Session Chair: Jean-Jacques Delaunay, The University of Tokyo Session Chair: Alfred Tok, Nanyang Technological University
1:30pm - 2:00pm Invited
Nanometer-Thick Oxides Thin Films for High Performance Photoelectrochemical Electrode Development
University of Wisconsin Madison, United States
Two-dimensional nanomaterials play an important role in the development of novel photoelectrochemical (PEC) electrodes for solar fuel generation. In this talk, we present two types of nanometer-thick oxides thin films along this research direction. We developed an ionic layer epitaxy (ILE) technique to synthesizing large-area crystalline oxide nanosheets from solution. Wafer-scale nanometer-thick CoO nanosheets was synthesized by ILE using a monolayer of ionized surfactants at water-air interface as a flexible template. Due to the large surface atom ration and short cross-plane charge diffusion path, this CoO nanosheet exhibited substantially higher catalytic property towards oxygen evolution reaction (OER) compared to bulk CoO. Owing to its wafer-scale film size, the CoO nanosheet could be easily integrated with photoactive n-type silicon wafer, yielding an efficient and stable PEC photoanode. On the other hand, supported amorphous oxide thin film has recently been reorganized as an effective protection layer for PEC electrodes. We showed that an ultrathin amorphous TiO2 film can simultaneously promote the charge separation efficiency and improve the operational lifetime of black-Si (b-silicon) PEC photoanode. The TiO2 film was deposited by low-temperature atomic layer deposition (ALD) conformally covering the entire nanostructured surface of b-Si. Combined with an optimized Co(OH)2 thin film as the oxygen evolution catalyst, this b-Si/TiO2/Co(OH)2 heterostructured photoanode was able to produce a very high saturated photocurrent density of 32.3 mA/cm2 at a low external potential of 1.48 V vs. RHE, noticeably exceeding planar Si and unprotected b-Si photoelectrodes. TiO2-induced photocurrent gain was attributed to the enhanced charge separation efficiency as a result of the effective passivation of defective sites on b-Si surface. Moreover, the 8-nm ALD TiO2 layer can impressively extend the function endurance of b-Si from less than half an hour to four hours. Both research demonstrated novel functional oxide ultrathin nanosheets can become promising solutions for efficient and stable electrochemical system innovation.
2:00pm - 2:30pm Keynote
Semiconducting Nanomaterials for Photoelectrochemical Energy Conversion
The University of Queensland, Australia
The capability of designing functional nanomaterials with desirable structures and properties remains an important challenge to R&D sectors. In this talk, we will give a brief overview of our recent progresses in designing semiconductor metal oxides materials for photoelectrochemical energy conversion including photocatalytic solar fuel generation and low cost solar cells. In more details, we have been focusing the following a few aspects; 1) band-gap engineering of layered semiconductor compounds including layered titanate, tantalate and niobate-based metal oxide compounds for visible light phtocatalysis, and 2) two-dimensional nanosheets/nanoplates of TiO2, Fe2O3 and WO3 as building blocks for new photoelectrode design，and 3) the design of semiconductor nanoparticles for low cost solar cells including perovskite and quantum dot solar cell applications. The resultant material systems exhibited efficient visible light photocatalytic performance and improved power conversion efficiency in solar energy, which underpin important solar-energy conversion applications including solar electricity and solar fuel production.
2:30pm - 2:45pm Oral
Al2O3 Surface Complexation for Photocatalytic Organic Transformations
The use of sunlight to drive organic reactions constitutes a sustainable and environmentally-friendly strategy for the conversion of raw materials to valuable products. We utilized the earth-abundant and commercially-available aluminum oxide (Al2O3), though paradigmatically known to be an insulator, to immensely enhance the selective photocatalytic oxidation of benzyl alcohols in the presence of different photosensitizers and O2. The unique mechanism is based on the surface complexation of benzyl alcohol (BnOH) with the Al2O3 surface Brønsted base sites, which causes an upshift in its HOMO for electron abstraction by the photosensitizer. Surface complexation with Al2O3 also activates adsorbed O2 for receiving electrons from the photosensitizer. This discovery demonstrates the potential of utilizing surface complexation mechanisms between organic reactants and earth abundant materials to achieve a wider range of photoredox transformations.
 Leow, W. R.; Ng, W. K. H.; Sum, T. C.; Hirao, H.; Chen, X. J. Am. Chem. Soc.2017, 139, 269.
