Seung Hyun Anna Lee

Bio: Seung Hyun Anna Lee is an academic researcher from Pennsylvania State University. The author has contributed to research in topics: Dye-sensitized solar cell & Water splitting. The author has an hindex of 8, co-authored 9 publications receiving 2144 citations. Previous affiliations of Seung Hyun Anna Lee include Arizona State University & Northeastern University.

Visible Light Water Splitting Using Dye-Sensitized Oxide Semiconductors

Abstract: Researchers are intensively investigating photochemical water splitting as a means of converting solar to chemical energy in the form of fuels. Hydrogen is a key solar fuel because it can be used directly in combustion engines or fuel cells, or combined catalytically with CO2 to make carbon containing fuels. Different approaches to solar water splitting include semiconductor particles as photocatalysts and photoelectrodes, molecular donor-acceptor systems linked to catalysts for hydrogen and oxygen evolution, and photovoltaic cells coupled directly or indirectly to electrocatalysts. Despite several decades of research, solar hydrogen generation is efficient only in systems that use expensive photovoltaic cells to power water electrolysis. Direct photocatalytic water splitting is a challenging problem because the reaction is thermodynamically uphill. Light absorption results in the formation of energetic charge-separated states in both molecular donor−acceptor systems and semiconductor particles. Unfortuna...

Photoassisted Overall Water Splitting in a Visible Light-Absorbing Dye-Sensitized Photoelectrochemical Cell

Abstract: Iridium oxide nanoparticles stabilized by a heteroleptic ruthenium tris(bipyridyl) dye were used as sensitizers in photoelectrochemical cells consisting of a nanocrystalline anatase anode and a Pt cathode. The dye coordinated the IrO2·nH2O nanoparticles through a malonate group and the porous TiO2 electrode through phosphonate groups. Under visible illumination (λ > 410 nm) in pH 5.75 aqueous buffer, oxygen was generated at anode potentials positive of −325 mV vs Ag/AgCl and hydrogen was generated at the cathode. The internal quantum yield for photocurrent generation was ca. 0.9%. Steady-state luminescence and time-resolved flash photolysis/transient absorbance experiments were done to measure the rates of forward and back electron transfer. The low quantum yield for overall water splitting in this system can be attributed to slow electron transfer (∼2.2 ms) from IrO2·nH2O to the oxidized dye. Forward electron transfer does not compete effectively with the back electron transfer reaction from TiO2 to the ...

Coupling of Titania Inverse Opals to Nanocrystalline Titania Layers in Dye-Sensitized Solar Cells†

Abstract: We report a quantitative comparison of the photoaction spectra, short circuit current densities, and power conversion efficiencies of dye-sensitized solar cells (DSSCs) that contain bilayers of nanocrystalline TiO2 (nc-TiO2) and titania inverse opal photonic crystals (PCs). Cells were fabricated with PC/nc-TiO2 and nc-TiO2/PC bilayer films on glass/tin oxide anode of the cell, as well as in a split configuration in which the nc-TiO2 and PC layers were deposited on the anode and cathode sides of the cell, respectively. Incident photon current efficiencies at single wavelengths and current-voltage curves in white light were obtained with both cathode and anode side illumination. The results obtained support a model proposed by Miguez and co-workers, in which coupling of the low refractive index PC layer to the higher index nc-TiO2 layer creates a standing wave in the nc-TiO2 layer, enhancing the response of the DSSC in the red region of the spectrum. This enhancement is very sensitive to the degree of physical contact between the two layers. A gap on the order of 200 nm thick, created by a polymer templating technique, is sufficient to decouple the two layers optically. The coupling of the nc-TiO2 and PC layers across the gap could be improved slightly by treatment with TiCl4 vapor. In the bilayer configuration, there is an enhancement in the IPCE across the visible spectrum, which is primarily caused by defect scattering in the PC layer. There is also an increase of 20-50 mV in the open circuit photovoltage of the cell. With anode side illumination, the addition of a PC layer to the nc-TiO2 layer increased the efficiency of DSSCs from 6.5 to 8.3% at a constant N719 dye loading of 155-160 nmol/cm2.

Photocatalytic Hydrogen Evolution from Hexaniobate Nanoscrolls and Calcium Niobate Nanosheets Sensitized by Ruthenium(II) Bipyridyl Complexes

Abstract: Hexaniobate nanoscrolls (NS-H4Nb6O17) and acid-restacked calcium niobate nanosheets (R-HCa2Nb3O10) were compared as oxide semiconductors in photocatalytic assemblies for H2 production using ethylenediaminetetraacetic acid (EDTA) as a sacrificial electron donor and platinum (Pt) nanoparticles as catalysts. Ru(bpy)32+ and Ru(bpy)2(4,4′-(PO3H2)2bpy)2+ (bpy = 2,2′-bipyridine) were employed as visible light sensitizers (abbreviated as Ru2+ and RuP2+, respectively). RuP2+, which is anchored by a covalent linkage to the NS-H4Nb6O17 surface, functions more efficiently than the electrostatically bound Ru2+ complex, because of more efficient electron injection from the excited sensitizer to NS-H4Nb6O17. RuP2+-sensitized NS-H4Nb6O17 and R-HCa2Nb3O10 both produce H2 photocatalytically using visible light (λ > 420 nm) with initial apparent quantum yields of 20−25%. At the optimum sensitizer concentration and Pt loading, the photochemical hydrogen evolution process is primarily limited by the efficiency of light absorp...

