Nanosheets
Nanosheet have a two-dimensional structure with atomic-scale thickness and lateral size in sub micrometer, and have intrinsically high surface area. In addition, the nanosheets show distinctive physical and chemical functions and have potential applications stem from electronic, photonic, catalytic, and electrochemical applications. Our research aims to explore and create novel platinum group metal-based layered materials, the exfoliated nanosheets, and its 3D architecture for electrochemical applications such as electrocatalysts, supercapacitors and batteries.
Platinum group metal (PGM)-based nanosheet:
PGM oxide and PGM is the promising materials for materials of energy conversion and storage. However, due to the scarcity and high cost of precious metals, it is essential that the active surface area of the material is increased and that the usage of the precious metal is decreased. We achieved to design the PGM oxide nanosheets through exfoliation of layered PGM oxides such as RuO2, IrO2 and PtO2 nanosheets with the atomic-scale thickness. Moreover, we have successfully prepared metallic PGM nanosheets with a thickness of single and double atomic layer by the reduction of PGM oxide nanosheets. In present, we study and explore the novel synthesis of PGM-based nanosheets, fundamental electrode reactions and develop high-performance electrode materials based on these nanosheets.
3D nanosheet assembly:
We attempt to design the three-dimensional nanosheet architecture with precisely controlled macrostructures and compositions through inexpensive processes such as electrophoretic deposition and layer-by-layer assembly. These porous designs can be applied to high-performance electrochemical devices such as supercapacitors, batteries and electrocatalysts. For example, we demonstrated vertically aligned reduced graphene oxide films fabricated by combination of electrophoretic deposition-freeze drying method. The film thickness and pore sizes are varied from 50 to 200 μm and from 10 to 100 μm, respectively, and the architecture enhances the specific capacitance and charging rate behavior of electrochemical capacitor.
Energy conversion
When an electrode material promotes an electrode reaction while remaining essentially unchanged before and after the reaction, it can be regarded as a catalyst. This function is known as electrocatalysis. Electrocatalysts play important roles in a wide range of energy conversion and chemical production processes. For example, they are used to convert chemical energy into electrical energy in fuel cells, and to drive chemical reactions using electrical energy, such as water electrolysis.
Electrocatalyst for Fuel cell:
Polymer electrolyte membrane fuel cells (PEMFCs), which use hydrogen as a fuel, are expected to play an important role as next-generation clean energy devices. Electrocatalysts are one of the key technological components that determine the performance and durability of PEMFCs. For the practical implementation and widespread use of fuel cells, it is essential to develop electrocatalysts that are highly active, durable, and cost-effective. In particular, the amount of platinum used in fuel-cell electrocatalysts must be drastically reduced, because platinum is expensive and its natural abundance is limited. Our research ranges from fundamental studies of electrocatalytic reaction mechanisms to the development of highly active and durable PGM-based electrocatalysts. In particular, for cathode catalysts, we have successfully synthesized Pt nanosheets, Pt-based alloy nanosheets, and Pt-based core–shell nanosheets with high activity and durability. For anode catalysts, we have proposed co-catalyst systems based on a variety of PGM-based materials.
Electrocatalyst for Water electrolyzer:
Polymer electrolyte membrane water electrolyzers (PEMWE), which generate hydrogen, are also key technologies for advancing a hydrogen-based society and promoting decarbonization across a wide range of fields. In order to achieve efficient production of hydrogen, electrocatalysts play important roles to promote the desired reactions with the low electric energy while remaining highly stable under harsh electrolysis conditions. Our research focuses on wide range from fundamental studies of electrocatalytic reaction mechanisms to the development of highly active and durable PGM-based electrocatalysts such as Ir-based nanosheets.
Energy storage
An electrochemical supercapacitor, also known as supercapacitor or ultracapacitor, is an energy storage device that can charge/discharge at extremely high speed (much faster than conventional batteries) with high capacity (much higher than conventional capacitors) and can be recharged almost eternally (over 10,000 times). Such devices find use in environmentally begin transportation such as hybrid vehicles, EV and HEV, as well as portable devices such as PDA, notebook computers, cell phones, and much more. Present R&D is concentrated on the improvement in the energy and power density (how much and how fast the device can store energy) of the device. We are presently developing noble electrode materials based on oxides that can fulfill the requirements of the next generation power sources.
Electrochemical capacitor:
Electrochemical supercapacitors based on metal oxide electrodes (called pseudocapacitors or redox capacitors) are promising next-generation energy storage devices because of their high capacitance (2-10 times higher than carbon electrodes) and rapid charge–discharge capability. The development of metal oxide electrode materials is one of the key technological challenges in this field. For the practical application of metal oxide-based supercapacitors, it is essential to develop electrode materials that are highly active, durable, and cost-effective. Our research focuses on fundamental studies of electrochemical reactions, as well as the exploration of highly active electrode based on layered materials and nanosheets, including PGM oxides, manganese oxides, and graphene oxide.
Battery:
Lithium-ion batteries are widely used as energy storage devices, but their applications are limited by power capability and cycle life. Our research focuses on battery–supercapacitor hybrid devices such as lithium-ion capacitors which combine the high energy density of batteries with the high power density and long cycle life of supercapacitors, and lithium-ion battery with Si-based anode which have high capacity. We aim to improve their energy storage capacity and durability through morphology control of electrode active materials, applying nanosheet binders, precise design of composite electrode structures, and optimization of cell architectures. These studies contribute to the development of next-generation energy storage devices for electric vehicles, grid-scale storage, and portable electronics.