone attachments. However, few studies have been focused on the direct attachment of molecular catalysts onto semiconductor surfaces. By carefully adjusting the energetics between semiconductor and molecular catalyst interface, the efficiency of energy extraction from the photogenerated electron-hole pairs can be optimized. Adding an active catalyst unit to the surface of semiconductor is a feasible strategy to both improve the stability and maintain catalytic activity of a photoelectrochemical device. In a previous study we showed that by using an atomic layer deposited TiO2 layer as well as an earth abundant molecular catalyst we were able to protect the GaInP2 surface.
In the natural photosynthetic process, chemical energy is generated by light conversion followed by proton and electron transfer events (or proton coupled electron process). This process typically begins with light being absorbed by a harvesting pigment. The energy generated by light absorption is then transferred through different chromophores via energy cascade and eventually reaches a reaction center. At the reaction center, the light energy is converted to chemical energy through a multi-electron, multi proton transfer reactions. The basis of artificial photosynthesis is to mimic the photosynthetic process using semiconductors and molecular catalyst assemblies. Through an improved understanding of the coupled electron and energy transfer process in design assemblies could provide significant information for the future design and implementation of industrial scale artificial photosynthesis systems.
Figure 1. Representation of a photocathode where the GaInP2 semiconductor has been coated with TiO2. This surface modification allows a cobaloxime molecular catalyst to be bonded to the semiconductor
Understanding the Electron and Energy Transfer Mechanism in Light Harvesting Systems
Graduate students who work in my lab will receive an interdisciplinary training in inorganic chemistry (i.e. organometallic ligand and catalyst development, solid state chemistry), physical chemistry (i.e. nanosecond charge transfer and surface chemistry) and material science (i.e. surface characterization and material chemistry). State-of-the-art analytical techniques such as NMR spectroscopy, IR, fluorimetry, and ICP-MS will be used to shine light on the reaction mechanism. SEM, TEM and XPS will help us to monitor the morphology change for the material interface. In addition, the interactive nature of our research would provide us various collaborative opportunities between departments, schools and national labs, resulting in excellent learning opportunities for the graduate students. We always welcome graduate students and postdocs who are talented, determined and responsible to join our lab and together we will work towards finding alternative solutions to solve our energy crisis and environmental issues.
Figure 2. Schematic of the transient photoreflectance measurement. A pump pulse modulates the reflectance of a broadband pulse and creates free charge carriers within the depletion region of a semiconductor. The technique helps us understand the semiconductor and protection layer charge transfer kinetic.