2:45pm - 3:00pm Oral
Controlled Synthesis of Sb2Se3 Nanosturctures with Varying Aspect Ratio for Efficient Photoelectrochemical Water Splitting
Wooseok YANG1, Joosun KIM2, Jooho MOON1
1Yonsei University, South Korea; 2Korea Institute of Science and Technology, South Korea
Synthesis of one-dimensional nanostructured chalcogenide compounds using nontoxic and abundant constituents provides an important pathway to the development of commercially feasible photoelectrochemical water splitting. In this study, we synthesized Sb2Se3 nanostructure on conductive substrate via a facile spin-coating and drying without any intricate processes. The resulting nanostructure was controlled from nanorod to nanowire through solvent engineering. The growth mechanism of the Sb2Se3 nanostructure was elucidated as a function of spin-coating iterations and drying temperature in conjunction with chemical reaction occured in the precursor solution. After sequential surface modification with TiO2 and Pt, the resistance to charge carrier trnasfer from the electrode to the electrolyte decreased significantly, yielding a remarkable photocurrent.
3:00pm - 3:15pm Oral
Single-Step Soft Process for Internal Air Cleanup by Visible Photocatalysis Coupled to Adsorption
Sana LABIDI, Mamadou TRAORE, Mounir BENAMAR, Khay CHHOR, Andreï KANAEV
Centre National de la Recherche Scientifique (CNRS) - Laboratoire de Science des Procédés et Matériaux (LSPM), UPR3407, France
Environmental authorities had classified few categories of molecules as atmospheric pollutants which are released mainly from human activities (transport, industrial activities, pesticides, etc.). Our project aims to develop advanced materials for internal air cleanup based on visible photocatalysis coupled to adsorption for ethylene gas as model pollutant. The use of a visible light source is an important advancement that allows decreasing the related cost of industrial implication. In this work, two active materials were elaborated: immobilised doped TiO2 (by Fe, Pd, Pt and Pd+Pt) using sol-gel technique as photocatalyst and immobilised apatite using co-precipitation method, as adsorbent. The photocatalytic tests were performed to optimize ethylene degradation. Pt(0.5%)-TiO2 showed the highest degradation yield and fastest kinetics. No saturation behaviour of photocatalyst surface was observed for continuous flow of 75 mL/min at 120 ppm of ethylene up to 3h30 of reaction time. The combination of Pt(0.5%)-TiO2 and apatite further promotes the ethylene degradation rate by 2 orders of magnitude. TEM, specific surface area and DRX characterization were performed for different prepared materials.
3:15pm - 3:30pm Oral
Plasmonic Octahedral Gold Nanoparticles of Maximized Near Electromagnetic Fields for Enhancing Catalytic Hole Transfer in Solar Water Splitting
Cheon Woo MOON, Seon Yong LEE, Woonbae SOHN, Dinsefa Mensur ANDOSHE, Do Hong KIM, Kootak HONG, Ho Won JANG
Seoul National University, South Korea
Due to their localized surface plasmon resonances in visible spectrum, noble metal nanostructures have been considered for improving the photoactivity of wide bandgap semiconductors. Improved photoactivity is attributed to localized surface plasmon relaxations such as direct electron injection and resonant energy transfer. However, the details on the plasmonic solar water splitting through near electromagnetic field enhancement have not been fully understood. Here, we report that shape-controlled gold nanoparticles on wide bandgap semiconductors improve the water-splitting photoactivity of the semiconductors with over-bandgap photon energies compared to sub-bandgap photon energies. It is revealed that hot hole injection into the oxygen evolution reaction potential is the rate-limiting step in plasmonic solar water splitting. The proposed concept of photooxidation catalysts derived from an ensemble of gold nanoparticles having sharp vertices is applicable to various photocatalytic semiconductors and provides a theoretical framework to explore new efficient plasmonic photoelectrodes. Here, we report that shape-controlled octahedral Au NPs greatly promote the photoactivity (photocurrent, onset potential and incident photon-to-current efficiency (IPCE)) of TiO2 thin film with over-bandgap photon energy rather than sub-bandgap photon energy. Interestingly, the octahedral Au NPs also promote photoactivity from hematite film, WO3 filmand SrTiO3 single crystal. Finite-Domain Time-Difference (FDTD) simulation demonstrates that octahedral Au NPs provide intensified LSPR-EFs in the entire UV-VIS region. This result can be explained by the presence of hot holes at the high energy, derived from the intensified LSPR-EFs at over-bandgap photon energy of the semiconductors. Due to the generality of photoactivity enhancements, hot hole injection is an essential process for efficient plasmonic solar water splitting.