INTERESTS
Nanomaterial Synthesis
Heterojunction of Metal Oxide
Metal oxides semiconductors are widely studied for electrochemical devices since their stability under oxidizing conditions. However, metal oxides usually have large band gap which will lead to a narrow absorption range in the visible light region, and the serious recombination occurring in the metal oxide semiconductor will cause poor charge transportation. These inabilities will reduce the performance of the pertinent photoelectrochemical devices, e.g., solar water splitting systems, solar cells, etc. Combination of two or more metal oxide semi-conductors with complimentary light absorption regions for increasing the light absorption and those with suitable related conduction/valence band positions for making a heterojunction structure to enhance the charge separation and injection efficiency are efficient ways to improve the performance of the pertinent photoelectrochemical devices.
Nano Lett. 2014, 14, 1099−1105
Two-dimensional (2D) Materials
Two-dimensional (2D) materials are flat films with only the height in the nano scale dimension. Since the thickness is only several nano meters, the quantum confinement effect within the materials is very likely to occur, but the bulk properties of the length and width dimensions lack of this phenomenon, the surface property are very different from its bulk form of the 2D materials. This feature changes the physical and chemical properties, and thereby affecting the applications in optical, electrical, thermal, magnetic, chemical and mechanical aspects of the 2D materials. We are mainly focused on the synthesis of MoS2, MoSe2, WS2, and WSe2 2D materials.
Nat. Commun. 3, 887, doi: 10.1038/ncomms1882
Graphene Quantum Dots (GODs)
http://www.azoquantum.com/news.aspx?newsID=717
Graphene quantum dots are small graphene fragments,where electronic transport is confined in all three spatial dimensions. Graphene is a zero-bandgap semiconductor with infinite exciton Bohr diameter. Thus, confinement can be observed in any fragment; however, GQDs typically have dimensions in the size range below 20 nm diameter. The experimental and theoretical study of GQDs has followed the work on graphene very closely. GQDs have been fabricated by fragmentation or “cutting” of graphene sheets(top-down approach). In parallel, organic chemists synthesized large graphene-like molecules with well-defined molecular structure (bottom-up approach).
Electrochemical Applications
Z-scheme Water Splitting
Water splitting on illuminated semiconductors has long been studied as a potential means of converting solar energy into chemical energy in the form of H2, a clean and renewable energy carrier. Photocatalytic water splitting through two-step photoexcitation using two different semiconductor powders and a reversible donor/acceptor pair (so-called shuttle redox mediator) is one of the possible forms of artificial photosynthesis. This system was inspired by natural photosynthesis in green plants and is called the “Z-scheme”. The development of Z-scheme water splitting systems has relied on both finding a new semiconductor photocatalyst that efficiently works in the presence of a shuttle redox mediator and creating active sites to promote surface chemical reactions while suppressing backward reactions involving redox mediators.
http://www.ehcc.kyoto-u.ac.jp/eh41/home/abe/en/research/
Electrochemical Supercapacitor (ES)
ES has attracted significant attention due to the high power density, long lifecycle, and bridging function for the power/energy gap between traditional dielectric capacitors (which have high power output) and batteries/fuel cells (which have high energy storage). Low energy density and high production cost have been identified as major challenges for the furtherance of ES technologies. The development of new materials for ES electrodes is necessary. Carbon materials show high surface areas for charge storage, but the charges physically stored in porous electrode layers are unfortunately limited. This kind of ES is called electrostatic or electrical double-layer supercapacitors (EDLS), possessing a limited specific capacitance and a low ES energy density. Hybridizing the electrode materials by adding electrochemically active materials to a carbon-particle-based ES electrode layer or to completely replace the carbon materials with electrochemically active materials is the other kind of ES called faradaic supercapacitors (FS). Faradaic or hybrid double-layer supercapacitors can yield much higher specific capacitance and ES energy density than EDLS.
Dye-sensitized Solar Cells (DSSCs)
A dye-sensitized solar cell is a low-cost solar cell belonging to the group of thin film solar cells. It is based on a semiconductor formed between a photo-sensitized anode and an electrolyte, a photoelectro-chemical system. It is simple to make using conventional roll-printing techniques, is semi-flexible and semi-transparent which offers a variety of uses not applicable to glass-based systems, and most of the materials used are low-cost. Although its conversion efficiency is less than the best thin-film cells, in theory its price/performance ratio should be good enough to allow them to compete with fossil fuel electrical generation by achieving grid parit.y.