Electron transfer kinetics in water splitting dye-sensitized solar cells based on core–shell oxide electrodes

Abstract: Photoelectrochemical water splitting occurs in a dye-sensitized solar cell when a [Ru(bpy)3]2+-based dye covalently links a porous TiO2 anode film to IrO2·nH2O nanoparticles The quantum yield for oxygen evolution is low because of rapid back electron transfer between TiO2 and the oxidized dye, which occurs on a timescale of hundreds of microseconds, When iodide is added as an electron donor, the photocurrent increases, confirming that the initial charge injection efficiency is high When the porous TiO2 film is coated with a 1–2 nm thick layer of ZrO2 or Nb2O5, both the charge injection rate and back electron transfer rate decrease The efficiency of the cell increases and then decreases with increasing film thickness, consistent with the trends in charge injection and recombination rates The current efficiency for oxygen evolution, measured electrochemically in a generator-collector geometry, is close to 100% The factors that lead to polarization of the photoanode and possible ways to re-design the system for higher efficiency are discussed

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

Abstract: 抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

Semiconductor-based Photocatalytic Hydrogen Generation

Abstract: 2.3. Evaluation of Photocatalytic Water Splitting 6507 2.3.1. Photocatalytic Activity 6507 2.3.2. Photocatalytic Stability 6507 3. UV-Active Photocatalysts for Water Splitting 6507 3.1. d0 Metal Oxide Photocatalyts 6507 3.1.1. Ti-, Zr-Based Oxides 6507 3.1.2. Nb-, Ta-Based Oxides 6514 3.1.3. W-, Mo-Based Oxides 6517 3.1.4. Other d0 Metal Oxides 6518 3.2. d10 Metal Oxide Photocatalyts 6518 3.3. f0 Metal Oxide Photocatalysts 6518 3.4. Nonoxide Photocatalysts 6518 4. Approaches to Modifying the Electronic Band Structure for Visible-Light Harvesting 6519

Plasmonic-metal nanostructures for efficient conversion of solar to chemical energy

Abstract: Recent years have seen a renewed interest in the harvesting and conversion of solar energy. Among various technologies, the direct conversion of solar to chemical energy using photocatalysts has received significant attention. Although heterogeneous photocatalysts are almost exclusively semiconductors, it has been demonstrated recently that plasmonic nanostructures of noble metals (mainly silver and gold) also show significant promise. Here we review recent progress in using plasmonic metallic nanostructures in the field of photocatalysis. We focus on plasmon-enhanced water splitting on composite photocatalysts containing semiconductor and plasmonic-metal building blocks, and recently reported plasmon-mediated photocatalytic reactions on plasmonic nanostructures of noble metals. We also discuss the areas where major advancements are needed to move the field of plasmon-mediated photocatalysis forward.

Metal-free efficient photocatalyst for stable visible water splitting via a two-electron pathway

Abstract: The use of solar energy to produce molecular hydrogen and oxygen (H2 and O2) from overall water splitting is a promising means of renewable energy storage. In the past 40 years, various inorganic and organic systems have been developed as photocatalysts for water splitting driven by visible light. These photocatalysts, however, still suffer from low quantum efficiency and/or poor stability. We report the design and fabrication of a metal-free carbon nanodot-carbon nitride (C3N4) nanocomposite and demonstrate its impressive performance for photocatalytic solar water splitting. We measured quantum efficiencies of 16% for wavelength λ = 420 ± 20 nanometers, 6.29% for λ = 580 ± 15 nanometers, and 4.42% for λ = 600 ± 10 nanometers, and determined an overall solar energy conversion efficiency of 2.0%. The catalyst comprises low-cost, Earth-abundant, environmentally friendly materials and shows excellent stability.

Nano‐photocatalytic Materials: Possibilities and Challenges

Abstract: Semiconductor photocatalysis has received much attention as a potential solution to the worldwide energy shortage and for counteracting environmental degradation. This article reviews state-of-the-art research activities in the field, focusing on the scientific and technological possibilities offered by photocatalytic materials. We begin with a survey of efforts to explore suitable materials and to optimize their energy band configurations for specific applications. We then examine the design and fabrication of advanced photocatalytic materials in the framework of nanotechnology. Many of the most recent advances in photocatalysis have been realized by selective control of the morphology of nanomaterials or by utilizing the collective properties of nano-assembly systems. Finally, we discuss the current theoretical understanding of key aspects of photocatalytic materials. This review also highlights crucial issues that should be addressed in future research activities.